Indian Patents
Title of Invention

AN IMAGING ARRANGEMENT WITH INCREASED DEPTH OF FOCUS
Abstract An imaging arrangement and method for extended the depth of focus are provided. The imaging arrangement comprises an imaging lens having a certain affective aperture, and an optical element associated with said imaging lens. The optical element is configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition. The optical element and the imaging lens define a predetermined pattern formed by spaced-apart substantially optically transparent features of different optical properties. Position of at least one phase transition region of the optical element within the imaging lens plane is determined by at least a dimension of said affective aperture.
Full Text ORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
"METHOD AND SYSTEM FOR EXTENDING THE DEPTH OF FOCUS"
XCEED IMAGING LTD., a company of Israel, of P.O.B. 4201, 1 Hermon Street, 48560 Rosh Haayin, Israel
The following specification particularly describes the invention and the manner in which it is to be performed.

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FIELD OF THE INVENTION
This invention is generally in the field of imaging systems, and relates to an imaging lens arrangement with increased depth of focus.
5 BACKGROUND OF THE INVENTION
Extending the depth of focus of imaging systems is a very important core technology allowing its incorporation into various applications, including inter alia medically related applications where elements, such as cameras, are to be inserted into the body in order to observe and detect problematic tissues; as well
10 as ophthalmic industry including glasses for spectacles, contact lenses, intraocular lenses or other lenses inserted surgically into the eye. The extended depth of focus solution is also needed for optical devices like microscopes or cameras for industrial, medical, surveillance or consumer applications, where focusing of light is required and where today focusing is being implemented by a
15 multitude of lenses with the need of relative displacement between the focusing arrangement and an image and/or object plane, by mechanical movement, either manually or electronically driven.
Various approaches have been developed for obtaining extended depth ol focus of an optical system. One of the known approaches, developed by the
20 inventor of the present invention, is disclosed in WO 03/076984. This technique provides an all-optical extended depth of field imaging. An imaging system produces images of acceptable quality of objects which are located at a wide variety of distances from the imaging system. A preferred embodiment of the imaging system includes an object, an auxiliary lens, a composite phase mask

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and a sensor arranged along an optical axis. Light from the object is focused by
the auxiliary lens in tandem with the composite phase mask, producing an image
which is incident on the detector. This technique is based upon placing a spatially highly resolved phase element on top of the lens aperture such that continuous set
5 of focal length is generated.
Another approach is disclosed for example in the following publications: US 6,069,738; US 6,097,856; WO 99/57599; WO 03/052492. According to this approach, a cubic phase mask is used in the aperture plane, and digital post processing is required to realize a focused image. More specifically:
10 US 6,069,738 discloses an apparatus and methods for extending depth of
field in image projection systems. An optical system for providing an in-focus, extended depth of field image on a projection surface includes an encoded mask or light encoder for preceding the light to include object information (or, equivalently, information about the desired image), and an extended depth of
15 field (EDF) mask, for extending the depth of field of the projection system. In addition to including object information, the encoded mask encodes the light from the light source to account for the variations introduced by the EDF mask in extending the depth of field, so that no post processing is required.
US 6,097,856 discloses an apparatus and method for reducing imaging
20 errors in imaging systems having an extended depth of field. An improved optoelectronic imaging system is adapted for use with incoherently illuminated objects, and which produces final images having reduced imaging error content. The imaging system includes an optical assembly for forming an intermediate image of the object to be imaged, an image sensor for receiving the intermediate
25 image and producing an intermediate image signal, and processing means for processing the intermediate image signal to produce a final image signal having a reduced imaging error content. A reduction in imaging error content is achieved, in p art, by including in the optical assembly a phase mask for causing the OTF of the optical assembly to be relatively invariant over a range of working distances,
30 and an amplitude mask having a transmittance that decreases continuously as a

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function of distance from the center thereof. The reduction in imaging error content is also achieved, in part, by including in the processing means an improved generalized recovery function that varies in accordance with at least the non-ideal calculated IOTF of the optical assembly under a condition of
5 approximately optimum focus.
WO 99/57599 discloses an optical system for increasing the depth of field and decreasing the wavelength sensitivity of an incoherent optical system. The system incorporates a special purpose optical mask into the incoherent system. The optical mask has been designed to cause the optical transfer function to
10 remain essentially constant within some range from the in-focus position. Signal processing of the resulting intermediate image undoes the optical transfer modifying effects of the mask, resulting in an in-focus image over an increased depth of field. Generally the mask is placed at or near an aperture stop or image of the aperture stop of the optical system. Preferably, the mask modifies only
15 phase and not amplitude of light, though amplitude may be changed by associated filters or the like. The mask may be used to increase the useful range of passive ranging systems.
WO 03/052492 discloses a technique providing extended depth of focus (EDF) to human eyes by modifying contact lenses, intraocular implants, or the
20 surface of the eye itself. This is accomplished by applying selected phase variations to the optical element in question (for example, by varying surface thickness). The phase variations EDF-code the wavefront and cause the optical transfer function to remain essentially constant within some range away from the in-focus position. This provides a coded image on the retina. The human brain
25 decodes this coded image, resulting in an in-focus image over an increased depth of focus.
Yet other approaches, disclosed for example in US 6,554,424 (as well as U.S. patent application publications 20040114103; 20040114102; and 20030142268) and US 4,955,904, utilize apodization of the aperture plane. More
30 specifically:

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US 6,554,424 describes a system and method for increasing the depth of focus of the human eye. The system is comprised of a lens body, an optic in the lens body configured to produce light interference, and a pinhole-like optical aperture substantially in the center of the optic. The optic may be configured to
5 produce light scattering or composed of a light reflective material. Alternatively, the optic may increase the depth of focus via a combination of light interference, light scattering, light reflection and/or light absorption. The optic may also be configured as a series of concentric circles, a weave, a pattern of particles, or a pattern of curvatures. One method involves screening a patient for an ophthalmic
10 lens using a pinhole screening device in the lens to increase the patient's depth of focus. Another method comprises surgically implanting a mask in the patient's eye to increase the depth of focus.
US 4,955,904 describes a masked intraocular lens for implantation into a human eye. The mask, which blocks only part of the lens body, together with the
15 pupil of the eye, defines a small aperture in the eye when the pupil is constricted, thereby increasing the depth of focus, as a pinhole camera does. When the pupil of the eye is dilated, additional light is allowed to pass through the pupil around the mask and to reach the retina to allow a person to see in dimmer light conditions. In one embodiment, the mask defines a small circular aperture and a
20 larger exterior annulus; the small circular aperture has an additional power intermediate between that needed for distance and close vision. Also provided is. a method for treating a patient with cataracts comprising replacing the patient's lens with this masked intraocular lens.
Some other vision improvement techniques are disclosed in the following
25 patent publications:
U.S. Patent No. 5,748,371 discloses extended depth of field optical systems. The system for increasing the depth of field and decreasing the
wavelength sensitivity and the effects of misfocus-producing aberrations of the
lens of an incoherent optical system incorporates a special purpose optical mask
30 into the incoherent system. The optical mask has been designed to cause the

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optical transfer function to remain essentially constant within some range from
the in-focus position. Signal processing of the resulting intermediate image
undoes the optical transfer modifying effects of the mask, resulting in an in-focus image over an increased depth of field. Generally the mask is placed at a
5 principal plane or the image of a principal plane of the optical system. Preferably, the mask modifies only phase and not amplitude of light. The mask may be used to increase the useful range of passive ranging systems.
WO 01/35880 discloses multifocal aspheric lens, an optical surface in close proximity to a person's pupil for correcting presbyopia, a method for
10 obtaining that optical surface, and a laser surgery system to carry out the method. The optical surface includes a first vision area, a second vision area surrounding the first area, and a third vision area surrounding the second vision area, the first vision area having a first substantially single power, the second vision area having a range of powers, the third vision area having a second substantially
15 single power distinct from the first single power, at least one of the first, second and third vision areas having an aspheric surface, and the other areas having spherical surfaces. The method includes reshaping the cornea to obtain this optical surface. The cornea may be reshaped on the anterior or an underlying surface by ablation or collagen shrinkage, wherein the ablation is performed by
20 applying an excimer laser, surgical laser, water cutting, fluid cutting, liquid
cutting or gas cutting technique. The method also includes obtaining this optical surface by placing a contact lens having the desired optical characteristics on the cornea. The laser surgery system includes a laser beam generator and a laser beam controller to regulate the beam striking the cornea to remove a selected
25 volume of corneal tissue from a region in an optical zone of the cornea with the ablative radiation, thereby forming a reprofiled region which has a first vision area, a second vision area surrounding the first area, and a third vision are* surrounding the second vision area.
U.S. Patent No. 5,965,330 discloses methods for fabricating annular mask
30 lens having diffraction-reducing edges. According to this technique, the lens

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body has an annular mask that forms a "soft edge" by gradually decreasing the
transmissivity radially from the center aperture to the annular mask area. The methods introduce varying levels of a coloring agent (e.g., dye) into certain portions of the lens.
5 WO 03/012528 describes an apparatus for generating a light beam with an
extended depth of focus. The apparatus includes a binary phase mask that generates a diffraction pattern including bright main ring and two side-lobe rings, an annular aperture mask that passes only part of the diffraction pattern, and a lens that causes the light passing through the annular aperture to converge
10 towards and cross the optical axis. Where the converging light crosses the optical axis, constructive interference takes place, generating a light beam that has an extended depth of focus.
U.S. Patents Nos. 5,786,883; 5,245,367 and 5,757,458 describe an annular mask contact lens designed to operate with the normal functioning of the human
15 pupil. An annular mask forms a small pinhole-like aperture on the contact lens enabling continual focus correction. The outer diameter of the annular mask allows the wearer to transmit more light energy through the pupil as brightness levels decrease. The contact lens may be structured with two separate and distinct optical corrections, both at the small aperture region and in the region beyond the
20 annular mask. Functional imaging is thus achieved for both bright and dim lighting, and over a wide range of viewing distances.
U.S. Patent No. 5,260,727 discloses wide depth of focus intraocular and contact lenses. According to this technique, the lens power can be a constant but the amplitude and phase of the wave across the pupillary aperture are variables.
25 The lens can be constructed by shading regions thereof in accordance with a mathematical function, e.g., a Gaussian distribution or Bessel function over a predetermined geometry, such as e.g., concentric, parallel or radial. The lens may be of single power or multiple power, e.g., of the bi-focal type.
U.S. Patent No. 5,905,561 discloses an annular mask lens for vision
30 correction having diffraction reducing edges. The lens body has an annular mask

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that forms a "soft edge" by gradually decreasing the transmissivity radially from
the center aperture to the annular mask area.
U.S. Patent No. 5,980,040 describes a pinhole lens and contact lens. The
contact lens comprises an optically transparent lens body having a concave
5 surface adapted to the patient's eye curvature and a convex surface. The lens has
three regions: (1) an annular region of a first optical power; (2) at the center of
said annular region, which is also at the optical center of said lens, a substantially pinhole-like aperture; and (3) a second larger annular region exterior to the first annular region.
10 U.S. Patent No. 5,662,706 discloses a variable transmissivity annular
mask lens for the treatment of optical aberrations, such as night myopia, spherical aberration, aniridia, keratoconus, corneal scarring, penetrating keratoplasty, and post refractive surgery complication. The lens has an annular mask having an aperture larger than conventional pinhole contact lens. The
15 aperture having a "soft" inside edge and which mask has a gradually increasing transmissivity radially toward the outer edge of the mask.
U.S. Patent No. 5,225,858 describes a multifocal ophthalmic lens adapted for implantation in the eye or to be disposed on or in the cornea. The lens has an optical axis, a central zone and a plurality of annular zones circumscribing the
20 central zone. Two of the annular zones have a first region with a far vision correction power and a second region with a near vision correction power. In an IOL embodiment, the vision correction power between far and near is progressive, and each of the second regions has a major segment in which the near vision correction power is substantially constant. The power in the central
25 zone varies.
U.S. patent No. 6,554,859 discloses an intraocular lens for implantation in an eye of a patient. The lens includes a multifocal optic and a movement assembly. The optic has maximum add power which is less than the add power required for full near vision for a pseudophakic eye. The movement assembly is
30 coupled to the optic and is adapted to cooperate with the eye of the patient to

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effect accommodating movement of the optic in the eye. Lens systems including two optics and two movement assemblies are also provided. The intraocular
lenses and lens systems are particularly useful when implanted in the eyes of a
patient after removal of the natural lenses.
5 U.S. Patent Nos. 6,576,012 and 6,537,317 disclose a binocular lens system
for improving the vision of a patient. The system includes first and second ophthalmic lenses. Each of these lenses is adapted for implantation in an eye or to be disposed on or in the cornea. The first lens has a first baseline diopter power for distance vision correction and the second ophthalmic lens has a second
10 baseline diopter power for other than distance vision correction. The ophthalmic lenses may be intraocular lenses which are implanted in the eyes of a patient or has natural lenses or following removal of the natural lenses.
U.S. Patent No. 6,474,814 discloses a multifocal ophthalmic lens with induced aperture. The multifocal lenses are defined by nonconical aspheric
15 optical surfaces. Various alternative surface shapes provide a central distance vision region surrounded by an optical step. The optical step has rapidly increasing power in the radial direction which creates an induced aperture through which the cortical elements of the vision system are induced to concentrate. The induced aperture results in increased clarity in distance vision.
20 Nonconical aspheric optical surfaces are defined to produce the desired optical power distributions. These surface functions are also provided in form of polynomial series for simplicity of use in computer driven lathes for shaping contact lenses. This technique refers to contact lenses, scleral lenses, intraocular lenses, and lenses impressed or surgically shaped within the corneal tissue.
25 U.S. Patent No. 6527389 describes an improved multifocal ophthalmic
lens, which has a plurality of alternating power zones with a continuously varying power within each zone, as well as in transition from one zone to another. In other words, a plurality of concentric zones (at least two) are provided in which the variation from far to near vision correction is continuous, i.e., from
30 near correction focal power to far correction focal power, then back to near, and

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again back to far, or vice versa. This change is continuous (progressive), without any abrupt correction changes, or "edges". Two versions of this technique are disclosed. In the first version continuous, alternating power variation is accomplished by a continuously changing curvature of the lens posterior surface,
5 thereby altering the angle of impact of light rays on the eye. In the second version continuous, alternating power variation is accomplished by creating non-homogeneous surface characteristics having refractive material indexes which continuously vary in the lens radial direction (out from the optical axis).
U.S. Patent No. 5,715,031 discloses concentric aspheric multifocal lens
10 designs which use a combination of an aspheric front surface, which results in aberration reduction and contrast vision enhancement, along with a concentric multifocal back surface, to produce a lens design which affords clear vision at a distance and also near without a loss in contrast which is generally typical of prior art simultaneous vision, concentric multifocal lens designs. The aspheric
15 surface improves the modulation transfer function (MTF) of the lens eye combination which improves the focus and contrast of both distance and near images. The design form is valid for contact lenses and intraocular lenses.
U.S. Patent No. 6,024,447 discloses an enhanced monofocal ophthalmic lens for providing a monofocal vision correction power with an enhanced depth
20 of focus. The lens is adapted to be implanted into an eye, placed over the eye, or to be disposed in a cornea of the eye. The ophthalmic lens includes a baseline diopter power for far vision correction, a first zone having a first vision correction power, and a second zone having a second vision correction power. The second zone is located radially outwardly of the first zone. The first zone
25 includes a near vision correction power, and the second zone includes a far vision correction power. A maximum diopter value of the first zone is approximately 0.7 diopters above the baseline diopter, and a minimum diopter value of the second zone is approximately 0.5 diopters below the baseline diopter power. The first zone is adapted for focusing light at a first predetermined distance from the
30 retina of the user, and the second zone is adapted for focusing light at a second

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predetermined distance from the retina of the user. The second predetermined distance is approximately opposite and equal to the first predetermined distance.
A third zone, which is substantially similar to the first zone, is located radially outwardly of the second zone, and a fourth zone, which is substantially similar to
5 the second zone, is located radially outwardly of the third zone. A third vision correction power of the third zone is approximately the same as the first vision correction power of the first zone, and a fourth vision correction power of the fourth zone is approximately the same as the second vision correction power of the second zone.
10 U.S. Patent No. 6,451,056 describes an intraocular lens for increased
depth of focus. The intraocular lens provides substantially increased depth of focus for accurate near and far vision with an optic much thinner than a natural lens, the lens being rigid, vaulted posteriorly and adapted for posterior positioning in the capsular bag. The optic is positioned substantially farther from
15 the cornea man a natural lens, so that a cone of light exiting the optic to impinge upon the retina is much smaller than a cone of light from a natural lens. Typically, the optic may be about 1.0 mm thick and its distance from the cornea 7.0-8.0 mm.
WO 03/032825 discloses a method of designing a contact lens or other
20 correction for providing presbyopia correction to a patient. The method relies on wavefront aberration measurement data for providing a best form correction. Preferably the correction is in the form of a multifocal translating style alternating vision contact lens or a simultaneous vision style correcting lens. A method for designing a correction for improving a person's vision is directed to
25 correcting higher order aberrations in such a manner that a residual amount of the higher-order rotationally symmetric aberration is greater than a residual amount of the higher-order rotationally asymmetric aberration after the correction. The design method is directed to correcting asymmetric higher order aberrations induced by decentering of a multifocal contact lens that has residual spherical
30 aberration which provides increased depth of field.

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EP 0369561 discloses a system and process for making diffractive contact and intra-ocular lenses. The optical system includes the following principal elements in optical alignment along an optical axis, for accomplishing the indicated steps of the process: a laser for emission of ultraviolet light along the
5 optical axis; a zone plate mask in the path of irradiation by the laser; and an imaging lens to project, with radiation from the laser, an image of the mask on the concave inner surface of an eye lens mounted coincident with the image surface of the optical system, thereby ablating the eye lens imagewise of the mask to generate a phase zone plate on the eye lens. The laser beam scans the
10 zone plate mask to generate a composite image on the image surface. Alternatively, the phase zone plate is generated on the concave surface of a glass blank at the image surface to form a tool from which molds, and in turn lenses, are replicated. The light source is an argon fluoride excimer laser, emitting at 193 nm. The lens is a variable magnification lens to project various size images of the
15 mask for producing zone plates of various powers as desired.
The known techniques, however, suffer from such drawbacks as unavoidable scattering of a significant part of energy towards the outer regions of a field of view of the system; the need for digital post processing; damaging the spatial frequencies transmission and the energetic efficiency.
20
SUMMARY OF THE INVENTION
There is accordingly a need in the art for an all-optical extended depth of focus technique.
The present invention solves the above problems by providing an imaging
25 arrangement utilizing an optical element located adjacent to, attached to the surface of, or incorporated within an effective aperture of the imaging arrangement. It should be noted that the term "effective aperture of the imaging arrangement" used herein signifies a light collecting aperture, which may be the actual size of an imaging lens itself or an aperture in front of the imaging lens, as
30 the case may be, for example the eye's pupil in ophthalmic applications. It should

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also be noted that the imaging arrangement of the present invention may utilize a
an array of lenses (lenslet array), in which case an array of optical elements is
used, each optical element being associated with a corresponding one of the
lenses.
5 The optical element of the present invention is configured as a phase-
affecting, non-diffractive, thin-layer optical element that codes the lens aperture so as to provide an all-optical effect of extending the depth of focus. The optical element may be configured as a phase-only element or as a phase and amplitude affecting element. The term "all-optical" used herein signifies that a need for
10 image processing is eliminated or at least substantially reduced.
The optical element is thus insensitive to wavelength and polychromatic
illumination, does not scatter energy towards the outer regions of the field of
view thus providing a very high energetic efficiency at the region of interest
(close to 100%), and does not require apodization. It is important to note that
15 such a high efficiency cannot be achieved by a diffractive optical element even if
it is phase-only element, because of the divergence of light to unwanted diffraction orders. Since the technique of the present invention does not require digital post processing, it is adequate for ophthalmic applications or other "non-computer" based applications.
20 The optical element of the present invention is configured to define a
mask (preferably a binary mask) of spatially low frequencies transitions. This may actually be achieved by designing the optical element so as to define at least one transition region (e.g., line or circle), to be surrounded by regions of the imaging lens, in the plane of the imaging lens. This at least one region of the
25 optical element together with the imaging lens' regions define a predetermined pattern formed by spaced-apart optically transparent features of different optical properties (i.e., differently affecting the phase of light passing through the imaging lens arrangement).
The position(s) of the transition region(s) of the optical element within the
30 imaging lens plane (i.e., the affective aperture plane) are selected, considering at

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least the affective aperture size of the imaging lens. These positions are
appropriately selected so as to generate proper phase interference relation
between light portions passing through different regions of the lens arrangement
corresponding to the different features of the pattern, to thereby enable reducing
5 a quadratic phase factor resulting from light getting out of focus of the imaging lens and thus maximize a defocused optical transfer function (OTF) of the imaging lens arrangement.
As indicated above, in order to design the optimal configuration for the extended depth of focus (EDOF) optical element, the effective aperture of the
10 imaging lens is to be taken into consideration. The optical power distribution of
the imaging lens and/or focal length may also be taken into consideration: since
the EDOF has no optical power, it may be added to an imaging lens in order to
shift the range of extended depth of focus around a certain given optical power.
The optimal geometry and dimensions of the EDOF element (i.e., at least
15 one transition region) are determined using an optimization algorithm (based on a numerical or analytical approach, resulting in a spatially low frequency all-optical extended depth of focus), which determines N positions) for the transition region(s) of the element within a given imaging lens (i.e., for a given effective aperture size).
20 Considering ophthalmic applications, where the effective aperture of the
lens (eye pupil, or contact lens, or lens of spectacles) can be defined by a certain relatively narrow range of values common for most of patients, the EDOF of the present invention can be designed to be universal for a great amount of patients. Such a universal EDOF is configured to allow the depth of focus region
25 equivalent to 5 diopters for the effective aperture of 2-3mm. For a smaller percentage of patients having a higher difference between the near and far vision, the design of the EDOF element takes into account the optical power of the imaging lens with which the element is associated.
The position of the transitions) (being pi-phase transition for a certain
30 wavelength for which the EDOF is designed) generates invariance to quadratic

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phase distortions (which multiply the CTF of the imaging lens, corresponding to
the effect of getting out of focus) under the operation of auto correlation. Due to the fact that the aperture mask (formed by the EDOF and imaging lens) is constructed out of spatially low-frequency transitions, it does not spread energies
5 away from the zero order of diffraction and its energetic efficiency is close to 100%.
It should be noted that auto correlating the CTF is done to compute the optical transfer function (OTF) of the imaging system. The position of the EDOF transition(s) may be computed using iterative algorithm in which M positions are
10 examined and eventually those of them are selected, which provide maximal contrast of the OTF under a set of out of focus locations. The meaning of OTF's contrast optimization (maximizing) is actually having the out of focused OTF bounded as much as possible away from zero.
The extended depth of focus (EDOF) element of the present invention is
15 configured to generate proper phase interference relation allowing significant cancellation of the quadratic phase factor obtained due to getting out of focus. The EDOF element is a phase-affecting element (e.g., phase-only binary mask element), which is neither a refractive nor a diffractive element. In contrast to a refractive element, the EDOF filter of the present invention can be produced as a
20 thin phase layer constructed in a low-cost lithographic technique with the thickness of the phase layer being of only one wavelength (e.g., around 0.5 micron in the case of ambient light illumination), similar to the fabrication approaches used for the conventional diffractive optical elements. On the other hand, in contrast to diffractive optical elements, the EDOF of the present
25 invention has the spatial feature(s) of very low frequency. The element contains only very limited number of features and periods at low spatial frequency (period of about 1,000 wavelengths). The property of the optical element of the present invention allows for obtaining truly energetic efficient EDOF, since not only all the energy is passed through the element itself (it is substantially phase only) but
30 also all of the energy is concentrated at the proper transversal and longitudinal

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region of interest (in contrast to a diffractive element that has energetic split
either between multiple longitudinal focal planes or between traversal diffraction
orders).
Hence, high energetic efficiency (close to 100%) of the optical element of
5 the present invention provides extended depth of focus, in contrast to approaches based on the use of diffractive optical elements that split the energy between several diffraction orders/focal planes and that are basically equivalent to smaller lens aperture (also having larger depth of focus). In addition, the low spatial frequency of the invented approach eliminates its sensitivity to wavelength and
10 polychromatic illumination which is a problematic topic with diffractive optical elements. Additionally, it is important to note that the invented approach is an all-optical technique that does not require numerical computation, and when it is used for ophthalmic applications it does not assume brain based decoding or adaptation process since an extended depth of focus image is identical to the
15 image of an object itself.
There is thus provided according to one broad aspect of the present invention, an imaging arrangement comprising: an imaging lens assembly
including at least one lens having a certain affective aperture, and at least one
optical element associated with said at least one lens and configured to provide
20 an extended depth of focus of the imaging arrangement, said optical element being configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition, said optical element together with its associated lens defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least
25 one phase transition region of the optical element within the lens plane being determined by at least a dimension of said affective aperture.
According to another broad aspect of the invention, there is provided an imaging arrangement comprising: an imaging lens assembly including at least one lens having a certain affective aperture, and at least one optical element
30 associated with said at least one lens and configured to provide an extended

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depth of focus of the imaging arrangement, said optical element being configured
as a phase-only, non-diffractive binary mask defining a spatially low frequency
phase transition, said optical element together with its associated lens defining a
predetermined pattern formed by spaced-apart optically transparent features of
5 different optical properties, position of at least one phase transition region of the optical element within the lens plane being determined by at least a dimension of said affective aperture.
According to yet another aspect of the invention, there is provided an imaging arrangement comprising: an imaging lens assembly including at least
10 one lens having a certain affective aperture, and at least one optical element
associated with said at least one lens and configured to provide an extended depth of focus of the imaging arrangement, said optical element being configured
as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition, said optical element together with its associated lens
15 defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least one phase transition region of the optical element within the lens plane being determined by at least a dimension of said affective aperture such that the optical element produces proper phase interference relation between light portions passing through
20 different regions of the imaging arrangement corresponding to the different features of the pattern to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of the imaging lens arrangement by providing the out of focus OTF as much as possible away from zero.
25 According to yet another broad aspect of the invention, there is provided
an imaging arrangement comprising an imaging lens assembly including at least one lens having a certain affective aperture, and at least one optical element associated with said at least one imaging lens and configured to provide an extended depth of focus of the imaging arrangement, said optical element being
30 configured as a phase-affecting, non-diffractive element defining a certain

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pattern of spatially low frequency phase transitions within a plane of the imaging lens, such that said optical element together with its associated imaging lens determine a predetermined pattern formed by spaced-apart optically transparent features differently affecting phase of light passing through the imaging
5 arrangement, positions of the phase transitions of the optical element within the imaging lens plane being determined by at least a dimension of said affective aperture to reduce sensitivity of the imaging arrangement to shifts of a Coherent Transfer Function (CTF) of the imaging lens while getting out of focus.
According to yet another broad aspect of the invention, there is provided
10 an imaging arrangement comprising an array of lenses each having a certain affective aperture, and an array of optical elements each optical element being associated with one lens of the lenslet array and being configured to provide an extended depth of focus of the imaging arrangement, said optical element being configured as a phase-affecting, non-diffractive optical element defining a
15 spatially low frequency phase transition, said optical element together with its associated lens defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least one phase transition region of the optical element within the lens plane being determined by at least a dimension of said affective aperture.
20 According to yet another aspect of the invention, there is provided an
imaging lens for use in patients' spectacles, the imaging lens being configured to define a certain affective aperture and carrying an optical element configured to provide an extended depth of focus, said optical element being configured as a phase-affecting, non-diffractive optical element defining a spatially low
25 frequency phase transition, said optical element together with its associated lens defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least one phase transition region of the optical element within the lens plane being determined by at least a dimension of said affective aperture.

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19
According to yet another aspect of the invention, there is provided a display device carrying an imaging arrangement, which comprises an array of imaging lenses each having a certain affective aperture, and an array of optical elements each associated with a corresponding one of said lenses and configured
5 to provide an extended depth of focus, said optical element being configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition, said optical element together with its associated lens defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least one phase transition
10 region of the optical element within the lens plane being determined by at least a dimension of said affective aperture.
It should be understood that such a display device may be a dynamic-type device for use with or being part of an electronic device (such as a mobile phone) or may be a static display device.
15 According to yet another aspect of the invention, there is provided a
system for creating an image of an object on a detector plane, the system comprising an imaging lens arrangement formed by an imaging lens assembly including at least one lens having a certain affective aperture and at least one optical element configured to provide an extended depth of focus of the imaging
20 arrangement, said optical element being configured as a phase-affecting, non-diffractive element defining a spatially low frequency phase transition, said optical element together with its associated imaging lens defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least one phase transition region of the
25 optical element within the imaging lens plane being determined by at least a dimension of said affective aperture such that the optical element produces proper phase interference relation between light portions passing through different regions of the imaging arrangement corresponding to the different features of the pattern to thereby enable reducing a quadratic phase factor

WO 2006/018834 20 PCT/IL2005/000868
resulting from light getting out of focus of the imaging lens and maximize a
defocused optical transfer function (OTF) of the imaging arrangement.
According to yet another aspect of the invention, there is provided an
optical element for use with an imaging lens for extending depth of focus of
5 imaging, the optical element being configured as a phase-affecting, non-
diffractive optical element defining a predetermined pattern of spatially low
frequency phase transitions, said pattern being defined by an affective aperture of the given imaging lens.
According to yet another aspect of the invention, there is provided an
10 optical element for use with an imaging lens for extending depth of focus of imaging, the optical element being configured as a phase-only, non-diffractive binary element defining a predetermined pattern of spatially low frequency phase transitions, said pattern being defined by an affective aperture of the given imaging lens. According to yet another aspect of the invention, there is provided
15 an optical element for extending depth of focus of imaging, the optical element being configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition.
According to yet another aspect of the invention, there is provided an optical element for extending depth of focus of imaging, the optical element
20 being configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition, the optical element defining a predetermined pattern of phase transition regions, said transition regions being arranged in accordance with an affective aperture of a given imaging lens for which the optical element is designed, so as to provide said transition regions of
25 the optical element within predetermined positions in the imaging lens plane, to provide periodic replication of a lateral phase shape of a light field propagating through the imaging lens with said optical element.
According to yet another aspect of the invention, there is provided an optical element for extending depth of focus of imaging, the optical element
30 being configured as a phase-only, non-diffractive binary element defining a

WO 2006/018834 21 PCT/BL2005/000868
spatially low frequency phase transition, the optical element defining a
predetermined pattern of phase transition regions, said transition regions being
arranged in accordance with an affective aperture of a given imaging lens for which the optical element is designed, so as to provide said transition regions of
5 the optical element within predetermined positions in the imaging lens plane, to provide periodic replication of a lateral phase shape of a light field propagating through the imaging lens with said optical element.
According to yet another aspect of the invention, there is provided a method for providing a certain extended depth of focus of an imaging system, the
10 method comprising applying an aperture coding to an imaging lens having a certain effective aperture, by applying to the imaging lens a phase-affecting non-diffractive optical element configured to define a spatially low frequency phase transition arrangement and thereby provide a predetermined pattern of spaced-apart substantially optically transparent features of different optical properties
15 within the imaging lens plane, thereby producing phase interference relation between light portions passing through different regions of the lens arrangement corresponding to the different features of the pattern so as to reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of the imaging lens
20 arrangement.
According to yet another aspect of the invention, there is provided a method for providing a certain extended depth of focus of an imaging system, the method comprising designing a phase-affecting non-diffractive optical element to be used with an imaging lens having a certain effective aperture, said designing
25 comprising selecting N positions for phase transitions within the imaging lens effective aperture as those providing maximal contrast of an Optical Transfer Function (OTF) of the imaging system under a set of out of focus locations, thereby providing the out of focus OTF as much as possible away from zero.

WO 2006/018834 PCT/IL2005/000868

BRIEF DESCRIPTION OF THE DRAWINGS
In order to understand the invention and to see how it may be carried out
in practice, preferred embodiments will now be described, by way of non-
limiting example only, with reference to the accompanying drawings, in which:
5 Fig. 1A is a schematic illustration of an example of an imaging system
utilizing an imaging lens arrangement configured according to the present invention;
Fig. 1B schematically illustrates another example of an imaging lens
arrangement of the present invention;
10 Fig. 1C schematically illustrates yet another example of an imaging lens
arrangement of the present invention, suitable to be used with a display device;
Figs. ID and IE show two examples, respectively, of the optical element
of the present invention being implemented integral with an imaging lens;
Figs. 2A to 2C show three examples, respectively, of the contour of the
15 optical element of the present invention suitable to be used in the imaging lens arrangement;
Figs. 3A to 3D illustrate the effect of the present invention as compared to the conventional approach;
Figs. 4A to 41 exemplify face images obtained with the out of focus
20 parameter 4y/D2 varying from -0.2 (Fig. 4A) up to 0.2 (Fig. 41) at steps of 0.05, for the case where the optical element of the present invention is used;
Figs. 5A to 51 exemplify face images obtained with the out of focus
parameter 4v[//D varying from -0.2 (Fig. 5A) up to 0.2 (Fig. 51) at steps of 0.05,
for the case where no optical element of the present invention is used;
25 Fig. 6 shows the results of examining the sensitivity of the optical element
to wavelength variations;
Figs. 7A to 7D show experimental results for imaging a Rosette with and without the EDOF element of the invention: Fig. 7A corresponding to the in focus position of Rosette with no EDOF element, Fig. 7B corresponds to in-
30 focus position with the EDOF element, Fig. 7C corresponds to the out of focus

WO 2006/018834 23 PCT/IL2005/000868
position of Rosette with no EDOF element, and Fig. 7D corresponds to the out of focus position with the EDOF element;
Figs. 8A to 8D and Figs. 9A to 9H show experimental verification of the extended depth of focus technique of the present invention for polychromatic
5 spatially non coherent illumination;
Fig. 10A illustrates the performance of the ophthalmic depth of focus application of the present invention, for the case where the optical element is attached to a contact lens; and
Fig. 10B illustrates the performance of the ophthalmic depth of focus
10 application of the present invention, for the minimal range at which focus is obtained with and without the optical element of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Fig. 1A, there is schematically illustrated an imaging system
15 10 utilizing an imaging lens arrangement 12 of the present invention. The imaging system 10 is formed by an object 13 that is to be imaged, the imaging lens arrangement 12, and a light detector unit 16. The imaging lens arrangement 12 includes a certain number of lenses 12A (generally at least one lens, single lens being shown in the present example) having a certain effective aperture D
20 (which in the present example is the lens diameter), and a certain number of optical elements 12B (single element in the present example) associated with the lens(es) 12A. Such optical element 12B is configured and operable as an extended depth of focus (EDOF) element.
The optical element 12B is configured in accordance with the parameters
25 of the lens 12A, i.e., its effective aperture and optionally also the optical power
distribution and/or focal length. The optical element 12B is configured as a
phase-affecting non-diffractive mask. Preferably, as shown in the present
example, the mask 12B is implemented integral with the lens, namely as a pattern
on the lens surface.

WO 2006/018834 24 PCT/IL2005/000868
Generally, the mask 12B may be a separate element attached to the lens or
located close thereto. This is illustrated in Fig. IB showing an imaging system
100 utilizing a lens arrangement 112 that includes a lens 12A and a phase-
affecting non-diffractive optical element 12B located close to the lens in front
5 thereof.
Fig. 1C shows schematically an imaging system 200 according to yet
another example of the invention. Here, an imaging lens arrangement 212
includes an array of lenses 12A, formed by four such lenses Li, L2, L3 and L4 in
the present example, and an array 12B of optical elements OE1, OE2, OE3 and
10 OE4 each associated with a corresponding lens of the lenslet array.
Such system 200 may for example be used with a display panel or screen
13 (constituting an object) aimed at facilitating the imaging of the display/screen
(e.g., of a mobile phone device) by people having close vision problems. The
imaging arrangement 212 is accommodated at a small distance (a few millimeters
15 from a surface 13' of the display panel 13. Also, in the present example the
optical elements' array 12B is located downstream of the lenslet array 12A with
respect to light propagation from the object 13 towards a light detector 16 (patient's eye). The use of such lenslef and EDOF elements' arrays provides for bringing the closest focus plane FP of the imaging arrangement 212 as close as
20 possible to the object 13 plane, so that people with the close vision problems as well as people with normal vision will be able to see the screen. In addition, bringing the closest focus plane closer to the object plane reduces the demagnification ratio of the object that is to be focused.
Preferably, the optical element 12B is configured as a phase-only binary
25 mask. It should, however be noted that generally the element 12B may be configured as a phase and amplitude mask.
The optical element 12B is configured to define at least one spatially low frequency transition region, and, together with the lens 12A regions, define a predetermined pattern of spaced-apart substantially optically transparent features
30 differently affecting the phase of light passing therethrough. The pattern is thus

WO 2006/018834 25 PCT/IL2005/000868
formed by one or more transition regions of the optical element, spaced by the
regions of the lens, in the imaging lens plane. The transition regions are pi-phase
transitions for a certain wavelength for which the mask 12B is designed. The
arrangement of these transition regions (positions within the lens 12A plane) is
5 determined by the effective aperture of the given imaging lens 12 A (and possibly
also optical power of the lens) so as to maximize the defocused OTF of the entire
imaging arrangement. To this end, the pattern is such as to generate proper phase
interference relation between light portions passing through different regions of
the lens arrangement to thereby enable reducing a quadratic phase factor
10 resulting from light getting out of focus of the imaging lens.
As shown in Figs. ID and IE, the optical element may be implemented as
a surface relief on the imaging lens (Fig. ID), namely, a pattern of spaced-apart
regions R1 and R2 of variable lens thickness; or as a pattern of lens regions R1
and R2 made of materials with different refractive indices n} and n2 (Fig. IE). In
15 the case of different refractive index materials, a certain optically transparent
material of a refractive index different from mat of the lens may be coated on
selective spaced-apart regions of the lens surface.
Figs. 2A to 2C show two specific but not limiting examples, respectively,
of the contour of the optical element 12B. In the example of Fig. 2A, the mask 20 12B is designed as an annular transition region 14 (generally, at least one such
region; an array of concentric rings may be used as well). In the example of Fig.
2B the mask is designed as a grid formed by two mutually perpendicular pairs of
bars (lines) B1-B’1 and B2-B'2. In the example of Fig. 2C, the element 12B is a
mask formed by a two-dimensional array of basic grid-elements BE. For
25 example, the transition regions along the bar line are pi-phase transitions and the
regions of intersection between the perpendicular bars are zero-phase transitions.
The optimized contour for the optical element is obtained solving an algorithm,
which will be described further below.
It should be noted that the mask (pattern) may and may not be
30 symmetrical relative to the center of me lens. In such an arrangement, for

WO 2006/018834 26 PCT/BL2005/000868
example, the four n-phase bars, two vertical (along Y-axis) and two horizontal (along X-axis) bars, that are illustrated in Fig. 2A, may be shifted transversally along the x-y plane to be not centered around the center of the lens.
It should also be noted, although not specifically shown, that the pattern
5 may be configured to define microstructures inside the phase transition region
(e.g., inside the pi-phase transition ring of Fig. 2A), namely, each phase
transition region may be of a variable spatially low frequency of phase transition
such as for example TI/2, K, ....
The present invention provides the EDOF element 12B in the form of a
10 mask of TV segments within the effective aperture of the imaging lens 12A. It should be understood that instead of having a mask that blocks energy in some of segments and transmits in the other, the invention provides the substantially phase-only, non-diffractive mask 12B, that is either 1 or (-1) depending on the segment
15 As indicated above, the mask 12B is designed to maximize the defocused
OTF of the imaging system, by generating invariance to quadratic phase factor (which factor is generated when the image is defocused and multiplies the CTF of the imaging lens). To this end, in order to optimally design the mask 12B, a search is made for the segments that will obtain the transmission value of (-1)
20 such that the OTF, due to the out of focus distortion, is bounded as much as possible away from zero. Since the mask 12B is a binary phase mask, no energy efficiency consideration is used (the transmission is 100%). Following these criteria, a search is made over all the possibilities and combinations for the aperture coding mask. The out of focus distortion is modeled by multiplying the
25 aperture with the following expression:

(1)


wherein D(v) is the CTF of the imaging lens 12A corresponding to the out of focus position of the object being imaged, D is the diameter of the imaging lens 12A (generally, the effective aperture of the lens), v is the coordinate of the

WO 2006/018834 27 PCT/IL2005/000868

aperture of the lens (in the plane of CTF), and ^is the phase factor representing the amount of getting out of focus:



wherein X is the wavelength, u is the distance between the imaging lens 12A and
5 the object 13, v is the distance between the imaging lens 12A and the sensor 16 (detector), and F is the focal length of the imaging lens. It should be noted that the term "imaging lens " refers here to the effective aperture thereof.
When imaging condition is fulfilled:

(3)

10 the distortion phase factor y equals zero.
The OTF is computed by auto-correlating the CTF with itself:
OTF(v) = CTF(v) ® CTF(v) (4)
The auto correlation operation consists of shifting two CTF functions to the
opposite directions, respectively, and then multiplying and summing the
15 result The so-obtained OTF relates to a spatial frequency that corresponds to the amount of the shift At high frequencies (large shifts), the multiplication and the summing are averaged to zero in the case of out of focus. Hence, the OTF does not transmit high frequencies when the image is defocused.
The phase mask (e.g., ring) of the present invention is aimed at reducing
20 the high-frequency cancellation at large shifts of the CTF (the OTF is an auto
correlation of the CTF). To this end, the mask is configured to invert the sign of
part of the light field that before (i.e., pure lens with no EDOF correction) was
averaged to zero (and this is why the OTF did not transmit the high spatial
frequencies).
25 The OTF is the Fourier transform of the intensity point spread function,
and it is used to express the spatial-frequencies transmission function for intensity, when incoherent illumination is applied. Thus, the mathematical formulation for maximizing the OTF is as follows:

WO 2006/018834

PCT/IL2005/000868










i.e., find the values for a„ that provide maximum for the minima of the auto
correlation expression where an = (l,-l) (it equals either 1 or -1).
5 It should be noted that the above-described iterative numerical algorithm
is a specific but not limiting example of defining the EDOF element configuration. Other techniques can be used as well, for example numerical approached based on entropy minimization, or maximal likelihood, or other numerical or analytical approaches, resulting in a spatially low frequency all-
10 optical extended depth of focus.
Figs. 3A to 3D illustrate the effect of the present invention. Three examples of absolute value of the OTF (called Modulation Transfer Function -MTF) are obtained for different phase factor values: y=1.6 in Fig. 3A; y=4.8 in Fig. 3B; y=9.8 in Fig. 3C and y=12.8 in Fig. 3D. In each of these figures, curve
15 C1 corresponds to the MTF while at the in-focus state, curve C2 corresponds to the defocused MTF of an imaging system without the use of the correction optical element (EDOF element) of the present invention (mask 12B in Fig. 1), and curve C3 corresponds to the defocused MTF of the system with the correction element.
20 The transversal invariance may be obtained using the phase element
producing periodic replication of the phase shape, namely lateral replication of the phase shape. Turning back to Fig. 2C exemplifying a mask formed by a two-dimensional array of basic elements BE, when large lateral shifts (high frequencies) exclude part of the phase shape, a complimentary part is inserted
25 from another spatial period of the mask thus producing the phase period by replication. The replication of the basic period of the transitions (that of the basic element BE) thus reduces the sensitivity to lateral shifts. The longitudinal invariance is obtained as follows: Given the longitudinal distance between the phase element and a sensor (the imaging lens plane or the effective aperture


WO 2006/018834 PCT/IL2005/000868
plane), which is the lens of the human eye in case of ophthalmic applications, free space propagation of the mask function for this distance is considered. The result is a phase and amplitude distribution. The amplitude is dropped, leaving only the phase profile. In many cases, binarization of the phase function may
5 provide sufficiently good results as well. The binarization realizes spatial mask which is easier for fabrication.
Reference is made to Figs. 4A-4I and Figs. 5A-5I illustrating how a face image looks like when the defocusing parameter 4y/D is varied from -0.2 (Figs. 4A and 5A) up to 0.2 (Figs. 41 and 51) at steps of 0.05. Figs. 4A-4I show the case
10 where the mask (optimally designed) of the present invention is used, and Figs. 5A-5I shows the case where no such aperture coding mask is used. In the present example, the EDOF element configured similar to that of Fig. 2B was used. As clearly seen in the figures, a difference in distortions between images of Figs. 4A-4I and 5A-5I exists due to the aperture coding mask of the present invention.
15 Fig. 6 shows the results of examining the sensitivity of the coding mask
(EDOF element) of the present invention to wavelength variations. In the present example, an imaging lens arrangement (imaging lens with a coding mask) was illuminated with wavelength l1=0.8lo, wherein l0 is the wavelength for which the mask was designed and fabricated to present pi-phase transition(s), and the
20 defocusing parameter of 4y/D2=0.15 was used. As could be seen, the out of focus distortion obtained due to the usage of the mask is still very low despite the fact that the mask is no longer optimized (since the mask pattern features are pi-phase transitions for l0 and not for l1).
Figs. 7A-7D show another experimental results obtained for imaging a
25 Rosette. Here, Fig. 7A shows an image corresponding to the in focus position of
the Rosette obtained with no EDOF element of the invention; Fig. 7B shows an in-focus image obtained with the EDOF element; Fig. 7C corresponds to the out of focus position of the Rosette with no EDOF element; and Fig. 7D shows an
image of the out of focus Rosette obtained with the EDOF improvement of the 30 present invention. In the present example, the EDOF element configured similar

WO 2006/018834 29 PCT/IL2005/000868
to that of Fig. 2A was used. As shown, the use of the EDOF element of the present invention provides improvement in spatial high frequencies and the effect
on the input when the system is in focus.
It should be noted that in all the images presented in Figs. 4A-41,5A-51,6
5 and 7A-7D, showing sufficient extension of the depth of focus, no digital post processing was applied. Applying such processing might further improve the obtained results.
The inventor has performed experimental verification of the extended depth of focus approach for polychromatic spatially non coherent illumination
10 (general lighting). The experimental conditions were as follows: the focal length of the imaging lens F=90mm, the distance between the imaging lens and the object v=215.9mm, the distance between the imaging lens and detector (CCD) u=l 54.3mm, the aperture of the imaging lens D=16mm. Thus, the measurement for the phase distortion y equals to 13 for the case where the object is moved a
15 distance of 1.5mm from the in cofus plane, and y=17 for moving the object a distance of 2mm. The value of the phase factor \\t is computed following equation
2 above and using the distances and the diameter of the lens (affective aperture of
the lens) in the optical system. The experimental results under these conditions are shown in Figs. 8A-8D and Figs. 9A-9H. In the present example, the EDOF
20 element configured similar to mat of Fig. 2A was used.
Here, Fig. 8A corresponds to an in-focus position without the use of the optical element of the present invention; Fig. 8B corresponds to the in-focus with such element, Fig. 8C corresponds to the defocused position without the optical element at y=13(+1.5mm), and Fig. 8D corresponds to the defocused position
25 with the optical element at y=13(+1.5mm).
Fig. 9A shows an in focus image obtained without the optical element; Fig. 9B shows the defocused image at y=13 (+1.5mm) without the element; Fig. 9C shows the defocused image at y=17 (+2mm) without the element; Figs. 9D-9F correspond to Figs. 9A-9C but with the optical element; Fig. 9G shows the
30 defocused image at y=13(+1.5mm) obtained without the element with

WO 2006/018834 31 PCT7IL2005/0O0868

polychromatic illumination; Fig. 9H shows the defocused image at y=13(+1.5mm) obtained with the optical element for polychromatic illumination.
As indicated above, the imaging lens arrangement of the present invention
may be used for ophthalmic applications. In order to allow insertion of the
5 imaging lens arrangement into the eye, the surface of the lens arrangement is to be flat. The fabrication techniques suitable to manufacture such an imaging lens arrangement (i.e., flat patterned imaging lens) include for example etching (wet
or dry) or laser drilling or lathe grinding to obtain the desired spatial structure
(surface relief), and then filling the evacuated volume by a material of a
10 refraction index different from that of the lens, providing a refraction index difference is such that the outer region of the mask is flat while the desired phase difference is generated, required as buffering phase region that generates proper equalization between regions of the lens aperture for the interference effect Another realization could be by diffusion or photo polymerization mat does not
15 include developing or removing of the polymerized material. Yet another approach which is related to eye surgery could be by implanting artificial tissue having difference in refraction index in comparison to the existing tissue of the eye. The EDOF element of the present invention (having no optical power) is added to the focal power of a certain lens which is to be obtained. For example, if
20 a patient needs -1 diopter glasses and 3 diopters glasses for near and far visions, the EDOF element of the present invention may be appropriately designed to be used on either one of these glasses, being configured in accordance with the respective lens aperture to allow a depth of focus region equivalent to 5 diopters. Actually, in this specific example, a 1 diopter glasses with the EDOF element of
25 the present invention can be used, where the EDOF element is operating around the optical power of the lens (1 diopter) and provides the depth of field region from -1.5 to 3.5 diopters. Hence, the patient may use only one pair of glasses with 1 diopter. This focal power of the glasses (imaging lens) will be added to the EDOF element Such an EDOF element maximizes the defocused OTF of the
30 lens arrangement (appropriately modulates the CTJF profile of the imaging lens of

WO 2006/018834 32 PCT/IL2005/000868
the respective glasses) by generating proper phase interference relation between
light portions passing through different regions of the lens, to reduce a quadratic
phase factor resulting from light getting out of focus of the imaging lens. The inventor has found that for most patients a common EDOF element configuration
5 can be used, preferably as that of Fig. 2C. Turning back to Fig. 2C, the basic period (of the basic element BE) is about 3mm, a distance between two adjacent bars is about 1.875mm, and the bar thickness is about 0.375mm. .
If the EDOF element with its range of depth of focus is used on top of a lens in ophthalmic applications, such as a contact lens, then it may be translated
10 into Diopters range. The diameter of the eye lens (effective aperture of the imaging lens) varies from 2mm up to 6-7mm depending on the lighting conditions. The optical element generates a Diopter range within which the image is in focus. The inventor has found that for the resulted range of the phase factor y (about up to 17) for lightened environment in which the eye pupil has a
15 diameter of 2mm, the obtained Diopter range P is more than 5 (from -2.5 up to 2.5). The simulations followed the formula:


Figs. 10A-10B present the simulation results visualizing the performance
of the ophthalmic depth of focus application of the present invention. The
20 simulation of Fig. 10A corresponds to the overall Diopter range obtained due to the fact that the EDOF element is attached to a contact lens. The diameter of the eye lens varies from 2mm up to 6-7mm depending on the lighting conditions.
The simulations follow Eq. 6 above.
In the simulation of Fig. 10B, an imaging lens with a fixed focal length is
25 used. If the distance between the lens and sensor equals to its focal length (v=F) then the image will be in focus starting from a certain distance, Umin, up to infinity, wherein the distance Umin, is determined as:



WO 2006/018834 33 PCT/IL2005/000868
and for v=F one obtains:

The chart for umin with and without the EDOF element of the present invention is plotted in Fig. 10B. As could be seen, the minimal distance is much
5 smaller when the invented element is in use. Thus, the overall range of focus is much larger. It should be noted that for the human eye, v=15mm.
Turning back to Fig. 1C exemplifying an imaging arrangement of the present invention formed by a lenslet array and an EDOF elements' array (suitable to be used with a display panel or screen), the required parameters of
10 the imaging arrangement can be estimated as follows:
Let us assume that u, which is the distance between the screen 13 and the lenslet array 12A is about 2mm; v, which is the distance between the screen 13 and the closest focus plane FP is 40cm; and R, which is the distance between the eye 16 and the closest focus plane FP, is about lm. The object 13 is constituted
15 by the display of the mobile phone or the screen. Basically, the lenslet array 12A images the object plane 13 on the closest focus plane FP, i.e.:



which provides f=2.01mm.
The defocusing parameter is defined as:

20

where l is the wavelength.
With the use of EDOF, this parameter can reach the value of 15 and
without the EDOF element - the value of 2-3 without distorting the image
quality. The diameter, D, of the lenses in the lenslet array can be found such that
25 the minimal value for the distance between the screen 13 and the closest focus

WO 2006/018834 34 PCT/IL2005/000868

plane FP, (vmin) will be very close to the object plane 13 to have minimal demagnification. The demagnification factor is:







It should be noted that without the EDOF element the minimal distance v
would have been:
10


which means a demagnification factor of 8 (16mm/2mm). Such a demagnification would not have allowed seeing the characters in the display.
Attachment of the lenslet array 12A to the screen decreased the visible resolution. The resolution of such an imaging system is limited by the factor of:
15

Since the details appearing in the screen are larger than that, the resolution is not damaged by the imaging lenslet array.
Following the computations presented above, a person with normal vision that will focus his eyes on the screen (or on a plane positioned 2mm behind it)
20 will see the image in focus as well.
The technique of the present invention could be barrier breaking in a vast
set of applications including, but not limited to, the following: conventional
office devices containing camera such as camcorders, scanners (e.g., barcode
scanners) and web cams; conventional imaging systems including camera and
25 detectors, i.e. cellular cameras, car cameras, surveillances cameras, machine

WO 2006/018834 35 PCT/IL2005/000868


vision, photography, HDTV, video conferences, radar imaging systems (that
typically suffer from defocus problems), endoscopy and passive bio medical
inspections, tomography, display panels, etc. The usage of the depth of focus
extending element of the present invention in endoscopy and passive biomedical
5 inspections allows for in-body imaging to see organs in focus that otherwise are
not, since there is no control on the exact position of the medical apparatus.
Some other possible applications of the present invention include correcting chromatic aberrations in various optical systems, for example in optical communication; media reader/writers used with information carriers such as
10 conventional DVD, or multi-layer information carriers utilizing light reflection or fluorescence.
The present invention may also be used in ophthalmic applications as a contact lens, a spectacle lens, an intraocular lens, or any other lens used around or inserted into any part of the eye. An obvious example is the use of the
15 invention for the benefit of short sighted (myopic) people who develop presbyopia, the need for reading glasses as a result of age-related changes in then-natural eye lens. In such an application, those people may use a single lens, as a spectacle lens, contact lens, intracorneal lens, phakic intraocular lens or aphakic intraocular lens, or a lens inserted elsewhere in the eye. In this fashion, they will
20 use one lens for seeing at any distance, near or far. Another obvious utilization of the invention is in an intraocular lens, the artificial lens implanted in the eye after removal of a cataract. Currently, the regular artificial lens has only a single focus and thus the person into whose eye the lens was implanted has a very limited depth of focus and has to use spectacles for most distances of regard.
25 Incorporation of the invention into the implanted lens will afford the patient focused vision at all distances. Another example of ophthalmic use is as a replacement of multifocal (progressive) spectacle lenses, which are conventionally designed such that every segment of the lens surface has a different focus and thus the patient has to move his eyes to focus on objects at
30 different distances. Incorporation of the invention into a spectacle or contact lens

WO 2006/018834 36 PCT/IL2005/000868
will enable the presbyopic wearer to see objects in focus at all distances through
any part of the tens.
In all the applications of the invention, including the examples above, the image from objects at different distances are focused on the retina (or sensor)
5 without appreciable loss of energy, in contradistinction to the situation in multifocal contact or intraocular lenses.
Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention described hereinbefore without departing from its scope defined in and by the appended
10 claims.

37
CLAMS;
1. An imaging arrangement comprising: an imaging lens assembly
including at least one lens having a certain affective aperture, and at least one optical element associated with said at least one lens and configured to provide an extended depth of focus of the imaging arrangement, said optical element being configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition, said optical element together with its associated lens defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least one phase transition region of the optical element within the lens plane being determined by at least a dimension of said affective aperture.
2. The arrangement of Claim 1, wherein said lens assembly includes the single lens associated with the single optical element
3. The arrangement of Claim 1, comprising the lens assembly including an array of lenses, and an array of die optical elements, each optical element being associated with the corresponding one of the lenses.
4. The arrangement of any one of preceding Claims, wherein said optical element is configured as a phase-only element
5. The arrangement of Claim 4, wherein said optical element is configured as a binary mask.
6. The arrangement of any one of Claims 1 to 3, wherein said optical element is a configured as a phase and amplitude affecting element
7. The arrangement of any one of preceding Claims, wherein the optical element is configured to maximize a defocused optical transfer function (OTF) of the imaging arrangement by providing the out of focus OTF as much as possible away from zero.
8. The arrangement of Claim 7, wherein the optical element is configured to produce proper phase interference relation between light portions passing through different regions of the imaging arrangement corresponding to the

different features of the pattern to thereby reduce a quadratic phase factor
resulting from light getting out of focus of the imaging lens.
9. The arrangement of any one of preceding Claims, wherein said at least one transition region is configured as a pi-phase transition for a certain wavelength for which the optical element is designed.
10. The arrangement of any one of preceding Claims, wherein said at least one transition region is configured as a Tt/2-phase transition for a certain wavelength for which the optical element is designed.
11. The arrangement of any one of preceding Claims, wherein the position of said at least one transition region with respect tq the imaging lens is determined by optical power of the imaging lens.
12. The arrangement of any one of Claims 7 to 11, wherein the position for N transition regions of the optical element within the imaging lens plane maximizing the OTF is determined as:




values for a, providing maximum for minima of an expression for auto correlation of a Coherent Transfer Function (CTF) of the imaging lens, where an
equals either 1 or -1, ċ⌂V being a width of the transition regions,D(V)being
the CTF of the imaging lens corresponding to out of focus position of an object

being imaged and being determined as

the affective aperture dimension, V is a coordinate of the affective aperture in the CTF plane, and y is a phase factor representing a degree of getting out of focus being determined as


where u is a distance between the imaging lens and an object, v is the
distance between the imaging lens and a detector, A. is a wavelength, and F is a focal distance of the imaging lens.
13. The arrangement of any one of preceding Claims, wherein said at least one transition region has a sub-pattern formed by an array of variable phase transition sub-regions.
14. The arrangement of any one of Claim 9, wherein said at least one pi-phase transition region has a sub-pattern formed by an array of variable pi-phase transition sub-regions.
15. The arrangement of any one of preceding Claims, wherein the optical element is configured as at least one annular or line transition region.
16. The arrangement of any one of Claims 1 to 15, wherein the optical element is configured as a grid.
17. The arrangement of any one of preceding Claims, wherein said optical element is spaced-apart from the imaging lens along an optical axis of the imaging lens.
18. The arrangement of any one of Claims 1 to 16, wherein said optical element is attached to the imaging lens.
19. The arrangement of any one of Claims 1 to 16, wherein said optical element is made integral with the imaging lens.
20. The arrangement of any one of preceding Claims, wherein said optical element is configured as a mask formed by an array of said transition regions arranged in a spaced-apart relationship being spaced by the optically transparent regions of the imaging lens within the imaging lens plane.
21. The arrangement of Claim 19, wherein said at least one transition region is formed as a surface relief on the imaging lens surface, defining a lens thickness within said at least one region different from that within other regions of the lens.
22. The arrangement of Claim 19 or 21, wherein said at least one transition region is formed by a material having refractive index different from that of the imaging lens material.


23. The arrangement of Claim 19 or 22, wherein said optical element is configured as a mask formed by an array of the phase transition regions formed by a material having refractive index different from that of the imaging lens material.
24. The arrangement of any one of Claims 7 to 23, wherein the optical element is configured to maximize the OTF by reducing high-frequency cancellation at large shifts of a Coherent Transfer Function (CTF) of the imaging lens.
25. The arrangement of any one of Claims 7 to 24, wherein the optical element is configured,to maximize the OTF by reducing sensitivity of the lens arrangement to shifts of a Coherent Transfer Function (CTF) of the imaging lens while getting out of focus.
26. The arrangement of Claim 25, wherein the optical element is configured to produce periodic replication of a lateral phase shape of a light field propagating through the imaging lens.
27. The arrangement of Claim 25, wherein the optical element is configured in accordance with a free space propagation of fee optical element function for a distance between the optical element and the imagine lens plane. .
28. The arrangement of any one of preceding Claims, for use in patients' spectacles.
29. The arrangement of any one of Claims 1 to 27, wherein said imaging lens is a contact lens.
30. An optical element for use with an imaging lens in the imaging arrangement of any one of preceding Claims for extending depth of focus of imaging, the optical element being configured as a phase-affecting, non-diffractive optical element defining a predetermined pattern of spatially low frequency phase transitions, said pattern being defined by an affective aperture of the given imaging lens.
31. A system for creating an image of an object on a detector plane, the system comprising the imaging lens arrangement of any one of Claims 1 to 26.


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32. The system of Claim 31, wherein said object is a screen of a display device to be imaged on the eye retina constituting the detector plane.
33. A display device carrying the imaging arrangement of any one of preceding Claims.
34. A method for providing a certain extended depth of focus of an imaging system, the method comprising applying an aperture coding to an imaging lens, having a certain effective aperture, by applying to the imaging lens a phase-affecting non-diffractive optical element configured to define a spatially low frequency phase transition arrangement and thereby provide a predetermined pattern of spaced-apart substantially optically transparent features of different optical properties within the imaging lens plane, thereby producing phase interference relation between light portions passing through different regions of the lens arrangement corresponding to the different features of the pattern so as to reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximise a defocused optical transfer function (OIF) of the imaging lens arrangement.
35. A method for designing the optical element of Claim 30, said designing comprising selecting N positions for the phase transitions within the imaging lens effective aperture as those providing maximal contrast of an Optical Transfer Function (OTF) of the imaging system under a set of out of focus locations, thereby providing the out of focus OTF as much as possible away from zero.
36. The method of Claim 35, wherein the positions for said N transition regions of the optical element within the imaging lens plane maximizing the OTF are determined as:




values for a,, providing maximum for minima of an expression for auto correlation of a Coherent Transfer Function (CTF) of the imaging lens, where a„

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equals either 1 or -1, ⌂V being a width of the transition regions, D(v) being the
CTF of the imaging lens corresponding to out of focus position of an object

being imaged and being determined as , wherein D is the
affective aperture dimension, v is a coordinate of the affective aperture in the CTF plane, and , and ^is a phase factor representing a degree of getting out of focus being determined as

where u is a distance between the imaging lens and an object, v is the
distance between me imaging lens and a detector, l is a wavelength, and F is a focal distance of the imaging lens.
37. The method of Claim 35 or 36, comprising fabricating a mask formed by an arrangement of the .AT transitions spaced-apart from each other in accordance with said selected ^positions.
38. The method of Claim 37, comprising attaching said mask to the surface of the imaging lens aperture.
39. The method of Claim 35, comprising patterning the surface of the imaging lens aperture to form a mask of the N transitions spaced-apart from each other in accordance with said selected # positions.
40. The method of Claim 38 or 39, comprising providing said surface substantially flat to thereby allow insertion of the patterned imaging lens into a
patient's eye.
41. The method of any one of Claims 35 to 40, wherein the designing of the optical element comprises producing a phase interference relation between light portions passing through said N regions and spaces between them to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of an
arrangement formed by the imaging lens and the optical element.

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42. The method 01 claim 39, wherein said patterning comprises applying material removal to the lens regions within said N positions, and filling said regions, 'from which the lens material has been removed, by a material of a refraction index different from that of the lens, so as to provide a refraction index difference such that the outer region of the patterned lens is flat and proper equalization between the different material regions is provided to produce a phase interference relation between light portions passing through different material regions to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of the patterned imaging lens.
43. The method of Claim 39, wherein said patterning comprises applying diffusion or photo polymerization to the lens regions within said N positions, so as to provide a refraction index difference between said N regions and spaces between them such mat the outer region of the patterned lens is flat and proper equalization between the different material regions is provided to produce a phase interference relation between light portions passing through different material regions to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of the patterned imaging lens.
44. The method of Claim 35, comprising implanting in the patient's eye tissue, within said selected N positions, an artificial tissue having a refraction index different from mat of the eye tissue.

Dated this 9th day of March, 2007

ANAND CHOUBEY
OF K & S PARTNERS
AGENT FOR THE APPLICANT(S)

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Abstract
"METHOD AND SYSTEM FOR EXTENDING THE DEPTH OF FOCUS"
An imaging arrangement and method for extended the depth of focus are provided. The imaging arrangement comprises an imaging lens having a certain
affective aperture, and an optical element associated with said imaging lens. The optical element is configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition. The optical element and the imaging lens define a predetermined pattern formed by spaced-apart substantially optically transparent features of different optical properties. Position of at least one phase transition region of the optical element within the imaging lens plane is determined by at least a dimension of said affective aperture.

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Patent Number 268668
Indian Patent Application Number 357/MUMNP/2007
PG Journal Number 37/2015
Publication Date 11-Sep-2015
Grant Date 10-Sep-2015
Date of Filing 12-Mar-2007
Name of Patentee XCEED IMAGING LTD.
Applicant Address P.O.B. 4201, 1 HERMON STREET, ROSH HAAYIN
Inventors:
# Inventor's Name Inventor's Address
1 ZALEVSKY ZEEV 1 HACHERMON STREET, 48560 ROSH HAAYIN
PCT International Classification Number G02B3/10
PCT International Application Number PCT/IL2005/000868
PCT International Filing date 2005-08-11
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/974,943 2004-10-28 U.S.A.
2 60/601,638 2004-08-16 U.S.A.