|Title of Invention||
A PROCESS FOR FABRICATION OF FIBRES FOR OPTICAL LENSES
|Abstract||Process of fabrication of fibers for optical lenses in monomode format or multimode from a multimode fiber or analogue by formation of at least a pick (3,8), of extremity in transparent polymer comprising a stage of deposit of at least an extremity of optical fiber,under the form of a drop, of a fluid mixture including a substance with a base that is photopolymeri sable, and at least a photo initiator of polymerization then a stage of exhibition of the drop deposited at a lighted source in order to furnish a photopolymer light(7), characterized in which a selection stage for or from desired modes is realized while undergoing the multimode fiber at least a mechanical force and in this a control of the form and some dimensions of the pick(3,8) is realized at a time when the said Stages of deposit and the exhibition of the drop in such a fashion is so as to obtain a height of pick determined between some microns and several hundreds of microns, the said procedure comprises the following stages: - A stage in condition of mixture at a temperature determined to give the mixture a viscosity adapted, permitting to attain a height of the desired drop before the stage of exhibition. A stage of adjustment of the duration of exhibition and/or of the intensity of the light photopolymerisant in order to adjust the final curve of the pick (3,8)|
|Full Text||FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
COMPLETE SPECIFICATION (See Section 10, rule 13)
A PROCESS FOR FABRICATION OF FIBRES FOR
UNIVERSITE DE TECHNOLOGIE DE TROYES of 12, RUE MARIE CURIE BP 2060 10140 TROYES, FRANCE, FRENCH Company
The following specification particularly describes the nature of the invention and the manner in which it is to be performed : -
IMPROVEMENTS TO OPTICAL FIBRES PROVIDED WITH A LENS BY PHOTOPOLYMERISATION AND RELATED NOVEL OPTICAL COMPONENTS
This invention relates to lens-ended optical fibres, for which the first embodiments and applications by the inventors were described in a previous invention patent application issued by the INPI under No. 98 14385 entitled "New lens-ended optical fibres with a high end numerical aperture. Application to the production of new High Performance optoelectronic components".
Lens-ended optical fibres equipped at their ends with transparent polymer micro-tips, enable very much improved optical connections between the optical fibres themselves and between optical fibres and active or passive components connected to them. The result is that it becomes possible to make complex high performances devices.
However, the optical characteristics required by the various designers are becoming more and more remarkable while applications, now frequently in a worldwide market, are developing quickly and require the development of new technologies in many optics fields.
The general purposes of this invention are, non-limitatively, the use of new technological parameters and processes to create polymer micro-tips with general characteristics optimised for the case of applications with monomode and multimode optical fibres, and the corresponding development of new particularly innovative devices searched for by users.
The invention will be better understood after reading the following applications and looking at the figures:
Figure 1 shows the end of an optical fibre 4 comprising a core 1 and a duct 2 equipped with a polymer micro-tip 3 made using a Photopolymerisable resin type material, for which the dimensions and geometry may be adjusted by optimising new physicochemical parameters, for example as a function of envisaged applications.
According to a first purpose of the invention, the operational process used to make the micro-tips gives excellent diversity in values of the height (from a few microns to a few hundred microns) and the radius of curvature of the drop deposited at the beginning of the process. The result is that the dimensions of the micro-tip that depend directly on the dimensions of the formulation drop can be precisely controlled depending on the required applications.
The first micro-tip production operation which is shown as an example in figure 2, consists of depositing a formulation drop as shown in figure 2a using a pipette 5, at the end of a cleaved fibre 4 instantaneously forming a capillarity meniscus 6 for which the heights and radii of curvature of the formulation drop are directly related to the diameter of the fibre and to surface tensions (capillarity), as can be seen in figure 2b. These values depend essentially on the viscosity of the formulation used. The viscosity parameter takes an overriding importance for the first objective of the invention. According to the invention, the chemical composition of the formulation is firstly adapted to the required viscosity value, but the formulation temperature also plays a very important role.
Thus, the height of the deposited drop will be reduced by slightly heating the formulation which will make it less viscous. Conversely, the deposited drop will be cooled in advance to make the formulation more viscous and to obtain a larger drop height. For example, a variation of the resin temperature making up the formulation between 10°C and 65°C will result in drops with a height of between 10 and 50 microns.
In general, it was specified in the text of the first industrial protection deposited by the inventors that the photopolymerisable formulation is a means of making the micro-tip at the end of the fibre behave like a liquid material sensitive to green light and composed of photoinitiators (eosine + MDEA) and a monomer (PETIA).
According to improvements according to our invention, photoinitiators can be modified so that the formulation is sensitive to wave lengths longer than the wave length for green light, namely red light, near infrared light and more precisely
to wave lengths frequently used in the field of telecommunications (for example 1.3 and 1.55 urn).
According to another aspect of the first purpose of the invention, the surface tensions that are directly related to the viscosity of the formulation can also be modified by applying a preliminary treatment to the fibre before the drop is deposited. Preferably (but not limitatively) this treatment consists of dipping the cleaved optical fibre into sulfochromic acid for 24 hours. The surface of the fibre is made hydrophilic, and the attenuated capillarity phenomenon results in a small drop height (for example 10 microns).
The final width of the micro-tip depends on the diameter of the fibre core that guides almost all of the light (usually green light) to the end of the fibre at which the formulation drop was deposited.
The light exposure conditions, and particularly the value of polymerising light intensity and its application time, are also important parameters that should be adjusted as a function of needs.
The final radius of curvature of the micro-tip to be made is much smaller than the radius of curvature of the drop, and is an important factor in obtaining the lens-ended characteristics required for the micro-tip. This radius of curvature may be adjusted as a function of the exposure time (0.5 to 90 seconds as a non-limitative example) and the intensity of photopolymerising light injected into the fibre (fibre output current from 1 to 100 uwatts, as a non-limitative example).
The radius of curvature of the micro-tip also depends on oxygen effects at the drop / air interface. According to the invention, oxygen effects are controlled by adjusting the air composition close to the operational field. Non-limitatively, nitrogen can be injected into a glove box type sealed compartment in which the end of the fibre is inserted.
According to this first purpose of the invention, the operational process and the various micro-tip parameters concerned are not only optimised in order to have good control over production of the various micro-tips and their required characteristics in the many possible applications, but also with the objective of
developing a simple and inexpensive manufacturing process capable of "mass production" of fibre end micro-tips.
According to a non-limitative aspect of the first purpose of the invention, the laser radiation necessary for photopolymerisation is distributed into a large number of optical fibres that will be equipped with an end micro-tip, after broadening and homogenisation of the light beam by known optical processes.
The optical power necessary for photopolymerisation is only a few microwatts per micro-tip, consequently "mass production" of more than 100 micro-tips simultaneously (non-limitative example) would be possible according to our invention.
According to a second purpose of the invention and in accordance with figure 3, essential aspects of previous technologies and processes improved according to the first purpose of the invention, are applied to multimode and monomode fibres to make fibrous compounds providing a beam that can be either focused (figure 3a) or collimated (figure 3b).
In the special case of multimode fibres, incident light initialising polymerisation preferably originates from a source external to the multimode fibre associated with shaping components of the beam output by the source.
Photopolymerisation is then done without any longitudinal propagation of polymerising light in the multimode fibre itself. The result is thus to avoid illuminating the formulation with all the various transverse modes propagating in multimode fibres when the photopolymerising light is injected at the end of the fibres.
In this case, the geometry of the micro lens produced is similar to the geometry of the formulation drop that was previously deposited.
According to other aspects of the second purpose of the invention, and when some applications make it necessary for the geometry of the micro-tip to be independent of the current distribution between fibre modes, the polymer micro-tip can be made by coupling a white light source to the other end of the fibre outputting incoherent light chosen such that the spectrum of transmitted wave
lengths is compatible with the various modes that could be propagated in the fibre. Also in the case of some applications that require compact installations in which it is difficult to envisage the presence of a monochromatic light source close to the end of the usually multimode fibre and therefore the micro-tip to be made, either for location reasons or more generally due to a complex arrangement of the micro-tip production equipment as a whole, the photopolymerising light source used is also non-limitatively an incoherent white light source.
According to a third purpose of the invention, the various improvements made described in the first ancf seconcf purposes of the invention ancf associated with the corresponding detailed knowledge of micro-tip properties as a function of the conditions for their production and general techniques for the connection of optical elements, were developed and are applicable for many applications.
The main connection types according to the invention and given non-limitatively are shown in the following figures.
Figure 4 shows a type of monomode or multimode fibre-to-fibre connection.
The photopolymerising light 7 is injected into the ends of two fibres 4 to be connected and aligned. The contact between the fibres is made by a polymer formulation in the form of a film 8 made using the same technological process claimed for making the micro-tips. The result is a "cold" solder together with an optical jacket such as glue with an index less than the index of the film, and by a mechanical protective jacket. The insertion losses of such a connection may be as low as 0.1 db.
Figure 5 diagrammatically shows a laser diode 9 to an optical fibre 4 type connection.
In this type of connection, the micro-tip 3 made at the end of the fibre 4 is sized such that the coupling between the radiation from the laser 10 and the micro-tip 3 is maximum.
The connections shown in figures 4 and 5 are only given as examples and are therefore non-exhaustive.
In the context of this third purpose of the invention, integrated optical wave guides, for example, can be connected using the same simple technologies described above, despite the number and complexity of optoelectronic circuits included in them.
According to a fourth purpose of the invention, micro-tips are made at the ends of multimode fibres capable of propagating one or several modes only.
Before exposure of the formulation drop to light, the required mode(s) is (are) selected by applying mechanical stresses to the multimode fibre and modifying the conditions of injection of green light until the required mode(s) is (are) obtained.
As an example shown in figure 6, a double polymer micro-tip 11, which is made (Figure 6a) on a fibre with a 9 micron core, only transmits mode LP 11 of fibre 4, starting from radiation 12. The intensity distribution 12 bis transmitted by the double micro-tip 11 is shown in figure 7a, which is the same intensity distribution used to create the double micro-tip 11. Figure 7b shows the double micro-tip polymer element after its manufacture.
Conversely, the polymer micro-tip 11 can be used as "input" to a fibre illuminated by an incident light beam 12 (figure 6b), light energy is transmitted by micro-tip 11 in the multimode fibre according to a spatial distribution corresponding to the LP mode 11 in the example chosen. Only the LP mode 11 is excited in the fibre, regardless of the injection conditions in the fibre.
According to another example embodiment, a polymer multi-micro-tip was made that can be used to select the LP mode 21 on a multimode fibre with a core diameter of 9 microns. The intensity distribution at the output from the fibre in which the light 12a was injected by the micro-tip according to LP mode 21 is shown in figure 8a. Figure 8b shows the polymer element with 4 micro-tips after manufacturing.
Thus according to our invention, it is possible to make "Transverse mode filters" and more generally new devices called "Mode selectors".
According to a fifth purpose of the invention, the new lens-ended optical fibres optimised according to the invention are used as optical radiation measurement probes with an excellent resolution better than 1 micron.
As an example of the use of these new probes, figure 9 diagrammatically shows a device according to the invention for measuring energy emitted by a laser 13 and particularly the configuration of the optical field curves at the output from the laser.
The laser 13 used in the experiment is a laser diode marketed by the SHARP Company with a 200 urn wide active layer.
The end of the lens-ended optical fibre 4 fitted with its micro-tip 3 is moved successively along 3 planes at distances of 2.5 urn, 1 urn and 0.1 urn respectively from the diode.
The other end of the non lens-ended fibre 4 is connected to a photomultiplier 14, increasing the measurement sensitivity.
Figure 10 shows optical radiation images of the laser diode recorded at three distances (2.5, 1 and 0.1 urn), the lens-ended optical fibre being moved within an area of 8 x 8 urn2. Note in figure 10 that as the distance from the micro-tip to the laser diode decreases, the active layer of the laser becomes more visible. Furthermore, a clear distinction can be seen between curves of progressively decreasing optical levels for a distance for example of 2.5 urn from the micro-tip to the surface of the fibre 4.
According to a sixth purpose of the invention, some optimisations of lens-ended optical fibres according to the invention are particularly aimed at applications of these fibres in microscopy and in the manufacture of the corresponding measurement probes.
In the case of optical microscopy with conventional scanning, the new lens-ended optical fibres are used as shown in figure 11 as a measurement probe for light diffused by the surface of an object 15 illuminated by an external source 16. An optical image of the studied area can be produced by moving the lens-ended optical fibre above the object.
Thus, high resolution optical scanning microscopy can be done using a simple very low cost probe. Resolutions of 300 to 500 nm can easily be obtained.
In the case of optical microscopy applications in near field, the polymer micro-tip of a lens-ended fibre optimised according to the invention is fully metallised, as is shown in figure 12, except for a circular nano-aperture 18 formed in the metallisation 17, with a typical diameter of a few tens of nanometres. This nano-aperture remains capable of emitting or receiving light in optical microscopic experiments in the near field. This type of lens-ended fibre with a metallised micro-tip generally acts as a nano-source or a nano-collector, depending on the needs.
The nature of the metal used covering almost the entire micro-tip is preferably but not limitatively chromium or gold.
According to one variant of a submicronic probe shown in. figure 13, fluorescent particles 19 are included in the photopolymerisable formulation in order to obtain a micro-tip end containing some particles for which the selective optical excitation improves the spatial resolution in optical microscopy. The size of the fluorescent particles added to the formulation is less than one micron. The particle concentration is adjusted to obtain one or several particles at the end of the micro-tip, after formation of the micro-tip. The fluorescence of the particles is then selectively excited through the fibre to obtain a localised light source 15 capable of probing the optical properties of a sample in the near field with a precision better than one micron.
Note that an apparently similar approach for producing probes with a resolution better than one micron in optical microscopy applications in the near field by particle integration, was recently validated by research workers J. MICHAELLS et al. However, the method used by these research workers is very complex, and moreover it is not certain that particle adhesion takes place at the ends of the probes.
The particle probe type according to one of the purposes of our invention enables the use of a much simpler and more reliable process.
For the sixth purpose of the invention, the metallised probes described above but without nano-apertures can be used as surface plasmon sensors. A monomode or multimode lens-ended optical fibre improved according to the invention is used.
The polymer micro-tip is coated with fine metallisation, preferably with gold or silver.
The characteristics of plasmons can be modified by varying the optical index of the external medium, by injecting light into the other cleaved end of the fibre and setting up conditions for excitation of surface plasmons at the metal-air interface. Thus, the presence of chemical or biological substances in contact with the metallic layer will cause modifications of the optical properties of plasmons, therefore variations of the light signal transmitted or reflected by the end of the fibre fitted with the metallised polymer micro-tip.
1. Process of fabrication of fibers for optical lenses in monomode format or
multimode from a multimode fiber or analogue by formation of at least a pick
(3,8), of extremity in transparent polymer comprising a stage of deposit of at least
an extremity of optical fiber,under the form of a drop, of a fluid mixture including
a substance with a base that is photopolymeri sable, and at least a photo initiator of
polymerization then a stage of exhibition of the drop deposited at a lighted source
in order to furnish a photopolymer light(7), characterized in which a selection
stage for or from desired modes is realized while undergoing the multimode fiber
at least a mechanical force and in this a control of the form and some dimensions
of the pick(3,8) is realized at a time when the said Stages of deposit and the
exhibition of the drop in such a fashion is so as to obtain a height of pick
determined between some microns and several hundreds of microns, the said
procedure comprises the following stages: -
A stage in condition of mixture at a temperature determined to give the mixture a viscosity adapted, permitting to attain a height of the desired drop before the stage of exhibition.
A stage of adjustment of the duration of exhibition and/or of the intensity of the light photopolymerisant in order to adjust the final curve of the pick (3,8)
2. Procedure of fabrication of fibers for optical lenses in monomode format or
multimode according to the claim 1, in which a stage of adjustment of the
composition of the oxygen in the air surrounding the pick (3) in course of the
formation is equally realized in order to adjust the final curve of the pick (3), the
nitrogen being injected in a watertight compartment in order to control the oxygen
effects at the interface of drop, air on the final curve of the pick (3)
3. Procedure of fabrication of fibers for optical lenses in monomode or multimode according to claim 1 or 2, characterized in which it comprises a stage ofpre treatment of a type "soaking" in an acid of extremity of fibers to modify the viscosity of the formulation linked to the tensions of the surface and thus obtaining some weak heights of the drops,
4. Procedure of fabrication of fibers for optical lenses in monomode or multimode according to one of the claims 1 to 3 in which the photopolymer light (7) utilized in the stage of exhibition of the drop furnished by a luminous source to cross the optic fiber.
5. Procedure of fabrication of fibers for optical lenses in monomode or multimode According to one of the claims 1 to 3 in which the necessary polymerization to the formation of the picks (3) notably in the case of multimode fibers is obtained by an exterior source to the multimode fiber delivering the polymer light (7) to the direct proximity of the pick (3) without injection of another light to the other extremity of fibers, spread longitudinally in the fibers.
6. Procedure of fabrication of fibers for optical lenses in monomode or multimode according to one of the claims 1 to 3 in which the photopolymerisation nece ssary to the formation of the pick (3) notably in the case of the multimode fibers is obtained by a course of white luminous light injected to the extremity of the fiber opposed to the pick3).
7. Procedure of fabrication of fibers for optical lenses in monomode or multimode according to one of the claims 1 to 6 in which the dimensions of the pick (3) and the form of extremity of pick (3) was chosen.
8. Procedure of fabrication according to claim 1, in which the dimensions and the form of the picks are adjusted in order to permit the realization of the connections guide of air to the photopolymer (7) being injected as of the said stage of exhibition to the extremities of the 2 guides to connect in order to form a film (8) of formulation of weak pressure assuring the contact between the guides of air.
9. Procedure of fabrication of fibers for the optical lenses monomode or multimode according to one of the claims 1 to 7,in which the dimensions and the form of the extremity of the picks (3) are chosen in order to obtain maximum optic between one fiber (4) and a diode laser (9).
10. Procedure of fabrication of fibers of the optical lenses monomodc or multimode according to one of the claims 1 to 7 in which the fibers are used for the connections for air guides or optic circuits integrated by complex polyvalent, the picks (3), of each one of the fibers utilized in the connections being adjusted separately according to the need.
11. Procedure of fabrication of fibers for optical lenses in monomode or multimode according to one of the claims 1 to 7 in which the optimized picks (3) are utilized according to the depth of measure of optic radiation which permits the obtaining of a lateral spatial resolution of sub micro type, for the applications of the optic microscopic with high resolutions scanning.
12. Procedure of fabrication of fibers for optical lenses in monomode or multimode according to one of the claims 1 to 7 and 11 in which the fluorescent particles (19) are integrated to the forming of polymer of the picks (3) those which composes itself after polymerization like a source localized in extremity of picks (3) and constituted by one or several fluorescent particles (19) sufficient to probe the optic property of a product in close quarters
|Indian Patent Application Number||52/MUMNP/2004|
|PG Journal Number||26/2007|
|Date of Filing||21-Jan-2004|
|Name of Patentee||UNIVERSITE DE TECHNOLOGIE DE TROYES|
|Applicant Address||12, RUE MARIE CURIE BP 2060 10140 TROYES,|
|PCT International Classification Number||G 02 B 6/26|
|PCT International Application Number||PCT/FR02/02678|
|PCT International Filing date||2002-07-26|