Title of Invention

"DISPERSION -SHIFTED OPTICAL FIBER"

Abstract A dispersion-shifter optical fiber comprising a core region extending along a predetermined axis, and a cladding region provided on the outer periphery of said core region, characterized by arranging said core region and said cladding region so as to obtain an effective area of 70 u m2 or more with respect to light whose center wavelength falls within the range of 1500 to 1600 nm, and a refractive index profile designed such that a peak position where optical power of said light in a fundamental mode is maximized is radially shifter from a center of said core region by a predetermined distance and that optical power at a position radially separated from said peak position by a predetermined distance and that optical power at a position radially separated from said peak position by a distance which is five times the center wavelength of said light becomes 1/100 or less of the optical power at said peak position.
Full Text The present invention relates to a dispersion-shifted optical fiber.
Technical Field
The present invention relates to a single-mode optical fiber used as a transmission line in optical communications or the like; and, in particular, to a dispersion-shifted optical fiber suitable for wavelength-division multiplexing (WDM) transmission.
Background Art
Conventionally, in optical communication systems employing single-mode optical fibers as their transmission lines, light in the wavelength band of 1.3 µm. or 1.55 µ m has often been utilized as signal light for communications . Recently, among others, the use of light in the wavelength band of 1.55 µm. has been increasing from the viewpoint of reducing transmission loss in transmission lines. Single-mode optical fibers employed in such transmission lines for light in the wavelength band of 1.55 µm have been designed such that their wavelength dispersion (phenomenon in which pulse waves are broadened due to the fact that the propagation speed of light varies depending on wavelength) with respect to light in the wavelength band of 1.55 µm is nullified (to yield dispersion-shifted optical fibers having a zero-dispersion wavelength of 1550 nm).
Also, as long-haul transmission has become possible with the advent of WDM transmission or optical amplifiers
In recent years, in order to reduce nonlinear phenomena (to suppress distortion of signal light), a dispersion-shifted optical fiber of a dual-shape core structure having an effective area Aoff of 70 µm2 or more, such as that shown in Fig. 1A, has been proposed (Japanese Patent Application paid-Open No. 8-24825F „ Here, nonlinear optical effects reter to phenomena in which signal light pulses are distorted in proportion to density of light intensity or the like due to nonlinear phenomena such as four-wave mixing (FWM), self-phase modulation (SPM) / cross-phase modulation [XPM) , and the like, thereby restrictina transmission speed or repeater spacing in relay transmission systems.
Tn such a dispersion-shifted optical fiber, as shown in Fig. IB, the refractive index profile of its. core region 10 is designed such that the power distribution PA(r) of propagating light attains its maximum value PAmax at the center position 0, (r = 0) in the core region 10. Further, at the outer periphery of the center part of this core region 10 having a higher refractive index, a peripheral area having a lower refractive index is provided. The introduction of peripheral area broadens the skirts of optical power distribution PA(r). since the skirts are broadened, the effective area Aoff becomes 70 µm1 or more (so as to prevent the optical power from being concentrated at the center of the core), thereby reducing the above-mentioned nonlinear phenomena.
In the conventional dispersion-shifted optical fiber shown in Fig. IA, the center part of the core region 10 with a higher refractive index has an outside diameter of 4.1 Aim, and a relative refractive index difference of 0.94% with respect, to its cladding region 20. The peripheral area of the core region 10 with a low refractive index has an outside diameter of 31.5 µm, and a relative refractive index difference of 0.20% with respect to the cladding region 20. When the refractive index profile of the core region 10 is
thus designed, its effective area Aoff becomes 70 µm2 or more. Disclosure of the Invention
Having studied the conventional dispersion-shifted optical fiber, however, the inventors have found the following problems. Namely, as shown in Fig, ].B, the power distribution PA(r) of light propagating in the inventional dispersion-shifted optical fiber has such a form as the normalized power attains its maximum PA at the center of the core region and decreases toward the outer periphery• Hence, when a dispersion-shifted optical fiber yielding such an optical power distribution employs a refractive index profile which can attain a greater effective area, the skirts of the optical power distribution become wider, thereby weakening its function of confining light therein. AS a result, the optical loss caused by macrobending or microbending (hereinafter simply referred to as bending loss) would increase, thereby making it difficult to transmit light over a long distance without attenuation. In view of such problems of the prior art, it is an object of the present invention to provide a dispersion-shifted optical fiber comprising a structure which reduces optical, loss, such as bending in particular, and restrains nonlinear phenomena from occurring.
In order to effectively restrain the above-mentioned nonlinear phenomena from occurring, the dispersion-shifted optical fiber according to the present invention has a core region extending along a predetermined axis, and a cladding region provided on the outer periphery of the sore region, having such a refractive index profile that can yield an effective area of 70 µm2 one or more signal light components whose center wavelengths fall within the range of about 1500 to 1600 nm. In particular, in order to obtain an effective area Aoff of 70 µm2 or more, the refractive index profile of the dispersion-shifted optical fiber according to the present invention is designed such that a peak position where the optical power of the signal light component in its fundamental mode is maximized is radially separated from the center of the core region, by a predetermined distance. Here, as disclosed in Japanese Patent Application Open No. 8-248251 the above-mentioned effective area is given by the following expression (1):
(Formula Removed)
where E is the electric field accompanying the propagating light, and r is the radial distance from the center of the core region.
On the other hand, the refractive index profile is represented by the relative refractive index difference A
n, given by the following expression (2):
(Formula Removed)
where ncd is the average refractive index of the reference area (Sio2) in the cladding region, and n1 is the average refractive index in each part i constituting the core region. Thus, the relative refractive index difference ∆n. is expressed with reference to the average refractive index nd of the reference area in the cladding region. In this specification, relative refractive index difference is expressed in terms of percentage, and an area having a negative relative refractive index difference indicates an area having a refractive index lower than that of the reference area.
When effective area is increased alone in order to restrain nonlinear phenomena from occurring, the skirts of optical power distribution would also be broadened, thereby making it difficult to reduce bending loss. Hence, the refractive index profile of the dispersion-shifted optical fiber according to the present invention is designed such
that optical power remarkably decreases at a position separated, by a distance which is five times the center wavelength of the signal light, from the peak position where the optical power of the signal light component is maximized.
The optical power distribution broadens as the wavelength of propagating light shifts to the longer wavelength side. Hence, using the signal light wavelength as a parameter, the optical power at A position radially separated from the peak position by a distance which is five times the signal wavelength is employed as a reference for evaluating bending loss. As a result of measurements, the inventors have confirmed that, in the case where the optical power at the evaluation reference position (position radially separated from the peak position by a distance which is five times the signal wavelength) is not greater than 1/100 of the optical power at the peak position (maximum value), bending loss can remarkably be reduced (to about 1/20) as compared with the conventional disgersion-shifted optical fiber.
In order to suppress a microbending less caused by cable-fabrication to a sufficient level in practice, it is necessary that the microbending loss is substantially suppressed to 1 dB/km or less. On the other hand, as can be seen from Fig. 2, in order to suppress the microbending loss to 1 dB/km or less, it is necessary that the ratio (P/Pmax) of an optical power P at the evaluation reference position
with respect to a maximum optical power Pmax becomes 1/100 or less.
Thus, when the effective area Aoff is set to 70 µm1 or more, nonlinear phenomena are reduced, thereby the distortion of signal light is restrained from occurring. Further, since the refractive index profile is designed such that the peak position where the optical power in the fundamental mode is maximized is shifted from the center of the core region and that the optical power at the evaluation reference position radially separated from the peak position by a distance which is five times the signal wavelength becomes 1/100 or less of the maximum optical power at the peak position, the effective area Aoff can sufficiently be enhanced without broadening the skirts of optical power distribution. Consequently, light is fully confined, thereby the bending loss caused by macrobending and microbending would decrease.
Accordingly, there is provided a dispersion-shifted optical fiber (100: 200; 300) comprising a core region (110; 210; 310) extending along a predetermined axis, and a cladding region (120; 220; 320) provided on the outer periphery of said core region (110; 210; 310),
characterized by arranging said core region (110; 210; 310)and said cladding region (120; 220; 320) so as to obtain an effective area of 70 µ m2 or more with respect to light whose center wavelength falls within the range of 1500 to 1600 nm, and a refractive index profile designed such that a peak position where optical power of said light in a fundamental mode is maximized is radially shifted from a center of said core region and that optical power at a position is radially separated from said peak position by a distance which is five times the center wavelength of said light becomes 1/100 or less of the optical power at said peak position.
Here, in order to realize the above-mentioned refractive index profile, the dispersion-shifted optical fiber according to the present invention may employ either a ring-shaped core structure in which the core region comprises a first core having a predetermined refractive index and a second core, provided on the outer periphery of the first core, having a refractive index higher than that of the first core; or a multilayer core structure in which the core region comprises a first core having a predetermined refractive index; a second core, provided on the outer periphery of he first core, having a refractive index higher than that of the first core; a third core, provided on the outer periphery of the second core, having a refractive index lower than that of the second core; and a fourth core, provided on the outer periphery of the third core, having a refractive index higher than that of third core. On the other hand, the cladding region may have either a single layer or a depressed cladding structure comprising a first cladding, provided on the outer periphery of the core region, having a refractive index lower than that of the outermost layer of the core region and a second cladding, provided on the outer periphery of the first cladding, having a refractive index higher than that of the first cladding. Further employable as the refractive index profile of the dispersion -shifter optical fiber according to the present invention are refractive index profiles in which a depressed cladding structure and a ring-shaped core structure or a multilayer core structure are combined together.
Brief description of the accompanying drawings:
Fig. 1A is a refractive index profile of a conventional dispersion-shifted optical fiber, whereas Fig. 1B is a view showing a power distribution of light propagating through the conventional dispersion-shifter optical fiber;
Fig 2 is a graph showing a relationship between a microbending loss and a ratio (P/Pmex) of an optical power.
P at an evalution reference position with respect to a maximum optical power Pmax;
Pig. 3A is a view showing a cross-sectional structure of a first embodiment of dispersion-shifted optical fiber according to the present invention, Fig. 3B is u refractive index profile of the dispersion-shifted optical fiber of the first embodiment shown in Fig. 3A, and Fig. 3C is a view showing a power distribution of light propagating through the dispersion-shifted optical fiber of the first embodiment shown in Fig. 3A;
Pig. 4 is a view showing skirt portions in power distribution of light propagating through the dispersion-shifted optical fiber of the first embodiment shown in Pigs. 3A to 3C and in the conventional dispersion-shifted optical fiber as compared with each other;
Fig. 5A is a view showing a cross-sectional structure of a second embodiment of dispersion-shifted optical fiber according to the present invention, Fig. 5B is a refractive index profile of the dispersion-shifted optical fiber of the second embodiment shown in Fig. 5A, and Fig. 5C is a view showing a power distribution of light propagating through the dispersion-shifted optical fiber of the second embodiment shown in Fig. 5A; and
Fig. 6A is A view showing a cross-sectional structure of a third embodiment of dispersion-shifted optical fiber
according to the present invention, Fig. 6B is a refractive index profile of the dispersion-shifted optical fiber of the third embodiment shown in Fig. 6A, and Fig, 6C is a view showing a power distribution of light propagating through the dispersion-shifted optical fiber of the third embodiment shown in Fig. 6A. Best Modes for Carrying Out the Invention
In the following, dispersion-shifted optical fibers according to the present invention will be explained with reference to Figs. 2, 3A to 3C, 4, and 5A to 60. Among the drawings, constituents identical or equivalent to each other will be referred to with numerals or letters identical to each other. In each of the optical power distributions P(r) shown in Figs. 3C, 5C, and 6C, the optical power in the ordinate is normalized with reference to the maximum value pmax; whereas the relative refractive index difference is expressed in terms of percentage in each of the refractive index profiles shown in Figs. 3B, 5B, and 6E. First Embodiment
Pig. 3A is a view showing a cross-sectional structure of the first embodiment of dispersion-shifted optical fiber according to the present invention.
The dispersion-shifted optical fiber according to the first embodiment is a single-mode optical fiber which guides signal light in a 1.55µm wavelength band whose center wavelength A falls within the range of about 1500 to 1600
run. Also, as shown in Pig. 3A, this dispersion-shifted optical fiber 100 comprises a core region 110 and a cladding region 120 provided on the outer periphery of the core region 110.
The core region 110 is constituted by a first core ill and a second core 112 provided on the outer periphery of the first core 111 (thus forming a ring-shaped core structure). The first core 111 has an outside diameter of 4.3 µm, whereas the second core 112 has en outside diameter bl of 7.1 µm.
Fig. 3B is a refractive index profile of the dispersion-shifted optical fiber 100 of the first embodiment shown in Fig. 3A, which is represented by the relative refractive index difference of each part along the line L1 passing through the center O1 of the dispersion-shifted optical fiber 100. Here, the relative refractive index difference is given by the above-mentioned expression (2), with reference to the cladding region 120 as a reference area.
In the refractive index profile of Fig. 3B, the first core 111 with an outside diameter of al (4.3 µm) has a step index profile whose relative refractive index difference
∆n1 with respect to the cladding region 120 is -0.58%. On the other hand, the second core 112 with an outside diameter of bl (7.1 µm) has a step index profile whose relative refractive index difference ∆n2 with respect to
the cladding region 120 is 1.09%, while substantially yielding a thickness of (bl - al)/2. Here, as fluorine is introduced into Si07: by MCVD method, the first core 111 is set to an average refractive index n. which is lower than the average refractive index n0 of the cladding region 120; whereas, as GeO2 is added into Si03 by MCVD method,, the second core 112 is set to an average refractive index n2 which is higher than the average refractive index n, of "he cladding region 120.
Fig, 3C shows the power distribution P(r) of signal light propagating through the dispersion-shifted optical fiber 100 of the first embodiment. In this graph, optical power attains the maximum value Pmax at a position {hereinafter referred to as a peak position) shifted from the center position (r = 0) of the core region 110, and drastically decreases toward the outer periphery. In particular, the optical power P(5λ) at a position (hereinafter referred to as evaluation reference position) radially separated from the peak position by 1 distance {5 λ) which is five times the wavelength λ A becomes 1/100 or less of the maximum optical power Pmax. Also, the effective area Aoff becomes 70 µm2 or more.
Fig. 4 is a view magnifying the respective skirt portions of the power distribution PA(r) of light propagating through the conventional dispersion-shifted optical fiber shown in Figs. 1A and 1B and the power
distribution P(r) of light propagating through the dispersion-shifted optical fiber 100 according to the first embodiment. As can be seen from Fig. 4, the optical power P(5λ) at the evaluation reference position radially separated from the peak position by 5 λ. in the dispersion-shifted optical fiber 100 according to the first embodiment is p(5 A )sPMaX/100, whereas the optical power PA (5A) at the evaluation reference position (position radially separated by 5 λ from the core center yielding its maximum optical power PAmax in the conventional dispersion-shifted optical fiber 100 is much larger than 1/100 of the maximum optical power PAmax.
The inventors evaluated the optical loss caused by macrobending in each of the conventional dispersion-shifted optical fiber 100 and the dispersion-shifted optical fiber according to the first embodiment. This evaluation was carried out by measuring the loss of light at 1550 nm before and after each of these optical fibers was wound around a cylindrical reel having a diameter of 20 mm. As a result, the dispersion-shifted optical fiber 100 according to the first embodiment yielded an increase of 0.1 dB/m in optical loss between before and after the winding, whereas the conventional dispersion-shifted optical fiber yielded an increase of 2.0 dB/m in optical loss between before and after the winding. Thus, the superiority of the dispersion-shifted optical fiber 100 according to the first embodiment
was confirmed.
Further, the inventors evaluated the optical loss caused by microbending in each of the conventional dispersion-shifted optical fiber 100 and the dispersion-shifted optical fiber according to the first embodiment. This evaluation was carried out by measuring the loss of light at 1550 nm before and after each of these optical fibers was wound around a cylindrical reel having a diameter of 280 mm whose surface carried sandpaper attached thereto. AS a result, the dispersion-shifted optical fiber 100 according to the first embodiment yielded an increase of 0,2 dB/km in optical loss, whereas the conventional dispersion-shifted optical fiber yielded an increase of 11.2 dB/km in optical loss. It has also proved the superiority of the dispersion-shifted optical fiber 100 according to the first embodiment.
As explained in the foregoing, when the refractive index profile is designed such that optical power attains its maximum Pmax at a position (peak position) shifted from the center position of the core region and that the optical power p(5λ)at the evaluation reference position radially separated from the peak position by a distance (5λ) which is five times the signal light wavelength λ becomes 1/100 or less of the Pmax the effective area Aoff can be increased without extremely broadening the skirts of optical power distribution P(r). As a result, light can fullybe confined,
thereby the optical loss caused by macrobending or microbending can be reduced.
Further, when the effective area Aoff is set to 70 µ m2 or more, nonlinear phenomena such as self-phase modulation, cross-phase modulation, four-wave mixing, and the like can be reduced, whereby distortion of signal light can be restrained from occurring.
Fig, 2 is a graph showing, as a relationship between a bending loss and an optical power, a relationship between a microbending loss (dB/km) and a ratio (P/Pmax) of an optical power at an evaluation position with respect 1to a maximum optical power Pmax.
In order to suppress the microbending loss caused by cable-fabrication to a sufficient level in practice, the microbending loss should be suppressed to 1 dB/km or less. Thus, it is necessary that the ratio {P/Pmax) of an optical power at the evaluation reference position with respect to a maximum optical power Pmax becomes 1/100 or less. Accordingly, the dispersion-shifted optical fiber according to the first embodiment realizes both expansion of the effective area and suppression of bending loss. Second Embodiment
Pig. 5A is a view showing a cross-sectional structure of the second embodiment Of dispersion-Shifted optical fiber according to the present invention.
As with the above-mentioned first embodiment, the
dispersion-shifted optical fiber according to the second embodiment is a single-mode optical fiber which guides signal light in a 1.55µm wavelength band whose center wavelength A falls within the range of about 1500 to 1600 nm. Also, as shown in Fig. 5A, this dispersion-shifted optical fiber 200 comprises a core region 210 and a cladding region 220 provided on the outer periphery of the core region 210. The core region 210 is constituted by a first core 211 having an outside diameter a2 (5,8 µm) and a second core 212, provided on the outer periphery of the first core 211, having an outside diameter b2 (9.2 µm) (thus, forming a ring-shaped core structure). On the other hand, the cladding region 220 comprises a first cladding 2.21, provided on the outer periphery of the second core 212, having an outside diameter c2 (13.6 µm), and a second cladding 222 provided on the outer periphery of the first cladding 221 (thus forming a depressed cladding structure).
Fig. 5B is a refractive index profile of the dispersion-shifted optical fiber 200 of the second embodiment shown in Fig. 5A, which is represented by the relative refractive index difference of each part along the line L2 passing through the center 02 of the dispersion-shifted optical fiber 200. Here, the relative refractive index difference is given by the above-mentioned expression (2), with reference to the second cladding 222 as a reference area.
In the refractive index profile of Fig. 5B, the first core 211 with an outside diameter of a2 (5.8 µm) has a relative refractive index difference ∆n of -0.30% with respect to the second cladding 222, whereas the second core 212 with an outside diameter of b2 (9.2 µm) has a relative refractive index difference ∆n2 of 0.95% with respect to the second cladding 222. The first cladding 221 with an outside diameter of c2 (13.6 µm) has a relative refractive index difference ∆n1 of -0.30% with respect to the second cladding 222. Here, as fluorine is introduced into Si02 by MCVD method, the respective refractive indexes nt and n} of the first core 211 and first cladding 221 are set to a value lower than the refractive index n, of the second cladding 222; whereas, as GeO, is added into Si02 by MCV:5 method, the refractive index n2 of the second core 212 is set to a value which is higher than the refractive index n, of the second cladding 222.
Fig. 5C shows the power distribution ) of signal light propagating through the dispersion-shifted optical fiber 200 of the second embodiment. In this graph, optical power attains the maximum value PMaX at a peak position shifted from the center position (r * 0) of the core region 210, and drastically decreases toward the outer periphery. In particular, the optical power P(5λ.) at an evaluation reference position radially separated from the peak position by a distance (5 λ) which is five times the
wavelength A becomes 1/100 or less of the maximum optical power Pmax. Also, the effective area Aoff becomes 70 µm2 or more .
As explained in the foregoing, when the refractive index profile is designed such that optical power attains its maximum Pmax at a position (peak position) shifted from the center position of the core region and that the optical power P(5λ) at the evaluation reference position radially separated from the peak position by a distance: (5∆) which is five times the signal light wavelength A becomes 1/100 or less of the Pmax, the effective area Aoff can be increased without extremely broadening the skirts of optical power distribution P(r) . As a result, light can fully be confined, thereby the optical loss caused by macrobending or microbending can be reduced.
Further, when the effective area Aoff is set to 70 µ m2 or more, nonlinear phenomena such as self-phase modulation, cross-phase modulation, four-wave mixing, and the like can be reduced, thereby distortion of signal light can be restrained from occurring.
Fig. 6A is a view showing a cross-sectional structure of the third embodiment of dispersion-shifted optical fiber according to the present invention.
As with the above-mentioned first and second embodiments, the dispersion-shifted optical fiber
according to the third embodiment is a single-mode optical fiber which guides signal light in a 1.5 5- µm wavelength band whose center wavelength A falls within the range of about 1500 to 1600 nm. Also, as shown in Pig. 6A, this dispersion-shifted optical fiber 300 comprises a core region 310 and a cladding region 320 provided on the outer periphery of the core region 310. The core region 310 is constituted by a first core 311 having an outside diameter a3 (4.4 µm); a second core 312, provided on the outer periphery of the first core 311, having an outside diameter b3 (8.4 µm); a third core 313, provided on the outer periphery of the second core 312, having an outside diameter c3 (15.4 µum); and a fourth core 314, provided on the outer periphery of the third core 313, having an outside diameter d3 (19.4 µm) (thus forming a multilayer core structure).
Fig. 6B is a refractive index profile of the dispersion-shifted optical fiber 300 of the third embodiment shown in Fig. 6A, which is represented by the relative refractive index difference of each part along the line L3 passing through the center 03 of the dispersion-shifted optical fiber 300. Here, the relative refractive index difference is given by the above-mentioned expression (2), with reference to the cladding region 320 as a reference area.
In the refractive index profile of Fig. 6B, with respect to the cladding region 320, the first core 311 with
an outside diameter of a3 (4.4 µm) has a relative refractive index difference ∆nt of -0.40%, the second core 312 with an outside diameter of b3 (8.4 µm) has a relative refractive index difference An, of 0.7%, the third core 313 with an outside diameter of c3 (15.4 µm) has a relative refractive index difference An, of -0.40%, and the fourth sore 314 with an outside diameter of d3 (19.4 µm) has a relative refractive index difference ∆n4 of 0.35%. Here, as fluorine is introduced into Si02 by MCVD method, the respective refractive indexes nl and n3 of the first core 311 and third core 313 are set to a value lower than the refractive index n0 of the cladding region 320; whereas, as GeO2 is added into Sio, by MCVD method, the respective refractive indexes n2 and n4 of the second core 312 and fourth core: 314 are set to values which are higher than the refractive index nc of the cladding region 320.
Pig. 6c shows the power distribution P(r) of signal light propagating through the dispersion-shifted optical fiber 300 of the third embodiment. In this graph, optical power attains the maximum value Pmax at a peak position shifted from the center position (r = 0) of the core region 310, and drastically decreases toward the outer periphery. In particular, the optical power P(5λ) at an evaluation reference position radially separated from the peak position by a distance (5 λ) which is five times the wavelength A becomes 1/100 or less of the maximum optical
power Pmax. Also, the effective area Aoff becomes 70 µm2 or more.
As explained in the foregoing, when the refractive index profile is designed such that optical power attains its maximum Pmax at a position (peak position) shifted from the center position of the core region and that; the optical power P(5λ) at the evaluation reference position radially separated from the peak position by a distance (5 λ) which is five times the signal light wavelength A becomes 1/100 or less of the Pmax the effective area Aoff can be increased without extremely broadening the skirts of optical power distribution P(r) . As a result, light can fully be confined, thereby the optical loss caused by macrobending or microbending can be reduced.
Further, when the effective area Aoff is set to 70 µ. m2 or more, nonlinear phenomena such as self-phase modulation, cross-phase modulation, four-waves mixing, and the like can be reduced, whereby distortion of signal light can be restrained from occurring.
The dispersion-shifted optical fiber according to the present invention should not be restricted to those having refractive index profiles shown in the above-mentioned first to third embodiments, but can also be realized by a greater number of cores while adjusting the relative refractive index difference of each core. Industrial Applicability
In the dispersion-shifted optical fiber according to the present invention, as explained in the foregoing, since the refractive index profile is designed such that the peak position where the optical power in the fundamental mode is maximized is shifted from the center of the core region and that optical power at the evaluation reference position radially separated from the peak position by a distance which is five times the signal light wavelength becomes 1/100 or less of the maximum optical power at the peak position, the effective area Aoff can sufficiently be enhanced without broadening the skirts of optical power distribution•
As a result, light can fully be confined, thereby the optical loss caused by macrobending or microbending can be reduced. Further, since the effective area Aoff is 70 µ. m2 or more, nonlinear phenomena such as self-phase modulation, cross-phase modulation, four-wave mixing, and the like can be reduced, whereby distortion of signal light can be restrained from occurring. Thus, since it becomes possible to reduce optical loss and suppress nonlinear phenomena, a dispersion-shifted optical fiber suitable for further long-haul transmission and wavelength-division multiplexing transmission can be provided.




WE CLAIM:
1. A dispersion-shifted optical fiber (100: 200; 300) comprising a cote region (110; 210; 310) extending along a predetermined axis, and a cladding region (120; 220; 320) provided on the outer periphery of said core region (110; 210; 310),
characterized by arranging said core region (110; 210; 310) and said cladding region (120; 220; 320) so as to obtain an effective area of 70 µl m2 or more with respect to light whose center wavelength falls within the range of 1500 to 1600 nm, and a refractive index profile designed such that a peak position where optical power of said light in a fundamental mode is maximized is radially shifted from a center of said core region and that optical power at a position is radially separated from said peak position by a distance which is five times the center wavelength of said light becomes 1/100 or less of the optical power at said peak position.

2. A dispersion-shifted optical fibre (100; 200) as claimed in claim 1,
wherein said core region (110; 210) has a first core (111; 211); and a second core (112; 212) provided on the outer periphery of said first core (111; 211) and having a refractive index higher than that of said first core
3. A dispersion-shifted optical fibre (200) as claimed in any of the preceding claims, wherein said cladding region (220) has a first cladding (221) provided on the outer periphery of said second core (212) and having a refractive index lower than that of said second core (212); and a second cladding (222) provided on the outer periphery of said first cladding (211) and having a refractive index higher than that of said first (cladding (221).
4. A dispersion-shifted optical fibre (300) as claimed in claim 1, wherein said core region (310) has a first core (311); a second core (312) provided on the outer periphery of said first core (311) and having a refractive index higher than that of said first core (311); a third core (313) provided on the outer periphery of said second core (312) and having a refractive index lower than that of said second core (312); and a fourth core (314) provided on the outer periphery of said third core (313) and having a refractive index higher than that of said third core (313).
5. A dispersion-shifted optical fibre as claimed in any of the preceding
claims, wherein said cladding region has a first cladding provided on the
outer periphery of said fourth core (314) and having a refractive index
lower than that of said fourth core (314); and a second cladding provided
on the outer periphery of said first cladding and having a refractive
index higher than that of said first cladding.
6. A dispersion-shifter optical fibre substantially as hereinbefore
described with reference to and as illustrated in the accompanying
drawings.

Documents:

2905-del-1998-abstract.pdf

2905-del-1998-claims.pdf

2905-del-1998-correspondence-others.pdf

2905-del-1998-correspondence-po.pdf

2905-del-1998-description (complete).pdf

2905-del-1998-drawings.pdf

2905-del-1998-form-1.pdf

2905-del-1998-form-13.pdf

2905-del-1998-form-19.pdf

2905-del-1998-form-2.pdf

2905-del-1998-form-3.pdf

2905-del-1998-form-4.pdf

2905-del-1998-form-6.pdf

2905-del-1998-gpa.pdf

2905-del-1998-petition-138.pdf


Patent Number 214523
Indian Patent Application Number 2905/DEL/1998
PG Journal Number 08/2008
Publication Date 22-Feb-2008
Grant Date 12-Feb-2008
Date of Filing 28-Sep-1998
Name of Patentee SUMITOMO ELECTRIC INDUSTRIES LTD
Applicant Address 5-33 KITAHAMA 4-CHOME CHOU-KU OSAKA-SHI OSAKA 541-0041 JAPAN.
Inventors:
# Inventor's Name Inventor's Address
1 EISUKE SASAOKA C/O YOKOHAMA WORKS OF SUMITOMO ELECTRIC INDUSTRIES LTD 1 TAYA-CHO SAKAE-KU YOKOHAMA-SHI KANAGAWA 244-0844,JAPAN.
2 TAKATOSHI KATO
PCT International Classification Number GO2B 6/02
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA