Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2001-10-25
2004-01-27
Healy, Brian (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S126000, C385S124000, C385S123000, C398S147000
Reexamination Certificate
active
06684018
ABSTRACT:
TECHNICAL FIELD
This invention relates to a low-dispersion optical fiber used for example when wavelength division multiplexing optical transmission is carried out in the 1.5 &mgr;m band, and to an optical transmission system using this low-dispersion optical fiber.
BACKGROUND ART
With the development of the information society the amount of information communicated has been increasing dramatically, and the realization of high bit-rate and high capacities in optical fiber communications has become an urgent and unavoidable issue. As an approach to this realization of more high bit-rate and capacities, optical fiber type optical amplifiers, which by using an optical fiber doped with a rare earth element, such as an erbium-doped optical fiber (EDF) doped with Er
3+
, can amplify an optical signal in the form of light, have been developed. And with the development the optical amplifiers which uses those optical fiber, the realization of high-power signal light has been progressing rapidly.
Meanwhile, to increase communication capacities in optical communications, communications using wavelength division multiplexing optical transmission, wherein optical signals having different wavelengths are transmitted down a single optical fiber, have been being developed. And from the application of the optical amplifier which uses above-mentioned optical fiber to optical communication using this wavelength division multiplexing optical transmission (wavelength multiplexing optical transmission systems), further increases in communication capacity and the realization of long-distance transmission are anticipated.
One representative example of an optical fiber type optical amplifier is the EDFA (Erbium-Doped optical Fiber Amplifier), which has an EDF of the kind mentioned above. The use of the EDFA to conduct the above-mentioned wavelength division multiplexing optical transmission with the 1.5 &mgr;m wavelength band (wavelength 1520 nm to 1620 nm), which is the gain band of the EDFA, as the transmission band has been being studied.
FIGS. 6A and 6B
show examples of refractive index profiles of optical fibers that have been proposed in related art as optical fibers for wavelength division multiplexing optical transmission with, of the above-mentioned 1.5 &mgr;m wavelength band, particularly the 1550 nm vicinity wavelength band (the 1.55 &mgr;m wavelength band) as the transmission band (used wavelength band).
FIG. 6A
shows a dual shaped refractive index profile, and
FIG. 6B
shows a W-shaped refractive index profile.
The optical fiber with the dual shaped refractive index profile is made up of a cladding
5
, a center core
1
having a larger refractive index than that of the cladding
5
, and a first side core
2
having a refractive index smaller than that of the center core
1
but larger than that of the cladding
5
. The optical fiber with the W-shaped refractive index profile is made up of a cladding
5
, a center core
1
having a larger refractive index than that of the cladding
5
, and a first side core
2
having a refractive index smaller than that of the cladding
5
.
Among optical fibers with the dual shaped refractive index profile described above, those having their zero dispersion wavelength in the 1.55 &mgr;m wavelength vicinity are called dispersion-shifted optical fibers. Because a dispersion-shifted optical fiber has its zero dispersion wavelength in the vicinity of the wavelength 1.55 &mgr;m, which is the center wavelength of the 1.55 &mgr;m wavelength band, distortion of the signal light waveform caused by dispersion in the 1.55 &mgr;m wavelength band is suppressed. On the down side, however, the occurrence of the nonlinear phenomenon of four-wave mixing is marked. Consequently, with this dispersion-shifted optical fiber, four-wave mixing light arising causes distortion to occur in the waveform of the signal light, and it is impossible to realize high-quality wavelength division multiplexing optical transmission.
To overcome this, dual shaped refractive index profile optical fibers having their zero dispersion wavelength shifted from the 1.55 &mgr;m wavelength band have been developed. However, it is known that in this kind of optical fiber the dispersion gradient in the 1.55 &mgr;m wavelength band is large. And because of that, with this kind of optical fiber it is difficult to make small the chromatic dispersion differential in the used wavelength band in wavelength division multiplexing optical transmission (the difference between the maximum value and the minimum value of the chromatic dispersion in the used wavelength band). Consequently, when this kind of optical fiber is used, it is not possible for the used wavelength band used for wavelength division multiplexing optical transmission to be made wide.
An optical fiber having the W-shaped refractive index profile functions as a dispersion flattened optical fiber, because the above-mentioned chromatic dispersion differential is small. However, whereas the effective core area (the region through which light effectively propagates: A
eff
) of the dual shaped refractive index profile optical fiber is about 45 &mgr;m
2
, the effective core area of a W-shaped refractive index profile optical fiber is for example about 30 &mgr;m
2
, or about ⅔ of that of the dual shaped refractive index profile optical fiber. And when the effective core area is small like this, in wavelength division multiplexing optical transmission there has been the problem that the transmitted signal deteriorates as a result of nonlinear phenomena arising in the optical fiber.
To overcome this, the idea of increasing the effective core area by using an optical fiber having a segment core refractive index profile of the kind shown in
FIG. 6C
has been proposed. In
FIG. 6C
,
1
denotes a center core;
2
a first side core;
3
a second side core; and
5
a cladding. However, with this kind of optical fiber, because the chromatic dispersion gradient in the 1.5 &mgr;m wavelength band is large and the chromatic dispersion differential in the same wavelength band is large, when the optical fiber of this proposal is applied to wavelength division multiplexing transmission, the problem arises that signal light waveform deterioration caused by chromatic dispersion becomes marked.
Also, to apply an optical fiber to a wavelength division multiplexing transmission system, the optical fiber must be incorporated into a cable. And because the cable is required to have the property that loss increases caused by bending of the optical fiber and side pressures on the optical fiber are low, it is also required of an optical fiber for wavelength division multiplexing transmission use that its bending property be good.
However, as explained above, there has not yet been realized an optical fiber with which it is possible to obtain both the effective core area and the reduced chromatic dispersion differential necessary to realize a high-quality wavelength division multiplexing transmission system, and additionally it has been difficult to realize an optical fiber whose bending loss property are also good.
Also, in recent years, as optical amplifiers, the Raman amplifier has been approaching practical introduction. The Raman amplifier has a wider amplifiable wavelength band than existing EDFAs, and can amplify a light signal of any specified wavelength band within for example the wavelength range of 1450 nm to 1650 nm. However, studies of, optical fibers in this wavelength range have not yet advanced.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide a low-dispersion optical fiber with which it is possible to obtain both increased effective core area and reduced chromatic dispersion differential in a used wavelength band and furthermore to reduce loss increases caused by bending and side pressures when the optical fiber is made into a cable, and an optical transmission system using this low-dispersion optical fiber.
A low-dispersion optical fiber of a first construction provided by the invention to achieve this and
Aiso Keiichi
Arai Shinichi
Inoue Katsunori
Koaizawa Hisashi
Oyama Naoto
Healy Brian
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
The Furukawa Electric Co. Ltd.
LandOfFree
Low-dispersion optical fiber and optical transmission system... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low-dispersion optical fiber and optical transmission system..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low-dispersion optical fiber and optical transmission system... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3217144