Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1998-09-14
2001-10-23
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000, C385S126000, C385S127000
Reexamination Certificate
active
06307993
ABSTRACT:
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for OPTICAL FIBER FOR WAVELENGTH DIVISION MULTIPLEXING COMMUNICATIONS earlier filed in the Korean Industrial Property Office on the 13
th
of Sep. 1997 and there duly assigned Ser. No. 47450/1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber for wavelength division multiplexing (WDM) communications, and more particularly, to an optical fiber having a profile which optimizes chromatic dispersion in a desired wavelength band by adjusting the refractive index of an optical waveguide.
2. Description of the Related Art
In general, WDM communications transmits a plurality of optical signals having different wavelengths via an optical fiber, and can effectively use the low loss characteristics of an optical fiber over a wide wavelength band. Thus, at present, communications techniques using WDM are being used more widely.
It is known that an optical fiber, which is the most widely used in the above WDM communications, must have a wide communications region to transmit a signal having a 1550 nm wavelength band. As an advantage, an optical fiber having a communications region in the wavelength band of 1550 nm has low attenuation, since light in the wavelength band of 1550 nm is attenuated the least when propagating the core of a optical fiber according to the characteristics of a silica optical fiber. Accordingly, when communications is made using an optical fiber having a transmission region capable of transmitting the 1550 nm wavelength band signal, repeaters can be spaced widely apart, thereby drastically reducing costs for maintenance and repair for long distance transmission.
As another advantage, optical communications of the 1550 nm wavelength band signal can amplify an optical signal using an optical fiber itself. Such optical amplification can not only reduce the size of an external amplifier but also does not require an external generator, so that the size of a transmission system can be remarkably diminished as well.
For example, a dispersion shifted fiber (DSF) is commonly used of late as an optical fiber having a communications region of the 1550 nm wavelength band. The DSF, having chromatic dispersion of “0” in a wavelength of 1550 nm, is effectively used to transmit a 1550 nm-wavelength signal. A representative example of such a DSF is disclosed in U.S. Pat. No. 4,715,679 entitled “Low-dispersion Low- Attenuation Single Mode Optical Waveguide” by Venkata A.Bhagavatula.
Also, an optical amplifier uses a rare earth ion doped fiber formed by doping a rare earth material to the core of an optical fiber. The rare earth material is generally erbium, neodymium or praseodymium. An erbium doped fiber amplifier (EDFA), where erbium among the rare earth materials is doped to the core, is the most widely used, and allows an optical communications network to be realized.
The EDFA has characteristics representing a maximum gain at a wavelength band of 1530 nm, and it is known that a wavelength band capable of using the amplification effect is usually, approximately between 1530 nm and 1565 nm. As to a current optical fiber and an optical communications technique using the same, much effort is made to widen a wavelength band which can sufficiently utilize the amplification properties of the EDFA and to flatten the difference between gains over wavelength bands.
At present, single mode optical fibers for WDM communications are manufactured so that the inclination of chromatic dispersion and a zero dispersion wavelength are suitable for a wavelength of 1550 nm. However, in this case, this WDM communications single mode fiber is limited with respect to multi-channel transmission because of nonlinear effects such as four-wave mixing, and the multichannel transmission is more difficult since the wavelength band of the optical fiber is not equal to a gain wavelength region of the EDFA. Also, in the optical fibers having a zero dispersion wavelength set to 1550 nm, the inclination of the chromatic dispersion is not consistent with the gain wavelength band of the EDFA. As described above, the optical fibers having a zero dispersion wavelength cause a limit where transmission quality is precipitously deteriorated even when there is little change in the inclination of chromatic dispersion.
In order to suppress an increase in the aforementioned nonlinear effect, an optical fiber must have the characteristics in which zero dispersion is not made in the gain wavelength band of the EDFA by controlling chromatic dispersion of the optical fiber. That is, the optical fiber is designed to have characteristics in which zero dispersion is not made in a wavelength region of between 1350 nm and 1560 nm, in order to minimize or remove the nonlinear effect such as the four-wave mixing in the gain wavelength region of the current EDFA.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an optical fiber having a profile which allows the optical fiber to receive relatively little influence due to external tension or stress by having a flat refractive index at the core center of the optical fiber and reducing the diameter of the core.
It is another objective of the present invention to provide an optical fiber having a relatively wide non-zero dispersion region to minimize a nonlinear effect in a gain wavelength region of an erbium doped fiber amplifier (EDFA).
Accordingly, to achieve the first objective, there is provided an optical fiber for wavelength division multiplexing (WDM) communications, comprising: an inner core having a predetermined refractive index, formed to have a first predetermined radius from a central axis of the optical fiber; an outer core having a refractive index which is lower than the refractive index of the inner core and gets linearly smaller from its inner side to its outer side, formed on an outer side of the inner core to have a second predetermined radius; and a cladding formed on the outer side of the outer core to have a third predetermined radius.
To achieve the second objective, there is provided an optical fiber for wavelength division multiplexing (WDM) communications, comprising: an inner core having a predetermined refractive index, formed to have a first predetermined radius from the central axis; an outer core having a refractive index which is lower than the refractive index of the inner core and gets linearly smaller from its inner side to its outer side, formed on an outer side of the inner core to have a third predetermined radius; an inner cladding formed on the outer side of the outer core to have a third predetermined radius; and an outer cladding having a refractive index which is lower than the refractive index of the inner cladding and gets linearly smaller from its inner side to its outer side, formed on an outer side of the inner cladding to have a fourth predetermined radius.
REFERENCES:
patent: 4070091 (1978-01-01), Taylor et al.
patent: 4715679 (1987-12-01), Bhagavatula
patent: 4755022 (1988-07-01), Ohashi et al.
patent: 5483612 (1996-01-01), Gallagher et al.
patent: 5675688 (1997-10-01), Nouchi et al.
patent: 5703986 (1997-12-01), Brehm et al.
patent: 5835655 (1998-11-01), Liu et al.
patent: 5956448 (1999-09-01), Smolka et al.
Li Xiao-Jun
Namkoong Ki-Un
Oh Kyung-Hwan
Oh Seung-Hun
Paek Un-Chul
Bushnell , Esq. Robert E.
Samsung Electronics Co,. Ltd.
Sanghavi Hemang
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