Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2000-12-14
2002-11-05
Healy, Brian (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
C385S123000, C385S095000, C385S096000, C385S098000, C385S124000, C385S126000, C385S127000, C385S141000
Reexamination Certificate
active
06477306
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dispersion-compensating optical fiber which compensates for the chromatic dispersion and dispersion slope of a dispersion-shifted optical fiber, an optical transmission line including the dispersion-shifted optical fiber and dispersion-compensating optical fiber, and a dispersion-compensating module formed by winding the dispersion-shifted optical fiber like a coil.
2. Related Background Art
For achieving further higher speed and larger capacity in optical transmission systems which carry out wavelength division multiplexing (WDM) optical transmission, it is important that the absolute value of accumulated chromatic dispersion be as small as possible in a wide signal wavelength band. In general, since it is hard to achieve in an optical transmission line using only one kind of optical fiber, a plurality of kinds of optical fibers have been connected so as to construct an optical transmission line, thereby lowering the absolute value of accumulated chromatic dispersion in the optical transmission line in a wide band.
For example, Japanese Patent Application Laid-Open No. HEI 6-11620 discloses a technique in which a standard single-mode optical fiber (SMF) having a zero-dispersion wavelength near a wavelength of 1.3 &mgr;m and a dispersion-compensating optical fiber (DCF) which compensates for the chromatic dispersion of this standard single-mode optical fiber at a wavelength of 1550 nm are connected to each other, so as to reduce the absolute value of accumulated chromatic dispersion of the optical transmission line constructed by thus connected optical fibers in a 1.55-&mgr;m wavelength band.
Also, U.S. Pat. No. 5,838,867 discloses a technique in which a non-zero dispersion-shifted optical fiber (NZDSF) having a small positive chromatic dispersion at a wavelength of 1550 nm and a dispersion-compensating optical fiber which compensates for the chromatic dispersion and dispersion slope of this dispersion-shifted optical fiber are connected to each other, so as to lower the absolute value of accumulated chromatic dispersion of the optical transmission line constructed by thus connected optical fibers in a 1.55-&mgr;m wavelength band.
Here, the chromatic dispersion of a standard single-mode optical fiber (SMF) at a wavelength of 1550 nm is referred to as D
SMF
, and its dispersion slope is referred to as S
SMF
. The chromatic dispersion of a non-zero dispersion-shifted optical fiber (NZDSF) at a wavelength of 1550 nm is referred to as D
DSF
, and its dispersion slope is referred to as S
DSF
. The chromatic dispersion of a dispersion-compensating optical fiber (DCF) at a wavelength of 1550 nm is referred to as D
DCF
, and its dispersion slope is referred to as S
DCF
. Then, for reducing the absolute value of accumulated chromatic dispersion of an optical transmission line in a wide band including a wavelength of 1550 nm, it is required in a dispersion-compensating optical fiber (hereinafter referred to as “dispersion-compensating optical fiber for SMF”) for compensating for both of the chromatic dispersion and dispersion slope of the single-mode optical fiber that its ratio (S
DCF
/D
DCF
) of dispersion slope S
DCF
to the chromatic dispersion D
DCF
be substantially equal to the ratio (S
SMF
/D
SMF
) of dispersion slope S
SMF
to the chromatic dispersion D
SMF
of the single-mode optical fiber. Also, it is required in a dispersion-compensating optical fiber (hereinafter referred to as “dispersion-compensating optical fiber for DSF”) for compensating for both of the chromatic dispersion and dispersion slope of the dispersion-shifted optical fiber that its ratio (S
DCF
/D
DCF
) of dispersion slope S
DCF
to the chromatic dispersion D
DCF
be substantially equal to the ratio (S
DSF
/D
DSF
) of dispersion slope S
DSF
to the chromatic dispersion D
DSF
of the dispersion-shifted optical fiber.
SUMMARY OF THE INVENTION
The inventors have studied conventional optical transmission lines in detail and, and as a result, have found problems as follows.
As compared with standard single-mode optical fibers, dispersion-shifted optical fibers have a greater ratio (S
DSF
/D
DSF
) at a wavelength of 1550 nm. Therefore, it is necessary for dispersion-compensating optical fibers for DSF to have a greater ratio (S
DSF
/D
DSF
) at the wavelength of 1550 nm as compared with dispersion-compensating optical fibers for SMF.
The dispersion-compensating optical fiber for SMF a disclosed in Japanese Patent Application Laid-Open. No. HEI 6-11620 compensates for the chromatic dispersion of a standard single-mode optical fiber having a zero-dispersion wavelength near a wavelength of 1.3 &mgr;m and a large chromatic dispersion at a wavelength of 1550 nm, and has a negative chromatic dispersion with a large absolute value. Therefore, this dispersion-compensating optical fiber for SMF is suitable for compensating for the chromatic dispersion of the standard single-mode optical fiber. However, this dispersion-compensating optical fiber for SMF is not sufficient for compensating for the dispersion slope.
On the other hand, the dispersion-compensating optical fiber for DSF disclosed in U.S. Pat. No. 5,838,867 can compensate for both of the chromatic dispersion and dispersion slope of a non-zero dispersion-shifted optical fiber having a small positive chromatic dispersion at a wavelength of 1550 nm. Since this dispersion-compensating optical fiber for DSF has a chromatic dispersion with a small absolute value, a long dispersion-compensating optical fiber for DSF is needed for compensating for both of the chromatic dispersion and dispersion slope of the non-zero dispersion-shifted optical fiber.
For example, the non-zero dispersion-shifted optical fiber disclosed in the document 1, S. Bigo, et al., “1.5 Terabit/s WDM transmission of 150 channels at 10 Gbit/s over 4×100 km of TeraLight™ fibre,” ECOC'99, PD (1999), has a chromatic dispersion of +8 ps
m/km and a dispersion slope of +0.06 ps
m
2
/km at a wavelength of 1550 nm. On the other hand, the non-zero dispersion-shifted optical fiber disclosed in the document 2, D. W. Peckham, et al., “Reduced dispersion slope, non-zero dispersion fiber, ” ECOC'98, pp. 139-140 (1998), has a chromatic dispersion of +4 ps
m/km and a dispersion slope of +0.046 ps
m
2
/km at a wavelength of 1550 nm. For compensating for both of the chromatic dispersion and dispersion slope of any of the non-zero dispersion-shifted optical fibers disclosed in these documents having a length of 80 km, a dispersion-compensating optical fiber for DSF having a length of 8 km to 16 km is necessary.
Meanwhile, even upon slight bending, fundamental-mode light is likely to leak out from dispersion-compensating optical fibers for DSF in general, so that bending loss is large in the fundamental-mode light. Consequently, transmission loss becomes greater when a dispersion-compensating optical fiber for DSF is laid as being cabled or is formed into a dispersion-compensating module as being wound like a coil. Therefore, in an optical transmission system which carries out optical communications by propagation of signals through an optical transmission line constructed by a dispersion-shifted optical fiber and a dispersion-compensating optical fiber for DSF which are connected to each other, transmission loss is so large in the optical transmission line that its repeater section cannot be elongated, whereby higher speed and larger capacity cannot further be achieved in optical communications.
In order to overcome the problems mentioned above, it is an object of the present invention to provide a dispersion-compensating optical fiber which can compensate for the chromatic dispersion and dispersion slope of a non-zero dispersion-shifted optical fiber by a short length, an optical transmission line with a low transmission loss including the dispersion-shifted optical fiber and dispersion-compensating optical fiber, and a dispersion-compensating module with a low transmission loss in which the di
Hirano Masaaki
Kato Takatoshi
Healy Brian
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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