Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2002-10-18
2004-01-27
Patel, Tulsidas (Department: 2839)
Optical waveguides
Optical fiber waveguide with cladding
C359S199200
Reexamination Certificate
active
06684017
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transmission line employed in a repeatered transmission line disposed between stations, and an optical transmission system including the same.
2. Related Background Art
Wavelength division multiplexing (WDM) optical transmission utilizing signals of a plurality of channels included in a 1.55-&mgr;m wavelength band enables high-speed, large-capacity information transmissions. Factors restricting the transmission capacity in this WDM optical transmission include the nonlinearity and dispersion slope of the optical transmission line. Therefore, in order to improve the performance of a WDM optical transmission system, it is important to suppress the nonlinearity of the optical transmission line (e.g., by increasing its effective area) and lower the dispersion slope of the optical transmission line.
Proposed as an optical transmission line aimed at suppressing the nonlinearity and lowering the dispersion slope as such is an optical transmission line having a configuration in which a single-mode optical fiber and a dispersion-compensating optical fiber are connected to each other. The single-mode optical fiber (hereinafter referred to as SMF) has a zero-dispersion wavelength in a 1.3-&mgr;m wavelength band and exhibits, in the 1.55-&mgr;m wavelength band, a positive chromatic dispersion and a positive dispersion slope. On the other hand, the dispersion-compensating optical fiber (hereinafter referred to as DCF) exhibits, in the 1.55-&mgr;m wavelength band, a negative chromatic dispersion and a negative dispersion slope. Hence, the respective lengths of the SMF and DCF are appropriately adjusted, so as to lower the dispersion slope of the optical transmission line as a whole. Also, since the SMF having a relatively large effective area is disposed on the upstream side in the signal propagating direction, the effective area of the whole transmission line is enhanced, and the nonlinearity of the optical transmission line is suppressed.
For example, the conventional optical transmission line disclosed in T. Naito, et. al, “1 Terabit/s WDM Transmission over 10,000 km,” ECOC′ 99, PD-2-1 (1999), hereinafter referred to as first conventional technique, comprises a configuration in which an SMF and a DCF are connected to each other. The conventional optical transmission line disclosed in Chikutani, et al., “Low Nonlinear PSCF+DCF Complex Transmission Line having Low Dispersion Slope and Low Nonlinearity,” IEICE Technical Report, OCS99-97, pp. 67-72 (1999), hereinafter referred to as second conventional example, comprises a configuration in which an SMF (hereinafter referred to as A
eff
-enlarged PSCF) exhibiting an effective area A
eff
greater than a commonly known value thereof and having a core region made of pure silica (non-intentionally doped silica), and a DCF are connected to each other. The conventional optical transmission line disclosed in M. Murakami, et al., “Quarter Terabit (25×10Gb/s) over 9288 km WDM Transmission Experiment Using Nonlinear Supported RZ Pulse in Higher Order Fiber Dispersion Managed Line,” ECOC′ 98, PD, pp. 79-81 (1998), hereinafter referred to as third conventional example, comprises a configuration in which an SMF (hereinafter referred to as Ge-SM) having a core region doped with Ge and a DCF are connected to each other.
The conventional optical transmission line disclosed in K. Fukuchi, et al., “1.1-Tb/s (55×20-Gb/s) Dense WDM Soliton Transmission Over 3,020-km Widely-Dispersion-Managed Transmission Line Employing 1.55/1.58-&mgr;m Hybrid Repeaters,” ECOC′ 99, PD-2-10 (1999), hereinafter referred to as fourth conventional example, comprises a configuration in which an SMF (hereinafter referred to as PSCF (Pure Silica Core Fiber)) having a core region made of pure silica and a DCF are connected to each other. The conventional optical transmission line disclosed in T. Tsuritani, et al., “1 Tbit/s (100×10.7 Gbit/s) Transoceanic Transmission Using 30 nm-Wide Broadband Optical Repeaters with A
eff
-Enlarged Positive Dispersion Fibre and Slope-Compensating DCF,” ECOC′ 99, PD-2-7 (1999), hereinafter referred to as fifth conventional example, comprises a configuration in which an A
eff
-Enlarged PSCF and a DCF are connected to each other.
SUMMARY OF THE INVENTION
The inventors studied the above-mentioned optical transmission lines according to the first to fifth conventional examples and, as a result, have found the following problems. Namely, effects of fully lowering the nonlinearity and dispersion slope may not be obtained in the optical transmission lines according to the first and second conventional examples since their bending loss is about 1 dB/m so that they are designed to become excessively resistant to bending. In the optical transmission lines according to the third and fourth conventional examples, the effect of lowering the nonlinearity may not fully be obtained since the relative refractive index difference of the core region in the DCF is assumed to be about 1.2%. The effect of fully lowering the nonlinearity may not be expected in the optical transmission line according to the fifth conventional example, since the relative refractive index difference of the core region in the DCF is assumed to be about 2.0%. Here, none of the optical transmission lines according to the third to fifth conventional examples is optimized in terms of the ratio of length of DCF in the whole optical transmission line, and the like.
In order to overcome the problems mentioned above, it is an object of the present invention to provide an optical transmission line comprising a structure for effectively lowering both the nonlinearity and dispersion slope, and an optical transmission system including the same.
The optical transmission line according to the present invention is a repeatered transmission line which has a predetermined span length of L and is disposed between stations, such as transmitting stations, repeater stations, and receiving stations, as a transmission medium suitable for WDM optical transmission utilizing signals of a plurality of channels different from each other. This optical transmission line comprises a single-mode optical fiber having a zero-dispersion wavelength in a 1.3-&mgr;m wavelength band, and a dispersion-compensating optical fiber for compensating for a chromatic dispersion of the single-mode optical fiber. The single-mode optical fiber and the dispersion-compensating optical fiber are successively disposed in this order along a signal propagating direction and are fusion-spliced to each other. The optical transmission line as a whole has an average dispersion slope S
ave
of −0.0113 ps
m
2
/km or more but 0.0256 ps
m
2
/km or less at a wavelength of 1550 nm, and an equivalent effective area EA
eff
of 50 &mgr;m
2
or more at the wavelength of 1550 nm.
In particular, the above-mentioned average dispersion slope S
ave
and equivalent effective area EA
eff
in the optical transmission line according to the present invention satisfy the following relationship:
f
(
S
ave
)≦
EA
eff
≦g
(
S
ave
) (1)
where f (S
ave
) is a lower limit function which yields the lower limit of EA
eff
by the expression:
942
×S
ave
+0.609
×L
+45.7
while using the average dispersion slope S
ave
and the span length L as variable, and g(S
ave
) is an upper limit function which yields the upper limit of EA
eff
by the expression:
885
×S
ave
+0.609
×L
+60.7
while using the average dispersion slope S
ave
and the span length L as variable.
The relationship represented by the above-mentioned expression (1) indicates an appropriate range of equivalent effective area EA
eff
for controlling the bending loss within the range from 2 dB/m to 10 dB/m as a permissible range at a span length of 50 km in order to enable high-speed, large-capacity WDM optical transmission not only in C band (having a wavelength of 1530 to 1565 nm) but also in L band (having a wavelength of
Sasaoka Eisuke
Tsukitani Masao
McDermott & Will & Emery
Patel Tulsidas
Sumitomo Electric Industries Ltd.
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