Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2001-06-21
2004-08-24
Healy, Brian (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
C385S126000, C385S127000
Reexamination Certificate
active
06782172
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dispersion compensating optical fiber that compensates the chromatic dispersion and the dispersion slope of a dispersion-shifted optical fiber, an optical transmission line that includes the dispersion-shifted optical fiber and the dispersion compensating optical fiber, and a dispersion compensating module made of the dispersion compensating optical fiber.
2. Related Background Arts
In order to increase the transmission capacity in a Wavelength Division Multiplexing (WDM) transmission system, it is important to lessen the absolute magnitude of the cumulative chromatic dispersion of an optical transmission line as much as possible at a broad optical signal spectrum band. Generally, an attempt is made to reduce the absolute magnitude of the cumulative chromatic dispersion of an optical transmission line in a wide wavelength range by producing an optical transmission line by connecting plural kinds of optical fibers because it is difficult to do so in an optical transmission line using only one kind of optical fiber.
For example, Japanese Patent Application Laid-Open No. 6-11620 discloses a technique to reduce the absolute magnitude of the cumulative chromatic dispersion in the 1.55 &mgr;m wavelength band by connecting a standard single-mode fiber (SMF) which has a zero dispersion wavelength in the vicinity of the 1310 nm wavelength and which has a chromatic dispersion of about 15 ps·nm
−1
·km
−1
at the 1550 nm wavelength and a dispersion compensating fiber (DCF) which compensates the chromatic dispersion of the single mode fiber at the 1550 nm wavelength. It is set forth that in order to reduce the absolute magnitude of the cumulative chromatic dispersion of an optical transmission line in a broad wavelength range that includes the 1550 nm wavelength, the relationship (S
DCF
/D
DCF
)=(S
SMF
/D
SMF
) should be satisfied, when D
SMF
is the chromatic dispersion of a standard SMF at the 1550 nm wavelength, S
SMF
is the dispersion slope thereof, D
DCF
is the chromatic dispersion of a dispersion compensating optical fiber, and S
DCF
is the dispersion slope thereof.
When the chromatic dispersion at the 1550 nm wavelength of a non-zero dispersion shifted fiber (NZDSF) which has a positive small chromatic dispersion at the 1550 nm wavelength is represented as D
DSF
, and the dispersion slope thereof is represented as S
DSF
, S
DSF
/D
DSF
is substantially great as compared with S
SMF
/D
SMF
. Therefore, with a dispersion compensating optical fiber for SMF described in the specification of Japanese Patent Application Laid-Open No. 6-11620, it is impossible to compensate the chromatic dispersion of the dispersion-shifted fiber and reduce the absolute magnitude of the cumulative chromatic dispersion of an optical transmission line with respect to all of the wavelengths over a wide range that includes the 1550 nm wavelength.
Also, U.S. Pat. No. 5,838,867 discloses a technology for reducing the absolute magnitude of the cumulative chromatic dispersion at the 1.55 &mgr;m wavelength band of an optical transmission line that is produced by connecting a non-zero dispersion shifted fiber and a dispersion compensating optical fiber which compensates the chromatic dispersion and the dispersion slope of the non-zero dispersion shifted fiber at the 1550 nm wavelength. However, in order to compensate both the chromatic dispersion and the dispersion slope of a non-zero dispersion shifted fiber, a long length of dispersion compensating optical fiber for NZDSF is needed because the dispersion compensating optical fiber for NZDSF of U.S. Pat. No. 5,838,867 has a small absolute magnitude of the chromatic dispersion.
For example, in the case of the non-zero dispersion shifted fiber described in Literature 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), the chromatic dispersion is +8 ps·nm
−1
·km
−1
and the dispersion slope is +0.06 ps·nm
−2
·km
−1
at the 1550 nm wavelength. In the case of the non-zero dispersion shifted fiber described in Literature 2: David W. Peckham, et al., “Reduced dispersion slope, non-zero dispersion fiber”, ECOC '98, pp.139-140 (1998), the chromatic dispersion is +4 ps·nm
−1
·km
−1
and the dispersion slope is +0.046 ps·nm
−2
·km
−1
at the 1550 nm wavelength. In the case of the non-zero dispersion shifted fiber described in Literature 3: Valeria L. da Silva, et al., “Error free WDM transmission of 8×10 Gbit/s over km of LEAF™ Optical Fiber”, ECOC '97, No.448, pp.154-158 (1997), the zero dispersion wavelength is 1506 nm to 1514 nm, and the chromatic dispersion is about +4 to 5 ps·nm
−1
·km
−1
and the dispersion slope is about +0.1 ps·nm
−2
·km
−1
at the 1550 nm wavelength. To compensate the chromatic dispersion of 80 km of non-zero dispersion shifted fibers described in these literatures requires 8 km to 16 km lengths of the dispersion compensating optical fiber for NZDSF described in U.S. Pat. No. 5,838,867. Furthermore, in such case, it is impossible to sufficiently compensate both the chromatic dispersion and the dispersion slope at the same time.
Generally, a dispersion compensating optical fiber for a dispersion-shifted optical fiber is prone to leakage of the fundamental mode light at a slight bend thereof, and the bending loss of the fundamental mode light is large. Therefore, the transmission loss increases when it is formed into a cable and installed, or when it is wound on a bobbin to form a dispersion compensating module. As a result, in an optical transmission system that performs optical communication by allowing light signals to propagate through an optical transmission line that is produced by connecting a dispersion-shifted optical fiber and a dispersion compensating optical fiber for the dispersion-shifted optical fiber, the transmission loss is large in the optical transmission line. Accordingly, increasing the span of a transmission section (i.e. a distance between repeater stations) is not feasible, and it is difficult to achieve further increase in capacity of optical communication.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dispersion compensating optical fiber that can, with a relatively short length thereof, compensate both the chromatic dispersion and the dispersion slope of a non-zero dispersion shifted fiber at a wide spectrum band that includes the 1550 nm wavelength. Another object of the present invention is to provide an optical transmission line that includes a non-zero dispersion shifted fiber and a dispersion compensating optical fiber whose transmission loss is relatively small. A further object of the present invention is to provide a dispersion compensating module that compensates both the chromatic dispersion and the dispersion slope of a non-zero dispersion shifted fiber.
In order to achieve these objects, an optical fiber that satisfies the following relational expressions is provided:
−250 ps·nm
−1
·km
−1
≦D
DCF
≦−40
ps·nm
−1
·km
−1
0.015 nm
−1
≦S
DCF
/D
DCF
≦0.030 nm
−1
,
where D
DCF
is the chromatic dispersion at the 1550 nm wavelength and S
DCF
is the dispersion slope thereof.
In this optical fiber, the effective area may be in a range of from 13 &mgr;m
2
to 17 &mgr;m
2
, from 17 &mgr;m
2
to 20 &mgr;m
2
, or equal to or more than 20 &mgr;m
2
at the 1550 nm wavelength. The cutoff wavelength may be from 1.2 &mgr;m to 1.8 &mgr;m, and the transmission loss may be 0.5 dB/km or less at the 1550 nm wavelength. The term “cutoff wavelength” as used herein means the cutoff wavelength of the LP
11
mode that is measured in a state where an optical fiber of 2 m length is loosely wound once at a radius of 140 mm.
This optical fiber may have a central core region having a first refractive index, a first cladding region surroun
Hirano Masaaki
Kato Takatoshi
Healy Brian
McDermott Will & Emery LLP
Sumitomo Electric Industries Ltd.
Wood Kevin S
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