Optical waveguides – Optical fiber waveguide with cladding – With graded index core or cladding
Reexamination Certificate
2001-07-09
2003-02-11
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
With graded index core or cladding
C385S123000, C385S126000
Reexamination Certificate
active
06519402
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dispersion compensating optical fiber, and to a dispersion compensating optical fiber module. This specification is based upon Japanese Patent Application 2000-359772, and hereby incorporates the contents thereof by reference.
2. Background Art
A dispersion compensating optical fiber is an optical fiber which compensates for chromatic dispersion which accumulates due to propagation through a single mode optical fiber which is incorporated in a transmission line of an optical communication system. In concrete terms, although for example chromatic dispersion occurs when a single mode optical fiber (such as one for use at 1.3 &mgr;m) which has a zero dispersion wavelength on the short wavelength side of the 1.55 &mgr;m band is used for this 1.55 &mgr;m band, it is possible to compensate for this chromatic dispersion by utilizing a dispersion compensating optical fiber. As a result, it is possible to enhance the transmission speed of the optical communication system. In the following, for the convenience of description, the single mode optical fiber which is the object of compensation by this type of dispersion compensating optical fiber will be termed by the present inventors, ‘the single mode optical fiber for transmission’.
On the other hand, in optical communication systems, widening of the wavelength band and increase of the number of multiplexed wavelengths is making rapid progress in accompaniment with the requirements for increase of capacity and increase of transmission speed.
In this connection, dispersion compensating optical fibers are also being developed which can compensate for chromatic dispersion of a single mode optical fiber for transmission in a wide wavelength band. For this it is necessary, not only to compensate for chromatic dispersion, but also to compensate for the dispersion slope which specifies the tendency of chromatic dispersion with respect to wavelength.
It should be understood that the chromatic dispersion and the dispersion slope in the 1.55 &mgr;m band of a single mode optical fiber for transmission such as a single mode optical fiber for use at 1.3 &mgr;m or the like are generally both positive values. Thus, a requirement for a dispersion compensating optical fiber is to have negative values of chromatic dispersion and dispersion slope.
A dispersion compensating optical fiber which has a so-called W-shaped refractive index profile, as shown in
FIG. 1
, has been proposed as one which can perform compensation for both chromatic dispersion and dispersion slope, as discussed above.
This dispersion compensating optical fiber with this refractive index profile is made up from a core
1
and a cladding layer
2
which is provided at an outer periphery of the core
1
. And this core
1
is made up from a central core portion which is provided in its center and an intermediate core portion
4
which is provided at an outer periphery of this central core portion
3
. The central core portion
3
is endowed with a higher refractive index than that of the cladding layer
2
, while the intermediate core portion
4
is endowed with a lower refractive index than the cladding layer
2
.
In
FIG. 1
, &Dgr;1 is the relative refractive index difference of the central core portion
3
when the refractive index difference of the cladding layer
2
is taken as a reference. And &Dgr;2 is the relative refractive index difference of the intermediate core portion
4
when the refractive index difference of the cladding layer
2
is taken as a reference. Further, a is the radius of the central core portion
3
, while b is the radius of the intermediate core portion
4
.
By adjusting the values of &Dgr;1, &Dgr;2, and b/a for a dispersion compensating optical fiber which has this W-shaped refractive index profile, characteristics are obtained which make it possible to compensate for the chromatic dispersion and the dispersion slope of a single mode optical fiber for transmission which has positive values of chromatic dispersion and dispersion slope, in for example the 1.55 &mgr;m band.
Further, a dispersion compensating optical fiber which has a so-called segmented W-shaped refractive index profile as shown in
FIG. 2
has also been developed, with the objective of increasing the effective area (hereinafter termed “Aeff”), improving the bending loss, and widening the band of dispersion slope compensation.
This dispersion compensating optical fiber with this refractive index profile is made up from a core
11
and a cladding layer
12
which is provided at an outer periphery of the core
11
. And this core
11
is made up from a central core portion which is provided in its center, an intermediate core portion
14
which is provided at an outer periphery of this central core portion
13
, and a ring core portion
15
which is provided at an outer periphery of this intermediate core portion
14
. The central core portion
13
is endowed with a higher refractive index than that of the cladding layer
12
and the intermediate core portion
14
is endowed with a lower refractive index than the cladding layer
12
, while the ring core portion
15
is endowed with a refractive index which is lower than that of the central core portion
13
but is higher than that of the cladding layer
12
.
In
FIG. 2
, &Dgr;1 is the relative refractive index difference of the central core portion
13
when the refractive index difference of the cladding layer
12
is taken as a reference, &Dgr;2 is the relative refractive index difference of the intermediate core portion
14
when the refractive index difference of the cladding layer
12
is taken as a reference, and &Dgr;3 is the relative refractive index difference of the ring core portion
15
when the refractive index difference of the cladding layer
12
is taken as a reference. Further, a is the radius of the central core portion
13
, b is the radius of the intermediate core portion
14
, and c is the radius of the ring core portion
15
.
In this case as well, by adjusting the values of &Dgr;1, &Dgr;2, &Dgr;3, b/a, and c/b for a dispersion compensating optical fiber which has this segmented W-shaped refractive index profile, characteristics are obtained which make it possible to compensate for the chromatic dispersion and the dispersion slope of a single mode optical fiber for transmission which has positive values of chromatic dispersion and dispersion slope, in for example the 1.55 &mgr;m band.
A dispersion compensating optical fiber may be, for example, incorporated into a cable which is inserted into a transmission line. Furthermore, it may be incorporated into a small sized dispersion compensating optical fiber module (sometimes hereinafter simply termed a “module”), which can be arranged at the receiving side or at the transmitting side of a transmission line which already exists. It should be understood that such a module may, for example, also incorporate a housing, within which there is stored a reel upon which the dispersion compensating optical fiber is wound. And within the housing the two ends of the dispersion compensating optical fiber are connected to single mode optical fibers for transmission which are for leading them out, and these optical fibers for leading out project to the outside of the housing through two lead out holes provided therein. Thus the dispersion compensating optical fiber module may be inserted into a transmission line by connecting a single mode optical fiber for transmission which is disposed externally to said housing to the end portions of these two optical fibers for leading out. Moreover, as a construction for this module, connection portions may also be provided upon the side surfaces of the housing for connecting the external single mode optical fiber for transmission.
By the way, it is desirable to obtain the benefit of compensation by using a comparatively short length of dispersion compensating optical fiber. In order to do this, it is desirable for the absolute value of the chromatic dispersion of th
Aikawa Kazuhiko
Himeno Kuniharu
Suzuki Takaaki
Bell Boyd & Lloyd LLC
Fujikura Ltd.
Song Sarah N.
Ullah Akm E.
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