Optical communications – Multiplex – Wavelength division or frequency division
Reexamination Certificate
2001-02-14
2004-12-14
Pascal, Leslie (Department: 2633)
Optical communications
Multiplex
Wavelength division or frequency division
C398S081000, C398S082000
Reexamination Certificate
active
06832048
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dispersion compensation apparatus and a dispersion compensation system which allows a reduction in the crosstalk when waves are multiplexed and demultiplexed in an optical transmission system, particularly in a wavelength multiplexing system.
BACKGROUND ART
It is known that the same medium refracts light of different wavelength differently. That is, velocity of light (to be precise, phase velocity) propagating through a medium depends upon the wavelength of the light. This phenomenon is referred to as dispersion. Dispersion brings a problem when an optical signal is transmitted using an optical fiber in particular or the like.
When transmission is performed in a state where light is confined within a part of a transmission medium like an optical fiber, a propagation velocity of a signal is also different depending on how the light is confined in the transmission medium, what is called a propagation mode (TE, TM, HE, EH, etc.). Propagation velocity differences (hereafter called Mode distribution) due to differences of the propagation modes occur in a multi-mode optical fiber which can propagate signals in a plurality of propagation modes at one wavelength.
On the other hand, a single-mode optical fiber which has only a basic mode as a propagation mode is mainly used for high-speed optical transmission because the mode distribution does not occur. However, in this single-mode optical fiber, the problem on the propagation velocity differences (hereafter called Material dispersion), caused by the fact that the refractive index depends on its wavelength, can not be avoided, so that propagating pulse widths lengthen (pulse distortion) caused by this material dispersion. That is, the dispersion becomes a cause of degradation in a signal waveform due to its transmission even in the single-mode optical fiber.
For example, when a 10 Gb/s-signal is to be transmitted, an allowable dispersion value is about 1000 ps
m, which corresponds to the amount of dispersion in the single-mode optical fiber of about 70 km. Therefore, dispersion compensation becomes extremely important to perform long-haul transmission. As a device for dispersion compensation, a dispersion compensation fiber, for example, is commercially available. The dispersion compensation fiber is a special optical fiber that compensates for dispersion of a transmission line by inserting any optical fiber, that has a dispersion characteristic of sign opposite to a dispersion value indicating how an optical signal propagating inside the optical fiber is affected thereby, into the transmission line.
In the optical transmission using an optical fiber, it is generally highly efficient and preferable to perform wavelength multiplexing (WDM) transmission in which a transmission band is widened by the number of wavelengths to be used by simultaneously using a line of optical fiber at various wavelengths. The dispersion is a function of a wavelength, and its dispersion value is different in each wavelength. Therefore, in the WDM transmission, when a wavelength-multiplexed optical signal is to be transmitted by a single-mode optical fiber, each wavelength undergoes different dispersion. Therefore, as dispersion compensation for the wavelength-multiplexed optical signal, it is required to discretely compensate for a different dispersion value of each multiplexed wavelength.
With regard to dispersion compensation in such WDM transmission, there have been proposed, for example, “Wavelength multiplex transmission” disclosed in Japanese Patent Laid-Open Publication No. HEI09-116493 and “Wavelength dispersion compensation system for optical transmission line” disclosed in Japanese Patent Laid-Open Publication No. HEI09-191290. These proposals are characterized in that each of the systems comprises a wavelength demultiplexing unit that demultiplexes a wavelength-multiplexed optical signal at each wavelength, and a dispersion compensation unit that independently compensates for wavelength dispersion of an optical signal due to an optical transmission line in each optical signal of demultiplexed wavelengths.
FIG. 11
is a block diagram showing an example of the conventional wavelength dispersion compensation system as disclosed in Japanese Patent Laid-Open Publication No. 09-116493. This figure shows a dispersion compensation system that performs respective dispersion compensation particularly on the following stage of an optical transmitter and the previous stage to an optical receiver.
In the wavelength dispersion compensation system shown in
FIG. 11
, at first, its transmission side comprises n units of transmitters
101
A
1
to
101
A
n
which oscillate different wavelengths from one another, dispersion compensation sections
102
A
1
to
102
A
n
provided on respective following stages of the transmitters
101
A
1
to
101
A
n
and each of which performs dispersion compensation for a wavelength oscillated by each of the transmitters, and an optical branching/coupling device (coupler)
100
A that combines the optical signals transmitted through respective blocks comprising these transmitters
101
A
1
to
101
A
n
and dispersion compensation sections
102
A
1
to
102
A
n
. The optical signal combined in this optical branching/coupling device (coupler)
100
A is transmitted to a transmission line
109
.
On the other hand, its reception side comprises an optical branching/coupling device
100
B that demultiplexes (separates) the wavelength into the wavelengths corresponding to those in the optical branching/coupling device
100
A, band-pass filters
105
B
1
to
105
B
n
through which predetermined wavelengths pass, dispersion compensation sections
102
B
1
to
102
B
n
which perform dispersion compensation for the wavelengths of the optical signals having passed through the band-pass filters
105
B
1
to
105
B
n
, and receivers
101
B
1
to
101
B
n
which receive the optical signals transmitted through respective blocks consisting of these band-pass filters
105
B
1
to
105
B
n
and dispersion compensation sections
102
B
1
to
102
B
n
.
In
FIG. 11
, for example, the transmitter
101
A
1
oscillates a wavelength &lgr;
1
, and the band-pass filter
105
B
1
selectively passes an optical signal of the wavelength &lgr;
1
therethrough. Accordingly, the dispersion compensation sections
102
A
1
and
102
B
1
perform dispersion compensation only for the optical signal of the wavelength &lgr;
1
. The dispersion compensation sections
102
A
1
and
102
B
1
can use a dispersion compensation fiber having a dispersion value of sign opposite to the dispersion value for the wavelength &lgr;
1
indicated by the transmission line
109
. The above configuration allows compensation for all the wavelengths in the transmitter side and the receiver side of the WDM transmission system so as to become zero dispersion.
FIG. 12
is block diagram showing the invention disclosed in Japanese Patent Laid-Open Publication No. HEI09-191290 as explained above, which is the diagram for explaining particularly a wavelength dispersion compensation system for an optical transmission line in a WDM transmission relay system.
The wavelength dispersion compensation system shown in
FIG. 12
comprises transmission lines
119
A and
119
B which propagate optical signals of wavelengths &lgr;
1
to &lgr;
n
multiplexed at n wavelengths, an optical branching/coupling device
110
A which demultiplexes (separates) the wavelengths, band-pass filters
115
A
1
to
115
A
n
which pass predetermined wavelengths for optical signals of the separated wavelengths therethrough, dispersion compensation sections
112
A
1
to
112
A
n
which perform dispersion compensation for the wavelengths of the optical signals having passed through the band-pass filters
115
A
1
to
115
A
n
, and an optical branching/coupling device (coupler)
110
B which combines again the optical signals transmitted through respective blocks consisting of these band-pass filters
115
A
1
to
115
A
n
and dispersion compensation sections
112
A
1
to
112
A
n
.
In t
Ishida Kazuyuki
Shimizu Katsuhiro
Mitsubishi Denki & Kabushiki Kaisha
Pascal Leslie
LandOfFree
Dispersion compensation apparatus and a dispersion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dispersion compensation apparatus and a dispersion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dispersion compensation apparatus and a dispersion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3325885