Optical waveguides – Polarization without modulation
Reexamination Certificate
2003-02-19
2004-10-19
Lee, Michael G. (Department: 2876)
Optical waveguides
Polarization without modulation
C385S027000, C385S037000
Reexamination Certificate
active
06807322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarization mode dispersion compensating apparatus (referred to as a PMD compensating apparatus hereinafter), and in particular, to a PMD compensating apparatus for compensating polarization mode dispersion of optical transmission lines which may become limitation factors for transmission rate and transmission distance in, for example, ultrahigh-speed optical communication systems.
2. Description of the Related Art
Recently, with a demand for higher transmission speeds for optical communication systems, there has been developed and practically used ultrahigh-speed optical communication systems of, for example, 40 Gbps or higher.
In optical fiber cables of such 40 Gbps or higher ultrahigh-speed optical communication systems, relatively large polarization dispersion may be caused which would be a cause of limitations on transmission rate or transmission distance. This polarization dispersion is caused as follows. Degeneracy of the base mode is resolved due to decentering of a core of an optical fiber cable
200
for transmission or due to application of non-axisymmetric stress to the core, so that a difference in propagation velocity between optical signals of two polarized wave components of TE and TM waves perpendicular to each other leads to a group delay time difference between TE and TM waves. As shown in
FIG. 28
, a group delay time difference is caused between TE and TM waves. As a result, the optical pulse signal spreads in the temporal axis direction, and this leads to limitation of the transmission rate and transmission distance in the communication systems.
In order to solve such problems, there is required a method of, at a receiving terminal, controlling the state of polarization and generating a group delay time difference inverse to that of the optical transmission line of the optical fiber cable
200
for transmission, thereby compensating the group delay time difference. Also, since this polarization mode dispersion of the optical transmission line changes due to change of environments, it is necessary to control the compensation amount according to environmental variations. Further, in the ultrahigh-speed optical communication systems, wavelength dependence of wavelength dispersion or polarization mode dispersion become problems, in addition to the polarization mode dispersion, and it is necessary to compensate them.
FIG. 29
is a block diagram showing a configuration of a PMD compensating apparatus equipped with a movable mirror
203
according to a prior art, as disclosed in Japanese Patent Laid-Open Publication No. 11-196046.
Referring to
FIG. 29
, in this PMD compensating apparatus, an inputted optical signal is split into a TM wave and a TE wave by a polarization splitter
201
, and then, movement of the movable mirror
203
between positions
203
a
and
203
b
in a direction of an arrow
203
c
can control the delay amount of the TE wave. As a result of this, such an adjustment is achieved that the group delay time difference between the TE wave and the TM wave is substantially minimized, and then, the adjusted TM wave and the TE wave are combined again by a polarization combiner
202
. Thus, the combined optical signal is outputted.
In the PMD compensating apparatus shown in
FIG. 29
, the inclusion of movable parts such as the movable mirror
203
causes mechanical deterioration, which leads to operational faults or the like, and this leads to such a problem that good reliability cannot be obtained. Also, this PMD compensating apparatus has another problem that it can control polarization mode dispersion but not wavelength dispersion or wavelength dependence of the polarization mode dispersion.
In order to solve the above problems, FIG. 2 of a second prior art document of the U.S. Pat. No. 6,271,952 shows a PMD compensating apparatus equipped with a differential delay system
1019
and an optical recombiner
1022
as shown in
FIG. 30
, and the following operation.
In order to solve the above problems, FIG. 2 of a second prior art document of the U.S. Pat. No. 6,271,952 shows a PMD compensating apparatus equipped with a differential delay system
1019
and an optical recombiner
1022
as shown in
FIG. 30
, and following operation is disclosed in the second prior art document.
More particularly, based on a control signal from a controller
1010
, an optical signal whose polarization state is controlled by a polarization controller
1007
is split into a TM wave and a TE wave by a polarized beam splitter
1008
. The split TE wave and TM wave are each outputted to the differential delay system
1019
, while at the same time they are detected by detectors
1015
and
1016
and converted into electric signals, which are outputted to a dispersion measurement circuit
1017
. The differential delay system
1019
applies continuous variable differential delay amount T to each of the inputted TE wave and TM wave, and outputs these two polarized waves to the optical recombiner
1022
for recombining these. The dispersion measurement circuit
1017
measures the time difference t between the split TE and TM waves, and controls the control signal to the controller
1010
so as to be the maximum based on the result of the measurement. The controller
1010
outputs a control signal
1024
, which depends on the magnitude of time difference t and influences the continuous variable differential delay amount T, to the differential delay system
1019
. In response to the control signal
1024
, the differential delay system
1019
controls the inputted TE wave and TM wave so as to be T=t, and outputs them to the optical recombiner
1022
.
In the PMD compensating apparatus of
FIG. 30
, the time difference t between respective optical signals split by the polarized beam splitter
1008
is measured, and by using the result of the measurement, both the polarization controller
1007
and the differential delay system
1019
are controlled, so that the control processing becomes quite difficult, and the response speed also becomes slow. Further, although polarization mode dispersion of the optical signal can be controlled, wavelength dependence of wavelength dispersion or polarization mode dispersion can not be controlled.
SUMMARY OF THE INVENTION
An essential object of the present invention is to provide a PMD compensating apparatus which solves the above-described problems and which is capable of controlling the polarization controller and the like reliably at a higher speed as compared with the prior art.
In addition to the above-mentioned object, another object of the present invention is to provide a PMD compensating apparatus which is capable of controlling the wavelength dispersion and the wavelength dependence of polarization mode dispersion.
According to one aspect of the present invention, a PMD compensating apparatus is equipped with a polarization control means, a polarization splitting and combining means, a first optical transmission line, a second optical transmission line, a first detection means, a second detection means, a first calculation means, and a first control means. The polarization control means controls a polarization state of an inputted optical signal so that a polarization axis of the optical signal becomes substantially coincident with an optical axis of an optical transmission line. The polarization splitting and combining means has first, second and third ports, and splits an optical signal outputted from the polarization control means and inputted via the first port, into optical signals of two polarized wave components substantially perpendicular to each other, and outputs the split optical signals respectively via the second and third ports. The polarization splitting and combining means further combines the two optical signals inputted via the second and third ports, and outputs a combined signal via the first port.
The first optical transmission line has a predetermined first grating, and reflects by the first grating and outputs one optical
Hashimoto Minoru
Hoshizaki Junichiro
Matsumoto Sadayuki
Matsuno Shigeru
Namiki Ryosuke
Lee Michael G.
Lee Seung H
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
LandOfFree
PMD compensating apparatus for controlling polarization... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with PMD compensating apparatus for controlling polarization..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and PMD compensating apparatus for controlling polarization... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3265492