Optical: systems and elements – Optical amplifier – Correction of deleterious effects
Reexamination Certificate
1998-10-07
2001-05-22
Moskowitz, Nelson (Department: 3642)
Optical: systems and elements
Optical amplifier
Correction of deleterious effects
C359S199200, C359S341430
Reexamination Certificate
active
06236495
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of European Patent Application No. 97307926.2, which was filed Oct. 7, 1997.
TECHNICAL FIELD
The present invention relates generally to the field of optical communication and particularly to optical communication techniques which compensate for dispersion such as that in optical fibers.
BACKGROUND OF THE INVENTION
Optical communications systems using optical fibers to couple a light source. Such as laser, and a photodetector are now widely used for high speed (for example, Gbit/sec data rates) and long distance (for example, trans-Atlantic or trans-Pacific) communications. Many technical problems have had to be overcome for these systems to reach their present state of development. Perhaps the most widely known problem was caused be the lossy nature of the first silica based optical fibers. The loss in such fibers was greatly reduced, to the order of a tenth of a dB/km or even less, by the development of fibers fabrication techniques that greatly reduced the presence of loss-creating impurities in the fibers.
After low loss optical fibers had been developed, other system parameters became important to the further development of optical communications systems. For example, fibers have chromatic dispersion; that is, the propagation velocity of the radiation depends upon its frequency. Narrow band light sources in the form of solid state lasers were developed. These lasers typically radiated in several relatively closely spaced modes which propagated at different velocities. The presence of multiple modes and the existence of chromatic dispersion limited either the data transmission rate of the transmission distance. Radiation sources, such as distributed feedback (DFB) lasers, that emitted only a single mode were developed to overcome these problems.
However, even the single mode modulated light of a DFB-laser has a finite bandwidth which causes a pulse to spread when chromatic dispersion is present. One approach to solving this problem was served by the development of dispersion shifted fibers, which are often referred to by the acronym DSF. Dispersion shifted fibers have a region of very low or no chromatic dispersion. However, the use of such fibers suffers from several drawbacks. Firstly, the laser must be selected to emit at the frequency at which the fiber has no chromatic dispersion. Secondly, much non-dispersion shifted fiber has already been installed.
Other techniques that compensate for fiber chromatic dispersion are desirable if they overcome the previously discussed limitations imposed be non-dispersion shifted fibers. One technique inserts, at an arbitrary point in the transmission path between the transmitter and the receiver, a dispersion compensating fiber (DCF). The length of fiber is selected to provide dispersion compensation for a certain transmission length and therefore enable transmission over either an extended distance or at a higher rate. This approach suffers from the added cost of the DCF and, more significantly, the losses introduced by such fibers. The losses are at least comparable to the losses in the system fibers and limit the system capabilities.
An apparatus which reduces the costs of the DCF and compensates for the losses introduced by the DCF is known from U.S. Pat. No. 5,404,413, issued Apr. 4, 1995 to Jean-Marc Delavaux et al. Under the title “Optical Circulator for Dispersion Compensation,” commonly assigned herewith. (A corresponding European Patent Application EP 0 658 988 A1 was published on Jun. 21, 1995.). The apparatus has an optical circulator with at least first, second and third ports. The apparatus also has return means and a dispersion compensating waveguide, such as a DC-fiber, connecting the return means to the second port. An amplifier is connected to the circulator. The amplifier has a pump laser, a multiplexer, and a doped fiber. The pump laser is connected to the multiplexer, and the fiber amplifier is connected between the return means and the second port of the circulator.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for the compensation of optical dispersion. It is one aim of the invention to further reduce the costs of the optical dispersion compensation.
According to a first aspect of the invention there is provided a method of compensating for optical dispersion of an optical signal passing through an optical communication system comprising steps of:
coupling the optical signal from the communication system into a dispersion compensating device and passing said optical signal through said dispersion compensating device for a first time;
returning said optical signal and passing said optical signal back though said dispersion compensating device for a second time; and
characterized by
returning said optical signal to pass back through said dispersion compensating device for at least a third time before coupling said optical signal back into said communications system.
According to a second aspect of the invention there is provided apparatus for compensating for optical dispersion of an optical signal passing through an optical communication system comprising:
a dispersion compensating device;
an input arrangement for coupling the optical signal from the communication system into the dispersion compensating device and for passing said optical signal though said dispersion compensating device for a first time;
a first return device, connected to said compensating device, for returning said optical signal back through said dispersion compensating device for a second time;
an output arrangement for coupling said optical signal back into said communication system; and
characterized in that
a second return device is connected to said input arrangement for returning said optical signal back though said dispersion compensating device for at least a third time before said optical signal is passed to said output arrangement.
An advantage of the present invention is that it allows further reduction in the length of the dispersion compensating fiber needed to compensate for the dispersion of the optical transmission line.
In particular, the object is achieved by providing an apparatus for compensation of optical dispersion which has a polarization beam splitter with a first, second and third port, a dispersion compensation means, a first return means that changes the direction of polarization of the returned signal and a second return means. One end of the dispersion compensation means is connected to the third port of the polarization beam splitter, the other end is connected to the first return means. The second return means is connected with the second port of the polarization beam splitter. The first port of the polarization beam splitter forms input and output of the apparatus for input and output signals of different polarization mode.
In a preferred embodiment, an optical circulator having a first, a second, and a third port is connected with its second port connected to the first port of the polarization beam splitter. The first and third ports of the optical circulator are connected to optical fibers which form an optical transmission line.
The present invention will become more fully understood from the detailed description given hereinafter and further scope of applicability of the present invention will become apparent. However, it should be understood that the detailed description is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
REFERENCES:
patent: 5404413 (1995-04-01), Delavaux et al.
patent: 5596448 (1997-01-01), Onaka
patent: 5867306 (1999-02-01), Isshiki
patent: 0 658 988 A1 (1994-12-01), None
patent: 08095095 (1996-04-01), None
patent: 18097488 (1998-07-01), None
Delavaux et al, COBRA, Doc. No. XP2036-270, Sta 40216 Jom Comp., Sep. 25, 1994.*
Yamashita et al, Jour. of Lightwave Techn., vol. 14, #3, pp. 385-390; Abst. only herewith, Mar. 1996.*
Chernikov, Taylor “All-
Finston Martin I.
Lucent Technologies - Inc.
Moskowitz Nelson
LandOfFree
Optical dispersion compensation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical dispersion compensation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical dispersion compensation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2568939