Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
2000-08-09
2003-12-09
Le, Dieu-Minh (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S704000
Reexamination Certificate
active
06662317
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of Japanese Patent Application No. 10-70654, filed Mar. 19, 1998, the contents being incorporated therein by reference, and a continuation of PCT/JP99/01424.
TECHNICAL FIELD
The present invention relates to optimizing the amount of dispersion in an optical communication system.
With the widespread use of the Internet and image communication and other services, there is a need to increase the capacity of optical communication systems. One way to achieve this is by increasing the transmission speed. Currently, 10-Gb/s optical communication systems are in the stage of commercial operation, and research into 40-Gb/s optical communication systems is under way. The present invention relates to dispersion amount control in a high-speed optical communication system.
BACKGROUND ART
The speed of light travelling through optical fiber varies subtly with wavelength (frequency) (this phenomenon is called chromatic dispersion). A light pulse contain a plurality of frequency components; if it experiences chromatic dispersion, the transmitted waveform distorts depending on the amount of dispersion (dispersion×distance) since different frequency components travel at different speeds. This imposes a limit on the amount of dispersion tolerable in transmission, and its value is proportional to 1/(transmission speed)
2
and thus decreases as the transmission speed increases. Chromatic dispersion is minimum at a zero dispersion wavelength; when using a wavelength at which chromatic dispersion is large, it is practiced to employ a system configuration in which a dispersion compensator having an inverse dispersion characteristic is inserted to reduce the total amount of dispersion.
The amount of dispersion can also vary during system operation. Since the zero dispersion wavelength of a fiber has temperature dependence, its dispersion value changes depending on the conditions of the environment where the fiber is laid, and also changes with time due to the change over time of the laser wavelength of the transmitter used.
In 10-Gb/s systems for which the tolerable amount of dispersion is relatively large, there is no problem if the compensation amount of the dispersion compensator is fixed once it is initially set; however, in the case of 40-Gb/s systems, the dispersion tolerance is reported to be as small as 30 ps
m (Ooi et al., 1997 General Convention of The Institute of Electronics, Information and Communication Engineers, B-10-165). Accordingly, the amount of dispersion must be adjusted even during system operation.
For example, if the variation of transmission wavelength over time is ±1 nm (2 nm in width), the temperature dependence of the zero dispersion wavelength of SMF (single-mode fiber) is 0.03 nm/° C., the variation of the environmental temperature of the fiber transmission channel is 50° C., the transmission distance is 100 km, and the dispersion slope is 0.07 ps
m
2
/km, then the amount of dispersion varies by 25 ps
m=(2+0.03+50)×0.07×100.
A. Sano et al., ECOC '96 Technical Digests Tud. 3.5, proposes a method that monitors the magnitude of a clock component to optimize the amount of dispersion during system operation.
Since the method of judging whether the amount of dispersion is optimum by monitoring the magnitude of the clock component relies on the shape of signal waveform, it may not be able to address the problem if the waveform is distorted due to a non-linear effect such as SPM or if there is a variation in the shape of the transmitted waveform.
DISCLOSURE OF THE INVENTION
It is, accordingly, an object of the present invention to provide a method and apparatus for adjusting the dispersion value of a transmission channel to an optimum value during system operation.
According to the present invention, there is provided a chromatic dispersion equalization method comprising the steps of: encoding a signal with an error-correcting code as a channel code; transmitting the encoded signal on a transmission channel; applying a perturbation to chromatic dispersion in the transmission channel; receiving the signal transmitted through the transmission channel; detecting and correcting an error by decoding the received signal; and changing the center of the perturbation in a direction towards fewer or no errors.
According to the present invention, there is also provided a chromatic dispersion equalization apparatus comprising: an encoder for encoding a signal with an error-correcting code as a channel code; a transmitter for transmitting the encoded signal on a transmission channel; means for applying a perturbation to chromatic dispersion in the transmission channel; a receiver for receiving the signal transmitted through the transmission channel; a decoder for detecting and correcting an error by decoding the received signal; and a controller for changing the center of the perturbation in a direction towards fewer or no errors.
REFERENCES:
patent: 4864573 (1989-09-01), Horsten
patent: 5717510 (1998-02-01), Ishikawa et al.
patent: 5793432 (1998-08-01), Mishima et al.
patent: 5991477 (1999-11-01), Ishikawa et al.
patent: 5-235917 (1993-09-01), None
patent: 8-321805 (1996-12-01), None
patent: 9-18408 (1997-01-01), None
patent: 9-326755 (1997-12-01), None
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