Wavelength-division multiplexed optical transmission system

Abstract

A wavelength-division multiplexed optical transmission system to keep the correlation of data patterns among wavelength channels to a low level, assuring a stable transmitting quality. The wavelength-division multiplexed optical transmission system has any of a frame phase changing circuit for mutually differing transmitting frame phases between at least two or more wavelength channels, a scrambling circuit using a data scrambler based on a pseudo random pattern for mutually differing scrambling patterns between two or more wavelength channels, or a dummy data generating circuit for mutually differing invalid data patterns between at least two or more wavelength channels in a wavelength channel group transmitted through the same optical fiber transmitting line when transmitting meaningless data.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a wavelength-division multiplexed optical transmission system, more particularly, to a wavelength-division multiplexed optical transmission system which is capable of reducing inter-channel correlation that may cause a serious transmission quality degradation. [0003] 2. Description of the Related Art [0004] In these days, according to digital standardized information communication used for an optical fiber transmission system, there is widely utilized a frame synchronous communication system which is called an SONET (Synchronous Optical Network) / SDH (Synchronous Digital Hierarchy) [0005] According to the SONET / SDH standard, relative phase difference information between a data signal and a frame phase, what is called a pointer, is given to an overhead area in a frame and transmitted, thereby enabling the change in phase difference between the data signal and the frame phase. [0006] Si...

AI Technical Summary

Benefits of technology

[0025] To solve the above-expressed problems, it is an object of the present invention to provide a wavelength-division multiplexed optical transmission system capable of keeping the correlation of data patterns among wavelength channels to the low level, preventing large XPM and XGM from occurring when the correlation is strong, and assuring a stable transmitting quality.

[0030] The wavelength-division multiplexed optical transmission system of the present invention also has a system for making it possible to select a pseudo random pattern used for scrambling from among a plurality of kinds of the pseudo random pattern, and for mutually differing data patterns transmitted upon inputting no transmitting data among wavelength channels.

[0032] Accordingly, according to the wavelength-division multiplexed optical transmission system of the present invention, it is possible to decrease the correlativity among the channels whose wavelengths are multiplexed and suppress the occurrence of abnormally large XPM and XGM.

Problems solved by technology

However, a problem might arise, when wavelength-multiplexing the SONET / SDH signal which took no account of the wavelength multiplexing transmission as it is.

In particular, according to a conventional SONET / SDH system, there is a problem to have no guarantee on no correlativity for data among a plurality of wavelength channels which are transmitted in parallel in the optical transmitting line.

In the case where the data among the parallel transmitted channels is strongly correlative, it is dangerous to cause the serious deterioration in transmission.

Particularly, the XPM is phase modulation caused by a signal having no correlation with information which the XPM itself has, and thus the transmitting characteristic is deteriorated certainly.

However, if all of the channels except for any noticed channel (referred to as λ3, herein) have the same data and same phase, as shown in FIG. 15, an abnormally large XPM occurs in the noticed channel.

Although such a situation should be prevented as much as possible, there is a great of risk for the conventional apparatus to get into such a situation.

The data matching hardly occurs upon normal operation and, however, there is a possibility that the data matching is caused exceptionally, such as alarm transferring case.

As another problem which arises by making the frame phase similar, there is a cross gain modulation effect (XGM: Cross Gain Modulation) in an optical amplifier in these days.

Corresponding thereto, there is a problem how low frequency component is included in the transmitted signal.

On the contrary, if the frame phases are made uniform, it is remarkably dangerous to transfer the intensity fluctuation to a channel of a channel except for the noticed channel.

Actually, if making a channel excluding the noticed channel have the same data and the same frame phase in an examining system as shown in FIG. 11, a serious bit error rate degradation is observed in the noticed channel.

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