Light receiver

Abstract

Provided is a light receiver which demodulates an optical signal modulated by DQPSK to a multi-level phase modulation signal, wherein demodulation can be performed by using one interferometer. In a light receiver which demodulates an optical signal (A) modulated by DQPSK to a multi-level phase modulation signal, the optical signal modulated by DQPSK is branched into two, one of the branched lights is delayed so that the two branched lights have a predetermined phase difference, and a polarization plane of at least one of the branched lights is rotated so that polarization planes of the two branched lights are orthogonal to each other, and thereafter, an interference means (2) combines the two branched lights, branch adjusting means (3 to 5) branch the output light from the interference means and adjust the polarization surfaces of the branched lights, detection means (6, 6'); detect light intensity of each branched light output from the branch adjusting means, and an I (In-phase) component signal and a Q (Quadrature) component signal are generated on the basis of each detection signal of the detection means.

Description

Technical field [0001] The present invention relates to an optical receiver, in particular to an optical receiver that demodulates a DQPSK modulated optical signal into a multi-level phase modulation signal. Background technique [0002] With the increase in communication transmission volume, the introduction of multi-value modulation and demodulation coding technology has been discussed in the next-generation long-distance and large-capacity optical communication system pursuing high-speed and large-capacity. One of the representative methods is the differential quadrature phase shift keying (DQPSK modulation, Differential Quadrature Phase Shift keying) method. In this method, compared with the conventional binary intensity modulation (OOK) method, the signal band is narrower, the frequency utilization efficiency can be improved and the transmission distance can be expanded, and higher sensitivity can be expected. [0003] First of all, the quadrature phase shift keying (QPSK mod...

AI Technical Summary

Problems solved by technology

However, due to the influence of the surrounding temperature of the optical receiver, etc., the optical path length in the delay interferometer changes and the phase becomes unstable, so it is difficult to perform high-precision demodulation

Moreover, there are problems such as being unable to identify which interferometer is used to demodulate which signal component

In addition, it is necessary to optimize the difference in optical path length until the optical signal is branched and introduced to two interferometers, and the difference in optical path length constituting each interferometer, which causes a problem that the control system is extremely complicated.

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