Optical 90-degree hybrid circuit and optical receiver using same

Patent metadata

Field	Value
Publication number	US-9800349-B2
Application number	US-201314389426-A
Country	US
Kind code	B2
Filing date	Mar 28, 2013
Priority date	Mar 30, 2012
Publication date	Oct 24, 2017
Grant date	Oct 24, 2017

Abstract

An object of the present invention is to provide an optical 90-degree hybrid circuit which is capable of easily adjusting the optical power ratio between signal and local oscillator and suppresses an optical system of an optical receiver becoming complex and optical receivers using the same. The optical 90-degree hybrid circuit for demodulating multilevel phase-modulated signals corresponding to individual polarized waves by multiplexing an optical wave having a predetermined plane of polarization contained in signal and local oscillator that has the same wavelength as the signal and has been adjusted to circularly-polarized signal, and polarization-splitting the multiplexed signal includes polarization splitting means (polarization splitting) for extracting an optical wave having a predetermined plane of polarization from the signal, a polarization conversion element for rotating a plane of polarization of the optical wave extracted from the polarization splitting means, and a polarizer that determines a plane of polarization of the signal before multiplexing the signal with the local oscillator, and the polarization splitting means, the polarization conversion element, and the polarizer adjust intensity of the optical signal (VOA function) in cooperation with each other.

First claim

The invention claimed is:

1. An optical receiver comprising an optical 90-degree hybrid circuit for demodulating multilevel phase-modulated signals corresponding to individual polarized waves by multiplexing an optical wave having a predetermined plane of polarization contained in a signal and a local oscillator that has the same wavelength as the signal and has been adjusted to a circularly-polarized signal, and polarization-splitting a multiplexed signal, comprising:
polarization splitting means for extracting two optical waves from the signal, each of the two optical waves having a different predetermined plane of polarization;
one polarization conversion element that receives input of the two optical waves extracted from the signal, and rotates the plane of polarization of each one of the two optical waves extracted from the signal;
two polarizers, each one of the two polarizers determining the plane of polarization of one of the two optical waves, before multiplexing of the optical wave with the local oscillator; and
signal quantity monitoring means for detecting intensity of one or more of the optical waves that have passed through one or more of the two polarizers, wherein
the polarization splitting means, the polarization conversion element, and each of the two polarizers function together to adjust intensity of each of the two optical waves, and
the polarization conversion element is controlled by the signal quantity monitoring means so that intensity of the optical waves reaches a predetermined quantity.

2. The optical receiver according to claim 1 ,
wherein the polarization conversion element is a liquid crystal element or a λ/2 wavelength plate equipped with a rotation function.

Assignees

• Sumitomo Osaka Cement Co Ltd

Inventors

• Hayami Yuji
• Kataoka Toshio

Classifications

• H04J14/0221

  Power control, e.g. to keep the total optical power constant · CPC title

• H04B10/6166 Primary

  Polarisation demultiplexing, tracking or alignment of orthogonal polarisation components · CPC title

• H04B10/614

  comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers (H04J14/06 takes precedence) · CPC title

• H04J14/06 Primary

  Polarisation multiplex systems · CPC title

• H04J14/02216

  by gain equalization · CPC title