Coherent optical receiver, apparatus and method for detecting inter-channel skew in coherent optical receiver

An apparatus for detecting inter-channel skew in a coherent optical receiver, comprising:

• a coherent optical receiver, a test light source, an analog to digital converter, an FFT operation unit, and a control block;
• wherein the coherent optical receiver comprises a local light source, a 90° hybrid circuit, and an optoelectronic converter;
• wherein the 90° hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components;
• the optoelectronic converter detects the optical signals and outputs detected electrical signals;
• the analog to digital converter quantizes the detected electrical signals and outputs quantized signals;
• the FFT operation unit performs a fast Fourier transform process on the quantized signals;
• and
• the control block calculates a difference in propagation delay between the plurality of signal components on the basis of a plurality of peak values with a central focus on one peak value in the results of performing the fast Fourier transform process.

An optical transmitter/receiver, comprising:

• a coherent optical receiver and an optical transmitter comprising a phase-modulation light source transmitting a modulated light which is modulated by phase modulation;
• wherein the coherent optical receiver comprises a local light source, a 90° hybrid circuit, an optoelectronic converter, an analog to digital converter, and a digital signal processing unit;
• wherein the 90° hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components;
• the optoelectronic converter detects the optical signals and outputs detected electrical signals;
• the analog to digital converter quantizes the detected electrical signals and outputs quantized signals;
• the digital signal processing unit comprises a skew compensation unit for compensating a difference in propagation delay between the plurality of signal components, and an FFT operation unit for performing a fast Fourier transform process on the quantized signals;
• and
• wherein the difference in propagation delay is calculated on the basis of a plurality of peak values with a central focus on one peak value in the results of performing the fast Fourier transform process in cases where the modulated light is inputted from the phase-modulation light source into the 90° hybrid circuit and is made to interfere with the local light.

A method for detecting inter-channel skew in a coherent optical receiver, comprising the steps of:

• outputting a plurality of optical signals separated into a plurality of signal components by making a test light from a test light source interfere with a local light from a local light source;
• detecting the optical signals and outputting detected electrical signals;
• quantizing the detected electrical signals and outputting quantized signals;
• performing a fast Fourier transform process on the quantized signals;
• and
• calculating a difference in propagation delay between the plurality of signal components on the basis of a plurality of peak values with a central focus on one peak value in the results of performing the fast Fourier transform process.