Coherent optical receiver, device and method for detecting inter-lane skew in coherent optical receiver

Patent metadata

Field	Value
Publication number	US-9686019-B2
Application number	US-201113995279-A
Country	US
Kind code	B2
Filing date	Dec 16, 2011
Priority date	Dec 21, 2010
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

Abstract

The disclosed coherent optical receiver includes a local light source; a 90-degree hybrid circuit; an optoelectronic converter; an analog-to-digital converter; a skew addition unit; and a FFT operation unit. The 90-degree hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs multiple optical signals separated into a plurality of signal components. The optoelectronic converter detects the optical signal and outputs a detected electrical signal. The analog-to-digital converter digitizes the detected electrical signal and outputs a detected digital signal. The skew addition unit adds to the detected digital signal an additional skew amount whose absolute value is equal to, whose sign is opposite to a skew amount of a difference in propagation delay in each lane connected to each output channel of the 90-degree hybrid circuit. The FFT operation unit performs a fast Fourier transform on the output from the skew addition unit.

First claim

The invention claimed is:

1. A coherent optical receiver, comprising:
a local light source;
a 90-degree hybrid circuit;
an optoelectronic converter;
an analog-to-digital converter;
a skew addition unit; and
a FFT operation unit, wherein
the 90-degree 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 plurality of optical signals and outputs a plurality of detected electrical signals;
the analog-to-digital converter digitizes the plurality of detected electrical signals and outputs a plurality of detected digital signals;
the skew addition unit adds to at least one of the plurality of detected digital signals an additional skew amount whose absolute value is equal to, whose sign is opposite to a skew amount of a difference in propagation delay in each lane connected to each output channel of the 90-degree hybrid circuit; and
the FFT operation unit performs a fast Fourier transform process on a signal output from the skew addition unit;
wherein the skew amount is calculated from peak information including a frequency at a peak frequency component included in FFT data obtained by performing the fast Fourier transform process and information on a phase angle at the frequency.

2. A device for detecting inter-lane skew in a coherent optical receiver, comprising:
a coherent optical receiver;
a test light source; and
a control block, wherein
the coherent optical receiver comprises a local light source, a 90-degree hybrid circuit, an optoelectronic converter, an analog-to-digital converter, a skew addition unit, and a FFT operation unit, wherein
the 90-degree 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 plurality of optical signals and outputs a plurality of detected electrical signals;
the analog-to-digital converter digitizes the plurality of detected electrical signals and outputs a plurality of detected digital signals;
the skew addition unit adds a predetermined additional skew amount to at least one of the plurality of detected digital signals;
the FFT operation unit outputs FFT data obtained by performing a fast Fourier transform process on a signal output from the skew addition unit; and
the control block calculates, from the FFT data, a skew amount of a difference in propagation delay in each lane connected to each output channel of the 90-degree hybrid circuit, and sets a value, whose absolute value is equal to, whose sign is opposite to the skew amount, for an additional skew amount in the skew addition unit;
wherein the skew amount is calculated from peak information including a frequency at a peak frequency component included in the FFT data obtained by performing the fast Fourier transform process and information on a phase angle at the frequency.

3. The device for detecting inter-lane skew in a coherent optical receiver according to claim 2 ,
wherein the control block comprises a peak detection unit, a skew calculation unit, an absolute value calculation unit, a skew amount holding unit, and a set skew amount controller;
the peak detection unit inputs the FFT data, calculates the peak information including the frequency at the peak frequency component included in the FFT data and the information on the phase angle at the frequency, and outputs the peak information to the skew calculation unit;
the skew calculation unit calculates the skew amount on the basis of the peak information and outputs the skew amount to the absolute value calculation unit;
the absolute value calculation unit calculates an absolute value of the skew amount;
the skew amount holding unit inputs and holds the absolute value of the skew amount, and calculates a calculated skew amount by adding a sign to the absolute value of the skew amount; and
the set skew amount controller sets a value, whose absolute value is equal to, whose sign is opposite to the calculated skew amount, for an additional skew amount in the skew addition unit.

4. The device for detecting inter-lane skew in a coherent optical receiver according to claim 3 ,
wherein the FFT operation unit, inputting real part input data and imaginary part input data, is connected to two output signal lanes of output signal lanes corresponding to output channels of the 90-degree hybrid circuit, and puts one output signal from the two output signal lanes at the real part input data and puts the other output signal from the two output signal lanes at the imaginary part input data.

5. The device for detecting inter-lane skew in a coherent optical receiver according to claim 3 ,
wherein the FFT operation unit is connected to two output signal lanes of output signal lanes corresponding to output channels of the 90-degree hybrid circuit, and comprises a switch unit disposed between the skew addition unit and the FFT operation unit in any one output signal lane of the two output signal lanes;
wherein the switch unit outputs a value of zero in a non-operating state, and outputs an input data without change in an operating state.

6. The device for detecting inter-lane skew in a coherent optical receiver according to claim 2 ,
wherein the FFT operation unit, inputting real part input data and imaginary part input data, is connected to two output signal lanes of output signal lanes corresponding to output channels of the 90-degree hybrid circuit, and puts one output signal from the two output signal lanes at the real part input data and puts the other output signal from the two output signal lanes at the imaginary part input data.

7. The device for detecting inter-lane skew in a coherent optical receiver according to claim 2 ,
wherein the FFT operation unit is connected to two output signal lanes of output signal lanes corresponding to output channels of the 90-degree hybrid circuit, and comprises a switch unit disposed between the skew addition unit and the FFT operation unit in any one output signal lane of the two output signal lanes;
wherein the switch unit outputs a value of zero in a non-operating state, and outputs an input data without change in an operating state.

8. A method for detecting inter-lane skew in a coherent optical receiver, comprising the steps of:
making test light from a test light source interfere with local light from a local light source, and outputting a plurality of optical signals separated into a plurality of signal components;
detecting the plurality of optical signals and outputting a plurality of detected electrical signals;
digitizing the plurality of detected electrical signals and outputting a plurality of detected digital signals;
performing a fast Fourier transform process on the plurality of detected digital signals;
calculating an absolute value of a skew amount corresponding to a difference in propagation delay between at least two of the plurality of signal components from the results of the fast Fourier transform process; and
determining a sign of the skew amount;
wherein the skew amount is calculated from peak information including a frequency at a peak frequency component included in FFT data obtained by performing the fast Fourier transform process and information on a phase angle at the frequency.

9. The method for detecting inter-lane skew in a coherent optical receiver according to claim 8 , further comprising:
in the step of determining the sign of the skew amount,
holding the absolute value of the skew amount;
calculating a skew compensation

Assignees

• Fukuchi Kiyoshi
• Abe Junichi
• Yasuda Wakako
• Nec Corp

Inventors

• Fukuchi Kiyoshi
• Abe Junichi
• Yasuda Wakako

Classifications

• H04B10/616 Primary

  Details of the electronic signal processing in coherent optical receivers · CPC title