Front end characterization of coherent receiver

Patent metadata

Field	Value
Publication number	US-9749060-B1
Application number	US-201514985754-A
Country	US
Kind code	B1
Filing date	Dec 31, 2015
Priority date	Dec 31, 2015
Publication date	Aug 29, 2017
Grant date	Aug 29, 2017

Abstract

Techniques are described for characterizing a receiver front end of a pluggable optical module. The pluggable optical module receives an optical signal that includes a first portion having a first polarization and a second portion having a second polarization. The first portion and second portion are not coherent with one another and the power of the first portion and second portion is equal.

First claim

What is claimed is:

1. A method for optical communication, the method comprising:
receiving, with an optical module of a receiver, a polarization-multiplexed optical signal that includes a first portion having a first polarization and a second portion having a second polarization, wherein the first portion and the second portion are not coherent with one another and a power of the first portion is equal to a power of the second portion;
determining, with a processor, characteristics of a front end of the receiver based on the received polarization-multiplexed optical signal, the front end comprising components of the optical module for converting optical signals into analog electrical signals, components of the receiver for converting the analog electrical signals into digital signals, and components and traces of the receiver that interconnect the optical module and the processor, wherein the front end comprises an analog-to-digital converter (ADC), and wherein determining the characteristics comprises at least:
determining, with the processor, a skew of an output of the ADC based on the received polarization-multiplexed optical signal;
correcting the skew of the output of the ADC; and
determining one or more of a frequency response and gain imbalance of the front end based on the output of the ADC with the skew correction; and

applying, with the processor, compensation to electrical signals received by the processor based on one or more of the determined frequency response and gain imbalance.

2. The method of claim 1 , wherein receiving the polarization-multiplexed optical signal comprises receiving the polarization-multiplexed optical signal that is generated from a first optical signal that is modulated at a first frequency and having the first polarization and a second optical signal that is modulated at a second, different frequency and having the second, different polarization.

3. The method of claim 2 , wherein the first optical signal that is modulated at the first frequency comprises an optical signal having a periodic signal having a narrowband frequency spectrum at around the first frequency, and wherein the second optical signal modulated at the second frequency comprises an optical signal having a periodic signal having a narrowband frequency spectrum at around the second frequency.

4. The method of claim 2 , wherein a difference between the first frequency and the second frequency is greater than a spectral width of a laser whose lightwave is used to generate the first optical signal and the second optical signal.

5. The method of claim 2 , further comprising:
receiving, from the processor with the optical module, a first electrical signal having the first frequency and a second electrical signal having the second frequency;
splitting, with a beam splitter of the optical module, a light of a laser of the optical module into a first lightwave and a second lightwave;
modulating, with the optical module, the first lightwave with the first electrical signal to generate the first optical signal that is modulated at the first frequency;
modulating, with the optical module, the second lightwave with the second electrical signal to generate the second optical signal that is modulated at the second frequency;
rotating, with a polarization rotator of the optical module, polarization of the first optical signal;
combining, with the optical module, the first optical signal having the rotated polarization and the second optical signal to generate the polarization-multiplexed optical signal; and
transmitting, with the optical module, the polarization-multiplexed optical signal.

6. The method of claim 5 , further comprising:
prior to transmitting the polarization-multiplexed optical signal, transmitting, with the optical module, a data optical signal; and
determining a bias loop lock point during the transmission of the data optical signal,
wherein transmitting the polarization-multiplexed optical signal comprises transmitting the polarization-multiplexed optical signal with a bias loop locked at the bias loop lock point.

7. The method of claim 5 , further comprising:
amplifying the received first electrical signal and the received second electrical signal with a plurality of drive amplifiers of the optical module, wherein the plurality of drive amplifiers are configured to provide linear gain;
wherein modulating the lightwave with the first electrical signal comprises modulating the lightwave with the first electrical signal that is amplified by a first set of the plurality of drive amplifiers, and
wherein modulating the lightwave with the second electrical signal comprises modulating the lightwave with the second electrical signal that is amplified by a second set of the plurality of drive amplifiers.

8. The method of claim 1 , further comprising:
mixing each one of a plurality of optical signals having different frequencies generated from a local oscillator of the optical module with the received polarization-multiplexed optical signal to generate a plurality of electrical signals,
wherein determining the characteristics of the front end of the receiver based on the received polarization-multiplexed optical signal comprises determining the characteristics of the front end based on the plurality of electrical signals generated from the mixing of the received polarization-multiplexed optical signal.

9. The method of claim 1 , wherein receiving the polarization-multiplexed optical signal comprises receiving the polarization-multiplexed optical signal having a changing optical carrier frequency.

10. The method of claim 1 , wherein the degree of polarization of the polarization-multiplexed optical signal is approximately zero.

11. The method of claim 1 , wherein receiving the polarization-multiplexed optical signal comprises receiving an optical signal generated from a combination of two different, de-coupled laser sources.

12. The method of claim 1 , wherein receiving the polarization-multiplexed optical signal comprises receiving an optical signal generated from combining via a polarization beam combiner two optical signals traveling via different polarization-maintaining optical paths, wherein the two optical signals are generated from a single laser source with output of the single laser source being split by a polarization beam splitter, and wherein a difference in a length between the optical paths is greater than a coherence length of the single laser source.

13. The method of claim 1 , wherein receiving the polarization-multiplexed optical signal comprises receiving an optical signal generated from combining via a polarization beam combiner two optical signals traveling via different polarization-maintaining optical paths, wherein the two optical signals are generated from a single laser source with output of the single laser source being split by a beam splitter, and wherein a difference in a length between the optical paths is greater than a coherence length of the single laser source, and wherein the polarization in one path is rotated by a polarization rotator.

14. An electronic device for optical communication, the
electronic device comprising:
a receiver having an optical module configured to receive a polarization-multiplexed optical signal that is generated from a first optical signal that is modulated at a first frequency and having a first polarization and a second optical signal that is modulated at a second, different frequency and having a second, different polarization, wherein the polarization-multiplexed optical signals includes a first portion having the first polarization and a second portion h

Assignees

• Juniper Networks Inc

Inventors

• Wang Qiang
• Yue Yang
• Arabaci Murat

Classifications

• H04B10/6151 Primary

  comprising a polarization controller at the receiver's input stage · CPC title

• H04J14/06

  Polarisation multiplex systems · CPC title

• H04B10/564

  Power control · CPC title

• H04B10/614 Primary

  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

• H04B10/0731

  Testing or characterisation of optical devices, e.g. amplifiers · CPC title