# US 2010/0142971 A1 · Apparatus for synchronizing digital signals of coherent optical receiver

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- Number: US 2010/0142971 A1
- Document ID: US20100142971A1
- Status: Published application
- Kind: A1
- Application number: 12/628,920
- Filed: 2009-12-01
- Published: 2010-06-10
- Earliest claimed: 2008-12-05
- Inventors: Sun-hyok Chang; Hwan-seok Chung; Kwang-joon Kim
- Web page: https://patentgrep.com/patent/US20100142971A1

## CPC

- H04B 10/614: {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)}
- H04B 10/61: Coherent receivers
- H04B 10/6164: {Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator}
- H04B 10/6165: {Estimation of the phase of the received optical signal, phase error estimation or phase error correction}
- H04B 10/65: {Intradyne, i.e. coherent receivers with a free running local oscillator having a frequency close but not phase-locked to the carrier signal}
- H04B: TRANSMISSION

## Abstract

Provided is a digital signal synchronization device of a coherent optical receiver. The digital signal synchronization device includes a digital signal processing unit to perform synchronization on a digital signal of an output optical signal generated by interfering an optical signal received through an optical fiber with an optical signal of laser output from a local oscillator and to perform decoding using the synchronized digital signal, and a digital signal managing unit to monitor the digital signal processing unit to output data of the optical signal normally, which has been received through the optical fiber, according to the synchronized digital signal.

## Claims

### Claim 1

A digital signal synchronization device comprising:
a digital signal processing unit to perform synchronization on a digital signal of an output optical signal generated by interfering an optical signal received through an optical fiber with an optical signal of laser (hereinafter, referred to as a laser optical signal) output from a local oscillator and to perform decoding using the synchronized digital signal; and
a digital signal managing unit to monitor the digital signal processing unit to output data of the optical signal normally, which has been received through the optical fiber, to according to the synchronized digital signal.

### Claim 2 (depends on 1)

The digital signal synchronization device of claim 1, wherein the digital signal processing unit comprises:
a frequency offset estimator to compensate the digital signal for a frequency difference between the optical signal received through the optical fiber and the laser optical signal and to combine the compensated digital signals;
a digital synchronizer to synchronize the compensated and combined digital signal; and
a decoder to decode the digital signal with reference to the synchronized digital signal.

### Claim 3 (depends on 2)

The digital signal synchronization device of claim 2, wherein the digital signal processing unit further comprises an optical fiber impairment compensator to check whether the digital signal generated from the optical signal received through the optical fiber has impairment due to impairment components in the optical fiber and compensate for the impairment according to the check result.

### Claim 4 (depends on 2)

The digital signal synchronization device of claim 2, wherein the optical fiber impairment compensator compensates for the impairment using the digital signal synchronized by the digital signal synchronizer.

### Claim 5

The digital signal synchronization device 2, wherein the optical fiber impairment compensator compensates for the impairment using the digital signal of which frequency is compensated for by the frequency offset compensator.

### Claim 6 (depends on 2)

The digital signal synchronization device of claim 2, wherein the digital signal managing unit comprises:
a digital signal detector to check whether the synchronized digital signal is decoded normally and to control operations of the decoder according to the check result; and
an initial condition setter to initialize a predefined condition of the digital signal synchronizer when the check result indicates that the decoding has been performed abnormally.

### Claim 7 (depends on 2)

The digital signal synchronization device of claim 2, wherein the digital signal managing unit comprises:
a digital signal detector to determine stability of the synchronized digital signal with reference to a changed parameter of the digital signal synchronized by the digital signal synchronizer; and
an initial condition setter to initialize a predefined parameter of the digital signal synchronizer when the check result indicates that the decoding has been performed abnormally.

### Claim 8

A coherent optical receiver comprising:
an optical hybrid to receive an optical signal transmitted through an optical fiber and an optical signal of laser (hereinafter, referred to as “laser optical signal”) output from a local oscillator and to output the optical signal and the laser optical signal such that the optical signal and the laser optical signal have a predetermined phase difference.
one or more photo-receivers, each to transform the optical signal and the laser optical signal output from the optical hybrid at a predetermined phase difference into electrical signals;
an analog-to-digital converter to convert the electrical signals transformed from the optical signal and the laser optical signal into digital signals; and
a digital signal control manager to combine the digital signals converted from the optical signal and the laser optical signal and synchronize the combined digital signals and to decode the synchronized digital signals such that data of the optical signal can be output normally.

### Claim 9 (depends on 8)

The coherent optical receiver of claim 8, wherein the optical hybrid outputs the optical signal and the laser optical signal with a phase difference of 90 degrees.

### Claim 10 (depends on 8)

The coherent optical receiver of claim 8, wherein the digital signal control manager comprises:
a frequency offset estimator to compensate the digital signal for a frequency difference between the optical signal received through an optical fiber and the laser optical signal and to combine the compensated digital signals;
a digital signal synchronizer to synchronize the compensated and combined digital signal;
a decoder to decode the digital signals; and
a digital signal managing unit to control the digital signal such that data of the optical signal can be output normally according to the synchronized digital signal.

### Claim 11 (depends on 10)

The coherent optical receiver of claim 10, wherein the digital signal control manager comprises an optical fabric impairment compensator to check whether the digital signal generated from the optical signal received through the optical fiber has impairment due to impairment components in the optical fiber and compensate for the impairment according to the check result.

### Claim 12 (depends on 11)

The coherent optical receiver of claim 11, wherein the optical fiber impairment compensator compensates for the impairment either after or before the synchronization is performed by the digital signal synchronizer.

### Claim 13 (depends on 10)

The coherent optical receiver of claim 10, wherein the digital signal manager comprises:
a digital signal detector to check whether the synchronized digital signal is decoded normally and control the decoder according to the check result; and
an initial condition setter to initialize a predefined condition of the digital signal synchronizer when the check result indicates that the decoding has been performed abnormally.

### Claim 14 (depends on 10)

The coherent optical receiver of claim 10, wherein the digital signal manager comprises:
a digital signal detector to determine stability of the synchronized digital signal with reference to a changed parameter of the digital signal synchronized by the digital signal synchronizer; and
an initial condition setter to initialize a predefined parameter of the digital signal synchronizer when the check result indicates that the decoding has been performed abnormally.