# US 12,119,880 B2 · Rapid polarization tracking in an optical channel

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 12,119,880 B2
- Document ID: US12119880B2
- Status: Granted
- Kind: B2
- Application number: 16/988,874
- Filed: 2020-08-10
- Published: 2022-02-10
- Granted: 2024-10-15
- Earliest claimed: 2020-08-10
- Assignees: Nokia Solutions and Networks Oy
- Applicants: Nokia Solutions and Networks OY
- Inventors: Thai Son Le
- Web page: https://patentgrep.com/patent/US12119880B2

## 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 10/077: using a supervisory or additional signal
- H04B 10/07951: {Monitoring or measuring chromatic dispersion or PMD}
- H04B 10/2569: due to polarisation mode dispersion [PMD]
- H04B 10/541: {Digital intensity or amplitude modulation}
- H04B 10/6164: {Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator}
- H04B 10/6166: {Polarisation demultiplexing, tracking or alignment of orthogonal polarisation components}
- H04J 14/06: Polarisation multiplex systems
- H04B 10/503: {Laser transmitters}
- H04B: TRANSMISSION
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)

## Abstract

An optical receiver, e.g., for an Optical Supervisory Channel (OSC), whose optical front end comprises a polarization-diversity coherent optical receiver configured to receive a conventional intensity-modulated (e.g., OSC) signal. Four quadrature components of the received OSC signal detected by the polarization-diversity coherent optical receiver are sampled at a relatively high sampling rate and are used to calculate the Stokes parameters of the OSC signal. As a result, the Stokes parameters can be updated at the high sampling rate, which can be suitably selected to enable polarization tracking with a relatively high time resolution and/or at relatively high SOP-rotation speeds. The four detected quadrature components are appropriately combined in the receiver DSP to determine the intensity of the received OSC signal, which is then used in a conventional manner to recover the OSC data encoded therein.

## Claims

### Claim 1

An apparatus comprising an optical data receiver for an intensity-modulated optical data signal intensity-modulated at a symbol rate, the optical data receiver comprising:
an optical hybrid configured to mix the intensity-modulated optical data signal and an optical local-oscillator signal to generate first and second pluralities of mixed optical signals, the first plurality corresponding to a first polarization of the optical data signal, the second plurality corresponding to a different second polarization of the optical data signal;
a first plurality of light detectors connected to generate first and second streams of digitalizations in response to the first plurality of mixed optical signals, the first and second streams of digitalizations providing measurements of different phase components of the first polarization of the optical data signal;
a second plurality of light detectors connected to generate third and fourth streams of digitalizations in response to the second plurality of mixed optical signals, the third and fourth streams of digitalizations providing measurements of different phase components of the second polarization of the optical data signal; and
a digital signal processor configured to:
obtain time-resolved measurements of a state of polarization (SOP), with a finer time resolution than one over the symbol rate, of the intensity-modulated optical data signal based on the first, second, third, and fourth streams of digitalizations;
compute, using a squaring circuit, a square of each received value of the first, second, third, and fourth streams of digitalizations; and
generate a combination, using an adder, by summing the computed squares of the first, second, third, and fourth streams of digitalizations for each sampling time, to be proportional to optical power of the intensity-modulated optical data signal; and
recover, using a carrier and data recovery circuit, data carried by the intensity-modulated optical data signal from the combination.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the first and second polarizations are mutually orthogonal.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the first and second polarizations are linearly independent polarizations of the intensity-modulated optical data signal.

### Claim 4 (depends on 1)

The apparatus of claim 1,
wherein the first, second, third, and fourth streams of digitalizations are characterized by a sampling rate; and
wherein the digital signal processor is capable of obtaining the time-resolved measurements of the SOP with a time resolution of one over the sampling rate.

### Claim 5 (depends on 4)

The apparatus of claim 4,
wherein the sampling rate is greater than the symbol rate by a factor of two or more.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the time-resolved measurements of the SOP comprise time-resolved measurements of two or more Stokes parameters of the intensity-modulated optical data signal.

### Claim 7 (depends on 1)

The apparatus of claim 1, wherein the time-resolved measurements of the SOP comprise time-resolved measurements of at least one of an elevation polarization-rotation angle and an azimuth polarization-rotation angle.

### Claim 8 (depends on 1)

The apparatus of claim 1, wherein the intensity-modulated optical data signal is an Optical-Supervisory-Channel signal.

### Claim 9 (depends on 1)

The apparatus of claim 1, wherein the optical data receiver further comprises a laser source to generate the optical local-oscillator signal and a feedback path from the digital signal processor to the laser source to control relative detuning of carrier frequency of the optical local-oscillator signal.

### Claim 10 (depends on 9)

The apparatus of claim 9, wherein the digital signal processor comprises a spectrum analyzer configured to send a control signal through the feedback path to a laser-source controller.

### Claim 11 (depends on 1)

The apparatus of claim 1, wherein the digital signal processor comprises a digital circuit configured to compensate for a difference between optical carrier frequencies of the optical local-oscillator signal and the intensity-modulated optical data signal.

### Claim 12 (depends on 1)

The apparatus of claim 1, wherein the optical data receiver further comprises:
a memory to store a data set representing a plurality of time-stamped Stokes vectors of the intensity-modulated optical data signal obtained using the time-resolved measurements of the SOP; and
an output port to export the data set from the optical data receiver.

### Claim 13 (depends on 1)

The apparatus of claim 1, wherein the digital signal processor does not include an adaptive digital filter capable of performing electronic polarization demultiplexing.

### Claim 14 (depends on 1)

The apparatus of claim 1, further comprising an Optical-Supervisory-Channel transmitter fiber-connected to the optical data receiver and configured to use intensity modulation to generate the intensity-modulated optical data signal.