# US 8,786,821 B2 · Polarization controller and polarization mode dispersion compensator

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- Number: US 8,786,821 B2
- Document ID: US8786821B2
- Status: Granted
- Kind: B2
- Application number: 12/780,523
- Filed: 2010-05-14
- Published: 2010-11-25
- Granted: 2014-07-22
- Earliest claimed: 2009-05-20
- Assignees: Fujitsu Limited
- Applicants: Takashi Shiraishi
- Inventors: Takashi Shiraishi
- Web page: https://patentgrep.com/patent/US8786821B2

## CPC

- G02F 1/0136: {for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation (G02F1/0353 takes precedence)}
- H04B 10/2569: due to polarisation mode dispersion [PMD]
- G02F 1/1326: {Liquid crystal optical waveguides or liquid crystal cells specially adapted for gating or modulating between optical waveguides}
- G02F 2203/05: wavelength dependent
- G02F 2203/12: spatial light modulator
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- H04B: TRANSMISSION

## Abstract

A polarization controller includes a first polarization controller, a demultiplexer, a second polarization controller, and a multiplexer. The first polarization controller controls the state of polarization of input light such that a part of the wavelength components of the input light is in a first state of polarization. The demultiplexer demultiplexes the light output from the first polarization controller into a plurality of wavelength components. The second polarization controller controls the plurality of wavelength components in a second state of polarization by using liquid crystal modulation devices. The multiplexer multiplexes the plurality of wavelength components output from the second polarization controller.

## Claims

### Claim 1

A polarization controller comprising:
a first polarization controller to control a state of polarization of an input modulated light such that a part of the wavelength components of the input light is in a first state of polarization;
a demultiplexer to demultiplex the light output from the first polarization controller into a plurality of wavelength components;
a second polarization controller including liquid crystal modulation devices to control the plurality of wavelength components to be in a second state of polarization; and
a multiplexer to multiplex the plurality of wavelength components output from the second polarization controller.

### Claim 2 (depends on 1)

The polarization controller according to claim 1, wherein the first polarization controller collectively controls the respective states of polarization of the wavelength components of the input light by using a crystal having the electro-optical effect, a response speed of the first polarization controller being faster than a response speed of the second polarization controller.

### Claim 3 (depends on 1)

The polarization controller according to claim 1, further comprising:
a monitor to monitor the Stokes parameters of the plurality of wavelength components,
wherein the first polarization controller controls the state of polarization of the input light based on the Stokes parameters of one of the plurality of wavelength components, and
wherein the second polarization controller controls the respective states of polarization of the plurality of wavelength components based on the Stokes parameters of the plurality of wavelength components.

### Claim 4 (depends on 3)

The polarization controller according to claim 3, wherein the first polarization controller controls the state of polarization of the input light based on the Stokes parameters of the central wavelength of the input light.

### Claim 5 (depends on 3)

The polarization controller according to claim 3, further comprising:
an optical splitter to guide the plurality of wavelength components to the monitor,
wherein the optical splitter is provided between the demultiplexer and the second polarization controller.

### Claim 6 (depends on 3)

The polarization controller according to claim 3, further comprising:
an optical splitter to guide the input light to the monitor,
wherein the optical splitter is provided on the input side of the demultiplexer.

### Claim 7 (depends on 1)

The polarization controller according to claim 1, further comprising:
a first monitor to monitor the Stokes parameters of the plurality of wavelength components;
an optical splitter provided on the input side of the demultiplexer or the output side of the multiplexer; and
a second monitor to monitor the state of polarization of the light divided by the optical splitter,
wherein the first polarization controller controls the state of polarization of the input light based on the state of polarization detected by the second monitor, and
wherein the second polarization controller controls the respective states of polarization of the plurality of wavelength components based on the Stokes parameters of the plurality of wavelength components obtained by the first monitor.

### Claim 8 (depends on 2)

The polarization controller according to claim 2, further comprising:
a first monitor to monitor the Stokes parameters of the plurality of wavelength components;
an optical splitter provided on the input side of the demultiplexer or the output side of the multiplexer; and
a second monitor to monitor the state of polarization of the light divided by the optical splitter,
wherein the first polarization controller controls the state of polarization of the input light based on the state of polarization detected by the second monitor, and
wherein the second polarization controller controls the respective states of polarization of the plurality of wavelength components based on the Stokes parameters of the plurality of wavelength components obtained by the first monitor.

### Claim 9

A polarization mode dispersion compensator comprising:
a first polarization controller to control a state of polarization of an input modulated light such that a part of the wavelength components of the input light is in a first state of polarization;
a demultiplexer to demultiplex the light output from the first polarization controller into a plurality of wavelength components;
a second polarization controller including liquid crystal modulation devices to control the plurality of wavelength components to be in a second state of polarization;
a phase controller to control the respective phases of the wavelength components, the respective states of polarization of which are controlled by the second polarization controller; and
a multiplexer to multiplex the plurality of wavelength components output from the phase controller.

### Claim 10

A polarization control method comprising:
causing a first polarization controller to control a state of polarization of an input modulated light such that a part of the wavelength components of the input light is in a first state of polarization;
demultiplexing, by a demultiplexer, the light output from the first polarization controller into a plurality of wavelength components;
causing a second polarization controller including liquid crystal modulation devices to control the plurality of wavelength components to be in a second state of polarization; and
multiplexing, by a multiplexer, the plurality of wavelength components output from the second polarization controller,
wherein the demultiplexer and the multiplexer are separate.

### Claim 11 (depends on 10)

The polarization control method according to claim 10, wherein the first polarization controller controls the state of polarization of the input light with a first period, and
wherein the second polarization controller controls the respective states of polarization of the plurality of wavelength components with a second period longer than the first period.

### Claim 12 (depends on 9)

The polarization mode dispersion compensator according to claim 9, wherein the first polarization controller collectively controls the respective states of polarization of the wavelength components of the input light by using the electro-optical effect.

### Claim 13 (depends on 10)

The polarization control method according to claim 10, wherein the first polarization controller collectively controls the respective states of polarization of the wavelength components of the input light by using the electro-optical effect.