# US 8,634,723 B2 · Optical communications with polarization dependent loss compensation

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- Number: US 8,634,723 B2
- Document ID: US8634723B2
- Status: Granted
- Kind: B2
- Application number: 12/969,045
- Filed: 2010-12-15
- Published: 2011-06-23
- Granted: 2014-01-21
- Earliest claimed: 2009-12-17
- Assignees: CeLight, Inc.
- Applicants: Yehouda Meiman; Raanan Ivry
- Inventors: Yehouda Meiman; Raanan Ivry
- Web page: https://patentgrep.com/patent/US8634723B2

## CPC

- H04B 10/2572: {due to forms of polarisation-dependent distortion other than PMD}
- H04B: TRANSMISSION

## Abstract

The invention related to the system and method for optical communication using light of two polarization states. Polarization distortion loss (PDL) is compensated by implementation of polarization controllers at both the transmitter and receiver sides. The transmitter controller performs a mixing transformation of beam with two polarizations, while the receiver controller performs the same transformation in the opposite direction with exactly same sequence as in the transmitter part. A cross scrambling and a polarization rotation represented by matrix multiplication are examples of such mixing polarization transformations. The averaged PDL induced errors are corrected by the FEC code plus interleavers.

## Claims

### Claim 1

An optical communication system for data transmitting from a transmitter to a receiver over fiber using dual polarization light, comprising: a first data controller at the transmitter side; the first controller performs a first polarization mixing transformation on a data for a first polarized beam and a data for a second polarized beam; the second polarized beam being orthogonal to the first polarized beam; a second data controller at the receiver side; the second controller performs a second mixing transformation on a received data transmitted in the first polarized beam and a received data transmitted in the second polarized beam; this second transformation is performed in an opposite direction to a transmitter transformation with exactly same sequence as in the transmitter part, wherein the data is transmitted in orthogonal frequency division multiplexed (OFDM) format, further comprising a forward error correction (FEC) encoder unit for data encoding at the transmitter side; a FEC decoder unit at the receiver side; and wherein FEC block is longer than polarization correlation time; further comprising an interleaver at the transmitter side; and a de-inverleaver at the receiver side; and wherein for the signal at rate R bit/sec, FEC block length of N bit and interleaving depth of M, the polarization correlation time T is T<=2*N*M/R.

### Claim 2 (depends on 1)

The system of claim 1, wherein the first mixing transformation is cross scrambling the data for the first polarized beam and the data for the second polarized beam; and the second transformation is cross scrambling in an opposite direction to a transmitter scrambling with exactly same sequence as in the transmitter part.

### Claim 3 (depends on 2)

The system of claim 2, wherein the data is scrambled randomly.

### Claim 4 (depends on 2)

The system of claim 2, wherein the data is scrambled using a periodical scrambling sequence.

### Claim 5 (depends on 1)

The system of claim 1, wherein the first data controller is digital, and it performs digital bit cross scrambling.

### Claim 6 (depends on 5)

The system of claim 5, wherein the second data controller is digital, and it performs digital bit cross scrambling.

### Claim 7 (depends on 1)

The system of claim 1, wherein the first mixing transformation is a polarization rotation.

### Claim 8 (depends on 7)

The system of claim 7, wherein the polarization rotation function is a matrix multiplication:
[
SIG
out
V
SIG
out
H
]
=
[
cos
⁡
(
α
)
sin
⁡
(
α
)
-
sin
⁢
⁢
(
α
)
cos
⁡
(
α
)
]
·
[
SIG
in
V
SIG
in
H
]
wherein SIGVin and SIGHin are input data in the first and the second polarizations respectively; and SIGVout and SIGHout are output data in the first and the second polarizations respectively, and α is a rotation angle.

### Claim 9 (depends on 8)

The system claim 8, wherein α changes on time, α (t).

### Claim 10 (depends on 7)

The system of claim 7, wherein the polarization rotation is digital.

### Claim 11 (depends on 1)

The system of claim 1, wherein a quadrature phase shift keying data encoding is implemented.

### Claim 12 (depends on 1)

The system of claim 1, wherein the data is transmitted over multiple WDM channels.

### Claim 13 (depends on 1)

The system of claim 1, wherein the first polarization state is vertical linear polarization and the second polarization state is horizontal linear polarization.

### Claim 14

A method of optical communication with PDL compensation,. comprising: sending information embedded in dual polarization light from a transmitter to a receiver over fiber; performing a first polarization mixing transformation on a data for a first polarized beam and a data for a second polarized beam at the transmitter; the second polarized beam being orthogonal to the first polarized beam; performing a second polarization mixing transformation on a received data transmitted in the first polarized beam and a received data transmitted in the second polarized beam at the receiver side; this second transformation is performed in an opposite direction to a first transformation with exactly same sequence as in the transmitter part, wherein the data is transmitted in orthogonal frequency division multiplexed (OFDM) format; further comprising data FEC encoding at the transmitter and decoding at the receiver, wherein FEC block is longer than polarization correlation time; performing interleaving at an interleaver at the transmitter side; and de-interleaving at a de-inverleaver at the receiver side; and wherein for the signal at rate R bit/sec, FEC block length of N bit and interleaving depth of M, the polarization correlation time T is T<=2*N*M/R.

### Claim 15 (depends on 14)

The method of claim 14, wherein the first mixing transformation is cross scrambling.

### Claim 16 (depends on 14)

The method of claim 14, wherein the first mixing transformation is a polarization rotation according to:
[
SIG
out
V
SIG
out
H
]
=
[
cos
⁡
(
α
)
sin
⁡
(
α
)
-
sin
⁢
⁢
(
α
)
cos
⁡
(
α
)
]
·
[
SIG
in
V
SIG
in
H
]
wherein SIGVin and SIGHin are input data in the first and the second polarizations respectively; and SIGVout and SIGHoutare output data in the first and the second polarizations respectively and α is rotation angle.