# US 10,374,718 B2 · Optical transmission distortion compensation device, optical transmission distortion compensation method, and communication device

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- Number: US 10,374,718 B2
- Document ID: US10374718B2
- Status: Granted
- Kind: B2
- Application number: 16/094,857
- Filed: 2017-06-21
- Published: 2019-05-02
- Granted: 2019-08-06
- Earliest claimed: 2016-08-29
- Assignees: NTT Electronics Corporation; Nippon Telegraph and Telephone Corporation
- Applicants: Ntt Electronics Corporation; Nippon Telegraph and Telephone Corporation
- Inventors: Yasuharu Onuma; Etsushi Yamazaki; Hiroyuki Nouchi; Tomohiro Takamuku; Katsuichi Oyama; Kazuhito Takei; Masanori Nakamura; Mitsuteru Yoshida; Masahito Tomizawa
- Web page: https://patentgrep.com/patent/US10374718B2

## CPC

- H04B 10/40: Transceivers
- H04B 10/5161: {Combination of different modulation schemes}
- H04B 10/58: Compensation for non-linear transmitter output
- H04B 10/588: in external modulation systems
- H04B 10/616: {Details of the electronic signal processing in coherent optical receivers}
- H04B 10/6163: {Compensation of non-linear effects in the fiber optic link, e.g. self-phase modulation [SPM], cross-phase modulation [XPM], four wave mixing [FWM]}
- H04L 27/01: Equalisers {(baseband equalizers at the transmitter end H04L25/03343; in analogue transmission systems H04B3/04, H04B7/005)}
- H04L 27/06: Demodulator circuits; Receiver circuits
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An I component compensation unit calculates an I component in which a distortion has been compensated, by forming a first polynomial expressing the distortion of the I component based on an I component and a Q component of a quadrature modulation signal and multiplying each term of the first polynomial by a first coefficient. A Q component compensation unit calculates a Q component in which a distortion has been compensated, by forming a second polynomial expressing the distortion of the Q component based on the I component and the Q component of the quadrature modulation signal and multiplying each term of the second polynomial by a second coefficient. A coefficient calculation unit calculates the first and second coefficients by comparing outputs of the I component compensation unit and the Q component compensation unit and a known signal.

## Claims

### Claim 1

An optical transmission distortion compensation device compensating a distortion in a receiving device comprising:
an I component compensation unit calculating an I component in which a distortion has been compensated, by forming a first polynomial expressing the distortion of the I component based on an I component and a Q component of a quadrature modulation signal and multiplying each term of the first polynomial by a first coefficient;
a Q component compensation unit calculating a Q component in which a distortion has been compensated, by forming a second polynomial expressing the distortion of the Q component based on the I component and the Q component of the quadrature modulation signal and multiplying each term of the second polynomial by a second coefficient; and
a coefficient calculation unit calculating the first and second coefficients by comparing outputs of the I component compensation unit and the Q component compensation unit and a known signal.

### Claim 2 (depends on 1)

The optical transmission distortion compensation device according to claim 1, wherein at least one of the first and second polynomials includes a term which compensates a distortion component that changes in an arch shape on an IQ plane.

### Claim 3 (depends on 2)

The optical transmission distortion compensation device according to claim 2, wherein as the term which compensates the distortion component that changes in an arch shape, the first polynomial includes at least one of a first-order term of the Q component, a second-order term of the Q component and a third-order term of the Q component, and the second polynomial includes at least one of a first-order term of the I component, a second-order term of the I component and a third-order term of the I component.

### Claim 4 (depends on 1)

The optical transmission distortion compensation device according to claim 1, wherein the first polynomial includes a third-order term of the I component,
the second polynomial includes a third-order term of the Q component, and
the optical transmission distortion compensation device compensates a nonlinearity of a transmitting modulator.

### Claim 5 (depends on 1)

The optical transmission distortion compensation device according to claim 1, wherein the coefficient calculation unit calculates the first and second coefficients, using a least mean square algorithm.

### Claim 6 (depends on 1)

A communication device comprising a receiving device receiving an optical signal,
wherein the receiving device includes the optical transmission distortion compensation device according to claim 1.

### Claim 7 (depends on 1)

A communication device comprising a transmitting and receiving device transmitting and receiving an optical signal,
wherein the transmitting and receiving device includes the optical transmission distortion compensation device according to claim 1.

### Claim 8 (depends on 1)

The optical transmission distortion compensation device according to claim 1, wherein the coefficient calculation unit calculates the first and second coefficients by comparing outputs of the I component compensation unit and the Q component compensation unit and a known signal for each symbol and optimizing the first and second coefficients of each term independently.

### Claim 9

An optical transmission distortion compensation device comprising:
an I component compensation unit calculating an I component in which a distortion has been compensated, by forming a first polynomial expressing the distortion of the I component based on an I component and a Q component of a quadrature modulation signal and multiplying each term of the first polynomial by a first coefficient;
a Q component compensation unit calculating a Q component in which a distortion has been compensated, by forming a second polynomial expressing the distortion of the Q component based on the I component and the Q component of the quadrature modulation signal and multiplying each term of the second polynomial by a second coefficient;
a coefficient calculation unit calculating the first and second coefficients by comparing outputs of the I component compensation unit and the Q component compensation unit and a known signal; and
a carrier phase recovery unit compensating phase fluctuation of outputs of the I component compensation unit and the Q component compensation unit,
wherein the coefficient calculation unit calculates the first and second coefficients, using a result from performing a reverse compensation process of a compensation in the carrier phase recovery unit, to an error between an output of the carrier phase recovery unit and the known signal.

### Claim 10 (depends on 9)

The optical transmission distortion compensation device according to claim 9, further comprising a skew compensation unit provided between the carrier phase recovery unit and each of the I distortion compensation unit and the Q distortion compensation unit,
the skew compensation unit includes a butterfly type filter that performs a skew compensation of the outputs of the I component compensation unit and the Q component compensation unit, and a filter coefficient calculation unit that calculates a filter coefficient of the filter using the result from performing, to the error, the reverse compensation process of the compensation in the carrier phase recovery unit, and
the coefficient calculation unit calculates the first and second coefficients, using a result from performing, to the error, the reverse compensation process of the compensations in the skew compensation unit and the carrier phase recovery unit.

### Claim 11

An optical transmission distortion compensation device comprising:
an I component compensation unit calculating an I component in which a distortion has been compensated, by forming a first polynomial expressing the distortion of the I component based on an I component and a Q component of a quadrature modulation signal and multiplying each term of the first polynomial by a first coefficient;
a Q component compensation unit calculating a Q component in which a distortion has been compensated, by forming a second polynomial expressing the distortion of the Q component based on the I component and the Q component of the quadrature modulation signal and multiplying each term of the second polynomial by a second coefficient;
a coefficient calculation unit calculating the first and second coefficients by comparing outputs of the I component compensation unit and the Q component compensation unit and a known signal; and
an adaptive equalization unit performing an equalization process to the quadrature modulation signal; and
a phase fluctuation compensation unit performing a compensation process to the quadrature modulation signal,
wherein the I component compensation unit and the Q component compensation unit are provided at a subsequent stage of the adaptive equalization unit and the phase fluctuation compensation unit, and
the adaptive equalization unit and the phase fluctuation compensation unit calculate a filter coefficient and a compensation amount for the equalization process and the compensation process, using a known signal to which an IQ distortion evaluated from a calculation result of the coefficient calculation unit has been added.

### Claim 12

An optical transmission distortion compensation method performed by an optical transmission distortion compensation device compensating a distortion in a receiving device, comprising:
calculating an I component in which a distortion has been compensated, by forming a first polynomial expressing the distortion of the I component based on an I component and a Q component of a quadrature modulation signal and multiplying each term of the first polynomial by a first coefficient;
calculating a Q component in which a distortion has been compensated, by forming a second polynomial expressing the distortion of the Q component based on the I component and the Q component of the quadrature modulation signal and multiplying each term of the second polynomial by a second coefficient; and
calculating the first and second coefficients by comparing the I component and the Q component in which the distortion have been compensated and a known signal.

### Claim 13 (depends on 12)

The optical transmission distortion compensation method according to claim 12, wherein the first and second coefficients are calculated by comparing the I component and the Q component in which the distortion have been compensated and a known signal for each symbol and optimizing the first and second coefficients of each term independently.