# US 2017/0288771 A1 · Apparatus and method for measuring frequency response characteristics of optical transmitter and optical receiver

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- Number: US 2017/0288771 A1
- Document ID: US20170288771A1
- Status: Published application
- Kind: A1
- Application number: 15/476,123
- Filed: 2017-03-31
- Published: 2017-10-05
- Earliest claimed: 2016-03-31
- Assignees: Fujitsu Limited
- Applicants: Fujitsu Limited
- Inventors: Cheng JU; Liang Dou; Zhenning Tao
- Web page: https://patentgrep.com/patent/US20170288771A1

## CPC

- H04B 10/0795: {Performance monitoring; Measurement of transmission parameters}
- H04B 10/0731: {Testing or characterisation of optical devices, e.g. amplifiers}
- H04B 10/548: Phase or frequency modulation
- H04B 10/691: {Arrangements for optimizing the photodetector in the receiver}
- H04L 27/2637: {with direct modulation of individual subcarriers}
- H04L 27/2697: {in combination with other modulation techniques}
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An apparatus and method for measuring frequency response characteristics of an optical transmitter and an optical receiver where the apparatus includes: a generating unit configured to generate a driving signal for driving the modulator of the optical transmitter, which comprises at least two frequencies; and a calculating unit configured to respectively calculate the frequency response characteristics of the optical transmitter and the optical receiver according to output signal components in output signals of the optical receiver corresponding to at least two detection signal components of identical amplitudes and different frequencies in detection signals. The frequency response characteristics of the optical transmitter and the optical receiver may be obtained, the amplitude responses and phase responses in the frequency response characteristics may be respectively obtained, and the measurement results are accurate and reliable.

## Claims

### Claim 1

An apparatus for measuring frequency response characteristics of an optical transmitter and an optical receiver; wherein, the optical transmitter comprises a modulator, and the optical receiver comprises a photoelectric detector, the modulator of the optical transmitter being connected to the photoelectric detector of the optical receiver, and signals outputted by the modulator being inputted into the photoelectric detector;
the apparatus comprising:
a generating unit configured to generate a driving signal for driving the modulator of the optical transmitter, which driving signal comprises at least two frequencies; and
a calculating unit configured to respectively calculate frequency response characteristics of the optical transmitter and the optical receiver according to output signal components in output signals of the optical receiver corresponding to at least two detection signal components of identical amplitudes and different frequencies in detection signals;
wherein, the detection signals are the detection signals having photoelectric conversion performed by the photoelectric detector of the optical receiver.

### Claim 2 (depends on 1)

The apparatus according to claim 1, wherein,
the driving signal generated by the generating unit is a group of orthogonal frequency division multiplexing symbols comprising at least two orthogonal frequency division multiplexing symbols.

### Claim 3 (depends on 2)

The apparatus according to claim 2, wherein,
the orthogonal frequency division multiplexing symbols in the group of orthogonal frequency division multiplexing symbols comprise one or more first subcarriers and one or more second subcarriers; and wherein, power of the second subcarriers is greater than or equal to power of the first subcarriers.

### Claim 4 (depends on 3)

The apparatus according to claim 3, wherein,
the group of orthogonal frequency division multiplexing symbols comprises N chronological orthogonal frequency division multiplexing symbols: wherein, for the M-th orthogonal frequency division multiplexing symbol, the first subcarriers are arranged in all even-numbered subcarriers of the M-th orthogonal frequency division multiplexing symbol of frequencies less than or equal to that of a 2M-th subcarrier, and the second subcarrier is arranged in a (2M+1)-th subcarrier of the M-th orthogonal frequency division multiplexing symbol; and wherein, M and N are positive integers, and M≦N.

### Claim 5 (depends on 3)

The apparatus according to claim 3, wherein,
for the orthogonal frequency division multiplexing symbols, the at least two detection signal components of identical amplitudes and different frequencies in the detection signals are at least two cross terms of the first subcarriers and the second subcarriers in the detection signals.

### Claim 6 (depends on 4)

The apparatus according to claim 4, wherein the calculating unit includes:
a first calculating unit configured to, for the first orthogonal frequency division multiplexing symbol, calculate a frequency response characteristic of the optical receiver corresponding to a frequency spot of a fifth subcarrier according to the first subcarrier and the fifth subcarrier of the first orthogonal frequency division multiplexing symbol of the output signal of the optical receiver, and calculate the frequency response characteristic of the optical receiver corresponding to the frequency spot of a third subcarrier according to the frequency response characteristic of the optical receiver corresponding to the frequency spot of the fifth subcarrier and a predetermined frequency response characteristic at the frequency spot of the first subcarrier.

### Claim 7 (depends on 6)

The apparatus according to claim 6, wherein the calculating unit further includes:
a second calculating unit configured to, for the M-th orthogonal frequency division multiplexing symbol, calculate the frequency response characteristic of the optical transmitter corresponding to the frequency spot of a [2M+1]-th subcarrier according to all odd-numbered subcarriers in a [2M−1+1, 2M−1]-th subcarrier of the M-th orthogonal frequency division multiplexing symbol in the output signal of the optical receiver; where, 2<M≦N;
a third calculating unit configured to calculate frequency response characteristics of the optical transmitter corresponding to frequency spots of all even-numbered subcarriers in a [2M−1+22M]-th subcarrier according to all odd-numbered subcarriers in a [1,2M−1−1]-th subcarrier of the M-th orthogonal frequency division multiplexing symbol in the output signal of the optical receiver; where, 2<M≦N; and
a fourth calculating unit configured to calculate the frequency response characteristics of the optical receiver corresponding to the frequency spots of all odd-numbered subcarriers according to all odd-numbered subcarriers in a [2M+32M+1+1]-th subcarrier of the M-th orthogonal frequency division multiplexing symbol in the output signal of the optical receiver; where, 2<M≦N.

### Claim 8

A method for measuring frequency response characteristics of an optical transmitter and an optical receiver; wherein, the optical transmitter comprises a modulator, and the optical receiver comprises a photoelectric detector, the modulator of the optical transmitter being connected to the photoelectric detector of the optical receiver, and signals outputted by the modulator being inputted into the photoelectric detector;
the method comprising:
generating a driving signal for driving the modulator of the optical transmitter, which driving signal comprises at least two frequencies; and
respectively calculating the frequency response characteristics of the optical transmitter and the optical receiver according to output signal components in output signals of the optical receiver corresponding to at least two detection signal components of identical amplitudes and different frequencies in detection signals; wherein, the detection signals are the detection signals having photoelectric conversion performed by the photoelectric detector of the optical receiver.

### Claim 9 (depends on 8)

The method according to claim 8, wherein,
the generated driving signal is a group of orthogonal frequency division multiplexing symbols comprising at least two orthogonal frequency division multiplexing symbols.

### Claim 10 (depends on 9)

The method according to claim 9, wherein,
the orthogonal frequency division multiplexing symbols in the group of orthogonal frequency division multiplexing symbols comprise one or more first subcarriers and one or more second subcarriers; and wherein, power of the second subcarriers is greater than or equal to power of the first subcarriers.

### Claim 11 (depends on 10)

The method according to claim 10, wherein,
the group of orthogonal frequency division multiplexing symbols comprises N chronological orthogonal frequency division multiplexing symbols; wherein, for the M-th orthogonal frequency division multiplexing symbol, the first subcarriers are arranged in all even-numbered subcarriers of the M-th orthogonal frequency division multiplexing symbol of frequencies less than or equal to that of a 2M-th subcarrier, and the second subcarrier is arranged in a (2M+1)-th subcarrier of the M-th orthogonal frequency division multiplexing symbol; and wherein, M and N are positive integers, and M≦N.

### Claim 12 (depends on 9)

The method according to claim 9, wherein,
for the orthogonal frequency division multiplexing symbols, the at least two detection signal components of identical amplitudes and different frequencies in the detection signals are at least two cross terms of the first subcarriers and the second subcarriers in the detection signals.

### Claim 13 (depends on 11)

The method according to claim 11, wherein the respectively calculating the frequency response characteristics of the optical transmitter and the optical receiver according to output signal components in output signals of the optical receiver corresponding to at least two detection signal components of identical amplitudes and different frequencies in detection signals includes:
for the first orthogonal frequency division multiplexing symbol, calculating a frequency response characteristic of the optical receiver corresponding to a frequency spot of a fifth subcarrier according to the first subcarrier and the fifth subcarrier of the first orthogonal frequency division multiplexing symbol of the output signal of the optical receiver, and calculating the frequency response characteristic of the optical receiver corresponding to the frequency spot of a third subcarrier according to the frequency response characteristic of the optical receiver corresponding to the frequency spot of the fifth subcarrier and a predetermined frequency response characteristic at the frequency spot of the first subcarrier.

### Claim 14 (depends on 13)

The method according to claim 13, wherein the respectively calculating the frequency response characteristics of the optical transmitter and the optical receiver according to output signal components in output signals of the optical receiver corresponding to the least two detection signal components of identical amplitudes and different frequencies in detection signals further includes:
for the M-th orthogonal frequency division multiplexing symbol, calculating the frequency response characteristic of the optical transmitter corresponding to the frequency spot of a [2M+1]-th subcarrier according to all odd-numbered subcarriers in a [2M−1+1, 2M−1]-th subcarrier of the M-th orthogonal frequency division multiplexing symbol in the output signal of the optical receiver; where, 2<M≦N;
calculating frequency response characteristics of the optical transmitter corresponding to frequency spots of all even-numbered subcarriers in a [2M−1+22M]-th subcarrier according to all odd-numbered subcarriers in a [1,2M−1−1]-th subcarrier of the M-th orthogonal frequency division multiplexing symbol in the output signal of the optical receiver; where, 2<M≦N; and
calculating the frequency response characteristics of the optical receiver corresponding to the frequency spots of all odd-numbered subcarriers according to all odd-numbered subcarriers in a [2M+32M+1+1]-th subcarrier of the M-th orthogonal frequency division multiplexing symbol in the output signal of the optical receiver; where, 2<M≦N.