# US 12,224,795 B2 · Optical transmission system and transmission quality monitoring method

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- Number: US 12,224,795 B2
- Document ID: US12224795B2
- Status: Granted
- Kind: B2
- Application number: 18/016,367
- Filed: 2020-07-30
- Published: 2023-08-31
- Granted: 2025-02-11
- Earliest claimed: 2020-07-30
- Assignees: Nippon Telegraph and Telephone Corporation
- Applicants: Nippon Telegraph and Telephone Corporation
- Inventors: Toshiaki Shitaba; Tomoaki Yoshida; Akihiro Tanabe; Takashi Mitsui
- Web page: https://patentgrep.com/patent/US12224795B2

## CPC

- H04B 10/032: using working and protection systems {(H04J14/0287 takes precedence)}
- H04B 10/077: using a supervisory or additional signal
- 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)}
- H04J 14/0227: {Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation}
- H04B 10/40: Transceivers
- H04B 10/50: Transmitters
- H04B 10/60: Receivers
- 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

In an optical transmission system including a plurality of optical transmitting units and a relay device, the plurality of optical transmitting units include a frequency modulation conversion unit that converts an input signal into a frequency modulation signal through frequency modulation conversion processing, a multiplexing unit that multiplexes monitoring signals with different frequencies with the frequency modulation signal, and an optical modulation unit that converts the frequency modulation signal that is an electric signal in which the monitoring signals are multiplexed into optical signals having different wavelengths, and the relay device includes a photoelectric conversion unit that acquires a combined signal obtained by combining optical signals having different wavelengths from each other and converts the combined signal into an electric signal, and a measuring unit that measures transmission quality of the plurality of monitoring signals included in the electric signal.

## Claims

### Claim 1

An optical transmission system comprising:
a plurality of optical transmitters; and
a relay device,
wherein the plurality of optical transmitters include
a frequency modulation converter configured to convert an input signal into a frequency modulation signal through frequency modulation conversion processing,
a multiplexer configured to multiplex monitoring signals, which are different in frequency from each other among the plurality of optical transmitters and are not frequency modulated, with the frequency modulation signal that is frequency modulated, and
an optical modulator configured to convert the frequency modulation signal that is an electric signal in which the monitoring signals are multiplexed, into optical signals having different wavelengths among the plurality of optical transmitters, and
the relay device includes
a photoelectric converter configured to acquire a combined signal obtained by combining optical signals having different wavelengths from each other and convert the combined signal into an electric signal, and
a measuring instrument configured to measure transmission quality of the plurality of monitoring signals with different frequencies included in the electric signal.

### Claim 2 (depends on 1)

The optical transmission system according to claim 1,
wherein the relay device further includes
an amplifier configured to amplify the combined signal.

### Claim 3 (depends on 1)

The optical transmission system according to claim 1,
wherein the plurality of optical transmitters include an operation-system optical transmitter that is an optical transmitter of an operation system, and a standby-system optical transmitter that is an optical transmitter of a standby system.

### Claim 4 (depends on 3)

The optical transmission system according to claim 3,
wherein the relay device further includes
a switcher configured to determine whether to transmit a combined signal obtained by combining the optical signal transmitted from the operation-system optical transmitter to an optical receiver or whether to transmit a combined signal obtained by combining the optical signal transmitted from the standby-system optical transmitter to the optical receiver based on the transmission quality measured by the measuring instrument.

### Claim 5 (depends on 1)

The optical transmission system according to claim 1, further comprising:
an optical wavelength multiplexer configured to receive a first optical signal having the first wavelength transmitted from the first optical transmitter and a second optical signal having the second wavelength transmitted from the second optical transmitter, and
transmit an optical signal obtained by multiplexing the first optical signal with the second optical signal to the relay device.

### Claim 6 (depends on 5)

The optical transmission system according to claim 5,
wherein the optical wavelength multiplexer includes a wavelength division multiplexing filter.

### Claim 7

A transmission quality monitoring method comprising:
in which a plurality of optical transmitters converting an input signal into a frequency modulation signal through frequency modulation conversion processing;
in which the plurality of optical transmitters multiplexing monitoring signals, which are different in frequency from each other among the plurality of optical transmitters and are not frequency modulated, with the frequency modulation signal that is frequency modulated;
in which the plurality of optical transmitters converting the frequency modulation signal that is an electric signal in which the monitoring signals are multiplexed, into optical signals having different wavelengths among the plurality of optical transmitters;
in which a relay device acquiring a combined signal obtained by combining the optical signals having the different wavelengths from each other and converting the combined signal into an electric signal; and
in which the relay device measuring transmission quality of the plurality of monitoring signals with different frequencies included in the electric signal.

### Claim 8

An optical transmitter comprising:
a frequency modulation converter configured to convert an input signal into a frequency modulation signal through frequency modulation conversion processing;
a multiplexer configured to multiplex monitoring signals which are different in frequency from each other among a plurality of optical transmitters and are not frequency modulated, with the frequency modulation signal that is frequency modulated; and
an optical modulator configured to convert the frequency modulation signal that is an electric signal in which the monitoring signals are multiplexed, into optical signals having different wavelengths among the plurality of optical transmitters.

### Claim 9 (depends on 3)

The optical transmission system according to claim 3,
wherein the relay device further includes
a switcher configured to transmit, based on the measured transmission quality of the plurality of monitoring signals, either the combined signal of the operation-system optical transmitter or the combined signal of the standby-system optical transmitter to the optical receiver.