# US 11,309,985 B2 · Light source device that includes a plurality of light sources with different wavelengths and method of controlling wavelengths

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- Number: US 11,309,985 B2
- Document ID: US11309985B2
- Status: Granted
- Kind: B2
- Application number: 17/136,177
- Filed: 2020-12-29
- Published: 2021-09-02
- Granted: 2022-04-19
- Earliest claimed: 2020-03-02
- Assignees: Fujitsu Optical Components Limited
- Applicants: Fujitsu Optical Components Limited
- Inventors: Koji Otsubo
- Web page: https://patentgrep.com/patent/US11309985B2

## CPC

- H01S 5/0078: {for frequency filtering}
- H04J 14/02: Wavelength-division multiplex systems
- H01S 5/02415: {by using a thermo-electric cooler [TEC], e.g. Peltier element}
- H01S 5/06804: {by monitoring an external parameter, e.g. temperature}
- H01S 5/0687: Stabilising the frequency of the laser
- H04B 10/572: Wavelength control
- H05B 47/155: Coordinated control of two or more light sources
- H10N 10/10: operating with only the Peltier or Seebeck effects
- H01S 5/0085: {for modulating the output, i.e. the laser beam is modulated outside the laser cavity}
- H01S 5/0683: by monitoring the optical output parameters
- H01S 5/4012: {Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms}
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- 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)
- H04B: TRANSMISSION
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## Abstract

A light source device includes: a plurality of light sources that generate rays of light with different wavelengths corresponding to a plurality of target wavelengths located on a designated wavelength grid; a plurality of photodetectors that detect output powers of the plurality of light sources; a plurality of optical bandpass filters that are provided between the plurality of light sources and the plurality of photodetectors; a temperature adjustment unit that adjusts a temperature of an area around the plurality of light sources; and a processor that controls the temperature adjustment unit based on output signals of the plurality of photodetectors. Widths of passbands of the optical bandpass filters are less than a wavelength spacing in the wavelength grid.

## Claims

### Claim 1

A light source device comprising:
a plurality of light sources that generate rays of light with different wavelengths corresponding to a plurality of target wavelengths located on a designated wavelength grid;
a plurality of photodetectors that detect output powers of the plurality of light sources and generate currents indicating the output powers of the plurality of light sources as output signals, respectively;
a plurality of optical bandpass filters that are provided between the plurality of light sources and the plurality of photodetectors;
a temperature adjustment unit that adjusts a temperature of an area around the plurality of light sources; and
a processor that calculates a total of the currents generated by the plurality of photodetectors and controls the temperature adjustment unit based on the total of the currents generated by the plurality of photodetectors,
wherein widths of passbands of the optical bandpass filters are less than a wavelength spacing in the wavelength grid.

### Claim 2 (depends on 1)

The light source device according to claim 1, wherein the processor
periodically calculates the total of the currents, and
stops operations of the temperature adjustment unit when an amount of decrease in the total of the currents is less than a specified threshold.

### Claim 3 (depends on 2)

The light source device according to claim 2,
further comprising: a temperature sensor that detects the temperature of the area around the plurality of light sources,
wherein the processor
drives the temperature adjustment unit so as to decrease the temperature of the area around the plurality of light sources when the amount of decrease in the total of the currents is greater than or equal to the threshold and the temperature of the area around the plurality of light sources increases, and
drives the temperature adjustment unit so as to increase the temperature of the area around the plurality of light sources when the amount of decrease in the total of the currents is greater than or equal to the threshold and the temperature of the area around the plurality of light sources decreases.

### Claim 4 (depends on 2)

The light source device according to claim 2,
further comprising: a temperature sensor that detects the temperature of the area around the plurality of light sources,
wherein the processor
drives the temperature adjustment unit so as to decrease the temperature of the area around the plurality of light sources when the amount of decrease in the total of the currents is greater than or equal to the threshold and the temperature of the area around the plurality of light sources is higher than a specified threshold temperature, and
drives the temperature adjustment unit so as to increase the temperature of the area around the plurality of light sources when the amount of decrease in the total of the currents is greater than or equal to the threshold and the temperature of the area around the plurality of light sources is lower than the threshold temperature.

### Claim 5 (depends on 1)

The light source device according to claim 1, wherein the processor stops operations of the temperature adjustment unit when a proportion of the total of the currents to a reference value determined in advance is greater than a specified value.

### Claim 6 (depends on 1)

The light source device according to claim 1, wherein a wavelength of the light generated by each of the light sources matches a center wavelength in the passband of a corresponding optical bandpass filter.

### Claim 7 (depends on 1)

The light source device according to claim 1, wherein a wavelength of the light generated by each of the light sources is shorter than a center wavelength in the passband of a corresponding optical bandpass filter.

### Claim 8 (depends on 1)

The light source device according to claim 1, wherein a wavelength of the light generated by each of the light sources is longer than a center wavelength in the passband of a corresponding optical bandpass filter.

### Claim 9 (depends on 1)

The light source device according to claim 1, further comprising: a power controller that adjusts the output powers of the plurality of light sources to specified target levels by using rays of light guided from the plurality of light sources to the plurality of photodetectors.

### Claim 10

A wavelength adjustment method that is performed by a light source device including a plurality of light sources that generate rays of light with different wavelengths corresponding to a plurality of target wavelengths located on a designated wavelength grid, a plurality of photodetectors that detect output powers of the plurality of light sources, a plurality of optical bandpass filters that are provided between the plurality of light sources and the plurality of photodetectors, and a temperature adjustment unit that adjusts a temperature of an area around the plurality of light sources, the wavelength adjustment method being a method of controlling the wavelengths of the rays of light generated by the plurality of light sources, wherein
widths of passbands of the optical bandpass filters are less than a wavelength spacing in the wavelength grid, and
an output signal of each of the photodetectors is a current indicating an output power of a corresponding light source,
the wavelength adjustment method comprising:
periodically calculating a total of currents generated by the plurality of photodetectors;
stopping operations of the temperature adjustment unit when an amount of decrease in the total of the currents is less than a specified threshold;
driving the temperature adjustment unit so as to decrease the temperature of the area around the plurality of light sources when the amount of decrease in the total of the currents is greater than or equal to the threshold and the temperature of the area around the plurality of light sources increases; and
driving the temperature adjustment unit so as to increase the temperature of the area around the plurality of light sources when the amount of decrease in the total of the currents is greater than or equal to the threshold and the temperature of the area around the plurality of light sources decreases.