# US 11,909,174 B2 · Reflection filter device and wavelength-tunable laser device

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- Number: US 11,909,174 B2
- Document ID: US11909174B2
- Status: Granted
- Kind: B2
- Application number: 16/986,343
- Filed: 2020-08-06
- Published: 2020-11-19
- Granted: 2024-02-20
- Earliest claimed: 2018-02-14
- Assignees: Furukawa Electric Co., Ltd.
- Applicants: Furukawa Electric Co., Ltd.
- Inventors: Yasumasa Kawakita; Yasutaka Higa
- Web page: https://patentgrep.com/patent/US11909174B2

## CPC

- H01S 5/068: Stabilisation of laser output parameters (H01S5/0625 takes precedence)
- H01S 5/142: {which comprises an additional resonator}
- H01S 3/08059: {Constructional details of the reflector, e.g. shape (mirrors in general G02B5/08; mountings for mirrors G02B7/18)}
- H01S 3/10053: {Phase control}
- H01S 5/021: {Silicon based substrates}
- H01S 5/026: Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers (stabilisation of output H01S5/06)
- H01S 5/06256: {with DBR-structure}
- H01S 5/1007: {Branched waveguides}
- H01S 5/101: {Curved waveguide (H01S5/1243 takes precedence)}
- H01S 5/141: {using a wavelength selective device, e.g. a grating or etalon (H01S5/146 takes precedence)}
- H01S 5/02453: {Heating, e.g. the laser is heated for stabilisation against temperature fluctuations of the environment (H01S5/0612 takes precedence, for monolithically integrated heaters see also H01S5/0261)}
- H01S 5/0261: {Non-optical elements, e.g. laser driver components, heaters (H01S5/0265 takes precedence)}
- H01S 5/06246: {controlling the phase}
- H01S 2301/166: Single transverse or lateral mode
- 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

## Abstract

A reflection filter device includes: a ring resonator filter including a ring-shaped waveguide and two arms, each of the two arms being optically coupled to the ring-shaped waveguide; and a dual-branch portion including a light input/output port and two branch ports, the light input/output port being configured to allow input and output of light, the two branch ports being configured to allow output of the light input from the light input/output port, the light being split into two, the two arms being connected to the two branch ports, respectively, at least one of the two arms being equipped with a phase adjuster.

## Claims

### Claim 1

A reflection filter device comprising:
a ring resonator filter including a ring-shaped waveguide and two arms, each of the two arms being optically coupled to the ring-shaped waveguide; and
a dual-branch portion including a light input/output port and two branch ports, the light input/output port being configured to allow input and output of light, the two branch ports being configured to allow output of the light input from the light input/output port, the light being split into two, the two arms being connected to the two branch ports, respectively, wherein both of the two arms are equipped with respective phase adjusters.

### Claim 2 (depends on 1)

The reflection filter device according to claim 1, wherein the two arms have a high mesa waveguide structure.

### Claim 3

A wavelength-tunable laser device comprising:
a laser resonator including a diffraction grating, a ring-shaped waveguide, two arms, a dual-branch portion, and a reflection filter device, each of the two arms being optically coupled to the ring-shaped waveguide, the dual-branch portion including a light input/output port and two branch ports, the light input/output port being configured to allow input and output of light, the two branch ports being configured to allow output of the light input from the light input/output port, the light being split into two, the two arms being connected to the dual-branch ports, respectively, at least one of the two arms being equipped with a phase adjuster and a refractive index changing unit arranged along the phase adjuster, the reflection filter device being optically coupled to the diffraction grating on the light input/output port;
a gain portion disposed in the laser resonator, wherein:
the phase adjuster and the refractive index changing unit are arranged in the arms and separated from the gain portion,
the diffraction grating generates a first comb-shaped reflection spectrum,
the reflection filter device generates a second comb-shaped reflection spectrum having a peak with a full width at half maximum narrower than a full width at half maximum of a peak of the first comb-shaped reflection spectrum and having a wavelength interval different from a wavelength interval of the first comb-shaped reflection spectrum, and
the diffraction grating and the reflection filter device are configured such that one of peaks of the first comb-shaped reflection spectrum and one of peaks of the second comb-shaped reflection spectrum are overlappable on a wavelength axis;
a first refractive index changing unit configured to change a refractive index of the diffraction grating; and
a second refractive index changing unit configured to change a refractive index of the ring-shaped waveguide, wherein one of peaks of the first comb-shaped reflection spectrum and one of peaks of the second comb-shaped reflection spectrum are overlapped on a wavelength axis by using at least one of the first refractive index changing unit and the second refractive index changing unit.

### Claim 4 (depends on 3)

The wavelength-tunable laser device according to claim 3, wherein the light input/output port side is optically coupled to a waveguide structure having the diffraction grating in a state in which optical propagation modes are substantially made equivalent.

### Claim 5 (depends on 3)

The wavelength-tunable laser device according to claim 3, wherein a semiconductor optical amplifier is integrated.

### Claim 6 (depends on 3)

The wavelength-tunable laser device according to claim 3, wherein the diffraction grating is disposed in a vicinity of the gain portion.

### Claim 7 (depends on 3)

The wavelength-tunable laser device according to claim 3, wherein the diffraction grating is disposed along the gain portion.

### Claim 8 (depends on 3)

The wavelength-tunable laser device according to claim 3, wherein the laser resonator is configured such that a spacing between resonator modes is such that two or more of the resonator modes are included in a peak of the first comb-shaped reflection spectrum.

### Claim 9 (depends on 3)

The wavelength-tunable laser device according to claim 3, wherein peaks of the first comb-shaped reflection spectrum have a Gaussian shape, and peaks of the second comb-shaped reflection spectrum have a double exponential distribution shape.

### Claim 10 (depends on 3)

The wavelength-tunable laser device according to claim 3, further comprising:
a third refractive index changing unit serving as the refractive index changing unit arranged along the phase adjuster and configured to adjust a refractive index of the phase adjuster,
wherein the first refractive index changing unit, the second refractive index changing unit, and the third refractive index changing unit are resistive heaters disposed in a vicinity of the diffraction grating, the ring-shaped waveguide, and the phase adjuster, respectively, to thermally change respective refractive indices.