# US 10,320,151 B1 · Single facet laser sources

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- Number: US 10,320,151 B1
- Document ID: US10320151B1
- Status: Granted
- Kind: B1
- Application number: 15/953,250
- Filed: 2018-04-13
- Granted: 2019-06-11
- Earliest claimed: 2018-04-13
- Assignees: Cisco Technology, Inc.
- Applicants: Cisco Technology, Inc.
- Inventors: Matthew J. Traverso; Dominic F. Siriani; Mark Webster
- Web page: https://patentgrep.com/patent/US10320151B1

## CPC

- H01S 5/1228: {DFB lasers with a complex coupled grating, e.g. gain or loss coupling}
- G02B 6/12004: {Combinations of two or more optical elements}
- H01S 5/101: {Curved waveguide (H01S5/1243 takes precedence)}
- H01S 5/1028: {Coupling to elements in the cavity, e.g. coupling to waveguides adjacent the active region, e.g. forward coupled [DFC] structures}
- H01S 5/1203: {over only a part of the length of the active region}
- H01S 5/125: Distributed Bragg reflector [DBR] lasers
- G02B 2006/12147: {Coupler}
- G02B 2006/1215: {Splitter}
- H01S 5/0225: Out-coupling of light
- H01S 5/026: Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers (stabilisation of output H01S5/06)
- H01S 5/0287: {Facet reflectivity}
- H01S 5/1003: {Waveguide having a modified shape along the axis, e.g. branched, curved, tapered, voids}
- H01S 5/1085: {Oblique facets}
- H01S 5/1215: {Multiplicity of periods}
- H01S 5/22: having a ridge or stripe structure
- H01S 5/3013: {AIIIBV compounds}
- 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
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

The embodiments herein describe a single-frequency laser source (e.g., a distributed feedback (DFB) laser or distributed Bragg reflector (DBR) laser) that includes a feedback grating or mirror that extends along a waveguide. The grating may be disposed over a portion of the waveguide in an optical gain region in the laser source. Instead of the waveguide or cavity being linear, the laser includes a U-turn region so that two ends of the waveguide terminate at the same facet. That facet is coated with an anti-reflective (AR) coating.

## Claims

### Claim 1

A laser source, comprising:
a facet coated with an anti-reflective (AR) coating;
an intermediate region;
a U-turn region, wherein the intermediate region is between the facet and the U-turn region;
a waveguide extending through the facet, the intermediate region, and the U-turn region, wherein a first portion of the waveguide in the U-turn region changes direction such that the waveguide exits the U-turn region in an opposite direction than the first portion of the waveguide entered the U-turn region, wherein first and second ends of the waveguide terminate at the facet; and
a grating disposed over a second portion of the waveguide, wherein the grating and the second portion extend through both the intermediate region and the U-turn region,
wherein at least one of the intermediate region and the U-turn region provides optical gain to a signal propagating in the waveguide.

### Claim 2 (depends on 1)

The laser source of claim 1, wherein the grating is disposed over a third portion of the waveguide extending through the intermediate region that is spaced apart from the second portion of the waveguide extending through the intermediate region, wherein the grating is continuous over the second and third portions of the waveguide.

### Claim 3 (depends on 1)

The laser source of claim 1, wherein the grating is disposed only in the intermediate region, wherein a third portion of the waveguide disposed in the intermediate region is spaced apart from the second portion of the waveguide in the intermediate region, wherein the third portion of the waveguide does not include any grating.

### Claim 4 (depends on 1)

The laser source of claim 1, wherein the grating is not disposed over any portion of the waveguide in the facet.

### Claim 5 (depends on 1)

The laser source of claim 1, wherein the laser source includes one continuous grating associated with the waveguide.

### Claim 6 (depends on 1)

The laser source of claim 1, wherein a material of the waveguide in the facet is different from a material of the waveguide in the intermediate region.

### Claim 7 (depends on 1)

The laser source of claim 1, wherein the U-turn region is a passive region.

### Claim 8 (depends on 1)

The laser source of claim 1, wherein the first and second ends are arranged in the facet to emit respective optical signals to an external optical component.

### Claim 9 (depends on 1)

The laser source of claim 1, further comprising:
an optical combiner disposed in the facet, wherein the first and second ends terminate at the optical combiner, wherein an output of the optical combiner is configured to emit an optical signal to an external optical component.

### Claim 10 (depends on 1)

The laser source of claim 1, further comprising:
a semiconductor substrate on which the U-turn region, the intermediate region, the facet, and the waveguide are disposed.

### Claim 11

An optical system, comprising:
a laser source comprising:
a facet coated with an anti-reflective (AR) coating,
an intermediate region,
a U-turn region,
a waveguide extending through the facet, the intermediate region, and the U-turn region, wherein a first portion of the waveguide in the U-turn region changes direction such that the waveguide exits the U-turn region in an opposite direction than the first portion of the waveguide entered the U-turn region, wherein first and second ends of the waveguide terminate at the facet, and
a grating disposed over a second portion of the waveguide, wherein the grating and the second portion extend through both the intermediate region and the U-turn region; and
a photonic chip comprising:
a first optical coupler aligned to the laser source to receive a first optical signal emitted from the first end of the waveguide via the facet, and
a second optical coupler aligned to the laser source to receive a second optical signal emitted from the second end of the waveguide via the facet.

### Claim 12 (depends on 11)

The optical system of claim 11, wherein the photonic chip comprises:
an optical combiner coupled to an output of the first optical coupler and an output of the second optical coupler and configured to combine the first and second optical signals into a combined optical signal; and
an optical component coupled to an output of the optical combiner to receive the combined optical signal.

### Claim 13 (depends on 11)

The optical system of claim 11, wherein the photonic chip comprises:
a first optical component coupled to an output of the first optical coupler; and
a second optical component coupled to an output of the second optical coupler, wherein the first optical component and first optical coupler establish a first optical path that is independent of a second optical path formed by the second optical component and the second optical coupler.

### Claim 14 (depends on 11)

The optical system of claim 11, wherein the grating is disposed over a third portion of the waveguide extending through the intermediate region that is spaced apart from the second portion of the waveguide extending through the intermediate region, wherein the grating is continuous over the second and third portions of the waveguide.

### Claim 15 (depends on 11)

The optical system of claim 11, wherein the grating is disposed only in the intermediate region, wherein a third portion of the waveguide disposed in the intermediate region is spaced apart from the second portion of the waveguide in the intermediate region, wherein the third portion of the waveguide does not include any grating.

### Claim 16 (depends on 11)

The optical system of claim 11, wherein the laser source includes one continuous grating associated with the waveguide.

### Claim 17 (depends on 11)

The optical system of claim 11, wherein a material of the waveguide in the facet is different from a material of the waveguide in the optical gain region.

### Claim 18 (depends on 11)

The optical system of claim 11, wherein the U-turn region is a passive region.