# US 9,882,349 B1 · Externally referenced wavelength-locking technique for hybrid lasers

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- Number: US 9,882,349 B1
- Document ID: US9882349B1
- Status: Granted
- Kind: B1
- Application number: 15/404,437
- Filed: 2017-01-12
- Granted: 2018-01-30
- Earliest claimed: 2017-01-12
- Assignees: Oracle International Corporation
- Applicants: Oracle International Corporation
- Inventors: Ashok V. Krishnamoorthy; Jin-Hyoung Lee; Xuezhe Zheng
- Web page: https://patentgrep.com/patent/US9882349B1

## CPC

- H01S 5/0617: {using memorised or pre-programmed laser characteristics}
- H01S 5/0687: Stabilising the frequency of the laser
- H01S 5/142: {which comprises an additional resonator}
- H01S 5/4006: {Injection locking}
- 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

The disclosed embodiments relate to a system that locks a wavelength of a hybrid laser to a wavelength of a reference laser, wherein a lasing cavity of the hybrid laser includes a reflective gain medium (RGM) comprising an optical gain material coupled with an associated reflector, a phase tuner, a laser ring filter and a silicon mirror. During operation, while the hybrid laser is turned off, the system tunes a reference ring filter to the wavelength of the reference laser. Next, the system turns on the hybrid laser. The system then tunes the laser ring filter in the hybrid laser to the reference ring filter. Finally, the system adjusts the phase tuner in the hybrid laser to align a lasing cavity mode of the hybrid laser with the tuned laser ring filter.

## Claims

### Claim 1

A method for locking a wavelength of a hybrid laser to a wavelength of a reference laser, comprising:
while the hybrid laser is turned off, tuning a reference ring filter to the wavelength of the reference laser;
turning on the hybrid laser, wherein a lasing cavity of the hybrid laser includes a reflective gain medium (RGM) comprising an optical gain material coupled with an associated reflector, a phase tuner, a laser ring filter and a silicon mirror;
tuning the laser ring filter in the hybrid laser to the reference ring filter; and
adjusting the phase tuner in the hybrid laser to align a lasing cavity mode of the hybrid laser with the tuned laser ring filter.

### Claim 2 (depends on 1)

The method of claim 1,
wherein the hybrid laser is part of an optical transmitter; and
wherein the reference ring filter comprises a ring modulator that modulates an optical signal based on an electrical input signal to produce an output for the optical transmitter.

### Claim 3 (depends on 1)

The method of claim 1, wherein the method further comprises periodically performing a continuous-calibration operation, which comprises:
turning on the reference laser;
measuring a first alignment between the reference laser and the reference ring filter;
turning off the reference laser;
adjusting a wavelength of the reference laser in an adjustment direction;
turning on the reference laser;
measuring a second alignment between the reference laser and the reference ring filter;
if the second alignment is closer than the first alignment, using the alignment direction in a subsequent continuous-calibration operation; and
if the second alignment is not closer than the first alignment, changing the adjustment direction for subsequent continuous-calibration operations.

### Claim 4 (depends on 1)

The method of claim 1, wherein the silicon mirror comprises a loop mirror.

### Claim 5 (depends on 1)

The athermal laser of claim 1, wherein the silicon mirror comprises a distributed Bragg reflector (DBR).

### Claim 6 (depends on 1)

The method of claim 1, wherein the silicon mirror is a tunable silicon mirror, which includes a thermal-tuning mechanism.

### Claim 7 (depends on 1)

The method of claim 1, wherein the hybrid laser further comprises a tuning waveguide that taps light from the silicon mirror and couples the tapped light to the reference ring filter to facilitate tuning the laser ring filter to the reference ring filter.

### Claim 8 (depends on 1)

The method of claim 1, wherein the reference ring filter and the laser ring filter have different radii, which creates a Vernier effect that facilitates tuning the laser ring filter to the reference ring filter.

### Claim 9 (depends on 1)

The method of claim 1, wherein the RGM is located on a gain chip that is separate from a silicon photonic chip, which includes the phase tuner, the laser ring filter and the silicon mirror.

### Claim 10 (depends on 1)

The method of claim 1, wherein the optical gain material comprises a III-V semiconductor.

### Claim 11

A hybrid laser, comprising:
a reflective gain medium (RGM) comprising an optical gain material coupled with an associated reflector;
a phase tuner coupled to an output of the RGM;
a laser ring filter coupled to an output of the phase tuner;
a silicon mirror optically coupled to the laser ring filter;
wherein the RGM, the phase tuner, the laser ring filter and the silicon mirror collectively form a lasing cavity for the hybrid laser;
a reference ring filter optically coupled to a reference laser and to the laser ring filter; and
a controller that controls the hybrid laser to lock a wavelength of the hybrid laser to a wavelength of the reference laser by performing the following operations,
while the hybrid laser is turned off, tuning the reference ring filter to the wavelength of the reference laser;
turning on the hybrid laser;
tuning the laser ring filter to the reference ring filter; and
adjusting the phase tuner to align a lasing cavity mode of the hybrid laser with the tuned laser ring filter.

### Claim 12 (depends on 11)

The hybrid laser of claim 11,
wherein the hybrid laser is part of an optical transmitter; and
wherein the reference ring filter comprises a ring modulator that modulates an optical signal based on an electrical input signal to produce an output for the optical transmitter.

### Claim 13 (depends on 11)

The hybrid laser of claim 11, wherein the controller additionally controls the hybrid laser to periodically perform a continuous-calibration operation, which comprises:
turning on the reference laser;
measuring a first alignment between the reference laser and the reference ring filter;
turning off the reference laser;
adjusting a wavelength of the reference laser in an adjustment direction;
turning on the reference laser;
measuring a second alignment between the reference laser and the reference ring filter;
if the second alignment is closer than the first alignment, using the alignment direction in a subsequent continuous-calibration operation; and
if the second alignment is not closer than the first alignment, changing the adjustment direction for subsequent continuous-calibration operations.

### Claim 14 (depends on 11)

The hybrid laser of claim 11, wherein the silicon mirror comprises a loop mirror.

### Claim 15 (depends on 11)

The athermal laser of claim 11, wherein the silicon mirror comprises a distributed Bragg reflector (DBR).

### Claim 16 (depends on 11)

The hybrid laser of claim 11, wherein the silicon mirror is a tunable silicon mirror, which includes a thermal-tuning mechanism.

### Claim 17 (depends on 11)

The hybrid laser of claim 11, wherein the hybrid laser further comprises a tuning waveguide that taps light from the silicon mirror and couples the tapped light to the reference ring filter to facilitate tuning the laser ring filter to the reference ring filter.

### Claim 18 (depends on 11)

The hybrid laser of claim 11, wherein the reference ring filter and the laser ring filter have different radii, which creates a Vernier effect that facilitates tuning the laser ring filter to the reference ring filter.

### Claim 19 (depends on 11)

The hybrid laser of claim 11, wherein the RGM is located on a gain chip that is separate from a silicon photonic chip, which includes the phase tuner, the laser ring filter and the silicon mirror.

### Claim 20

A system, comprising:
at least one processor;
at least one memory coupled to the at least one processor; and
a laser source for communicating optical signals generated by the system, wherein the laser source includes:
a reflective gain medium (RGM) comprising an optical gain material coupled with an associated reflector;
a phase tuner coupled to an output of the RGM;
a laser ring filter coupled to an output of the phase tuner;
a silicon mirror optically coupled to the laser ring filter;
wherein the RGM, the phase tuner, the laser ring filter and the silicon mirror collectively form a lasing cavity for the hybrid laser;
a reference ring filter optically coupled to a reference laser and to the laser ring filter; and
a controller that controls the hybrid laser to lock a wavelength of the hybrid laser to a wavelength of the reference laser by performing the following operations,
while the hybrid laser is turned off, tuning the reference ring filter to the wavelength of the reference laser;
turning on the hybrid laser;
tuning the laser ring filter to the reference ring filter; and
adjusting the phase tuner to align a lasing cavity mode of the hybrid laser with the tuned laser ring filter.