# US 12,763,549 B2 · Wavelength bandwidth expansion for tuning or chirping with a silicon photonic external cavity tunable laser

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- Number: US 12,763,549 B2
- Document ID: US12763549B2
- Status: Granted
- Kind: B2
- Application number: 17/962,137
- Filed: 2022-10-07
- Published: 2023-04-13
- Granted: 2026-10-13
- Earliest claimed: 2021-10-08
- Assignees: Lumentum Operations LLC
- Applicants: NeoPhotonics Corporation
- Inventors: Ergun Canoglu; Mark J. Dayel; Robert A. Carney; David J. Dougherty
- Web page: https://patentgrep.com/patent/US12763549B2

## CPC

- 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 5/0612: {controlled by temperature}
- H01S 5/1007: {Branched waveguides}
- H01S 5/142: {which comprises an additional resonator}
- G01S 7/4814: {of transmitters alone}
- 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
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

An external cavity diode laser has been developed to achieve a linear frequency chirp over a broad bandwidth using a silicon photonic filter chip as the external cavity. By appropriately chirping the cavity phase using the gain chip and/or a cavity phase modulator on the silicon photonic chip along with simultaneously varying the filter resonance, approximately linear frequency chirping can be accomplished for at least 50 GHz, although desirable structures with useful lesser chirp bandwidths are also described. With careful control of the chip design, it is possible to achieve predictable behavior of mode jumps along with large scannable ranges within a mode, which allows for stitching together segments of linear chirp through a mode jump to provide for very large chirp bandwidths greater than 1 THz.

## Claims

### Claim 1

A tunable solid-state laser device comprising:
a semiconductor-based gain chip; and
a silicon photonic filter chip with tuning capability,
wherein the silicon photonic filter chip comprises:
a connection silicon waveguide,
a heater interfaced with the connection silicon waveguide,
at least two ring resonators formed with silicon waveguides,
one or more interfacing silicon waveguides coupled with the at least two ring resonators, and
a respective heater associated with each ring resonator of the at least two ring resonators,
wherein the one or more interfacing silicon waveguides are configured to redirect light resonant with each of the at least two ring resonators back through the connection silicon waveguide,
wherein a chirp signal is sent simultaneously to the respective heater associated with each ring resonator to extend a chirped bandwidth,
wherein the at least two ring resonators are designed to have the same thermal properties such that a single signal can provide for a synchronized chirp of the at least two ring resonators,
wherein a cavity phase is modulated using:
a controller configured to adjust a driving power to the semiconductor-based gain chip;
a cavity phase modulator on the silicon photonic filter chip; or
both the controller and the cavity phase modulator,
wherein the connection silicon waveguide of the silicon photonic filter chip is coupled to the semiconductor-based gain chip with a spot size converter to provide for mode size matching to reduce loss due to an interface between the connection silicon waveguide and the semiconductor-based gain chip, and
wherein chirping a voltage of the heater interfaced with the connection silicon waveguide chirps a laser output frequency.

### Claim 2 (depends on 1)

The tunable solid-state laser device of claim 1,
wherein the chirp signal is further sent simultaneously to the heater interfaced with the connection silicon waveguide, and
wherein the single signal can provide for the synchronized chirp by designing an adjustment signal of the cavity phase modulator to have the same response as the at least two ring resonators.

### Claim 3 (depends on 1)

The tunable solid-state laser device of claim 1, wherein the chirp signal is further sent simultaneously to the semiconductor-based gain chip.

### Claim 4 (depends on 1)

The tunable solid-state laser device of claim 1,
wherein the one or more interfacing silicon waveguides are two interfacing silicon waveguides that branch at a splitter/coupler connected to the connection silicon waveguide,
wherein each interfacing silicon waveguide, of the one or more interfacing silicon waveguides, is coupled to a respective ring resonator of the at least two ring resonators, and
wherein the tunable solid-state laser device further comprises a coupling element configured to couple to the at least two ring resonators while reversing a direction of light propagation relative to the semiconductor-based gain chip.

### Claim 5 (depends on 4)

The tunable solid-state laser device of claim 4,
wherein the silicon photonic filter chip further comprises a distal coupler and a lasing waveguide connected to the distal coupler,
wherein the one or more interfacing silicon waveguides are configured to connect to the distal coupler, and
wherein the distal coupler is configured to couple respective optical signals of the one or more interfacing silicon waveguides in an interfering configuration with lasing output transmitted from the lasing waveguide.

### Claim 6 (depends on 1)

The tunable solid-state laser device of claim 1, wherein the semiconductor-based gain chip comprises indium phosphide.

### Claim 7 (depends on 1)

The tunable solid-state laser device of claim 1,
wherein the at least two ring resonators comprise one or more widened silicon waveguide segments between single mode waveguides, and
wherein the respective heater associated with each ring resonator is located at least in part at or near the one or more widened silicon waveguide segments.

### Claim 8 (depends on 1)

The tunable solid-state laser device of claim 1, wherein the connection silicon waveguide comprises a widened waveguide segment connected with a single mode waveguide segment and the cavity phase modulator.

### Claim 9 (depends on 8)

The tunable solid-state laser device of claim 8, wherein the widened waveguide segment is curved.

### Claim 10 (depends on 1)

The tunable solid-state laser device of claim 1, wherein the cavity phase modulator and the respective heater associated with each ring resonator are designed for adjusting a current simultaneously to the respective heater associated with each ring resonator and to the heater interfaced with the connection silicon waveguide to chirp the laser output frequency.

### Claim 11 (depends on 10)

The tunable solid-state laser device of claim 10, wherein a linear variation of heater power provides a linear laser frequency chirp.

### Claim 12 (depends on 10)

The tunable solid-state laser device of claim 10, further comprising:
a temperature sensor configured to measure a temperature of the silicon photonic filter chip; and
a controller connected to the temperature sensor.

### Claim 13 (depends on 12)

The tunable solid-state laser device of claim 12,
wherein a baseline current is supplied to the respective heater associated with each ring resonator and to the heater interfaced with the connection silicon waveguide, and
wherein the baseline current is distinct from the current to chirp the laser output frequency.

### Claim 14 (depends on 10)

The tunable solid-state laser device of claim 10, further comprising a tap connected to the connection silicon waveguide and directed to an optical device for evaluating frequency and phase shift.

### Claim 15 (depends on 14)

The tunable solid-state laser device of claim 14, wherein a plurality of chirped frequency ranges are sequentially obtained over staggered frequency ranges to form an extended stitched chirped range.

### Claim 16 (depends on 1)

A high-resolution fast-response light detection and ranging (LIDAR) imaging system comprising:
an imaging system comprising a transmitter and a receiver configured to receive reflected light,
wherein the transmitter projects light in a plurality of directions to assemble a three-dimensional image of objects in a field of view of the imaging system, and
wherein the transmitter comprises the tunable solid-state laser device of claim 1.

### Claim 17

A tunable solid-state laser device comprising:
a semiconductor-based gain chip; and
a silicon photonic filter chip with tuning capability,
wherein the silicon photonic filter chip comprises:
a connection silicon waveguide,
a heater interfaced with the connection silicon waveguide,
at least two ring resonators formed with silicon waveguides,
one or more interfacing silicon waveguides coupled with the at least two ring resonators, and
a respective heater associated with each ring resonator of the at least two ring resonators,
wherein a chirp signal is sent simultaneously to the respective heater associated with each ring resonator to extend a chirped bandwidth,
wherein the at least two ring resonators are designed to have the same thermal properties such that a single signal can provide for a synchronized chirp of the at least two ring resonators,
wherein the connection silicon waveguide of the silicon photonic filter chip is coupled to the semiconductor-based gain chip with a spot size converter to provide for mode size matching to reduce loss due to an interface between the connection silicon waveguide and the semiconductor-based gain chip, and
wherein chirping a voltage of the heater interfaced with the connection silicon waveguide chirps a laser output frequency.

### Claim 18 (depends on 17)

The tunable solid-state laser device of claim 17, wherein the chirp signal is further sent simultaneously to the semiconductor-based gain chip.

### Claim 19 (depends on 17)

The tunable solid-state laser device of claim 17, wherein the chirp signal is further sent simultaneously to the heater interfaced with the connection silicon waveguide.

### Claim 20 (depends on 17)

The tunable solid-state laser device of claim 17,
wherein the at least two ring resonators comprise one or more widened silicon waveguide segments between single mode waveguides, and
wherein the respective heater associated with each ring resonator is located at least in part at or near the one or more widened silicon waveguide segments.

### Claim 21

A tunable solid-state laser device comprising:
a semiconductor-based gain chip; and
a silicon photonic filter chip with tuning capability,
wherein the silicon photonic filter chip comprises:
a connection silicon waveguide coupled to the semiconductor-based gain chip,
a heater interfaced with the connection silicon waveguide,
at least two ring resonators formed with silicon waveguides,
one or more interfacing silicon waveguides coupled with the at least two ring resonators, and
a respective heater associated with each ring resonator of the at least two ring resonators,
wherein the one or more interfacing silicon waveguides are configured to redirect light resonant with each of the at least two ring resonators back through the connection silicon waveguide,
wherein a chirp signal is sent simultaneously to the respective heater associated with each ring resonator to extend a chirped bandwidth,
wherein the at least two ring resonators are designed to have the same thermal properties such that a single signal can provide for a synchronized chirp of the at least two ring resonators,
wherein a cavity phase is modulated using:
a controller configured to adjust a driving power to the semiconductor-based gain chip;
a cavity phase modulator on the silicon photonic filter chip; or
both the controller and the cavity phase modulator, and
wherein chirping a voltage of the heater interfaced with the connection silicon waveguide chirps a laser output frequency.

### Claim 22 (depends on 21)

The tunable solid-state laser device of claim 21, wherein the chirp signal is further sent simultaneously to the semiconductor-based gain chip.

### Claim 23 (depends on 21)

The tunable solid-state laser device of claim 21, wherein the chirp signal is further sent simultaneously to the heater interfaced with the connection silicon waveguide.

### Claim 24 (depends on 21)

The tunable solid-state laser device of claim 21,
wherein the at least two ring resonators comprise one or more widened silicon waveguide segments between single mode waveguides, and
wherein the respective heater associated with each ring resonator is located at least in part at or near the one or more widened silicon waveguide segments.