# US 10,483,718 B2 · Ultra-low noise, highly stable single-mode operation, high power, Bragg grating based semiconductor laser > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,483,718 B2 - Document ID: US10483718B2 - Status: Granted - Kind: B2 - Application number: 16/237,643 - Filed: 2018-12-31 - Published: 2019-05-23 - Granted: 2019-11-19 - Earliest claimed: 2016-08-22 - Assignees: Morton Photonics - Applicants: Morton Photonics, Inc. - Inventors: Paul Morton - Web page: https://patentgrep.com/patent/US10483718B2 ## CPC - H01S 5/146: {using a fiber as external cavity} - H01S 5/02415: {by using a thermo-electric cooler [TEC], e.g. Peltier element} - H01S 5/02438: {Characterized by cooling of elements other than the laser chip, e.g. an optical element being part of an external cavity or a collimating lens} - H01S 5/02476: {Heat spreaders, i.e. improving heat flow between laser chip and heat dissipating elements} - H01S 5/028: Coatings {; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers} - H01S 5/0612: {controlled by temperature} - H01S 5/0687: Stabilising the frequency of the laser - H01S 5/1039: {Details on the cavity length} - H01S 5/1225: {with a varying coupling constant along the optical axis} - H01S 5/125: Distributed Bragg reflector [DBR] lasers - H01S 5/141: {using a wavelength selective device, e.g. a grating or etalon (H01S5/146 takes precedence)} - G02B 6/02176: {due to temperature fluctuations} - G02B 6/4271: {with thermo electric cooling} - H01S 2301/163: Single longitudinal 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 - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A laser including: a gain chip; an external cavity incorporating a Bragg grating; and a baseplate; wherein a first end of the gain chip has a high reflectivity facet forming a first end of the laser cavity; a second end of the gain chip has a low reflectivity facet; and a second part of the external cavity comprises a Bragg grating, supported by the baseplate, the temperature of the baseplate being maintained through a feedback loop; wherein the optical length of the external cavity is at least an order of magnitude greater than the optical length of the gain chip; wherein the Bragg grating is physically long and occupies a majority of the length of the external cavity and is apodized to control the sidemodes of the grating reflection. ## Claims ### Claim 1 A laser comprising: a semiconductor gain chip to generate light; and a waveguide external cavity having a first end and a second end and including an integrated Bragg grating to reflect at least a portion of the light wherein a first end of the gain chip has a high reflectivity facet forming a first end of a laser cavity; a second end of the gain chip has a low reflectivity facet, allowing light generated from the gain chip to be coupled to the first end of the waveguide external cavity, wherein the physical length of the Bragg grating is greater than 20 mm and occupies at least 75% of the physical length of the waveguide external cavity. ### Claim 2 (depends on 1) The laser of claim 1, wherein the Bragg grating is apodized to control the sidemodes of the grating reflection. ### Claim 3 (depends on 1) The laser of claim 1, wherein the physical length of the Bragg grating is greater than 40 mm and occupies at least 75% of the physical length of the external cavity. ### Claim 4 (depends on 1) The laser of claim 1, wherein the optical length of the external cavity is at least an order of magnitude greater than the optical length of the gain chip. ### Claim 5 (depends on 1) The laser of claim 1, wherein the optical length of the external cavity is at least about twenty times the optical length of the gain chip. ### Claim 6 (depends on 1) The laser of claim 1, wherein the physical length of the gain chip is in the range of about 500 μm to 3 mm, and the physical length of the waveguide external cavity is more than about 40 mm. ### Claim 7 (depends on 1) The laser of claim 1, wherein the waveguide is made from Silicon or Silicon Nitride or Silica or other low loss waveguide material. ### Claim 8 (depends on 1) The laser of claim 1, further comprising a lens placed between the gain chip and the waveguide external cavity to increase a coupling efficiency between the gain chip and the waveguide external cavity. ### Claim 9 (depends on 1) The laser of claim 1, wherein the gain chip is modified to include a beam expander to increase a coupling efficiency between the gain chip and the waveguide. ### Claim 10 (depends on 1) The laser of claim 1, wherein the gain chip is attached to a first thermally conductive baseplate next to a first side of a trench in the baseplate while the Bragg grating is on a second side of the trench; wherein the temperature of the first thermally conductive baseplate being maintained through a feedback loop comprising a first thermo-electric cooler (TEC) and a first temperature sensor attached to the first thermally conductive baseplate; wherein heat generated by the gain chip creates a temperature variation along the length of the first thermally conductive baseplate; and wherein the Bragg grating includes a variation in grating pitch along its length to counteract the temperature variation created by the gain chip, such that a first long wavelength sidemode being suppressed in a reflection spectrum from the Bragg grating is maintained. ### Claim 11 (depends on 10) The laser of claim 10, wherein the first thermally conductive baseplate has a geometry that the temperature decreases linearly versus distance on the second side of the trench and the linear temperature variation of the Bragg grating is counteracted by a linear wavelength chirp in the Bragg grating, so that the overall effect is the suppression of the first long wavelength sidemode in the reflection spectrum from the Bragg grating. ### Claim 12 (depends on 10) The laser of claim 10, further comprising: at least a second thermally conductive baseplate on which the gain chip is mounted, wherein the external cavity waveguide end is mounted on the second baseplate adjacent to the second end of the gain chip; and at least a second temperature sensor placed next to the external cavity waveguide end; wherein the second temperature sensor provides feedback to a second TEC attached to the second thermally conductive baseplate, such that both the external cavity waveguide end and the rest of the external cavity waveguide are kept at the same temperature. ### Claim 13 (depends on 10) The laser of claim 10, further comprising: at least a second thermally conductive baseplate on which the gain chip is mounted, wherein the external cavity waveguide end is mounted on the second baseplate adjacent to the second end of the gain chip; wherein the external cavity waveguide comprises a non-grating section extending from a location within the first thermally conductive baseplate to the external cavity waveguide end. ### Claim 14 (depends on 13) The laser of claim 13, wherein the wavelength of the laser is tuned by adjusting the temperature of the Bragg grating on the first thermally conductive baseplate. ### Claim 15 (depends on 13) The laser of claim 13, wherein a temperature of the first thermally conductive baseplate is not actively controlled, rather is left to vary with a temperature of an external package containing the laser. ### Claim 16 (depends on 1) The laser of claim 1, wherein the Bragg grating is apodized using a Gaussian amplitude profile. ### Claim 17 (depends on 16) The laser of claim 16, wherein a sinusoidal chirp is further applied to the Bragg grating. ### Claim 18 (depends on 1) The laser of claim 1, wherein an output power of the laser is taken from the first end of the gain chip. ### Claim 19 (depends on 1) The laser of claim 1, further comprising a first monitor configured to measure light intensity as output power of the laser, and a second monitor configured to measure a back facet monitor (BFM) current representing light intensity from the high reflectivity facet of the gain chip, wherein a ratio of the BFM value to the output power is used provide a feedback signal for locking the laser to a specific position on the Bragg grating spectrum. ### Claim 20 (depends on 19) The laser of claim 19, wherein a fast feedback loop using the ratio of the BFM value to the output power is used to reduce the low frequency phase noise of the laser.