# US 10,873,173 B1 · Reducing back reflection in hybrid lasers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,873,173 B1 - Document ID: US10873173B1 - Status: Granted - Kind: B1 - Application number: 16/438,572 - Filed: 2019-06-12 - Published: 2020-12-17 - Granted: 2020-12-22 - Earliest claimed: 2019-06-12 - Assignees: Elenion Technologies, LLC - Applicants: Elenion Technologies, LLC - Inventors: Hang Guan; Yang Liu; Ran Ding; Andreas Weirich; Michael J. Hochberg - Web page: https://patentgrep.com/patent/US10873173B1 ## CPC - H01S 3/2375: {Hybrid lasers (H01S3/07 takes precedence)} - H01S 5/142: {which comprises an additional resonator} - G02B 6/1228: {Tapered waveguides, e.g. integrated spot-size transformers (for coupling with fibres G02B6/305)} - G02B 6/126: using polarisation effects {(G02B6/1226 takes precedence)} - G02B 6/14: Mode converters - G02B 6/30: for use between fibre and thin-film device - H01S 3/063: Waveguide lasers, {i.e. whereby the dimensions of the waveguide are of the order of the light wavelength (waveguide gas lasers H01S3/0315)} - G02B 2006/12152: {Mode converter} - G02B 2006/12195: {Tapering} - H01S 5/0287: {Facet reflectivity} - H01S 5/101: {Curved waveguide (H01S5/1243 takes precedence)} - H01S 2301/02: ASE (amplified spontaneous emission), noise; Reduction thereof - 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 In conventional hybrid lasers large back refection may lead to a degradation of relative intensity noise (RIN), linewidth broadening, mode hopping, etc. To solve the aforementioned problem a hybrid laser includes a mode converter for converting a higher-back-reflection mode of the light to a mode providing less back reflection to the gain chip. The mode converter may comprise a polarization rotator, a waveguide converter, or high-order mode converter. A routing waveguide may be provided including a phase shifter, e.g. a doped waveguide, for adjusting a cavity length of the laser cavity. ## Claims ### Claim 1 A hybrid laser comprising: a gain chip including a gain medium for generating and amplifying light; a first reflector optically coupled to the gain medium for reflecting at least a first portion of the light back through the gain medium; a photonic integrated circuit (PIC) chip comprising: an edge coupler for transmitting the light between the gain chip and a device layer on the PIC chip; a mode converter for converting a mode of the light to a mode providing less back reflection for light traveling back and forth within the PIC chip; a routing waveguide extending from the mode converter; and a second reflector coupled to the routing waveguide for reflecting at least a second portion of the light back to the gain medium forming a laser cavity with the first reflector; and an output port coupled to the first or second reflector for outputting laser light; wherein the mode converter comprises a waveguide converter for converting a ridge waveguide to a rib waveguide; and wherein the routing waveguide comprises the rib waveguide, comprising a wider lower slab region and a narrower upper ridge region. ### Claim 2 (depends on 1) The hybrid laser according to claim 1, wherein the routing waveguide includes a phase shifter for adjusting a laser cavity length of the laser cavity. ### Claim 3 (depends on 2) The hybrid laser according to claim 2, wherein the phase shifter comprises a doped waveguide; and further comprising a controller capable of applying a bias voltage to the doped waveguide. ### Claim 4 (depends on 1) The hybrid laser according to claim 1, wherein the edge coupler comprises a spot-size converter extending from the gain medium for reducing a mode size of the light exiting the gain medium. ### Claim 5 (depends on 4) The hybrid laser according to claim 4, wherein the edge coupler extends at an acute angled from a normal from the gain chip to reduce back reflection into the gain medium. ### Claim 6 A hybrid laser comprising: a gain chip including a gain medium for generating and amplifying light; a first reflector optically coupled to the gain medium for reflecting at least a first portion of the light back through the gain medium; a photonic integrated circuit (PIC) chip comprising: an edge coupler for transmitting the light between the gain chip and a device layer on the PIC chip; a mode converter for converting a mode of the light to a mode providing less back reflection for light traveling back and forth within the PIC chip; a routing waveguide extending from the mode converter; a second reflector coupled to the routing waveguide for reflecting at least a second portion of the light back to the gain medium forming a laser cavity with the first reflector; and an output port coupled to the first or second reflector for outputting laser light; wherein the mode converter comprises a polarization rotator comprising a bent and tapered optical waveguide polarization rotator. ### Claim 7 (depends on 6) The hybrid laser according to claim 6, wherein the polarization rotator is for converting between a TE0 mode and a TM0 mode. ### Claim 8 (depends on 6) The hybrid laser according to claim 6, wherein the polarization rotator comprises a high-order mode converter selected from the group consisting of a TM0-to-TE1 mode converter, and a TE0-to-TE1 mode converter. ### Claim 9 A hybrid laser comprising: a gain chip including a gain medium for generating and amplifying light; a first reflector optically coupled to the gain medium for reflecting at least a first portion of the light back through the gain medium; a photonic integrated circuit (PIC) chip comprising: an edge coupler for transmitting the light between the gain chip and a device layer on the PIC chip; a mode converter for converting a mode of the light to a mode providing less back reflection for light traveling back and forth within the PIC chip; a routing waveguide extending from the mode converter; a second reflector coupled to the routing waveguide for reflecting at least a second portion of the light back to the gain medium forming a laser cavity with the first reflector; and an output port coupled to the first or second reflector for outputting laser light; wherein the mode converter comprises a waveguide converter for converting a ridge waveguide to a bus waveguide; and wherein the routing waveguide comprises the a bus waveguide. ### Claim 10 (depends on 9) The hybrid laser according to claim 9, wherein the waveguide converter expands in width from a first end having a first width a same as the ridge waveguide to a second end having a second width a same as the bus waveguide, which is at least twice the first width of the first end. ### Claim 11 (depends on 9) The hybrid laser according to claim 9, wherein the waveguide converter comprises a gradually tapering waveguide which expands from 400 μm to 500 μm wide to between 800 μm to 1200 μm wide. ### Claim 12 (depends on 1) The hybrid laser according to claim 1, wherein the waveguide converter includes a slab region expanding in width from a first end having a first width a same as the ridge waveguide to a second end having a second width a same as the slab region of the routing waveguide, which is at least twice the first width of the first end. ### Claim 13 (depends on 1) The hybrid laser according to claim 1, wherein the waveguide converter comprises a tapering slab region, which gradually expands from 400 μm to 500 μm wide to between 800 μm to 1200 μm wide. ### Claim 14 (depends on 1) The hybrid laser according to claim 1, wherein the PIC chip includes a trench for receiving the gain chip. ### Claim 15 (depends on 1) The hybrid laser according to claim 1, wherein the first reflector comprises a reflective facet of the gain chip. ### Claim 16 (depends on 1) The hybrid laser according to claim 1, wherein the first reflector is <95% reflective to selected wavelengths in the light. ### Claim 17 (depends on 1) The hybrid laser according to claim 1, wherein the second reflector is between 30% and 90% reflective to selected wavelengths in the light. ### Claim 18 (depends on 17) The hybrid laser according to claim 17, wherein the second reflector comprises a reflector selected from the group consisting of a single ring reflector, a Sagnac loop mirror, a Vernier ring reflector, a distributed Bragg reflector, and a distributed feedback reflector. ### Claim 19 (depends on 17) The hybrid laser according to claim 17, wherein the output port is coupled to the second reflector.