# US 9,438,005 B1 · Calibration of a tunable DBR laser > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,438,005 B1 - Document ID: US9438005B1 - Status: Granted - Kind: B1 - Application number: 14/293,604 - Filed: 2014-06-02 - Granted: 2016-09-06 - Earliest claimed: 2014-06-02 - Assignees: Google Inc. - Applicants: Google Inc. - Inventors: Xiangjun Zhao; Cedric Fung Lam; Steven Fong - Web page: https://patentgrep.com/patent/US9438005B1 ## CPC - H01S 5/06256: {with DBR-structure} - H01S 5/0014: {Measuring characteristics or properties thereof (measuring techniques per se G01J, G01K, G01N, G01R)} - H01S 5/0625: in multi-section lasers - H01S 5/06255: {Controlling the frequency of the radiation} - H01S 5/02415: {by using a thermo-electric cooler [TEC], e.g. Peltier element} - H01S 5/0617: {using memorised or pre-programmed laser characteristics} - H01S 5/06804: {by monitoring an external parameter, e.g. temperature} - H01S 5/125: Distributed Bragg reflector [DBR] lasers - 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 A method of calibrating a tunable laser having a distributed Bragg reflector includes, aligning a reflection peak of the distributed Bragg reflector with a target cavity mode of a plurality of cavity modes defined by a total optical path length inside a resonant cavity of the tunable laser. The method includes aligning a resultant lasing mode with a target wavelength of an output wavelength grid. The resultant lasing mode is formed by alignment of the reflection peak of the distributed Bragg reflector with the target cavity mode. The method also includes setting a target output power and a target extinction ratio of the tunable laser. ## Claims ### Claim 1 A method of calibrating a directly modulated tunable laser having a distributed Bragg reflector, the method comprising: aligning a reflection peak of the distributed Bragg reflector with a target cavity mode of a plurality of cavity modes defined by a total optical path length inside a resonant cavity defined by the distributed Bragg reflector, a phase section, and a gain section of the tunable laser, the aligning of the reflection peak comprising altering a temperature of the resonant cavity of the directly modulated tunable laser by a threshold temperature increment to shift a cavity frequency grid defined by the plurality of cavity modes to align with the reflection peak of the distributed Bragg reflector; aligning a resultant lasing mode with a target wavelength of an output wavelength grid, the resultant lasing mode formed by alignment of the reflection peak of the distributed Bragg reflector with the target cavity mode; and setting a target output power and a target extinction ratio of the tunable laser. ### Claim 2 (depends on 1) The method of claim 1, further comprising altering a bias current applied to the grating section of the tunable laser to align the reflection peak of the distributed Bragg reflector with the target cavity mode. ### Claim 3 (depends on 2) The method of claim 2, further comprising: monitoring the bias current; and storing the bias current in non-transitory memory when the reflection peak is aligned with the target cavity mode. ### Claim 4 (depends on 1) The method of claim 1, further comprising altering a temperature of the tunable laser to align the reflection peak of the distributed Bragg reflector with the target cavity mode. ### Claim 5 (depends on 4) The method of claim 4, further comprising: monitoring the temperature of the tunable laser; and storing the temperature in non-transitory memory when the reflection peak is aligned with the target cavity mode. ### Claim 6 (depends on 1) The method of claim 1, further comprising determining an offset between the resultant lasing mode and the target wavelength of the output wavelength grid. ### Claim 7 (depends on 1) The method of claim 1, further comprising altering a temperature of the tunable laser to align the resultant lasing mode with the target wavelength of the output wavelength grid. ### Claim 8 (depends on 1) The method of claim 1, further comprising monitoring an output power of an optical output of the tunable laser at each wavelength of an output wavelength grid while varying a modulation current delivered to the gain section of the tunable laser between a minimum modulation current and a maximum modulation current. ### Claim 9 (depends on 8) The method of claim 8, further comprising determining the modulation current of the gain section of the tunable laser based on a relationship between the output power of the tunable laser and the modulation current applied to the gain section. ### Claim 10 (depends on 9) The method of claim 9, further comprising determining the modulation current of the gain section of the tunable laser using: I mod = OMA S wherein Imodis the modulation current, OMA is an optical modulation amplitude, and S is a slope efficiency of the laser. ### Claim 11 (depends on 8) The method of claim 8, further comprising monitoring the output power of the tunable laser using a photodiode of the tunable laser. ### Claim 12 A method of calibrating a directly modulated tunable laser having a distributed Bragg reflector, the method comprising: aligning a reflection peak of the distributed Bragg reflector with a target cavity mode of a plurality of cavity modes defined by a total optical path length inside a resonant cavity defined by the distributed Bragg reflector, a phase section, and a gain section of the tunable laser; monitoring an optical output of the tunable laser while aligning the reflection peak of the distributed Bragg reflector with the target cavity mode to identify side modes of a resultant lasing mode formed by alignment of the reflection peak of the distributed Bragg reflector with the target cavity mode; aligning the resultant lasing mode with a target wavelength of an output wavelength grid; determining that the reflection peak is aligned with the target cavity mode when the neighboring side modes have equal amplitudes; and setting a target output power and a target extinction ratio of the tunable laser. ### Claim 13 A method of calibrating a directly modulated tunable laser having a distributed Bragg reflector, the method comprising: aligning a reflection peak of the distributed Bragg reflector with a target cavity mode of a plurality of cavity modes defined by a total optical path length inside a resonant cavity defined by the distributed Bragg reflector, a phase section, and a gain section of the tunable laser, the aligning of the reflection peak comprising: monitoring an output power of an optical output of the tunable laser at each wavelength of an output wavelength grid while varying a modulation current delivered to the gain section of the tunable laser between a minimum modulation current and a maximum modulation current; determining the modulation current of the gain section of the tunable laser based on a relationship between the output power of the tunable laser and the modulation current applied to the gain section, the modulation current of the gain section of the tunable laser determined as: I mod = OMA S wherein Imod is the modulation current, OMA is an optical modulation amplitude, and S is a slope efficiency of the laser; and altering a bias current applied to the grating section of the tunable laser to align the reflection peak of the distributed Bragg reflector with the target cavity mode, the bias current of the distributed Bragg reflector of the tunable laser determined as: I bias = I mod E ⁢ ⁢ R - 1 + I mod 2 + I th wherein Ibias is the bias current, Imod is the modulation current, ER is a desired extinction ratio of the laser, and Ith is a threshold current; aligning a resultant lasing mode with a target wavelength of an output wavelength grid, the resultant lasing mode formed by alignment of the reflection peak of the distributed Bragg reflector with the target cavity mode; and setting a target output power and a target extinction ratio of the tunable laser. ### Claim 14 A tunable laser calibration system comprising: a tunable laser comprising: a gain section; a distributed Bragg reflector optically connected with the gain section; and a power monitor optically connected to the gain section; and a controller in communication with the tunable laser, the controller comprising: non-transitory memory; and one or more data processing devices in communication with the non-transitory memory, the one or more data processing devices executing instructions configuring the one or more data processing devices to execute a calibration routine comprising: aligning a reflection peak of the distributed Bragg reflector with a target cavity mode of a plurality of cavity modes defined by a total optical path length inside a resonant cavity defined by the distributed Bragg reflector and the gain section of the tunable laser, the aligning of the reflection peak comprising altering a temperature of the resonant cavity of the directly modulated tunable laser by a threshold temperature increment to shift a cavity frequency grid defined by the plurality of cavity modes to align with the reflection peak of the distributed Bragg reflector; aligning a resultant lasing mode with a target wavelength of an output wavelength grid, the resultant lasing mode formed by alignment of the reflection peak of the distributed Bragg reflector with the target cavity mode; and setting a target output power and a target extinction ratio of the tunable laser. ### Claim 15 (depends on 14) The tunable laser calibration system of claim 14, wherein the power monitor comprises a photodiode. ### Claim 16 (depends on 14) The tunable laser calibration system of claim 14, wherein the calibration routine further comprises altering a bias current applied to the distributed Bragg reflector of the tunable laser to align the reflection peak of the distributed Bragg reflector with the target cavity mode. ### Claim 17 (depends on 16) The tunable laser calibration system of claim 16, wherein the calibration routine further comprises: monitoring the bias current; and storing the bias current in the non-transitory memory when the reflection peak is aligned with the target cavity mode. ### Claim 18 (depends on 14) The tunable laser calibration system of claim 14, wherein the calibration routine further comprises altering a temperature of the tunable laser to align the reflection peak of the distributed Bragg reflector with the target cavity mode. ### Claim 19 (depends on 18) The tunable laser calibration system of claim 18, wherein the calibration routine further comprises: monitoring the temperature of the tunable laser; and storing the temperature in the non-transitory memory when the reflection peak is aligned with the target cavity mode. ### Claim 20 (depends on 14) The tunable laser calibration system of claim 14, wherein the calibration routine further comprises determining an offset between the resultant lasing mode and the target wavelength of the output wavelength grid. ### Claim 21 (depends on 14) The tunable laser calibration system of claim 14, wherein the calibration routine further comprises altering a temperature of the tunable laser to align the resultant lasing mode with the target wavelength of the output wavelength grid. ### Claim 22 (depends on 14) The tunable laser calibration system of claim 14, wherein the calibration routine further comprises: monitoring an optical output of the tunable laser while aligning the reflection peak of the distributed Bragg reflector with a target cavity mode to identify adjacent side modes of the resultant lasing mode formed by alignment of the reflection peak of the distributed Bragg reflector with the target cavity mode; and determining that the reflection peak is aligned with the target cavity mode when the adjacent side modes have equal amplitudes. ### Claim 23 (depends on 14) The tunable laser calibration system of claim 14, wherein the calibration routine further comprises monitoring an output power of an optical output of the tunable laser at each wavelength of the output wavelength grid while varying a modulation current delivered to the gain section of the tunable laser between a minimum modulation current and a maximum modulation current. ### Claim 24 (depends on 23) The tunable laser calibration system of claim 23, wherein the calibration routine further comprises determining the modulation current of the gain section of the tunable laser based on a relationship between the output power of the tunable laser and the modulation current applied to the gain section. ### Claim 25 (depends on 24) The tunable laser calibration system of claim 24, wherein the calibration routine further comprises determining the modulation current of the gain section of the tunable laser using: I mod = OMA S wherein Imod is the modulation current, OMA is an optical modulation amplitude, and S is a slope efficiency of the laser. ### Claim 26 (depends on 25) The tunable laser calibration system of claim 25, wherein the calibration routine further comprises determining a bias current of the distributed Bragg reflector of the tunable laser using: I bias = I mod E ⁢ ⁢ R - 1 + I mod 2 + I th wherein Ibias is the bias current, Imod is the modulation current, ER is a desired extinction ratio of the laser, and Ith is a threshold current. ### Claim 27 (depends on 23) The tunable laser calibration system of claim 23, wherein monitoring the output power of the tunable laser comprises monitoring the output power using a photodiode of the tunable laser.