# US 2021/0242660 A1 · Laser driver pulse shaping control > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0242660 A1 - Document ID: US20210242660A1 - Status: Published application - Kind: A1 - Application number: 16/780,761 - Filed: 2020-02-03 - Published: 2021-08-05 - Earliest claimed: 2020-02-03 - Assignees: Analog Devices International Unlimited Company - Applicants: Analog Devices International Unlimited Company - Inventors: Jonathan Ephraim David Hurwitz; Davide Portaluppi - Web page: https://patentgrep.com/patent/US20210242660A1 ## CPC - H01S 5/0428: {for applying pulses to the laser} - H01S 5/06835: {Stabilising during pulse modulation or generation} - G01S 7/484: Transmitters - G01S 7/4865: Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak (peak detection in noise, signal conditioning G01S7/487) - G01S 7/497: Means for monitoring or calibrating - G01S 17/10: using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) - G01S 17/894: Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar - H01S 5/0035: {Simulations of laser characteristics} - H01S 5/183: having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] - H01S 5/06216: {Pulse modulation or generation} - 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 Time-of-flight (ToF) systems which use pulsed laser diodes, are required to measure distances with high level of precision and control. The present disclosure provides a method and a corresponding system for controlling a temporal response of a laser diode, in particular pulsed laser diodes. In particular, the present disclosure provides a method and a related system for driving a laser diode so as to obtain predominantly a peak pulse response while minimising or completely avoiding the post-peak response in a temporal response of the laser diode. ## Claims ### Claim 1 A method of determining a duration, Tdr, for a laser drive signal, to minimise post-peak response in a temporal response of a laser diode driven by the laser drive signal, the method comprising: iteratively: applying a test laser drive signal having a test duration, Tt, to the laser diode; and monitoring an output of a photodetector, wherein the output is indicative of an energy of a light pulse output by the laser diode in response to the application of the test drive signal; varying the test duration, Tt, of the test drive signal with successive iterations; and determining the duration, Tdr, based on the monitoring of the output of the photodetector in successive iterations. ### Claim 2 (depends on 1) A method according to claim 1, wherein the test duration, Tt, of the test drive signal is increased between successive iterations. ### Claim 3 (depends on 1) A method according to claim 1, wherein the test duration, Tt, of the test drive signal is decreased between successive iterations. ### Claim 4 (depends on 1) A method according to claim 1, wherein determining the duration, Tdr, based on the monitoring of the output of the photodetector in successive iterations comprises: identifying, from the monitored output of the photodetector, a first post-peak minimum in the said temporal response of the laser diode; and setting the duration, Tdr, to be the test duration, Tt, corresponding to the identified first post-peak minimum. ### Claim 5 (depends on 4) A method according to claim 4, wherein monitoring of the output of the photodetector comprises: integrating the output of the photodetector to determine an accumulated value indicative of the cumulative light output of the laser diode in response to the application of the test drive signal. ### Claim 6 (depends on 5) A method according to claim 5, wherein identifying the first post-peak minimum in the said temporal response of the laser diode comprises: determining a rate of change of the accumulated value between successive iterations; and comparing the determined rate of change with a previously determined rate of change in an iteration immediately preceding the current iteration. ### Claim 7 (depends on 1) A method according to claim 1, wherein determining the duration, Tdr, based on the monitoring of the output of the photodetector in successive iterations comprises: determining a lasing delay, wherein the lasing delay is a minimum test duration, Ttmin, required to detect a light pulse output by the laser diode; and determining the said duration, Tdr, based on the lasing delay and a predetermined duration Tp of the light pulse output by the laser. ### Claim 8 (depends on 7) A method according to claim 7, further comprising: comparing the determined lasing delay against one or more previously determined lasing delays for the laser diode, to check the condition of the laser diode. ### Claim 9 (depends on 1) A method according to claim 1, further comprising: comparing the determined determining the duration, Tdr against one or more previously determined durations, Tdr for the laser diode, to check the condition of the laser diode. ### Claim 10 A control unit for determining a duration, Tdr, for a laser drive signal, to minimise post-peak power in a temporal response of a laser diode driven by the laser drive signal, and comprising an input for coupling to an output of a photodetector, and an output for coupling to an input of the laser diode, wherein the control unit is configured to: iteratively: apply a test laser drive signal having a test duration, Tt, to the laser diode; and monitor an output of the photodetector, wherein the output is indicative of an energy of a light pulse output by the laser diode in response to the application of the test drive signal; vary the test duration, Tt, of the test drive signal with successive iterations; and determine the duration, Tdr, based on the monitoring of the output of the photodetector in successive iterations. ### Claim 11 (depends on 10) A control unit according to claim 10, wherein the control unit is configured to increase the test duration, Tt, of the test drive signal between successive iterations. ### Claim 12 (depends on 10) A control unit according to claim 10, wherein the control unit is configured to decrease the test duration, Tt, of the test drive signal between successive iterations. ### Claim 13 (depends on 10) A control unit according to claim 10, wherein the control unit is configured to: identify, from the monitored output of the photodetector, a first post-peak minimum in the said temporal response of the laser diode; and set the duration, Tdr, to be the test duration, Tt, corresponding to the identified first post-peak minimum. ### Claim 14 (depends on 13) A control unit according to claim 13, wherein the control unit comprises: an integrator configured to receive the output of the photodetector and integrate the output of the photodetector to determine an accumulated value indicative of the cumulative light output of the laser diode in response to the application of the test drive signal. ### Claim 15 (depends on 14) A control unit according to claim 14, wherein the control unit is configured to: determine a rate of change of the accumulated value between successive iterations; and compare the determined rate of change with a previously determined rate of change in a previous iteration immediately preceding the current iteration in order to identify the first post-peak minimum in the said temporal response of the laser diode. ### Claim 16 (depends on 10) A control unit according to claim 10, wherein the control unit is configured to: determine a lasing delay, wherein the lasing delay is a minimum test duration, Ttmin, required to detect a light pulse output by the laser diode; and determine the said duration, Tdr, based on the lasing delay and a predetermined duration Tp of the light pulse output by the laser. ### Claim 17 (depends on 10) A control unit according to claim 10, further configured to compare the determined determining the duration, Tdr against one or more previously determined durations, Tdr for the laser diode, to check the condition of the laser diode. ### Claim 18 A system for determining a duration, Tdr, for a laser drive signal, to minimise post-peak response in a temporal response of a laser diode driven by the laser drive signal, the system comprising: a laser diode; a photodetector; a control unit to the laser diode and the photodetector, wherein the control unit is configured to: iteratively: apply a test laser drive signal having a test duration, Tt, to the laser diode; and monitor an output of a photodetector, wherein the output is indicative of an energy of a light pulse output by the laser diode in response to the application of the test drive signal; vary the test duration, Tt, of the test drive signal with successive iterations; and determine the duration, Tdr, based on the monitoring of the output of the photodetector in successive iterations. ### Claim 19 (depends on 18) A system according to claim 18 wherein the laser diode is a pulsed laser diode. ### Claim 20 (depends on 18) A system according to claim 18 wherein the laser diode is a vertical cavity surface emitting laser diode (VCSEL).