In-situ bias voltage measurement of VCSELs
Systems, methods, and devices are described for in-situ testing of vertical-cavity surface-emitting lasers (VCSELs), VCSEL arrays or laser diodes (each a laser). Testing may comprise bias voltage measurements of one or more lasers. Embodiments may comprise one of a laser, a driver circuit providing a bipolar drive to the laser, and a sensing circuit to measure and/or monitor damage or degradation of the laser. The bipolar drive may comprise a pulsed forward bias output configured to produce a light output during an on-time of the laser, and a pulsed reverse bias output during an off-time of the pulsed forward bias output. The pulsed outputs may comprise a variable, chirped frequency. One or more of a reverse leakage current, and a junction temperature may be measured to monitor a state of health of the laser.
1. A system comprising:
a vertical cavity surface emitting laser (VCSEL);
a driver circuit including a bipolar drive configured to:
provide one or more forward bias pulses to the VCSEL for light output, and
provide one or more reverse bias pulses after providing the one or more forward bias pulses and after a settling time period,
wherein a largest reverse bias voltage that is configured to be applied to the VCSEL is equivalent to a ratio of a change in reverse bias current to a change in forward bias voltage; and
a sensing circuit configured to:
monitor damage or degradation of the VCSEL based on the one or more reverse bias pulses.
2. The system of claim 1 , wherein the sensing circuit is further configured to:
measure a reverse bias leakage current through the driver circuit during off-times of the one or more forward bias pulses.
3. The system of claim 1 , wherein the sensing circuit is further configured to:
monitor a reverse bias leakage current relative to a breakdown threshold.
4. The system of claim 1 , further comprising:
a control circuit configured to:
adjust current drive levels to the VCSEL; and
wherein the sensing circuit is further configured to:
provide feedback to the control circuit to enable the control circuit to adjust the current drive levels to extend a life of the VCSEL.
5. The system of claim 4 , wherein the feedback is based on at least one of a measured reverse bias leakage current or a measured junction temperature of the VCSEL.
6. The system of claim 1 , wherein the driver circuit is further configured to:
apply a voltage ramp up from a reverse bias breakdown voltage to an avalanche breakdown knee voltage to monitor a health state of the VCSEL.
7. The system of claim 1 , wherein the sensing circuit is further configured to:
measure a junction temperature of the VCSEL.
8. The system of claim 1 , further comprising:
a dedicated test fixture configured for acceptance testing of the VCSEL.
9. The system of claim 1 , wherein the one or more reverse bias pulses comprise a plurality of frequencies.
10. The system of claim 9 , wherein the plurality of frequencies are adjusted to optimize at least one of an optical power output or an optical pulse shape.
11. The system of claim 1 , wherein at least one of the one or more forward bias pulses and the one or more reverse bias pulses comprises a variable chirped frequency.
12. The system of claim 11 , wherein the variable chirped frequency is adjusted to optimize at least one of an optical power output and an optical pulse shape.
13. A method comprising:
applying, by a device and to a vertical cavity surface emitting laser (VCSEL), one or more forward bias pulses during an on-time of the VCSEL;
applying, by the device and to the VCSEL, one or more reverse bias pulses after applying the one or more forward bias pulses and after a settling time period,
wherein a largest reverse bias voltage that is applied to the VCSEL is equivalent to a ratio of a change in reverse bias current to a change in forward bias voltage; and
measuring, by the device at a sensing circuit, a reverse bias leakage current to monitor damage or degradation of the VCSEL.
14. The method of claim 13 , wherein the reverse bias leakage current is measured relative to a breakdown threshold.
15. The method of claim 13 , further comprising:
providing feedback to a control circuit to adjust current drive levels to extend a life of the VCSEL.
16. The method of claim 13 , further comprising:
applying a voltage ramp up from a reverse bias breakdown voltage to an avalanche breakdown knee voltage to monitor a health state of the VCSEL.
17. The method of claim 13 , further comprising:
measuring a junction temperature of the VCSEL.
18. The method of claim 17 , further comprising adjusting current drive levels based on the junction temperature.
19. The method of claim 13 , wherein at least one of the one or more forward bias pulses or the one or more reverse bias pulses comprises a variable chirped frequency.
20. The method of claim 19 , wherein the variable chirped frequency is adjusted to optimize at least one of an optical power output or an optical pulse shape.
21. The method of claim 19 , wherein the variable chirped frequency is used in a test mode to probe VCSEL impedance changes from at least one of environmental conditions, device damage, or aging.