NASA’s Langley Research Center has developed a new technology for measuring the junction temperature of laser diode arrays (LDAs) that can support dramatically improved LDA fault analysis and lifetime estimates. This technology provides better spatial and temporal resolution than spectral chirp or thermal imaging methods, and can be integrated into existing LDA systems, such as laser diode drivers, without significant additional costs (including weight, power, and space). Potential applications include quality control and screening of LDAs for maximum lifetime, optimizing development of operational parameters, or providing real-time operational diagnostics/prognostics.
NASA’s forward voltage short-pulse technique provides a novel alternative means to measure LDA junction temperature. Laser diode systems contain a driver that provides nominal quasi-continuous wave pulses. In this technique, a second driver is used to provide precise pulses between operational pulses. This facilitates the accurate derivation of junction temperatures by precisely measuring the voltage of these second pulses. Furthermore, this technique uses small injections of current, and thus does not contribute to any heat cycling issues within the LDA.
Thermal cycling is a key mechanical stressor that can cause premature LDA failure. Competing technologies such as spectral chirp and thermal imaging do not provide the speed or spatial resolution to quickly locate hot spots at the junction of the LDA bars. Unlike those technologies, this technique can accurately measure the LDA thermal parameters, and with little cost, can be easily incorporated into the operation of existing LDAs for realtime junction temperature monitoring. This can facilitate the development of smart laser diode drivers that can adjust operating parameters to LDA conditions.
Accurate junction temperature for characterization and evaluation of LDAs can be used in telecommunications, material cutting and welding, military systems, pump sources for any solid-state laser, and the medical industry.