Highly reliable operation under high case temperature in 638-nm BA-LD

We developed two types of 638-nm high-power broad area-laser diodes (BA-LDs). One was dual-emitter LD mainly for CW operation and the others triple one for pulse. Total emitter width of dual-emitter LD was 150 µm and that of triple one 180 µm. Each LD was studied in terms of optical power-current and wall plug efficiency (WPE)-current dependence on case temperature and reliability under the pulse condition with frequency of 120 Hz, and duty of 40%. The dual-emitter LD emitted 2.5 W at case temperature of 55 °C, whereas triple one did 2.1 W at the same condition. This was mainly originated from low heat generation of dual-emitter LD because of the narrow emitter width. On the contrary, the narrow emitter width increased the optical power density and shortened the lifetime. We discussed how to estimate the lifetime of light sources using red LDs which have multiple degradation modes under pulse operation. And then, we proposed a dulled drive current waveform for dual-emitter LD to improve a lifetime, resulting in MTTF exceeding 20,000 h at the output over 2 W under the pulse condition.