Gain characteristic of continuous-wave InGaN multiple quantum well laser diodes during life testing

A method to measure small changes in gain and distributed loss in laser dio des during life testing is described. The evolution of the gain spectrum wa s computed by measuring the true spontaneous emission spectrum and the lasi ng wavelength of the diode with time. This method was applied to investigat e the gain spectrum of InGaN multiple quantum well ridge waveguide laser di odes operating under continuous-wave (cw) conditions during diode life test ing. During lasing there were large changes in the light output power versu s current characteristic, but no significant change in the forward current- voltage characteristic. No catastrophic failure occurred; the light output power decreased continuously during life testing until the device stopped l asing under cw conditions. We observed an increase in pulsed threshold curr ent of 15(+/- 1)%, a decrease in gain at fixed current of 11(+/- 2)%, and a slight increase in the total optical losses of 4(+/- 2)%. These changes oc curred primarily while the device was lasing under cw conditions. (C) 2000 American Institute of Physics. [S0021-8979(00)10319-6].