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

Abstract

A method to measure small changes in gain and distributed loss in laser diodes during life testing is described. The evolution of the gain spectrum was computed by measuring the true spontaneous emission spectrum and the lasing wavelength of the diode with time. This method was applied to investigate the gain spectrum of InGaN multiple quantum well ridge waveguide laser diodes operating under continuous-wave (cw) conditions during diode life testing. During lasing there were large changes in the light output power versus 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 lasing under cw conditions. We observed an increase in pulsed threshold current 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 occurred primarily while the device was lasing under cw conditions.