Measurements of mode partition noise of laser diodes

Power fluctuation of the longitudinal modes in laser diodes, a major source of mode partition noise, is analyzed and a mode partition coefficient, k, indicating the degree of mode fluctuations is defined. Two methods for measuring the mode partition coefficient k, a low-pass filter method and a sampling method, are demonstrated by measuring k for a proton-bombarded InGaAsP/InP strip laser, an InGaAsP/InP buried heterojunction laser, and a buried crescent heterojunction laser. It is shown that k decreases when the pulse width increases and saturates between 0.4 and 0.7 for narrowing pulses (1.4-5 ns).