Relative intensity noise of laser-diode arrays

Relative intensity noise in GaAs-GaAlAs semiconductor laser arrays was measured, compared with that in single-stripe lasers, and reviewed in the context of laser noise theory. When all the light is gathered and back reflections removed, all the arrays tested show comparable noise levels. Good agreement between theory and experiment is obtained for low drive currents where mode competition noise is relatively small. For low drive currents the noise is limited by the quantum noise, whereas for higher currents the noise saturates at about -145 dB/Hz under the best conditions, 10 dB below the level for a comparable single-stripe laser but 10 dB worse than for a single-mode distributed-feedback laser. The low noise in the array is explained quantitatively by considering the multiple transverse modes and the longer cavity length of the array.<>