Spontaneous-emission spectrum of the nonlasing supermodes in semiconductor laser arrays

It is shown that the interference between amplified spontaneous emission into the nonlasing supermode and the laser field of a semiconductor laser array causes spatial hole burning, which couples the dynamics of the amplified spontaneous emission with the laser field. In particular, phase locking between the amplified spontaneous emission and the lasing mode leads to the formation of a spectral triplet composed of in-phase relaxation oscillation sidebands and an out-of-phase line at the lasing frequency.