Anomalous polarization characteristics of 1.3-μm InGaAsP buried heterostructure lasers

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Abstract
The stimulated emission from lasers with a linear light‐current characteristic is polarized in the TE mode. For some lasers with a kink in the L‐I curve, the kink represents the onset of a higher order TM polarized stimulated emission. Both TE and TM modes are present above the kink. These TE and TM emissions usually have separate groups of longitudinal modes. Under pulsed operation, the TE mode appears before the TM mode. X‐ray diffraction measurements suggest the presence of an internal stress in lasers exhibiting stimulated TM emission. A possible explanation for the observation is discussed. The mechanism is based on (i) higher optical gain of the TM mode than that of the TE mode in the presence of a compressive stress and (ii) larger reflectivity of the higher order TM modes. The power output at which a kink appears can be increased by decreasing the active layer width.