Polarization-Controlled Surface Grating VCSELs Under Externally Induced Anisotropic Strain

The polarization control of surface grating vertical-cavity surface-emitting lasers (VCSELs) is tested under externally applied anisotropic stress and is compared to that of a nominally identical standard VCSEL without a surface grating. This is done by bending the VCSEL chip in a well-defined way. The anisotropic in-plane strain thus induced in the VCSELs leads to a polarization switch of the standard VCSEL for rather moderate strain. In contrast, the polarization of the surface grating VCSELs is fixed by the grating and remains unchanged despite a high strain which causes a wavelength splitting of the two polarization modes of about 130 pm. Such a result is of high practical relevance, since strain is unavoidably induced during VCSEL fabrication and mounting and counteracts any method applied for polarization control.