Experimental Study of Transverse Mode Selection in VCSELs Induced by Parallel Polarized Optical Injection

Modal selection induced by parallel polarized optical injection is studied experimentally in a vertical-cavity surface-emitting laser (VCSEL) with emission in two transverse modes. We report that the selection of the fundamental transverse mode can be achieved when the two transverse modes have parallel polarizations. The selection of the fundamental mode is accompanied by locking of that mode to the optically injected signal for large enough values of the wavelength detuning between the fundamental mode and the externally injected signal. The injected power needed to induce modal selection grows as the VCSEL bias current is increased and exhibits a minimum with respect to the injection wavelength at a value ¿_min that is slightly longer than the wavelength of the fundamental mode of the solitary VCSEL. We also report that the selection process exhibits a bistable behaviour when the wavelength of optical injection increases beyond ¿_min. The width of the observed bistable region grows linearly with the wavelength of the optically injected signal. Selection of the higher order transverse mode is achieved when the optical injection wavelength is close to that of the higher order transverse mode. The qualitative behavior associated with the selection of the higher order mode is similar to that of the fundamental mode.