Numerical analysis of photonic-crystal VCSELs

The introduction of a photonic-crystal to the VCSEL produces single mode emission in a very broad range of applied currents. The mechanism responsible for the discrimination of high-order modes originates from two counter-acting phenomena: 1) the PhC introduces lateral mode confinement through a strong waveguide effect and additionally by the Bragg reflections from a regular net of PhC holes 2) the holes of the PhC destroy the vertical periodicity of the DBR and contribute to the selective reduction in reflectivity of the mirror. As a result, the mode which overlaps the holes of the photonic crystal leaks through and becomes discriminated. We present numerical analysis of the influence of parameters of photonic crystal on the wavelength of emission, modal gain, slope efficiency, emitted power and tuning range in single mode VCSELs. We recognise several mechanisms determining high power emission in the single mode regime, which are: selective leakage, thermal focusing, waveguide effect induced by the photonic-crystal, gain spectrum red shift and its maximum reduction with increase of driving currents. We show that careful design of the photonic crystal allows for 10% increase in the emitted power of a singlemode regime and it allows for broad range of the steering currents from 5 to 50 mA. Such attributes support tuning of the single-mode emission over the 10 nm range of the spectrum.