Why phtonic-crystal VCSELs do not provide high power emission in the single-mode regime?

Summary form only given. The introduction of a photonic-crystal (PhC) 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.The PhC introduces lateral mode confinement through a strong waveguide effect and additionally by the Bragg reflections from a regular net of PhC holes. 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. Carefully designed PhC supports strong discrimination of higher order modes. The injected current is converted into photons supplying fundamental mode only. Is it enough to achieve high power emission in single mode regime? We present numerical analysis based on rigorous simulation of the physical phenomena taking place in the device. We use multi-physical model, which comprises in the selfconsistent manner three-dimensional models of optical (Plane Wave Admittance Method), thermal, electrical and diffusion (Finite Element Method) phenomena.We investigate the influence of parameters of photonic crystal on the slope efficiency, emitted power and tuning range in single mode VCSELs. We recognize 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 (Fig. 1) 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. However such lasing parameters can be reached if the etching dept- is controlled in 100 nm precision (Fig. 2). The variations of the threshold gain within a single period of the DBR are governed by the light leakage when the bottom of the PhC holes coincides with the node of mode and scattering when the bottom of the PhC holes coincides with the antinode of mode.