Analysis of single-mode efficiency of electrically pumped VECSELs

Abstract

We present a model and results of simulations and experiments investigating the L-I characteristics of electrically pumped (EP-) VECSELs in the single- and multi-mode regime. In our model we use a mode expansion ansatz to treat the electromagnetic field inside the VECSEL cavity. The eigenmodes of the passive cavity are computed using the bidirectional beam propagation method (BDBPM) to solve the Helmholtz equation. The BDBPM allows us to account for the complex refractive index distribution within the semiconductor heterostucture, composed of approximately thousand interfaces along the optical axis in addition to lateral refractive index variations in oxide-confined devices as well as the macroscopic external cavity. We simulate the time evolution of the modal powers of several transverse modes and the spatial distribution of the inversion carriers in the quantum well plane. Therefore we solve an differential equation system composed of multimode rate equations and the carrier diffusion equation. With this ansatz we are able to identify cavity geometries suitable for single-mode operation assuming typical current profiles that are taken from photoluminescence measurements of the devices under investigation. Furthermore, we identify effects limiting the single-mode efficiency, such as poor gain and mode matching, reabsorption in unpumped regions of the quantum wells or enhanced carrier losses due to strong spatial hole burning. Critical parameters of the equations, such as optical losses, injection effciency, carrier recombination constants and gain parameters are obtained from experiments, microscopic models and literature. The simulation results are compared to experimental results from EP-VECSELs from Philips Technologie GmbH U-L-M Photonics

High power electrically pumped VECSELs and arrays

“…As has been described earlier [3] the carrier density is highest in the wings of the intensity distribution for single mode operation. While this region does not efficiently contribute to the laser mode (optical field is low at the rim) it suffers from high losses scaling with the carrier density squared (spontaneous emission) or to the third power (Auger).…”

“…In addition a longer cavity length and therefore a larger mode radius becomes possible as predicted in [3] for a material with lower losses.…”

Brightness and average power as driver for advancements in diode lasers and their applications

“…In order to identify crucial effects limiting the efficiency of singlemode VECSELs, a model has been developed to predict the L-I characteristics and the modal decomposition of electrically pumped VECSELs in dependence upon the heterostructure design and the external cavity configuration. A description of the model is presented in [16]. In close cooperation with accompanying experimental work, the tendencies observed in the laboratory, or favorable resonator geometries in dependence upon the quality of the epitaxial material, could be understood.…”

Electrically Pumped Vertical-External-Cavity Surface-Emitting Lasers With Patterned Tunnel Junction for Single Transversal-Mode Emission

“…of up to 4% [10][11][12]. E-VECSELs emitting at longer wavelengths in a range from 1450 to 1550 nm have not exceeded 2 mW of emitted power and wall-plug efficiencies of 1% in the single mode regime [7], [9], [13].…”