VCSEL structures used to suppress higher-order transverse modes

Abstract

Currently unwanted excitation of higher-order transverse modes is the most serious drawback of vertical-cavity surface-emitting diode lasers (VCSELs) limiting their possible applications. In the present paper, various methods used to suppress those modes are described and their effectiveness is compared. It is well known that, because of a nearly uniform current injection into their active regions, small-aperture VCSELs without any modification offer quite high single-fundamental-mode (SFM) output. However, their series resistance is often too high, which aggravates their high-modulation performance. Similarly uniform current injection may be also achieved with the aid of a tunnelling junction. Generally, methods suppressing higher-order modes take advantage of higher optical gain within the central part of the active region, higher radiation losses outside this region and/or higher central mirror reflectivity. Currently, applications of a tunnel junction, an impurity-induced disordering or an inverted shallow surface relief seem to be the simplest and the most effective methods. The deep etched holey structure or the ARROW structure enable obtaining similar single-mode output powers but they may be used in special cases only because of their complex technology. Photonic crystals may probably enable more advanced mechanisms of suppressing higher-order modes in future because currently their application seems to be still far from being optimised.

Thermal management of GaInNAs/GaAs VECSELs

“…EELs may emit very intense high−power radiation of the order of many watts, but their output beams contain many longitudi− nal modes and are very divergent, with astigmatism effects [1]. On the other hand, VCSELs emit low−divergent circu− larly symmetric output beams without astigmatism, but their single−mode emission is limited to relatively low output power of the order of a few milliwatts [2]. New optically pumped vertical−external−cavity surface−emitting lasers (VECSELs), also known as semiconductor disk lasers (SDLs), combine simultaneously advantages of both above laser types, e.g., they may emit high−power radiation with high−quality output beams.…”

Demonstration of III-nitride vertical-cavity surface-emitting lasers with a topside dielectric curved mirror

“…However, it is possible that the higher order transverse modes are caused by non-uniform current injection into the active region due to non-uniform activation of the IIA TJ, an issue exacerbated by the wider 10 μm current aperture. 35,36) The pits are also the current theory as to why the threshold current densities for the reported VCSEL are higher than what was achieved by the authors with pulsed operation of the GaN lens VCSEL (6.7 kA cm −2 ), 25) despite the reduction in regrowth time. Regardless, the pitting in the lenses is a subject of immediate study, with the goal of total removal from future dielectric lens processing.…”

Power‐scaling properties of apertured microchip vertical external‐cavity surface‐emitting lasers

“…difficult to fabricate. The aperture‐based alternative is conceptually similar to oxide‐aperture or surface‐relief vertical‐cavity surface‐emitting lasers [8] but has only incidently been reported in [6] for devices with hundreds‐of‐wavelengths‐long cavities.…”