Impact of an Antiresonant Oxide Island on the Lasing of Lateral Modes in VCSELs

Abstract

Use of antiresonant structures is a proven, efficient method of improving lateral mode selectivity in VCSELs. In this paper, we analyze the impact of a low-refractive antiresonant oxide island buried in a top VCSEL mirror on the lasing conditions of lateral modes of different orders. By performing comprehensive thermal, electrical, and optical numerical analysis of the VCSEL device, we show the impact of the size and location of the oxide island on the current-crowding effect and compute threshold currents for various lateral modes. If the island is placed close to the cavity, the threshold shows strong oscillations, which for moderate island distances can be tuned to increase the side mode discrimination. We are therefore able to pinpoint the most important factors influencing mode discrimination and to identify oxide island parameters capable of providing single-lateral-mode emission.

Increasing Single-Mode Power in VCSELs With Antiresonant Oxide Island

“…For low island sizes, the modes have a tendency to focus on the high-effective-index region outside its radius, while with larger islands they are confined within it. Later, we have shown that the threshold currents of an electrically pumped device shows the same behavior [36] and its origin closely related to the oscillations of the optical losses and is only weakly modified by the overlap of the optical mode and pumping current profile.…”

“…2. This VCSEL, based on gallium arsenide, was previously analyzed in our work [36]. The resonant cavity is tailored to the freespace wavelength of 850 nm and boasts a length of 3 /2 λ.…”

“…The effect is stronger when the island is located closer to the cavity. This behavior results from the match or mismatch between the modal profile and the antiresonant oxide aperture [35], [36]. Consequently, there is a significant increase in threshold current discrimination for specific combinations of island position and diameter (marked in Fig.…”

“…In this case, the competing mode never reaches the threshold, resulting in the laser operating in a single-mode throughout its operational range. However, due to the proximity of the island to the cavity, which increases the diode resistance [36], the slope efficiency is not large, and the roll-over of the emitted power occurs at a value of 1.9 mW.…”

“…In our previous works, we have proposed such an S-ARROW structure for improving lateral modes discrimination in VCSELs. This structure has a form of an oxide disk manufactured in aluminum-rich AlGaAs layer inside of a VCSEL structure, either directly in the resonant cavity [35] or in one of the DBR layers [36]. This is possible through the use of a novel planar oxidation technology [37], [38], which allows to partially oxidize the Al-GaAs layer through a small hole etched in the a GaAs layer covering it, before the rest of the structure is grown.…”