Large-area single-mode VCSELs and the self-aligned surface relief

Abstract

The effect of mode-profile specific etching of the top layer in selectively oxidized VCSEL structures at 850 nm emission wavelength is examined. For high reproducibility, a selfaligned etching technique is used which aligns surface etch and oxide aperture by only one additional photoresist step. By optimizing layer structure and etch spot size, completely single-mode devices with aperture diameters up to 16 µm are obtained. Maximum singlefundamental mode output power of 3.4 mW at room temperature and over 4 mW at 0• C is obtained with a maximum far-field angle of 5.5• . Using parameters for etch spot height and diameter, Gaussian beam spot size and phase curvature, the measured diffracted farfield distribution is fitted well over a 20 dB intensity range. The chosen fit parameters therefore enable to estimate the amount of phase curvature within the VCSEL for different operation currents, which cannot be obtained with available measurement methods.

High-power single-mode vertical-cavity surface-emitting lasers

“…14,15 Thermal lensing and thermal redistribution of carriers in the active region are thought to be the main contribution to the single-mode operation under cw conditions. In contrast, regardless of pulsed or cw operation, the mode selection in our design is primarily established by the gain profile, which is determined by the double-aperture design.…”

Single-Mode VCSELs

“…By removing the anti-phase layer in the central part of the top DBR, a lower cavity loss is obtained for the fundamental mode and single-mode emission is achieved. This relaxes the requirement for precision in etch depth (to ± a few tens of nm's) [57] while the precision in epitaxial growth is used to ensure a large loss contrast between etched and unetched areas. With this technique, single-mode emission from threshold to thermal roll-over, with a maximum single-mode power exceeding 6 mW (MSR > 30 dB), has been achieved at an emission wavelength of 850 nm [58,59].…”

“…An early demonstration showed the remarkable effect of the surface relief on the modal and beam characteristics of an oxide-confined VCSEL [55]. With further optimizations of oxide and surface relief diameters, and using a fabrication technique for self-alignment of the surface relief to the oxide aperture [56], a single-mode power of 3.4 mW was achieved at 850 nm [57].…”

Numerical Self-Consistent Analysis of VCSELs

“…So as one can see, the requirements of higher-power single-mode operation and low lasing threshold usually contradict each other. Nevertheless, various approaches of enhancing the singlemode VCSEL output power have been reported [8][9][10][11][12][13][14].…”