Kevin L. Lear

Design, fabrication, and performance of infrared and visible vertical-cavity surface-emitting lasers

This paper discusses the issues involving the design and fabrication of vertical-cavity surface-emitting lasers (VCSELs). A review of the basic experimental structures is given, with emphasis on recent developments in distributed Bragg reflectors, gain media, as well as current and optical confinement techniques. The paper describes present VCSEL performance, in particular, those involving selective oxidation and visible wavelength operation.

Comprehensive numerical modeling of vertical-cavity surface-emitting lasers

We present a comprehensive numerical model for vertical-cavity surface-emitting lasers that includes all major processes affecting cw operation of axisymmetric devices. In particular, our model includes a description of the 2-D transport of electrons and holes through the cladding layers to the quantum well(s), diffusion and recombination of these carriers within the wells, the 2-D transport of heat throughout the device, and a multilateral-mode effective index optical model. The optical gain acquired by photons traversing the quantum wells is computed including the effects of strained band structure and quantum confinement. We employ our model to predict the behavior of higher-order lateral modes in proton-implanted devices and to provide an understanding of index-guiding in devices fabricated using selective oxidation.

Fabrication and performance of selectively oxidized vertical-cavity lasers

We report the high yield fabrication and reproducible performance of selectively oxidized vertical-cavity surface emitting lasers. We show that linear oxidation rates of AlGaAs without an induction period allows reproducible fabrication of buried oxide current apertures within monolithic distributed Bragg reflectors. The oxide layers do not induce obvious crystalline defects, and continuous wave operation in excess of 650 h has been obtained. The high yield fabrication enables relatively high laser performance over a wide wavelength span. We observe submilliamp threshold currents over a wavelength range of up to 75 nm, and power conversion efficiencies at 1 mW output power of greater than 20% over a 50-nm wavelength range.<<ETX>>

Cavity characteristics of selectively oxidized vertical‐cavity lasers

We show that a buried oxide layer forming a current aperture in an all epitaxial vertical‐cavity surface emitting laser has a profound influence on the optical and electrical characteristics of the device. The lateral index variation formed around the oxide current aperture leads to a shift in the cavity resonance wavelength. The resonance wavelength under the oxide layer can thus be manipulated, independent of the as‐grown cavity resonance, by adjusting the oxide layer thickness and its placement relative to the active region. In addition, the electrical confinement afforded by the oxide layer enables record low threshold current densities and threshold voltages in these lasers.

Modal analysis of a small surface emitting laser with a selectively oxidized waveguide

We describe studies of an index‐guided ∼4×3 μm2 vertical cavity surface emitting laser with a cw, room temperature 133 μA threshold current and 53% slope efficiency fabricated using selective wet thermal oxidation to provide optical and electrical confinement. While the device operates strictly single mode, a large number of transverse modes are evident in the subthreshold luminescence observed in both vertical and lateral directions. Despite the lumped nature of the index region, the transverse mode wavelengths agree very well with those predicted for a conventional distributed waveguide structure. Waveguide dimensions and an effective index step of 2% between the active and cladding region are determined by fitting the modal data.

Polarization modulation of cruciform vertical-cavity laser diodes

We demonstrate electrical switching and modulation between two orthogonal polarization modes of air‐post vertical‐cavity surface emitting lasers with cruciform transverse cavity geometry. The continuous‐wave lasing emission is switched from one polarization mode to the orthogonal mode at frequencies up to 50 MHz by a small signal modulation of the injection current. Furthermore, a polarized output signal at twice the input frequency is generated at frequencies up to 10 MHz by a large signal modulation of the injection current from below threshold to above the polarization switching transition.

Vertical cavity surface emitting lasers with 21% efficiency by metalorganic vapor phase epitaxy

Proton implanted, vertical cavity top-surface emitting lasers exhibit the highest single-mode and multi-mode output powers, highest power conversion efficiency, and lowest threshold voltage for such devices reported to date. These lasers use new mirror grading designs that are enabled by metalorganic vapor phase epitaxys capabilities of alloy grading and carbon doping. The results validate this growth technology by exceeding the previous best results which were based on molecular beam epitaxy.<<ETX>>

On-axis far-field emission from two-dimensional phase-locked vertical cavity surface-emitting laser arrays with an integrated phase-corrector

We have fabricated large, two‐dimensional (2D) arrays of optically pumped, phase‐locked vertical cavity surface‐emitting lasers that emit more than 50% of their light in a central on‐axis lobe. The emission of the arrays was modified from the usual four‐lobed far‐field of 2D coupled arrays by incorporation of a binary phase‐shift mask on the surface of the array. The array consists of Fabry–Perot resonators comprising GaAs/AlGaAs quantum wells surrounded by AlAs/AlGaAs quarterwave mirrors with a multiple order AlGaAs phase‐delay layer on the top mirror stack. The phase‐shift layer was etched away on alternating elements of the array. The resulting on‐axis emission had an angular width of 2° for an array of approximately 100 elements.

Polyimide-planarized vertical-cavity surface-emitting lasers with 17.0-GHz bandwidth

High-speed oxide-confined polyimide-planarized 850-nm vertical-cavity surface-emitting lasers exhibit -3-dB modulation bandwidths up to 17.0 GHz. The devices are fabricated using a reproducible, simple process incorporating polyimide with good adhesion that does not require implantation or semiinsulating substrates to achieve low capacitance.

UNIPARABOLIC MIRROR GRADING FOR VERTICAL CAVITY SURFACE EMITTING LASERS

We report details of mirror grading profiles for high efficiency vertical cavity surface emitting lasers. The mirrors provide low vertical resistance in conjunction with improvements in optical reflectivity, thermal conductivity, and lateral electrical conductivity in comparison to earlier grading profiles. The enhancement of these properties is verified by a comparison of thermal resistance and total electrical resistance for lasers of varying size.