Here we present a device concept utilizing GaSb-based laterally-coupled DFB-lasers. Fabrication procedure to define the
ridge waveguide and the grating makes use of nanoimprint lithography. This technology addresses issues related to mass
fabrication and cost of the DFB-lasers. We demonstrate state-of-the-art devices on a range of wavelengths around 2 μm.
These lasers exhibit single-mode operation with a maximum side-mode suppression ratio of more than 55 dB and high
output power of ~25 mW.
Fundamental mode, ~100 ps, ~40 W optical pulses are demonstrated from a laser diode with a strongly asymmetric
waveguide structure and a relatively thick (~0.1 μm) active layer driven with ~15 A, ~1.5 ns injection current pulses
produced by a simple avalanche transistor circuit. Using this compact laser source, pulsed time-of-flight laser
rangefinding measurements were performed utilizing a single-photon avalanche detector. The results show the feasibility
of a very compact overall device with centimeter-level distance measurement precision and walk-error compensated
accuracy to passive targets at tens to hundreds of meters in a measurement time of about ten milliseconds.
We report the development of a nanoimprint lithography patterning method and inductively coupled plasma etching
recipe designed for GaSb-based semiconductor materials. The developed processes were used to fabricate edge-emitting
ridge-waveguide lasers and laterally-coupled distributed feedback lasers operating at 1945 nm. For ridge-waveguide
laser with 1 mm cavity length, a threshold current of 32 mA was measured. Side-mode suppression ratio in excess of 30
dB was measured for the distributed feedback lasers with 2 mW output power and the output wavelength was
temperature-tunable with a tuning coefficient of 0.16 nm /°C.
The conventional distributed feedback (DFB) edge-emitting lasers with buried gratings require two or more epitaxial
growth steps. To avoid the problematic overgrowth we have used laterally-corrugated ridge-waveguide surface gratings,
which also enable easy integration of the resulting laterally-coupled DFB (LC-DFB) lasers with other devices and are
applicable to different materials, including Al-containing ones. The paper presents the modeling and design
particularities of LC-DFB lasers, the fabrication process, involving a highly productive and cost-effective UVnanoimprint
lithography technique, and the characteristics obtained for the LC-DFB lasers fabricated from GaAs-, GaSband
InP-based epiwafers. The first batches of GaAs-based LC-DFB lasers, emitting at 894 nm, GaSb-based LC-DFB
lasers emitting at 1.946 μm and InP-based LC-DFB lasers, emitting at 1.55 μm had relatively low threshold currents, a
high side-mode-suppression-ratio and exhibited linewidths in the range of 1 MHz and below, showing that the LC-DFB
lasers are an effective low-cost alternative for the conventional buried-grating DFB lasers.
We present a concept where GaAs chips with dilute nitride and quantum dot optoelectronics are hybrid integrated on a
silicon-on-insulator (SOI) waveguide platform and packaged into low-cost modules using silicon as the packaging
material. The approach aims to offer high energy efficiency, low cost and high bandwidth for optical interconnects
operating at 1.2-1.3 μm wavelengths. It presents technologies that could bridge the gap between long and short range
optical communication, which are presently based on incompatible wavelength ranges and waveguiding technologies
(single vs. multimode).
Mid-infrared semiconductor laser are highly attractive sources for environmental monitoring since the spectral
fingerprints of many environmentally important gases are located in the 2-3.3 μm wavelength regime accessible by
gallium-antimonide technology. Here an electrically-pumped vertical-external-cavity surface-emitting laser (EP-VECSEL)
was realized at 2.34 μm wavelength, using a gain mirror based on the GaSb material system. The gain mirror
was grown by molecular beam epitaxy on an n-type GaSb substrate and it included a distributed Bragg reflector made of
24-pairs of AlAsSb/GaSb layers, and a gain region with 5 GaInAsSb quantum wells placed in a 3-λ thick micro-cavity.
A structured buried tunnel junction (BTJ) with subsequent overgrowth was used in order to obtain efficient current
confinement, reduced optical losses and increased electrical conductivity. Different components were tested with
aperture sizes varying from 30 μm to 90 μm. Pulsed lasing was obtained with all tested components at 15 °C mount
temperature. We obtained a maximum peak power of 1.5 mW at wavelength of 2.34 μm.
We report on the development of monolithic two-section dilute nitride passively mode-locked ridge-waveguide lasers.
The dilute nitride material system can cover a wide wavelength range from 1.2 μm to 1.6 μm, while enabling fabrication
on low-cost GaAs substrates. The laser structure comprised 3 GaInNAs quantum wells embedded within GaAs
waveguide and AlGaAs claddings. To achieve mode-locking at 40 GHz repetition rate the laser chips consisted of a 950
μm long gain section and a 90 μm long reverse biased absorber section with a ridge width of 3.5 μm. The mode-locked
laser output exceeded 3 mW per as-cleaved facet with 80 mA current in the gain region and a reverse voltage of 3.8 V
applied to the saturable absorber. The corresponding pulse width was 3.4 ps.
To study the effect of increasing the number of N-related recombination traps present in the proximity of the quantum
wells, we have compared the performance of lasers employing GaAsN or GaAs as quantum well barriers. Time-resolved
photoluminescence measurements revealed that the material comprising GaAsN barriers exhibited a photoluminescence
lifetime of 12 ps with a reverse bias of 5 V. For similar reverse bias, the photoluminescence lifetime for material
comprising GaAs barriers was 108 ps.
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