[Show abstract][Hide abstract] ABSTRACT: 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
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: An asymmetric waveguide laser diode with a thick active layer operated with enhanced gain switching is shown to be able to produce ~100 ps, ~25 W optical pulses in fundamental transverse mode with ~15 A, ~1.5 ns injection current pulses. A pulsed time-of-flight distance measurement demonstration utilizing this laser diode and a SPAD detector indicates centimetre-level precision and compensated accuracy from uncooperative targets at tens to hundreds of metres in a measurement time of a fraction of a second.
Measurement Science and Technology 01/2012; 23(2):025202. · 1.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 mum 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).
[Show abstract][Hide abstract] ABSTRACT: The development of GaSb-based laterally-coupled distributed feedback diode lasers by means of cost-effective nanoimprint lithography process is presented. The separate confinement laser gain structure comprised two In<sub>0.2</sub>GaSb quantum wells. A grating pattern was defined and etched on the sides of the laser diode waveguide to enable distributed feedback. At room temperature the lasers emitted ~2mW output power in a single longitudinal mode at ~1945nm and exhibited a sidemode suppression ratio of over 30dB. A temperature dependent wavelength tuning coefficient of 0.16nm/°C was measured for the laser output.
[Show abstract][Hide abstract] ABSTRACT: 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 mum to 1.6 mum, 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 mum long gain section and a 90 mum long reverse biased absorber section with a ridge width of 3.5 mum. 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.
[Show abstract][Hide abstract] ABSTRACT: The performance of a strongly asymmetric waveguide laser diode structure with a relatively thick active layer and low optical confinement factor operated in gain switching mode has been studied experimentally. High-power optical pulse generation in the pulse width regime of ~100 ps has been demonstrated.
[Show abstract][Hide abstract] ABSTRACT: Thin organic films were deposited on silicon oxide surfaces with golden interdigitated electrodes (interelectrode gap was 2 mm), and the film resistivities were measured in dark and under white light illumination. The compounds selected for the measurements include molecules widely used in solar cell applications, such as polythiophene (PHT), fullerene (C60), pyrelene tetracarboxylic diimide (PTCDI) and copper phthalocyanine (CuPc), as well as molecules potentially interesting for photovoltaic applications, e.g. porphyrin–fullerene dyads. The films were deposited using thermal evaporation (e.g. for C60 and CuPc films), spin coating for PHT, and Langmuir–Schaeffer for the layer-by-layer deposition of porphyrin–fullerene dyads. The most conducting materials in the series are films of PHT and CuPc with resistivities 1.2 Â 103 V m and 3 Â 104 V m, respectively. Under light illumination resistivity of all films decreases, with the strongest light effect observed for PTCDI, for which resistivity decreases by 100 times, from 3.2 Â 108 V m in dark to 3.1 Â 106 V m under the light.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: We report a comparison between the high-speed gain and absorber dynamics of dilute nitride laser structures utilising GaAs or GaAsN barrier layers. The inclusion of dilute nitride barriers greatly reduces the absorber recovery time. The wafers were processed into two-section monolithic mode-locked lasers generating 2-5 ps pulses at 40 GHz.
[Show abstract][Hide abstract] ABSTRACT: The paper presents a simulation-based analysis of laterally-corrugated ridge-waveguide distributed feedback semiconductor
lasers emitting at 980nm. The simulations were performed using software developed in-house and the PICS3D software package
from Crosslight Software Inc. The effects of the corrugation geometry, phase-shift section, and mirror reflectivities on single
longitudinal mode operation are discussed. The lasers, designed along the guidelines derived from the simulation results,
were fabricated by using molecular beam epitaxy for wafer growth and low-cost nano-imprint lithography. They exhibited stable
single-mode operation with up to 50 dB side-mode suppression ratio.
Optical and Quantum Electronics 01/2009; 41(1):11-16. · 1.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Distributed feedback lasers with third-order surface gratings obtained by lateral corrugations of the ridge waveguide have been fabricated using low-cost nanoimprint lithography. The lasers, emitting in the 980 nm wavelength range exhibited stable single-longitudinal-mode operation with side-mode suppression ratios up to 50 dB.
Semiconductor Conference, 2008. CAS 2008. International; 11/2008
[Show abstract][Hide abstract] ABSTRACT: 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.