Kimmo Haring

3 nJ, 100 ps laser pulses generated with an asymmetric waveguide laser diode for a single-photon avalanche diode time-of-flight (SPAD TOF) rangefinder application

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.

2.34 μm electrically-pumped VECSEL with buried tunnel junction

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.

High Spectral Purity High-Power GaSb-Based DFB Laser Fabricated by Nanoimprint Lithography

The development of single-mode distributed feedback (DFB) lasers emitting high output powers in a broad wavelength range from 1980 to 2035 nm is reported. A unique feature of the development is the fabrication of lateral feedback gratings by nanoimprint lithography. We have varied a wide range of design parameters and studied their effect on the performance of the laser. The best uncoated devices exhibited a side-mode suppression ratio as high as >50 dB at output powers in excess of 14 mW. Moreover, a tuning range of over 12 nm was measured. After coating the facets with dielectric mirrors, the laser diodes could deliver an output power of more than 25 mW. In this letter, we prove the suitability of nanoimprint lithography to the fabrication of GaSb-DFB laser diodes by demonstrating the state-of-the-art devices made using imprint lithography.

40 GHz GaInNAs-based passively mode-locked laser diode

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.

Surface-grating-based distributed feedback lasers fabricated using nanoimprint lithography

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.

Compact laser pulser for TOF SPAD rangefinder application

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.

Laterally-coupled high power GaSb distributed feedback lasers fabricated by nanoimprint lithography at 2 μm wavelength

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.

GaAs-SOI integration as a path to low-cost optical interconnects

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).

Narrow-linewidth distributed feedback lasers with laterally-coupled ridge-waveguide surface gratings fabricated using nanoimprint lithography

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.

2 μm InGaSb/GaSb laterally coupled distributed feedback laser fabricated by nanoimprint lithography

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.