A. Garnache

Vertical-external-cavity semiconductor lasers

Surface-emitting semiconductor lasers can make use of external cavities and optical pumping techniques to achieve a combination of high continuous-wave output power and near-diffraction-limited beam quality that is not matched by any other type of semiconductor source. The ready access to the laser mode that the external cavity provides has been exploited for applications such as intra-cavity frequency doubling and passive mode-locking. The purpose of this Topical Review is to outline the operating principles of these versatile lasers and summarize the capabilities of devices that have been demonstrated so far. Particular attention is paid to the generation of near-transform-limited sub-picosecond pulses in passively mode-locked surface-emitting lasers, which are potentially of interest as compact sources of ultrashort pulses at high average power that can be operated readily at repetition rates of many gigahertz.

Multiwatt—power highly—coherent compact single—frequency tunable Vertical—External—Cavity—Surface—Emitting—Semiconductor—Laser

We demonstrate high power (2.1W) low noise single frequency operation of a tunable compact verical-external-cavity surface-emitting- laser exhibiting a high beam quality. We took advantage of thermal lens-based stability to develop a short (3-10 mm) plano-plano external cavity without any intracavity filter. The semiconductor structure emitting at 1microm is optically pumped by a 8W commercial 808 nm multimode diode laser at large incidence angle. For heat management purpose the GaAs-based VECSEL membrane was bonded on a SiC substrate. We measured a low divergence quasi-circular TEM00 beam (M2 = 1.2) close to diffraction limit, with a linear light polarization (>30 dB).We simulated the steady state laser beam of this unstable cavity using Fresnel diffraction. The side mode suppression ratio is > 45 dB. The free running laser linewidth is 37 kHz limited by pump induced thermal fluctuations. Thanks to this high-Q external cavity approach, the frequency noise is low and the dynamics is in the relaxation-oscillation-free regime, exhibiting low intensity noise (< 0.1%), with a cutoff frequency approximately 41MHz above which the shot noise level is reached. The key parameters limiting the laser power and coherence are studied. This design/properties can be extended to other wavelengths.

Single-frequency tunable Sb-based VCSELs emitting at 2.3 /spl mu/m

We present a comparison between two kinds of single-frequency Sb-based semiconductor VCSELs operating at 2.3 /spl mu/m in continuous-wave regime at room temperature. These lasers are studied in view of application to spectroscopy or trace gas detection. Both are based on a molecular beam epitaxy grown half-VCSEL. In the first configuration, a dielectric mirror is deposited on top to form a microcavity, while in the second a concave mirror is used to form an external cavity. The external cavity VCSEL exhibits 5-mW output power, a narrow linewidth (<<20 kHz), and 50-GHz continuous frequency tunability.

10-GHz train of sub-500-fs optical soliton-like pulses from a surface-emitting semiconductor laser

We report sub-500-fs operation of a passively mode-locked diode-pumped external-cavity surface-emitting semiconductor laser at a repetition rate of 10.014 GHz. For an incident pump power of 706 mW, the laser produced 486-fs soliton-like pulses, with an average output power of 30.3 mW. The role of the ac Stark effect in shaping subpicosecond pulses is demonstrated.

Experimental demonstration of a tunable dual-frequency semiconductor laser free of relaxation oscillations.

Tunable dual-frequency oscillation is demonstrated in a vertical external-cavity surface-emitting laser. Simultaneous and robust oscillation of the two orthogonally polarized eigenstates is achieved by reducing their overlap in the optical active medium. The class-A dynamics of this laser, free of relaxation oscillations, enables one to suppress the electrical phase noise in excess that is usually observed in the vicinity of the beat note.

Shot-noise-limited operation of a monomode high-cavity-finesse semiconductor laser for microwave photonics applications

Shot-noise-limited laser operation over a wide spectral bandwidth is demonstrated by using a semiconductor active medium inserted into a high-Q external cavity. This approach ensures, with a compact design, a sufficiently long photon lifetime to reach the oscillation-relaxation-free class A regime. The laser relative intensity noise is limited to the shot-noise relative floor, -156 dB/Hz for a 1 mA detected photocurrent, over the 100 MHz to 18 GHz bandwidth. The optimization of the laser cavity is discussed, and convenient shot-noise-limited operation is shown to be a trade-off between the cavity length and laser mode filtering.

High power single–frequency continuously–tunable compact extended–cavity semiconductor laser

Laser technology is maturing rapidly and is finding applications in areas such as high resolution spectroscopy, medicine, optical telecoms, radar-lidar, metrology… Thus there is a strong interest to develop high quality laser operating in the continuous-wave (cw) regime at room temperature (RT) in the λ = 0.5–3µm range. A highly coherent high power tunable laser design can be achieved using an extended-cavity quantum-well (QW) semiconductor surface emitting laser in a stable optical cavity, so called External-cavity VCSELs (VeCSELs).

AlAsSb/GaSb doped distributed Bragg reflectors for electrically pumped VCSELs emitting around 2.3 µm

This paper is dedicated to the study of electrical and optical properties of four different doped 21.5 pairs AlAsSb/GaSb distributed Bragg reflectors lattice-matched to GaSb and designed for the fabrication of electrically pumped VCSELs emitting around 2.3 µm. Three different doping profiles have been carried out: n-bulk doping, n-delta doping and p-bulk doping. An n-type bulk doped Bragg mirror with step composition at GaSb/AlAsSb interfaces was also tested. The n-type bulk doped sample with sharp interfaces exhibited the best electrical properties, a voltage drop per pair of 25 mV and a specific resistance of 1 × 10−4 Ω cm2 at 1 kA cm−2. Moreover, optical losses as low as 5–10 cm−1 have been measured for n-type doped mirrors.

Control of light polarization using optically spin-injected vertical external cavity surface emitting lasers

We fabricated and characterized an optically pumped (100)-oriented InGaAs/GaAsP multiple quantum well Vertical External Cavity Surface Emitting Laser (VECSEL). The structure is designed to allow the integration of a Metal-Tunnel-Junction ferromagnetic spin-injector for future electrical injection. We report here the control at room temperature of the electromagnetic field polarization using optical spin injection in the active medium of the VECSEL. The switching between two highly circular polarization states had been demonstrated using an M-shaped extended cavity in multi-modes lasing. This result witnesses an efficient spin-injection in the active medium of the LASER.

Single-frequency external-cavity semiconductor ring-laser gyroscope.

We report for the first time (to our knowledge) the experimental achievement of a single-frequency ring-laser gyroscope using a diode-pumped half-vertical-cavity semiconductor-emitting laser structure as a gain medium. Thanks to the control of mode competition by an active feedback loop, we observe a beat signal from recombined beams that has a frequency proportional to the rotation rate as predicted by the Sagnac effect. This promising result opens new perspectives for rotation sensing.