The polarization state (or relative phase) of each VCSEL in an injection-locked array can serve as an analogue Ising bit. We propose use of a spatial light modulator, along with associated collimation optics, to control the interaction strengths of the Ising Hamiltonian. The advantage of this approach is that it affectively allows all-to-all coupling between the Ising bits in a controllable way. The Ising computation would be particularly speedy since the feedback path is all-optical.

Two-dimensional hexagonal VCSEL arrays with up to 37 VCSELs per array and emitting at 940 nm to 1020 nm are produced on GaAs substrates. Arrays with variable oxide aperture diameters and new processing geometries, with a focus on optimizing the tradeoffs in optical output power, bandwidth, power conversion efficiency, and emitted far field pattern for applications in optical wireless communications are characterized and compared. Standard on wafer probing and packaged array tests are performed including terrestrial free space measurements demonstrating the viability of the core VCSEL array technology for fifth, sixth, and next generation optical wireless systems.

Applying coherent arrays of muti-aperture lasers was proposed to improve data transmission over multimode fiber. We propose a novel compact a coherent and incoherent multi-aperture VCSEL array design in which multiple single-mode VCSEL apertures are electrically driven in parallel. Such approach allows a high output power as in standard multimode devices but shows significantly reduced spectral width not exceeding 0.2nm as well as high speed performance exceeding 25GHz with current density ~20kA/cm2 and beam divergence of 22O (1/e2). Moreover, we study the application of such devices for IM/DD 100Gbit/s PAM-4 and 50Gbit/s OOK.

We report on the use of etching and regrowth to shift the longitudinal resonance wavelength of adjacent VCSELs by -4nm from 980nm. The etched VCSEL exhibited less than 5% change in threshold (from 0.36mA) and slope efficiency relative to neighboring un-etched VCSELs. This etch and regrowth technique can be applied to produce wavelength-division multiplexed (WDM) VCSEL arrays with close spacing (<100microns). We will also discuss applications to 2-dimensional index engineering of novel VCSEL devices, since wavelength shifting is equivalent to effective index tuning.

We present an extensive experimental analysis of two-dimensional gallium-arsenide-based VCSEL arrays considering the impact on performance of the VCSEL density (inter-VCSEL spacing and mesa diameters), the number and arrangement of VCSEL elements, and the VCSEL vertical epitaxial design. We include computer simulations that explain well the behavior and trends we observe in our experiments. We present the most efficient modifications of the lateral and vertical VCSEL arrays designs to optimize heat dissipation, optical output power scaling, and wall plug efficiency.

We report on the epi-design and characterisation of VCSELs for atomic sensors, including miniaturised clocks and magnetometers. To understand how epi-design impacts device performance and separate this from effects of growth and fabrication, we employ techniques to study the interplay between optically-active gain medium and the cavity-resonance. We experimentally determine the net modal-gain spectrum of VCSEL material using a single-pass stripe-length method covering the range of pumping and hence gain requirements of VCSELs. This is compared to photovoltage spectroscopic measurements, which are used to determine the quantum well transition energies and cavity resonance, aiding further optimisation of device design.

Recently, we presented the idea of a single-element gas detector based on a VCSEL, in which the top mirror is realised as subwavelength grating (SWG). The presence of gas in the vicinity of the grating causes a change in its reflectivity, which leads to a change in the quality factor of the laser cavity. We investigate the possibility of a realisation of a single-element detector based on the SWG VCSEL, in which a Fano-resonance occurs in the SWG. We analyse the performance of such a detector based on the example of an antimonide VCSEL designed as an ethane detector.

The key component of a quantum cascade vertical cavity surface emitting laser (QC VCSEL) is a monolithic high-contrast grating (MHCG) that replaces one of the distributed Bragg mirrors (DBR). The grating induces the polarization component necessary to stimulated emission in quantum cascade active regions embedded in MHCG. The complex electrical and optical phenomena defining the performance of the structure depends on the grating parameters (stripes dimensions, position, thickness and doping concentrations). This work presents optimization of QC VCSELs that is aimed to achieve minimal thresholds currents in the pulse operation regime.

Long Wavelength VCSELs and edge emitters have been grown by Molecular Beam Epitaxy (MBE) on GaAs substrates for applications in 3D sensing and LIDAR. Adding small amounts of nitrogen to the InGaAs QW material allows longer emission wavelengths to be achieved, but these alloys are notoriously difficult to achieve good optical material quality. Careful control of the layer structure and growth conditions of the dilute nitride active region has resulted in state of the art device characteristics at these wavelengths, which will be presented. Further optimization has been carried out to demonstrate appropriate device reliability under standard test conditions.

Emerging consumer applications of VCSEL arrays demand larger sizes and improved reliability. Significant wafer bow seen on a 150-mm GaAs-substrate wafer can impact fabrication, characterisation, and yields. It has been reported that Ge-substrates are drop-in replacements for GaAs, but also have additional benefits. We report on the spatial performance of identical 940 nm VCSELs, grown on both types of 200-mm substrate. Threshold current densities vary by 0.1μA/cm2 at the wafer centre, and a 0.78% and 0.59% decrease in centre-to-edge emission wavelengths for Ge and GaAs respectively. Results show a potential route to larger manufacturing volumes with lower costs per wafer.

We report on a study using VCSEL Quick Fabrication (VQF) devices for the rapid assessment of epitaxial structures designed for emission at 894nm grown on 100mm substrates. A comparison of measured VQF device results to the epitaxial design specification allows for the extraction of key variances across the wafer and the identification of their potential causes. We also demonstrate the applicability of this technique for the assessment of uniformity and reproducibility of 150mm VCSEL wafers for emission at 940nm, identifying the potential sources for observed variations in device performance that impact in specification device yield.