A new class of wireless technology is required to meet the surging global demand for data while significantly improving energy efficiency. We present a scalable, chip-based optical wireless system that addresses these challenges through the chip-scale integration of a custom-fabricated 5 & times;5 array of 940-nm vertical-cavity surface-emitting lasers with tailored beam-shaping micro-optics. This platform establishes a new benchmark by demonstrating, for the first time in a single chip-scale system, a record aggregate data rate of 362.71 Gbps, energy consumption nearly half that of state-of-the-art WiFi, and integrated optics for uniform spatial beam shaping. The high data rate is achieved using spectrally efficient orthogonal frequency-division multiplexing, despite system performance being constrained by the 1.4 GHz bandwidth of a commercial receiver. In parallel, a compact multielement optical system generates a uniform grid of collimated beams with over 90% spatial uniformity at a 2-m distance, enabling structured, multiuser indoor coverage. To our knowledge, this is the first fully integrated platform to simultaneously achieve such high data throughput, low-energy consumption, and beam shaping on a chip-compatible scale. These findings establish a new reference point and foundational architecture for future programmable, high-capacity, and energy-conscious photonic wireless systems.

With a directly modulated 850 nm single-mode vertical cavity surface emitting laser (SM-VCSEL), we experimentally achieve a gross data rate of ~38 Gbps over a 2.5 m optical wireless communication (OWC) link at the 7% Reed-Solomon forward error correction (RS-FEC) limit. The OWC link is demonstrated using an eye-safe transmitted optical power of −1.47 dBm and discrete multi-tone (DMT) modulation with adaptive bit-and-power loading. The SM-VCSEL has a relative intensity noise (RIN) of ~−137 dB/Hz, which is lower than that of a typical commercial 850 nm multimode VCSEL (~−129 dB/Hz). Therefore, under almost identical OWC link operating conditions, the SM-VCSEL provides a gross data-rate increase of ~19 Gbps and an optical signal-to-noise-ratio (SNR) gain of ~5 dB compared to its multimode counterpart having a similar modulation bandwidth. Furthermore, we demonstrate an error-free net data rate of ~17 Gbps at a received optical power of -7 dBm, which suggests the feasibility of utilising the SM-VCSEL to realise indoor gigabit OWC applications.

In this paper, we experimentally illustrate the effectiveness of neural networks (NNs) as non-linear equalisers for multilevel pulse amplitude modulation (PAM-M) transmission over an optical wireless communication (OWC) link. In our study, we compare the bit-error-rate (BER) performances of two decision feedback equalisers (DFEs)—a multilayer-perceptron-based DFE (MLPDFE), which is the NN equaliser, and a transversal DFE (TRDFE)—under two degrees of non-linear distortion using an eye-safe 850 nm single-mode vertical-cavity surface-emitting laser (SM-VCSEL). Our results consistently show that the MLPDFE delivers superior performance in comparison to the TRDFE, particularly in scenarios involving high non-linear distortion and PAM constellations with eight or more levels. At a forward error correction (FEC) threshold BER of 0.0038, we achieve bit rates of ~28 Gbps, ~29 Gbps, ~22.5 Gbps, and ~5 Gbps using PAM schemes with 2, 4, 8, and 16 levels, respectively, with the MLPDFE. Comparably, the TRDFE yields bit rates of ~28 Gbps and ~29 Gbps with PAM-2 and PAM-4, respectively. Higher PAM levels with the TRDFE result in BERs greater than 0.0038 for bit rates above 2 Gbps. These results highlight the effectiveness of the MLPDFE in optimising the performance of SM-VCSEL-based OWC systems across different modulation schemes and non-linear distortion levels.

A vertical cavity surface emitting laser (VCSEL) quick fabrication (VQF) process is applied to epitaxial materials designed for miniature atomic clock applications (MACs). The process is used to assess material quality and uniformity of a full 100 mm (4 ‐ inch) wafer against the stringent target specification of VCSELs for MACs. Target specifications in optical power ( > 0.6 mW) and differential efficiencies ( < 0.5 W/A) are achieved over large portions of a wafer; however, the variation in the oxide aperture diameter is shown to limit the yield. The emission of the fundamental mode

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.

We report direct measurements of the optical gain on vertical-cavity surface-emitting laser (VCSEL) material using a stripe-length method featuring segmented contacts. We utilise the similarity of the in-plane transverse electric (TE) polarised matrix element and that of the VCSEL lasing mode and a simple method to reduce round trip effects. The confinement factor is determined from cold-cavity simulations of the in-plane TE polarised slab waveguide mode and used to convert the measured in-plane modal gain into the vertical-cavity modal gain, as required for the VCSEL structure. This gives a threshold material gain of 1440 ± 140 cm −1 at 30 °C for this structure. A comparison with the threshold material gain values determined from the lasing condition, where internal optical losses due to doping induced absorption is included using parameters taken from the literature, indicates the presence of an additional source of optical loss in the experiment which increases the threshold material gain by ∼450 cm −1 . A best fit is obtained by increasing the optical loss in the n-DBR (distributed Bragg reflectors) layers to 40 cm −1 , which is consistent with previous work on additional scattering losses due to interface roughening in the n-DBR layers. To further demonstrate the utility of this method for rapid optimisation, the gain-peak wavelength is measured directly, and its temperature dependence is compared to the lasing wavelength.

We report on high resolution analysis of vertical cavity surface emitting lasers (VCSELs) to detect and assess defects in sub-surface layers. We employ a focussed ion beam scanning electron microscope (FIB-SEM) to sputter and image successive cross sections (slice and view technique) in order to produce a 3D reconstruction of the oxide aperture region. High resolution images and measurements of the multilayers and oxide apertures of VCSEL devices were obtained. The process took ∼2.5 h and produced over 270 slice SEM images for a device volume of approximately 13.2 × 16.0 × 13.8 μ m 3 , with a voxel size of 50 nm. On-wafer, single mode VCSEL devices with high and low output powers were analysed to compare their oxide apertures and distributed Bragg reflector (DBR) layer structures. It was found that the low output power VCSEL had DBR layer defects and a 41.8% reduction of effective oxide aperture area, explaining the lower power obtained. The results provide evidence that oxide aperture area and structural defects are major factors that affect the optical output power of VCSEL devices. Outcomes in this work show FIB-SEM slice and view is a valuable method for 3D reconstruction of VCSEL devices, which enables top view, cross-sectional view and angled view of the whole device region as well as designated structures such as oxide aperture or structural defects in various layers. This work demonstrates a promising technique with high resolution (50 nm) 3D imaging for analysis of complex semiconductor devices.

We report direct measurements of the optical gain profile for a vertical cavity surface emitting laser (VCSEL) epitaxial structure, by characterising the transverse electric (TE) in-plane net modal gain using the segmented contact method.

Compact coherent population trapping (CPT) based clocks require single-mode, low-power consumption, high-speed and polarization-stable laser sources. We report our progress in developing customized vertical cavity surface emitting laser (VCSEL) diodes designed for operating on the D1 transition of cesium, and specifically tailored for CPT-based atomic clocks. The VCSELs provide high power (>1 mW), narrow linewidths (<; 100 MHz), mode-hop free tunability over 8 nm, and are shown to be polarization stable over a wide range of operating bias conditions (average polarization suppression >15 dB). Preliminary spectroscopy has been observed.

We report on InGaN/GaN distributed feedback laser diodes with high order gratings emitting at a single wavelength around 428 nm. The 39th order notched gratings have the advantage of a simplified fabrication route with no need for overgrowth. The laser ridge and grating were formed by electron beam lithography followed by ICP etching. The as-cleaved lasers emitted in the pulsed regime with a peak single-mode output power of 15 mW. Optimization of the grating design should lead to higher power single wavelength operation.

We report on the design, fabrication, and characterization of InGaN/GaN distributed feedback laser diodes emitting at a single wavelength around 430 nm. Third-order sidewall-etched gratings were used which have the advantage of a simple fabrication route with no need for overgrowth. We carried out waveguide modeling to find the effective modal indices of the grating and calculate the coupling coefficient. The laser ridge and the grating were formed by electron beam lithography followed by inductively coupled plasma etching. The as-cleaved lasers emitted in the pulsed regime with an SMSR of 22 dB and a peak single-mode output power of 40 mW. Slope efficiency was similar for both Fabry-Perot and DFB chips demonstrating that performance is not compromised by the addition of the grating.

A concept of passive cavity surface–emitting laser is proposed aimed to control the temperature shift of the lasing wavelength. The device contains an all–semiconductor bottom distributed Bragg reflector (DBR), in which the active medium is placed, a dielectric resonant cavity and a dielectric top DBR, wherein at least one of the dielectric materials has a negative temperature coefficient of the refractive index, dn/dT < 0. This is shown to be the case for commonly used dielectric systems SiO2/TiO2 and SiO2/Ta2O5. Two SiO2/TiO2 resonant structures having a cavity either of SiO2 or TiO2 were deposited on a substrate, their optical power reflectance spectra were measured at various temperatures, and refractive index temperature coefficients were extracted, dn/dT = 0.0021 K-1 for SiO2 and dn/dT = –0.0092 K-1 for TiO2. Using such dielectric materials allows designing passive cavity surface–emitting lasers having on purpose either positive, or zero, or negative temperature shift of the lasing wavelength dλ/dT. A design for temperature–insensitive lasing wavelength (dλ/dT = 0) is proposed. Employing devices with temperature–insensitive lasing wavelength in wavelength division multiplexing systems may allow significant reducing of the spectral separation between transmission channels and an increase in number of channels for a defined spectral interval enabling low cost energy efficient uncooled devices.

We report on deeply etched sidewall grating DFB lasers in the InGaN/GaN material system emitting at a single wavelength around 434 nm. GaN lasers have a wide range of applications in communications, displays and storage. The availability of a single wavelength device with a good side mode suppression ratio (SMSR) would allow further applications to be addressed such as sources for laser cooling and Fraunhofer line operation for solar background free communications. Sidewall etched gratings have the advantage of fabrication with no need for overgrowth and have been demonstrated in a range of other material systems and wavelengths. Importantly for GaN based devices, this design has the potential to minimise fabrication induced damage to the epi structure.We investigated two laser designs, one with 80 % duty-cycle 3rd order gratings and another with 39th order partial gratings. Simulation of the 2D waveguide sections was carried out to find the optimal grating width. For fabrication, the laser ridge and gratings were patterned in a single step using electron beam lithography and ICP etched to a depth of 500 nm. Contact metal was deposited and the sample thinned and cleaved into 1 mm long cavities. The as-cleaved 3rd order lasers emit in the pulsed regime with a SMSR of 20 dB and a peak single-mode output power of 40 mW. The output power is similar to that of parallel processed FP lasers. The 39th order lasers also exhibit narrow spectral width at an output power of 10 mW.

Two blue (450 nm) light–emitting diodes (LED), which only differ in top p-GaN layer growth conditions, were comparatively investigated. I-V, C-V, TLM, Electroluminescence (EL) and Photoluminescence (PL) techniques were applied to clarify a correlation between MOCVD carrier gas and internal properties. The A-structure grown in the pure N2 environment demonstrated better parameters than the B-structure grown in the N2/H2 (1:1) gas mixture. The mixed growth atmosphere leaded to an increase of sheet resistances of p-GaN layer. EL and PL measurements confirmed the advantage of the pure N2 utilization, and C(VR) measurement pointed the increase of static charge concentration near the p-GaN interface in the B structure.

Existing optical networks are driven by dynamic user and application demands but operate statically at their maximum performance. Thus, optical links do not offer much adaptability and are not very energy-efficient. In this paper a novel approach of implementing performance and power adaptivity from system down to optical device, electrical circuit and transistor level is proposed. Depending on the actual data load, the number of activated link paths and individual device parameters like bandwidth, clock rate, modulation format and gain are adapted to enable lowering the components supply power. This enables flexible energy-efficient optical transmission links which pave the way for massive reductions of CO2 emission and operating costs in data center and high performance computing applications. Within the FP7 research project Adaptive Data and Power Aware Transceivers for Optical Communications (ADDAPT) dynamic high-speed energy-efficient transceiver subsystems are developed for short-range optical interconnects taking up new adaptive technologies and methods. The research of eight partners from industry, research and education spanning seven European countries includes the investigation of several adaptive control types and algorithms, the development of a full transceiver system, the design and fabrication of optical components and integrated circuits as well as the development of high-speed, low loss packaging solutions. This paper describes and discusses the idea of ADDAPT and provides an overview about the latest research results in this field.

We demonstrate the first low bandgap thermophotovoltaic (TPV) arrays capable of operating with heat sources at temperatures as low as 345 °C, which is the lowest ever reported. The individual array elements are based on narrow band gap InAs/InAs0.61Sb0.13P0.26 photodiode structures. External power conversion efficiency was measured to be ∼3% from a single element at room temperature, using a black body at 950 °C. Both 25-element and 65-element arrays were fabricated and exhibited a TPV response at different source temperatures in the range 345–950 °C suitable for electricity generation from waste heat and other applications.