We report a technique for scalable electro-optical on-chip addressing of semiconductor nanowire emitters via transfer-printed micro-LEDs. Thus driven individual waveguide-coupled nanowires demonstrate small-signal modulation in the 10's MHz range at room-temperature. The integration of micro-LEDs with nanowire emitters on a chip provides localized scalable excitation without the need for external optics. This method therefore opens new routes for the realization of programmable high-density nanowire networks.

Silicon photonic crystal cavities (PhCC) exhibit high sensitivity to their surrounding environments, making them suitable for a diverse range of sensing applications. These applications include chemical sensing, optomechanical pressure sensing, displacement and radiation pressure measurements, as well as biosensing with potential applications in rapid medical and clinical diagnostics [1]–[3]. The integration of these devices with optical fibre, which offers additional benefits such as flexibility, robustness and immunity to electromagnetic interference [4], enables the development of highly sensitive sensors that can be utilised in challenging environments, such as cryostats or gas chambers.

We report on the fabrication and micro-transfer printing (mu -TP) of InGaAs/InP avalanche photodiodes (APDs) onto silicon substrates. A process flow was developed to suspend the devices using semiconductor tethers. The developed process reduces the number of fabrication steps required compared to methods based on the use of photoresist tethers. Furthermore, our process is compatible with devices that may be susceptible to damage induced by the photoresist removal process. APDs were characterised in linear mode operation both before suspension and after printing. Despite the additional fabrication steps required to suspend the APD membranes and the physical nature of the mu -TP process, the electrical characteristics of the devices were preserved. No degradation in the optical performance of the devices was measured. Our work represents the first demonstration of mu -TP of InGaAs/InP APDs onto silicon substrates. The results highlight the viability of mu -TP for effective heterogeneous integration of InGaAs/InP APDs with silicon photonic integrated circuits for optical and quantum communication and other light detection applications.

Photonic crystal cavities (PhCCs) can confine optical fields in ultra-small volumes, enabling efficient light-matter interactions for quantum and non-linear optics, sensing and all-optical signal processing. The inherent nanometric tolerances of micro-fabrication platforms can induce cavity resonant wavelength shifts two-orders of magnitude larger than cavity linewidths, prohibiting fabrication of arrays of nominally identical devices. We address this device variability by fabricating PhCCs as releasable pixels that can be transferred from their native substrate to a receiver where ordered micro-assembly can overcome the inherent fabrication variance. We demonstrate the measurement, binning and transfer of 119 PhCCs in a single session, producing spatially ordered arrays of PhCCs, sorted by resonant wavelength. Furthermore, the rapid in-situ measurement of the devices enables measurements of the PhCCs dynamic response to the print process for the first time, showing plastic and elastic effects in the seconds to hours range.

Silicon, being the fundamental material for modern semiconductor devices, has seen continuous advancements to enhance its electrical and mechanical properties. Strain engineering is a well-established technique for improving the performance of silicon-based devices. In this paper, we propose a simple method for inducing and permanently maintaining strain in silicon through pure physical bending. By subjecting the silicon substrate to a controlled bending process, we demonstrate the generation of strain levels that persist even after the removal of external stress, with a maximum strain value of 0.4%. We present a comprehensive study of the mechanics behind this phenomenon, a full finite element mechanical model, and experimental verification of the bending-induced strain in Si membranes using electron backscatter diffraction measurements. Our findings show the potential of this approach for strain engineering in high-performance silicon-based technologies without resorting to complex and expensive fabrication techniques.

Smart cameras are a widespread technology for image recognition and robotic vision. However, these devices face bandwidth limitations related with the high number of pixels transmitted and analysed per image. Single Pixel Imaging (SPI) is an alternative imaging paradigm to conventional cameras offering unique advantages in resource-constrained environments. SPI can be combined with compressive sampling techniques to significantly enhance image acquisition efficiency and flexibility while reducing the system's complexity [1]. SPI has recently combined with digital light projectors based on chip-scale LED-on-CMOS technology [2] to achieve ultra-high image transmission rates [3]. In this study, we demonstrate an efficient SPI-based image classification system operating at kHz bandwidths. Furthermore, we study the performance of our SPI image classification approach for increasing levels of image compression, which correspond to higher transmission rates.

Recent years have seen a surge in the demand for application-specific neuromorphic hardware, alongside a growing applications space. In the context of optical neural networks, integrated Photonic Extreme Learning Machines (PELMs) offer key advantages for hardware implementation, while meeting requirements for scalability, energy-efficiency and operation bandwidth. PELMs are photonic neural networks with feed-forward connectivity whose operation exploits the intrinsically complex input-to-output information transformation of the network, with training only applied via the readout layer [1]. Chaotic microcavities, i.e. dielectric microcavities with geometries that sustain aperiodic ray trajectories, have been proposed for use as compact physical reservoirs [2], [3]. Previous studies have focussed on numerical modelling of the microcavities, where the wave propagation dynamics can be time-resolved and play the role of a short-term memory. In experimental implementations, the ultrashort time scales involved in the optical path propagation are unpractical to detect and a more efficient mode of operation of such microcavities is as PELMs in classification tasks. Here, we demonstrate fabrication of silicon nitride (SbN4) based chaotic resonators and show application of these as the hidden layer of a PELM for image classification.

The increase in demand for scalable and energy efficient artificial neural networks has put the focus on novel hardware solutions. Integrated photonics offers a compact, parallel and ultra-fast information processing platform, specially suited for extreme learning machine (ELM) architectures. Here we experimentally demonstrate a chip-scale photonic ELM based on wave chaos interference in a stadium microcavity. By encoding the input information in the wavelength of an external single-frequency tunable laser source, we leverage the high sensitivity to wavelength of injection in such photonic resonators. We fabricate the microcavity with direct laser writing of SU-8 polymer on glass. A scattering wall surrounding the stadium operates as readout layer, collecting the light associated with the cavity's leaky modes. We report uncorrelated and aperiodic behavior in the speckles of the scattering barrier from a high resolution scan of the input wavelength. Finally, we characterize the system's performance at classification in four qualitatively different benchmark tasks. As we can control the number of output nodes of our ELM by measuring different parts of the scattering barrier, we demonstrate the capability to optimize our photonic ELM's readout size to the performance required for each task.

Time of flight (ToF) ranging has become vital in applications from autonomous-vehicle navigation to facial recognition. We present a 128 x 128 GaN MicroLED display which can simultaneously transmit > 80 Mbps while acting as a nanosecond pulse source for ToF imaging with sub-cm accuracy.

Individually addressable micro-LED-on-CMOS arrays are promising candidates for scalable on-chip excitation of micro- and nano-photonic emitters. Using this technology platform, frequency modulated excitation of waveguide-embedded nanowire devices was demonstrated at MHz rates.

Planar 45o turning mirrors with metal coating embedded in SU8 polymer waveguides enable waveguide to vertical mode coupling across a broad range of wavelengths from the visible to IR. The fabrication of these 2.5D structures is achieved using relatively simple grayscale lithography in thin film resists, compatible with standard planar lithography methods. Mirror losses of <1 dB are measured from 516 -1630 nm, and direct coupling to single mode fibre is achieved.

Two-dimensional silicon photonic crystal cavities were transfer printed as individual pixels from their native substrate. In-situ spectral measurement during printing facilitated spatial ordering of 119 devices, with sub-linewidth deviations observed during printing.

Laser-written nitrogen vacancy (NV-) centers are combined with transfer-printed GaN micro-lenses to increase fluorescent light collection by reducing total internal reflection at the planar diamond interface. We find a 2x improvement of fluorescent light collection using a 0.95 NA air objective at room temperature, in agreement with FDTD simulations. The nature of the transfer print micro-lenses leads to better performance with lower numerical aperture (NA) collection, as confirmed by results with a 0.5NA air objective which show improvement greater than 5x. The approach is attractive for scalable integrated quantum technologies.

Integrated tuneable wavelength filters with high extinction and narrow lineshapes commonly underpin photonic chip architectures at infrared wavelengths, but are notably less mature at visible wavelengths. We address this, with high extinction (23 dB), narrow linewidth (1 pm) resonances achieved using cascaded tuneable SiN racetracks.

This study introduces and compares the lasing performance of micron-sized and sphere-shaped supraparticle (SP) lasers fabricated through bottom-up assembly of II-VI semiconductor colloidal quantum wells (CQWs) with their counterparts made of quantum dots (CQDs). CQWs consist of a 4-monolayers thick CdSe core and an 8-monolayers thick CdxZn1-xS shell with a nominal size of 14 x 15 x 4.2 nm, and CQDs of CdSxSe1-x/ZnS with 6 nm diameter. SPs are optically characterized with a 0.76 ns pulse laser (spot size: 2.88 x 10-7 cm2) at 532 nm, and emit in the 620-670 nm spectral range. Results show that CQW SPs have lasing thresholds twice as low (0.1-0.3 nJ) as CQD SPs (0.3-0.6 nJ), and stress tests using a constant 0.6 nJ optical pump energy demonstrate that CQW SPs withstand lasing emission for longer than CQD SPs. Lasing emission in CQW and CQD SPs under continuous operation yields half-lives of tau CQW SP approximate to 150 min and tau CQD SP approximate to 22 min, respectively. The half-life of CQW SPs is further extended to tau QW approximate to 385 min when optically pumped at 0.5 nJ. Such results compare favorably to those in the literature and highlight the performance of CdSe-based CQW SPs for laser applications. CdSe-based colloidal quantum well supraparticles display a lower laser threshold than their quantum dot counterparts. When benchmarked against other state-of-the-art CdSe-based microlasers, these devices also score amongst the ones with the longest half-lives (between 102 and 103 min), and their degradation fluences (108-109 mJ cm-2) surpass those of all the CdSe-based quantum dot microlasers. image

Transfer printing integration of planar membrane devices on photonic and electronic circuits is becoming a well established technology. Typical systems incorporate a single planar layer printed into full contact with the host substrate. In this work we present an advanced transfer print system that enables printing of optical devices in non-planar geometries and allows in-situ optical monitoring of devices. We show micro-resonators with air-clad whispering gallery modes coupled to on-chip waveguides, inverted device printing and three dimensionally assembled micro-cavities incorporating semiconductor micro-lenses and nanowire lasers. We demonstrate printing onto non-standard substrates including optical chip facets and single-mode fibre ends. The optical fibre printing was carried out with alignment assistance from in-situ optical coupling through the transfer printing system in real-time allowing active alignment of the system.

Silicon nitride (Si3N4) is an excellent material platform for visible wavelength photonic integrated circuits, in particular, as a host for the heterogeneous/hybrid integration of complementary materials. In this work, we characterise the performance of the Si3N4 from LIGENTEC as a base for hybrid integration.

Narrow-pulse visible light sources are crucial to time-resolved imaging. We present 16k-element MicroLED arrays spanning the visible region allowed by InGaN/GaN, achieving 3 ns pulses at up to 100 MHz repetition rate with programmable illumination patterns.