Ultra-sensitive UV solar-blind optical wireless communications with an SiPM.

In this Letter, an SiPM with a dedicated cooling system suitable for receiving ultra-low-power solar-blind wavelengths is reported. This is designed to decrease the temperature of the detector from 21°C to -10°C, and the corresponding dark count rate (DCR) is reduced by approximately 10 dB. A 275 nm optical wireless communication (OWC) system is established using on-off-keying (OOK) modulation. Transmission rates ranging from 100 kbit/s to 2 Mbit/s are demonstrated with this cooled SiPM. The received power is as low as 30 pW (corresponding to 41.5 photons per bit) at a data rate of 1 Mbit/s and a bit error rate of 2.4 × 10-3.

Demonstration of >1Tbit/s WDM OWC with wavelength-transparent beam tracking-and-steering capability.

Beam tracking-and-steering is crucial for the operation of high-speed, narrow beam, optical wireless communication (OWC) systems. Using a system based on two sets of low-cost cameras for continuous beam tracking and a set of mirrors for steering, we demonstrate here a high-capacity (>1Tbit/s) ten-channel wavelength-division multiplexed (WDM) OWC system based on discrete multitone transmission. The results, which are achieved over a 3.5-m perpendicular distance and across a lateral coverage up to 1.8 m, constitute to the best of our knowledge, the highest aggregate OWC capacity at this coverage.

Transmitter and receiver technologies for optical wireless.

Providing a reliable link, with sufficient signal-to-noise ratio (SNR) and bandwidth to deliver high-capacity communications is a critical challenge for optical wireless (OW) communications and understanding and jointly optimizing the performance of the transmitter and receiver subsystems is a key part of this. At the transmitter a source of light, either a laser or a light-emitting diode, must be modulated with the communications signal. The resulting emission must be directed, using optics or steering systems, as required for the particular application, and must be within any safety levels set by relevant standards. The receiver is the most critical part of any optical link, as its design is a dominant factor in determining the received SNR, which determines the capacity and ultimately the utility of the link. A receiver must collect, filter and concentrate signal radiation, then detect and amplify the resulting electrical signal. This review surveys the state-of-the-art transmitter and receiver technologies. Details of design constraints are discussed, and potential future directions discussed. This article is part of the theme issue 'Optical wireless communication'.

Wide field-of-view optical broadcasting for bi-directional indoor optical wireless communications employing PAM-4 modulation.

We present wide field-of-view (FOV) bi-directional point-to-multipoint indoor optical wireless communications operating over a range of 4 m. The system is designed to integrate with fiber-to-the-home/building networks realized by a passive optical network. A phase-only spatial light modulator (SLM)-based beam steering base station with a ±30° FOV broadcasts downstream transmissions to two nomadic user terminals that use mirror-based beam steering to provide a ±50° FOV. At the base station, a composite phase mask is constructed on the SLM not only to perform optical broadcasting, but also to steer upstream optical transmissions from user terminals at a different wavelength. Successful upstream and downstream data transmission of 25 Gbit/s PAM4 is achieved.

A spectrally efficient equalization technique for optical sources with direct modulation.

In this Letter, a novel equalization method for directly modulated optical sources is introduced. Conventional source equalization methods balance the low- and high-frequency responses of the source by cutting down the low-frequency components in any drive signal. Typically, this ensures a flat frequency and linear signal response up to some predetermined upper-frequency limit. It is conventionally done under a fixed linear dynamic range. However, in this Letter, it is found that the source's dynamic range varies by frequency. We describe a novel method that determines the limit of signal linearity at each frequency and uses this to create the enhanced equalizer response. This leads to an improved source bandwidth and, in practice, allows greater transmitted signal energy. Experimental results for a resonant-cavity LED transmitter show date-rate improvement of ∼40% and, to the best of our knowledge, a record date rate of 8.76 Gb/s with a bit-error-rate less than 3.8×10-3.

All-optical mode-group multiplexed transmission over a graded-index ring-core fiber with single radial mode.

We present a design of graded-index ring-core fiber (GI-RCF) supporting 3 linearly polarized (LP) mode-groups (i.e. LP01, LP11 and LP21) with a single radial index of one for mode-division multiplexed (MDM) transmission. Reconfigurable spatial light modulator (SLM) based spatial (mode) (de)multiplexers are used to systematically characterize spatial/temporal modal properties of the GI-RCF. We also demonstrate all-optical mode-group multiplexed transmissions over a 360m fabricated GI-RCF without using multiple-input multiple-output digital signal processing (MIMO DSP).

Handheld free space quantum key distribution with dynamic motion compensation.

Mobile devices have become an inseparable part of our everyday life. They are used to transmit an ever-increasing amount of sensitive health, financial and personal information. This exposes us to the growing scale and sophistication of cyber-attacks. Quantum Key Distribution (QKD) can provide unconditional and future-proof data security but implementing it for handheld mobile devices comes with specific challenges. To establish security, secret keys of sufficient length need to be transmitted during the time of a handheld transaction (~1s) despite device misalignment, ambient light and user's inevitable hand movements. Transmitters and receivers should ideally be compact and low-cost, while avoiding security loopholes. Here we demonstrate the first QKD transmission from a handheld transmitter with a key-rate large enough to overcome finite key effects. Using dynamic beam-steering, reference-frame-independent encoding and fast indistinguishable pulse generation, we obtain a secret key rate above 30kb/s over a distance of 0.5m.

High gain, wide field of view concentrator for optical communications.

The field of view and gain of optical concentrators used within free space optical communications systems are constrained by conservation of etendue. In this Letter, consideration of the processes in a fluorescent concentrator leads to a simple design strategy for these concentrators for this application. Significantly, because fluorescent concentrators do not conserve etendue, this can lead to concentrators with wider fields of view and higher gains. A model of a fluorescent concentrator containing a quantum dot material suggests that it could have a gain 50 times higher than an etendue conserving concentrator with the same field of view.

"My Dead Body": Development, production, and reception of a documentary that publicly displays the dissection of a human donor.

Recently, there has been an emphasis on keeping the study of anatomy using donor material confined to the domain of medical and allied healthcare professionals. Given the abundance of both accurate and inaccurate information online, coupled with a heightened focus on health following the COVID-19 pandemic, one may question whether it is time to review who can access learning anatomy using donors. In 2019, Brighton and Sussex Medical School (BSMS) obtained a Human Tissue Authority Public Display license with the aim of broadening the reach of who could be taught using donor material. In 2020, BSMS received its first full-body donor with consent for public display. Twelve workshops were delivered to student groups who do not normally have the opportunity to learn in the anatomy laboratory. Survey responses (10.9% response rate) highlighted that despite being anxious about seeing inside a deceased body, 95% felt more informed about the body. A documentary "My Dead Body" was filmed, focusing on the rare cancer of the donor Toni Crews. Viewing figures of 1.5 million, and a considerable number of social media comments highlighted the public's interest in the documentary. Thematic analysis of digital and social media content highlighted admiration and gratitude for Toni, the value of education, and that while the documentary was uncomfortable to watch, it had value in reminding viewers of life, their bodies, and their purpose. Fully consented public display can create opportunities to promote health-conscious life choices and improve understanding of the human body.

A Multicentre Analysis of Approaches to Learning and Student Experiences of Learning Anatomy Online.

Introduction: The approaches to learning students adopt when learning anatomy online could yield important lessons for educators. Dissection room teaching can encourage students to adopt a deep approach to learning anatomy. It was therefore hypothesized that the proportion of students adopting a deep approach to learning would be lower in a population learning anatomy online. This research aims to investigate the experiences of students learning anatomy online during the COVID-19 pandemic and the approaches to learning they adopted. Methods: A survey was distributed to medical students at 7 universities across the UK and Ireland. The survey included two previously validated questionnaires: Approaches and Study Skills Inventory for Students and Anatomy Learning Experience Questionnaire. Results: The analysis included 224 unique student responses. Students' approach to learning mirrored reports from previous studies conducted during face-to-face tuition with 44.3% adopting deep, 40.7% strategic, 11.4% surface, and 3.6% combined learning approaches. The university (p = 0.019) and changes to formative (p = 0.016) and summative (p = 0.009) assessments significantly impacted approach to learning. Students reported that online resources were effective but highlighted the need for clearer guidance on how to find and use them successfully. Conclusion: It is important to highlight that students value in-person opportunities to learn from human cadaveric material and hence dissection room sessions should remain at the forefront of anatomical education. It is recommended that future online and/or blended provisions of anatomy teaching include varied resources that maximize engagement with media featuring cadaveric specimens. Supplementary Information: The online version contains supplementary material available at 10.1007/s40670-022-01633-7.

A Wide-Area Coverage 35 Gb/s Visible Light Communications Link for Indoor Wireless Applications.

Visible Light Communications (VLC) can provide both illumination and communications and offers a means to alleviate the predicted spectrum crunch for radio-frequency wireless communications. In this paper, we report a laser diode based white-light communications link that operates over a wide area and supports high data rates. The proposed system is a four-colour multiplexed high-speed VLC system that uses a microelectromechanical system (MEMS) mirror-based beam-steering. The system operates at record data-rates of more than 35 Gb/s (Bit Error Rate(BER) < 3.8 × 10-3) with a coverage area of 39 m2 at a link distance of 4 m. To the best of our knowledge this is the fastest VLC demonstration reported thus far. The paper also addresses issues of eye-safety, showing data rates of  more than 10 Gb/s are feasible.

Order changes within receptor systems upon ligand binding: receptor tightening/oligomerisation and the interpretation of binding parameters.

Recent hydrogen-deuterium exchange experiments have highlighted tightening and loosening of protein structures upon ligand binding, with changes in bonding (DeltaH) and order (DeltaS) which contribute to the overall thermodynamics of ligand binding. Tightening and loosening show that ligand binding respectively stabilises or destabilises the internal structure of the protein, i.e. it shows positive or negative cooperativity between ligand binding and the receptor structure. In the case of membrane-bound receptors, such as G protein-coupled receptors (GPCRs) and ligand gated ion channel receptors (LGICRs), most binding studies have focussed on association/dissociation constants. Where these have been broken down into enthalpic and entropic contributions, the phenomenon of "thermodynamic discrimination" between antagonists and agonists has often been noted; e.g. for a receptor where agonist binding is predominantly enthalpy driven, antagonist binding is predominantly entropy driven and vice versa. These data have not previously been considered in terms of the tightening, or loosening, of receptor structures that respectively occurs upon positively, or negatively, cooperative binding of ligand. Nor have they been considered in light of the homo- and hetero-oligomerisation of GPCRs and the possibility of ligand-induced changes in oligomerisation. Here, we argue that analysis of the DeltaH and DeltaS of ligand binding may give useful information on ligand-induced changes in membrane-bound receptor oligomers, relevant to the differing effects of agonists and antagonists.

Understanding noncovalent interactions: ligand binding energy and catalytic efficiency from ligand-induced reductions in motion within receptors and enzymes.

Noncovalent interactions are sometimes treated as additive and this enables useful average binding energies for common interactions in aqueous solution to be derived. However, the additive approach is often not applicable, since noncovalent interactions are often either mutually reinforcing (positively cooperative) or mutually weakening (negatively cooperative). Ligand binding energy is derived (positively cooperative binding) when a ligand reduces motion within a receptor. Similarly, transition-state binding energy is derived in enzyme-catalyzed reactions when the substrate transition state reduces the motions within an enzyme. Ligands and substrates can in this way improve their affinities for these proteins. The further organization occurs with a benefit in bonding (enthalpy) and a limitation in dynamics (cost in entropy), but does not demand the making of new noncovalent interactions, simply the strengthening of existing ones. Negative cooperativity induces converse effects: less efficient packing, a cost in enthalpy, and a benefit in entropy.

Changes in motion vs. bonding in positively vs. negatively cooperative interactions.

From a consideration of the interactions between non-covalent bonds, it is concluded that positively cooperative binding will occur with a benefit in enthalpy and a cost in entropy, and that negatively cooperative binding will occur with a cost in enthalpy and a benefit in entropy; experimental data support these conclusions.

Direct current balancing algorithm for FLCOS binary phase holograms.

The need for DC balancing phase pixels in ferroelectric liquid-crystal-on-silicon spatial light modulators leads to control schemes that limit their use in beam steering applications where a continuous display of a routing hologram is required. By analyzing the phase redundancy in binary phase holograms, a new DC balancing algorithm has been developed that allows more general beam splitting and multiple beam steering functions. The theoretical derivation of the algorithm and experimentally measured properties of the optical beams are presented and discussed.

Cross-talk analysis in a telecentric adaptive free-space optical relay based on a spatial light modulator.

We present an analysis of the performance limit of an adaptive multichannel free-space optical interconnect based on a spatial light modulator (SLM). The SLM function is to provide an active alignment of the signal beam in the detector plane. A thorough cross-talk analysis based on the diffractive properties of an ideal SLM in an isoplanatic optical system is shown. We analyze the performance in terms of the bit-error rate (BER) due to cross talk between different channels in the optical interconnect for different alignment states and for different phase-modulation schemes.

Kinetic barriers and ordering of non-covalently bound states.

Binding of a dimer of a glycopeptide antibiotic to two molecules of a ligand that are bound to a membrane surface (by a hydrocarbon anchor) has been investigated. This binding on a surface is cooperatively enhanced (surface enhancement) relative to the binding in solution, because the former occurs intramolecularly on a template. Previously a correlation between surface enhancement and thermodynamic stability of the dimer in free solution (Kdimsol) was hypothesised. However, we found that two weakly dimerising antibiotics (vancomycin and ristocetin A) with similar Kdimsol give very different surface enhancements. We propose a model to explain the data correlating surface enhancement to the kinetic barrier to dissociation of the dimer. The surface enhancement of binding can be expected to increase with increasing tightness of the non-covalent interactions formed at the dimer interface. The effect should be found in general where cooperativity is exercised within an organised template (e.g., DNA duplexes and proteins).

Design and analysis of an adaptive board-to-board dynamic holographic interconnect.

We describe the design and analysis of an adaptive free-space optical interconnect between two circuit boards in a standard electronic backplane. An array of vertical-cavity surface-emitting lasers is used as the transmitter, and this communicates with a detector array on the receiver circuit board. Routing is achieved with a holographic crossbar that has a ferroelectric liquid-crystal spatial light modulator to display binary phase computer-generated holograms. A detailed analysis of a 48-channel interconnect designed to operate at 1 (Gbytes/s)/channel indicates that such a switch will operate successfully given typical components and card misalignments.