We demonstrate a photonic temperature sensor based on three silicon cascaded ring resonators (CRRs) integrated on a 3 µm thick silicon-on-insulator (SOI) platform for contact thermometry. A CRR-based sensor achieves an expanded free spectral range (FSR) of 23 nm, enabling a broader operational temperature range compared with the FSR of 1 nm for the single ring resonator. The thick SOI platform offers several advantages, including low propagation loss (less than 0.1 dB cm-1), negligible polarization dependence (approaching zero birefringence) and high-power handling capability (greater than 10 mW) without any resonance shape deformation from two-photon absorption (TPA). Optical coupling was achieved through edge-coupled fibre packaging to the photonic chip. The sensor exhibits a temperature sensitivity of 85 pm K-1 with an uncertainty of 16.1 mK, measured over a temperature range from -20 to 90°C. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.

Augmented reality (AR) displays demand optical engines that are compact, efficient, and highly directional. While micro-light-emitting diodes (µLEDs) provide exceptional brightness, fast response, and low power consumption, their poor light extraction and near-Lambertian emission severely limit optical coupling in AR systems. Here, we introduce a pixel-by-pixel on-chip silicon-based micro-reflector device (SMRD) for µLEDs that simultaneously integrates light-extraction enhancement and beam shaping within a scalable architecture. Simulation and experimental results show that the SMRD narrows the emission divergence from ±70.5° to ±39.4°, enhances luminous flux within ±20° by ∼64%, and suppresses pixel crosstalk to 4.75%. Beyond device-level improvements, a near-eye display prototype integrating the µLED/SMRD device with a projection lens, beam splitter, metal mask, and a camera acting as an eye substitute further verifies its system-level performance. The SMRD thus delivers a compact and fabrication-compatible route toward high-efficiency, miniaturized AR projection engines. This work establishes a foundation for µLED-based light-field control, with implications for next-generation near-eye displays, spatial light modulators, and advanced photonic systems.

The coupling of valley and spin degrees of freedom in 2D materials holds significant promise for advancing novel device applications. In this study, a highly polarized spin-valley transistor based on the circular dichroic photocurrent in WS2 is demonstrated. By integrating highly spin-selective tunneling spin detectors and leveraging the magnetic proximity effect of spin-polarized substrates, the spin degeneracy in optical transition and spin transport can be broken. A giant photocurrent polarization of 41.90% is realized at room temperature under ultraviolet light irradiation. Interestingly, the sign of the circular dichroism can be reversed by switching the magnetization of substrates and electrodes, showing an opposite resistance state under circularly polarized light. This device has removed the hurdle for developing complementary phototransistors (as they are always in low-resistance states under light illumination), which are further exploited to construct reconfigurable logic gates. The findings will pave the way for new developments in optical couplers and on-chip optical computing technologies.

Research on an abnormal respiration monitoring mattress based on a plastic optical fiber end-face coupling structure

This work reports the design and realization of a silicon-based micro photovoltaic generator (MPG) fabricated using a standard 0.18 μm complementary metal oxide semiconductor (CMOS) technology. The device harvests optical energy and converts it into electrical power through the photovoltaic effect, leveraging a network of engineered p–n junctions formed within the semiconductor. A grid-structured architecture is adopted, in which patterned p-type regions are embedded inside an n-well platform. This configuration expands the effective junction area, increases carrier-collection paths, and strengthens the internal electric field, thereby enhancing photocurrent generation. To further improve optical coupling, a specialized post-CMOS treatment is introduced. A wet etching is used to selectively remove the silicon dioxide layer that normally covers the junction regions in CMOS processes. Eliminating this dielectric layer enables direct photon penetration into the depletion region minimizes reflection-related losses, resulting in a significant improvement in device performance. Under an illumination intensity of 1000 W/m2, the fabricated microgenerator delivers an open-circuit voltage of 0.49 V, a short-circuit current of 239 µA, and a maximum output power of 90 µW. The device exhibits an overall energy conversion efficiency of 12.9%, confirming the effectiveness of the grid-like junction design and the post-processing oxide removal.

A reflective all-fiber optical current transformer based on a spatial non-reciprocal phase modulation technique is investigated by theoretical analysis and experimental measurement. The modulation unit, composed of a phase delay wave plate (LiNbO3) and two Faraday rotators, achieves flexible frequency adjustment by converting modulation from the time domain to the spatial domain. Therefore, the avoidance of the impact caused by delay coils is achieved in principle. The absence of intrinsic frequency limitations eliminates the demand for precise timing control in demodulation, thereby simplifying the demodulation circuit and reducing the cost and size of the transformer. In previous studies, redundancies were identified in the optical path coupling devices. The half-wave voltage of the modulator is excessively high, and its size is considerable due to constraints inherent in the manufacturing process. The measurement range is within 1800 A. The scheme simplifies some optical path components. By optimizing the phase delay wave plate, the half-wave voltage of the modulator is significantly reduced by a factor of 150. Experimental results demonstrate that the current transformer exhibits excellent detection consistency within the rated current range of 30–3600 A (1–120%), the response time is within 3 ms, and the measurement error and peak error reach 0.052% and 0.127%. This configuration provides a novel option for the design and practical application of all-fiber optical current transformers.

ABSTRACT The power conversion efficiency of bifacial Cu (In, Ga)Se 2 (CIGS) solar cells under rear illumination is limited by low short circuit current density (Jsc) values. This study investigates the potential of high‐mobility, low carrier concentration transparent conducting oxides (TCOs) as transparent rear contacts (TBCs) to enhance the performance of CIGS solar cells under rear illumination. We first show by optical simulations that TCO with high carrier mobility and low carrier concentration reduces parasitic absorption and improves light coupling into the CIGS absorber, respectively. Then, CIGS solar cells are realized by implementing In 2 O 3 :Sn (ITO) and the higher performing In 2 O 3 :H (IOH) and In 2 O 3 :Zr (InZrO) as TBC. These TBCs significantly improve the optical coupling of rear‐side illumination into the CIGS absorber, improving the rear external quantum efficiency maximum value from about 50% to above 80%. The optical transparency of IOH and InZrO TBC remains relatively unaffected after the CIGS growth process, outperforming ITO on this aspect as well. The observed poor rear EQE at short wavelength is ascribed to a strong rear interface recombination. Finally, a prospective analysis of realistically achievable rear Jsc gains is provided when introducing a steeper Ga gradient at the rear interface and a passivated rear contact.

Solution-processed perovskite heterojunction photodetectors have attracted widespread attention due to their low-cost, large-area processing techniques; however, they still suffer from low responsivity. In this work, we propose and demonstrate a vertical type FA0.4MA0.6PbI3/Cu2O heterojunction photodetector integrated with a D-shaped optical fiber coupling scheme to enhance responsivity. Microstructural characterization reveals that Cu2O contributes to enhancing light absorption and accelerating photoexcited carrier transport. Compared with the planar type, the vertical type FA0.4MA0.6PbI3/Cu2O photodetector achieves an order-of-magnitude improvement in responsivity. Experimental results indicate that the vertical type FA0.4MA0.6PbI3/Cu2O optical fiber device has a high built-in electric field and a light–matter interaction, which facilitates photocarrier transport, separation, and collection. Additionally, under illumination of 21.3 μW 650 nm light at a bias voltage of −1.5 V, photodetectors based on the vertical type FA0.4MA0.6PbI3/Cu2O and D-shaped fiber exhibit superior photoelectric performance, including a high responsivity of 22.1 A/W, a maximum photocurrent of 15.1 μA, an external quantum efficiency of 4.22 × 103%, and a detectivity of 7 × 1010 Jones. The responsivity of vertical type FA0.4MA0.6PbI3/Cu2O optical fiber integrated photodetector is not only superior to that of the planar type device in this work but also exceeds that of the recently reported solution-processed perovskite heterojunction photodetector. The research results provide a feasible strategy for designing the solution-processed perovskite heterojunctions for low-cost, high-performance photonic devices.

ABSTRACT Advancements in artificial intelligence (AI) and remote sensing have enhanced the feasibility of satellite-based precipitation nowcasting. The role of coupling strategies, particularly those involving optical flow methods, remains insufficiently studied. This research evaluated two classical model architectures to assess the impact of various optical flow-based coupling strategies on prediction performance. Results show notable performance differences: while some strategies (e.g. b4) degrade accuracy, others (e.g. b5) consistently outperform benchmarks. Specifically, strategy b5 improves mean synthesis of statistics (SS) by 7.52% and 4.70% over benchmarks a1 and b1, respectively. Regional analysis further highlights b5’s effectiveness, with SS of 6.84% and 6.74% in the northwest and southwest of China. These findings underscore the critical role of coupling strategy selection in hybrid nowcasting models, particularly across diverse geoclimatic regions, and the significance is expected to increase with further developments in remote sensing technology.

Photothermal-responsive liquid crystal elastomers (LCEs) face critical barriers in biomedical applications: phase transition temperatures exceeding80°C risk thermal injury, and free-space optical actuation fails in confined spaces. Here, a thiol-ene crosslinked LCE is developed with a biocompatible phase transition temperature (37.6°C), enabling safe actuation within biological tissues. Through coaxial extrusion, the fabrication of waveguide-structured LCE optical fibers is pioneered, achieving ultralow optical loss (0.76 dBcm-1) and enabling long-range light transmission and remote actuation via silica optical fiber coupling. Under 808 nm laser stimulation (375 mW), these LCE optical fibers generate 30% contraction strain in 23 s, maintaining maximum surface temperature < 48°C. Integrated into an endoscopic system, LCE optical fibers replaced rigid mechanical components. Ex vivo characterization reveals their omnidirectional bending capability (94° angular range), while in vivo trials on live rats and rabbits validate their operational functionality in anatomical environments, enabling hemorrhage detection and laser-steered tumor ablation via controlled navigation. Histopathological analysis confirms no thermal damage at fiber-tissue interfaces. This work establishes biocompatible LCE optical fibers as a photonic platform integrating photonic-driven soft actuation and tissue-compliant adaptability, enabling mechanically safe interventions in confined anatomical environments.

Photoacoustic spectroscopy (PAS) is a powerful technique for selective gas detection; however, its performance in non-resonant configurations is fundamentally constrained by the poor low-frequency response of conventional acoustic detectors. Commercial MEMS microphones, although compact and cost effective, exhibit limited infrasound sensitivity, which restricts the development of truly miniaturised and broadband PAS systems. To address this limitation, we present a novel MEMS fluidic microphone (f-mic) that operates on a thermal sensing principle and is explicitly optimised for the infrasound regime. The sensor demonstrates a constant sensitivity of 32 μV/Pa for frequencies below 20 Hz. A detailed analytical model incorporating frequency-dependent effects is developed to identify and investigate the critical design parameters that influence system performance. The overall system exhibits a band-pass frequency response, enabling broadband operation. Based on these insights, a miniaturised photoacoustic cell is fabricated, ensuring efficient optical coupling and f-mic integration. Experimental validation using a CO2-targeted laser system demonstrates a linear response up to 5000 ppm, a sensitivity of 6 nV/ppm, and a theoretical detection limit of 300 ppb over 100 s, resulting in an NNEA of W cm−1 Hz−0.5. These results establish the f-mic as a robust, scalable solution for non-resonant PAS, effectively overcoming a significant bottleneck in compact gas sensing technologies.

Mathematical modeling and experimental validation of optical coupling efficiency in Ultraviolet-C light emitting diode systems

Radioluminescent batteries, characterized by their high energy density and long lifespan, are ideal power sources for wireless sensor networks and micro-electromechanical systems. However, their practical application has been hindered by the inherent low energy conversion efficiency. Herein, we quantified the energy loss modes in RL batteries and demonstrated the corresponding efficiency enhancing strategies. A Monte Carlo model incorporating the coupled effects of the radiation and optical fields was first developed and revealed that the optical loss is accounting for around 75% in x-ray RL batteries. Reflective layers and optocoupler adhesive layers are employed and improve significantly the optical coupling efficiency from 23.6% to 51.7%, resulting in a 225% overall performance enhancement of CsI: Tl-based RL batteries. This study not only highlights the critical role of optical field engineering in boosting RL batteries performance but also provides insights to unlock the full potential of RL batteries.

Abstract Achieving efficient optical coupling between the emission from perovskite quantum dots (PQDs) and photonic integrated elements requires ultranarrow linewidths and highly directional emission. These are challenging goals at room temperature due to the broad and isotropic nature of perovskite emission. Here, we demonstrate ultranarrow‐linewidth emission from CsPbBr 3 PQDs at room temperature, in both spontaneous and stimulated regimes, by coupling to state‐of‐the‐art open‐access curved dielectric cavities under continuous wave excitation. The emission is confined to a single transverse electromagnetic mode of the cavity, achieving a remarkably narrow linewidth of 0.2 nm, ≈100× narrower than free‐space emission in both the emission regime. Single‐mode lasing from a small number of PQDs is observed, yielding a quality factor of ≈2590, among the highest reported for single‐mode lasing. The open‐access design enables precise tuning of cavity length and selective coupling of emitters in their native state, overcoming the limitations associated with closed and fixed‐length vertical‐cavity surface emitting laser geometries. The geometry's low divergence and tunability provide an efficient route for integrating perovskite emitters with on‐chip photonic circuits, advancing their use in quantum and optoelectronic technologies.

ABSTRACT This review delves into guided mode resonance (GMR) gratings, highlighting their significance in broadband reflection due to their exceptional frequency selectivity and ability to manipulate electromagnetic fields. GMR gratings have evolved from single‐mode to multi‐mode applications, expanding their utility from narrowband to broadband reflections, with GMR reflectors emerging as a viable alternative to traditional Distributed Bragg Reflectors. Through optimal parameters of grating structure, GMR reflectors can perform a high and broadband reflectivity. Advances in nanofabrication and measurement technologies have facilitated the realization of GMR gratings, which are now poised to enhance high‐power lasers, optical couplers, photodetectors, and optical communication systems. The paper provides a comprehensive overview of the resonant principles, implementation structures, fabrication techniques, and applications of GMR broadband reflectors, concluding with a future outlook on their potential in photonics.

Derived SmFeO3 nanoparticles exhibiting optical, magnetic, and ferroelectric coupling for multifunctional applications

In this work, the effects of luminescent coupling (LC) on the external quantum efficiency (EQE) of perovskite‐silicon tandem (PST) solar cells are quantified by means of monochromatic transient photocurrent measurements and comprehensive optoelectronic simulations that take into account both optical and electrical coupling of the subcells. It is shown that, at short wavelengths, a similar response results from both LC and silicon bottom‐cell shunts. The two contributions can be discriminated and quantified based on bias voltage and light intensity‐dependent measurements. Such measurements were conducted on state‐of‐the‐art PST cells and agree well with the behavior predicted by the simulations. For the case of polychromatic EQE simulations, a quenching of the LC effects with decreasing concentration of mobile ions is found, which is explained in terms of ion‐modulated recombination via bulk defects.

This study analyzes various optical couplings between an RC telescope and an MIR detector to develop a portable instrument for solar observation. The coupling systems included lenses or mirrors –custom-made and catalog types–, as well as direct coupling analysis. Simulations of the couplings were performed using the Zemax package to estimate the ray dispersion, Airy disk diameter, and PSF. Coupling with catalog lenses shows better performance, and their FOV allows the observation of a region as wide as the solar diameter. Direct coupling provides a higher spatial resolution for resolving smaller solar active regions, although it has a smaller FOV than indirect coupling. Therefore, depending on the observation goal on the Sun, the telescope can operate with either optical coupling configuration to cover a larger or smaller area on the solar disk.

Abstract A hybrid bilayer metasurface is prepared by placing a flexible metallic metasurface sticker onto another dielectric metasurface on solid substrate and the optical coupling between the two metasurfaces is investigated. The top layer supports a bright out‐of‐plane quadrupole surface lattice resonance (QSLR), while the bottom layer supports a dark quadrupole mode. When stacked together, they couple into two hybridized modes, symmetric and anti‐symmetric QSLRs. It is found that the splitting width, as well as the nature of these modes, depends on the spacer layer thickness t . The long decay length of the QSLR along the z ‐direction and its slow variation with t suggest that the interlayer coupling is mediated not by a local gap mode but by a nonlocal, extended mode. A key consequence of this nonlocal coupling is the insensitivity of the resonances to the lateral misalignment of the two layers. This alignment‐free property is highly advantageous for designing bilayer metasurfaces. Furthermore, it is demonstrated that photoluminescence enhancement from an emitter embedded in the spacer layer: The large field accumulation associated with the symmetric QSLR led to a remarkable photoluminescence enhancement up to 60 times compared to the bare spacer layer on the substrate. These findings pave the way toward quasi‐3D metasurfaces formed by stacking individual layers with precisely tuned interlayer distances, offering a promising approach for future photonic elements with integrated functionalities.

We report the development and characterisation of single‐dye luminescent solar concentrators (LSCs) fabricated using stereolithography (SLA) 3D printing, doped with Perylene Red and Perylene Orange dyes. A systematic study was carried out by varying the dye concentration in single‐dye LSCs and characterising their optical and electrical properties. The performance of the LSCs was studied under photosynthetically active radiation (PAR) illumination, which is relevant for indoor greenhouse applications and aligns with the broader goal of indoor photovoltaics and toward net‐zero energy systems. Optical coupling of the LSCs to the solar cells significantly enhanced device performance compared to air‐gap configurations. Optically coupled single‐dye LSC devices based on Orange and Red achieved power conversion efficiencies of 1.4% and 3.6%, respectively, with corresponding overall optical efficiencies of approximately 15% and 31%. Notably, despite the high reabsorption probability observed in the Red LSC–PV device, photon collection efficiencies reached 50%, demonstrating 3D printing as a rapid and effective research tool for investigating LSC–PV performance.