Conference Agenda

A dual-layer liquid crystal (LC) lens structure is designed by stacking two hole-patterned electrode (HPE) LC lens with opposite pretilt angles, each driven by an independent voltage. Since the two layers exhibit positive and negative spherical aberration (SA) at low and high voltages, respectively, the overall SA can be effectively compensated by adjusting the driving voltages. Experimental results show that the dual-layer configuration achieves nearly zero SA (≤ 0.03λ) within a tunable optical power range from 2.19 D to 2.76 D.

An electrically-addressed focus-tunable lens (FTL) enables fine, continuous, and dynamic power adjustment across a range of diopters. This lens encloses an optical fluid within a sealed container with an elastic membrane. An electromagnetic actuator applies pressure to the container, altering the curvature of the lens. This study investigates the optical performance of a gravity-compensated FTL (Optotune EL-16-40-GTC-VIS-5D) in terms of the addressed optical power and measured wavefront error, in both horizontal and vertical lens orientation. The results were compared with two standard, uncompensated models from the same manufacturer. All the analysed FTLs demonstrated excellent optical power performance regardless of orientation. The gravity-compensated FTL effectively corrected vertical coma in the upright orientation, but induced greater astigmatism compared to the standard models. These findings provide valuable insights for vision testing and adaptive optics applications.

Ultrafast laser processing has emerged as a powerful tool for precise material modification, enabling the micromachining of a wide range of materials, including polymers. The high intensities achieved with femtosecond pulses allow nonlinear absorption processes, such as multiphoton absorption, facilitating both surface structuring and bulk modification. Polymers, in particular, are of growing industrial interest due to their favorable properties, cost-effectiveness, and biocompatibility, making them suitable for advanced manufacturing applications such as microcavity fabrication. In this work, the ablation behavior and laser–polymer interaction are investigated in commercial films (PVC, PET, PP, and PDMS) by varying key parameters, including repetition rate (1 kHz–1 MHz), pulse duration (fs to ns), and wavelength (515 and 1030 nm). Experimental results, supported by thermal modeling, reveal distinct thermal regimes depending on repetition rate. The thermal properties of each material play a decisive role in heat diffusion processes and determine the different effects observed in each. Efficient material removal with reduced heat-affected zones is achieved in the sub-MHz regime, providing evidence of ablation cooling. These findings improve the understanding of high-repetition-rate effects and support the optimization of ultrafast laser micromachining strategies for polymer processing.

While conventional optical geometry measurements depend on the optical properties of the target's surface, they face limitations when evaluating advanced surfaces characterized by steep slopes or complex micro-structures that are optically non-cooperative. To overcome these challenges, an indirect optical geometry measurement paradigm is implemented, utilizing an optically trapped dielectric microsphere as a probe. By manipulating a single silica particle with an optical tweezer, the target surface is detected through the physical displacement of the probe rather than relying on optical scattering from the surface itself. We demonstrate the potential of this method by characterizing a Fresnel lens achieving 0.38 $\mu$m standard error in measured heights, proving the viability of this technique for advanced, non-destructive surface metrology.

This study investigates ultrasonic-assisted grinding processes using two contact kinematics: face and peripheral surface grinding with a variety of tools with different grain sizes and bond types. An experimental procedure was developed to analyse the influence of these configurations on surface properties, focusing on grinding forces and optical measurement of subsurface damage and roughness. First results show that the surface roughness of the face surface was improved during machining while using ultrasonic assistance.

Traditional techniques to determine laser-induced fluorescence lifetimes suffer in field applications where commonly used nanosecond pulsed lasers, non-exponential decay, and interest in a broad range of wavelengths make deconvolution impractical. We present an analytical model based on a linearised rate equation which accounts for a wavelength dependent instrument response function, incident pulse temporal distribution, and complex fluorescing and phosphorescing systems.

The rapid growth of AI and machine learning has intensified the need for energy-efficient computing, making optical computing a compelling alternative. We numerically present an optical approach by exploiting speckle formation as a mechanism for generating reservoir features using an integrated photonic reservoir cell, covered by a light-active azobenzene polymer superstrate. Encoding images into the film locally modifies its thickness and effective refractive index, altering ray paths and the resulting speckle pattern. Our system achieves an 88.89% classification accuracy, demonstrating the potential of utilizing speckle formation in an integrated photonic reservoir to perform classification tasks.

Organophosphate pesticides (OPP) remain a critical environmental contaminant, but the detection in real-world environments (soil, mud, groundwater) is hampered by the need for laboratory-based chromatographic analysis. This work demonstrates the early development of an optic fiber sensor system that can provide direct, in the field detection through optical transduction of pesticide-framework interactions. Tapered silica fibers were surface-functionalized to create hydroxide anchors, followed by in-situ crystallization of metal-organic frameworks (MOF) directly onto the fiber surface. The MOF coating exploits the evanescent field of the tapered region to couple pesticide binding (via coordination to either Lewis-acidic metal sites, Van der Waals(VDW) interaction or functional groups present within the framework) into measurable changes in optical transmission and reflectance. The aim would be for the MOF-coated fibers to demonstrate optical and structural response to malathion, chosen as a model of OPP. Fiber coatings were characterized by scanning electron microscopy and powder X-ray diffraction to confirm MOF crystallinity and coating uniformity. This work lays the foundations for MOF-functionalized fiber optics as a platform for rapid, field-compatible pesticide sensing in environmental matrices, with potential extension to a multiplexed sensor array for detection of organophosphates within more complex environments.

Kilonova spectroscopy provides a route to identifying heavy elements formed in these events, but interpretation remains limited by the lack of atomic data for many species and ionisation stages expected in neutron-rich ejecta.

We present the development of a mid-infrared pump–probe photoabsorption system for measuring absorption and emission in laser-produced plasmas of heavy-element targets. An Nd:YAG laser (1064 nm) generates a line plasma on a solid target, while a supercontinuum source provides a delayed probe spanning 1–4 µm. By varying the probe delay, different plasma conditions are accessed during plume expansion. Detection uses two fibre-coupled spectrometers (2–5 µm): one records the transmitted probe, while the other monitors a reference beam for normalisation. Mid-infrared detection is achieved via nonlinear upconversion to silicon photodetectors.

For each condition, three signals are acquired: probe only, probe transmitted through the plasma, and plasma emission with the probe blocked. Absorbance is extracted using Beer–Lambert analysis after subtracting plasma emission. Measurements on a BK7 window reproduce the expected absorption edge near 2.75 µm, validating the approach.

Preliminary results and limitations will be discussed, supporting development of experimentally validated mid-infrared atomic data for astrophysical plasma spectroscopy.

Structured Illumination Microscopy (SIM) is a super-resolution technique allowing for live cell imaging of 3D subcellular structures. It relies on illumination with spatially periodic patterns that are shifted and/or rotated with respect to the sample. The image reconstruction pipeline consists of several steps including unmixing, filtering and translation in Fourier space [1]. Although the impact of the experimental [2] and numerical processing [3] parameters has been investigated, there have not been definitive answers on whether, and to what extent, the existing SIM reconstructions are optimal in any sense. In this work, we introduce a formalism in which appearing image Fourier orders are seen as vectors in an abstract vector space. The key advantage is that this generalizes the standard Fourier-domain least-squares reconstruction algorithm to fully account for noise band cross-correlations. A key result is that we can prove how to achieve the highest theoretically possible object-independent spectral signal-to-noise ratio (SSNR). In a next step we show how the choice of illumination pattern shifts impacts SSNR and prove optimality for a unitary illumination phase matrix. Finally, we provide a simple algorithm to find the optimal (minimum) number of illumination pattern shifts for any conceivable SIM configuration in 2D and 3D.

This study investigates the impact of particle size on Raman signal intensity, aiming to support the development of standoff detection systems for aerosols. Lithium niobate powders with particle sizes ranging from 1000 to 20 µm were analysed using a 355 nm excitation source. Results show that Raman intensity decreases with decreasing particle size down to the 100–50 µm range, consistent with theoretical predictions that larger particles enhance signal through increased interaction volume and reduced scattering losses. However, for particles smaller than this range, the intensity approaches a plateau, indicating a diminished dependence on size. No significant peak broadening or spectral shifts were observed across the size range. These findings highlight the complex and non-monotonic relationship between particle size and Raman response, addressing inconsistencies reported in the literature. Understanding this behaviour is critical for optimising Raman-based standoff detection of aerosols, where particle size variability and low concentrations significantly impact signal strength and detection performance.

We report 1 kHz real-time operation of a 512-channel 850 nm photonic integrated circuit (PIC)-based arrayed waveguide grating (AWG)-CCD spectrometer, validated against laboratory reference equipment. Investigated as a lower-complexity spectrometer front-end approach in the context of spectral-domain optical coherence tomography (SD-OCT), the device is also directly relevant to fiber Bragg grating interrogation and optical source spectral monitoring.

We numerically investigate the propagation dynamics of chirped Airy beam in two-dimensional nonlocal media. The roles of input amplitude, chirp strength, and degree of nonlocality on beam evolution, collapse, and its suppression are systematically analyzed. The results show that chirp provides effective control over beam focusing, while nonlocality stabilizes the beam by redistributing optical energy and preventing collapse. These findings offer insight into the controlled manipulation of Airy beams in nonlinear media, with potential applications in beam shaping and optical trapping.

The North Western Meeting of Young Researchers in Optics and Matter (NW MYROM) is a student conference designed by and for early-stage researchers in Spain. Building on the previous NW MYRO initiative, this edition brings together OSAL, USC-OPTICA/LUZADA, Fotonekin, and Physics League to create an accessible pathway into academic life. The event offered a wide set of activities, comprising senior and junior scientific talks, poster sessions, round tables, laboratory visits, networking activities and outreach. NW MYROM aimed to approach students to a research culture beyond formal training, fostering confidence, multidisciplinarity, helping young scientists understand academic careers while sharing optics, photonics, materials and physics in a welcoming environment. This contribution seeks to share with the scientific community the scope of the conference and the impact of the activities on the audience.

Free-space optical (FSO) transmission is highly susceptible to atmospheric turbulence, which introduces random phase distortions and degrades transmitted information. In this work, we propose an all-optical decryption framework based on a reconfigurable diffractive neural network (Re-DNN) to recover images distorted under different turbulence conditions. Two datasets, MNIST and Fashion-MNIST, are independently encrypted using atmospheric turbulence with distinct strengths, emulating multi-condition FSO channels. An multi-layer diffractive neural network is trained to invert these distortions. Unlike conventional approaches, the same set of trained phase masks is reconfigured through controlled permutations and rotations to selectively decrypt images corresponding to specific turbulence regimes. This configuration-dependent functionality enables a single optical system to perform multiple decryption tasks without retraining. Numerical results demonstrate high-fidelity reconstruction under both turbulence conditions. The proposed framework highlights the potential of programmable diffractive optics for adaptive, multi-functional, and secure image recovery in dynamic free-space optical communication systems.

A simple multimode optical fiber tip sensor is proposed for fast liquid identification through droplet evaporation dynamics. By monitoring the interference pattern at the fiber tip, the system captures liquid-specific signatures. The results show clear discrimination between liquids and mixtures, confirming its potential for real-time characterization.

Fluids such as lubricants, fuels, or oils are critical components in industrial machinery. Predictive maintenance strategies employ fluid condition monitoring to plan maintenance intervals, avoiding critical downtime caused by unexpected machine failures. Depending on the application, various types of contaminants, such as solid particles or water droplets, are relevant. Current sensor technologies include electromagnetic, ultrasonic, and optical sensors, each with specific benefits and drawbacks. Two gaps in current sensor research are the classification of multiple different contaminants in the same sample, and obtaining 3D morphologies of solid contaminant particles to gain further insights into machine conditions. A candidate to address these gaps is digital holographic microscopy (DHM). Digital reconstruction of optical properties and 3D morphologies of a sample from interference patterns recorded by DHM methods has already been demonstrated. However, research into industrial fluid contamination detection with DHM appears underrepresented compared to other contamination sensor technologies. This work proposes to apply a polarisation-sensitive DHM as a new sensor for industrial fluid contamination.

This research presents a linear polarization rotator based on liquid crystal (LC) elements, utilizing a magnetic field rather than a conventional electric field for modulation. Magnetic control offers a significant advantage in applications where electrical interference or electrode integration is undesirable. By employing a hybrid alignment configuration, we achieved precise tuning of incident linearly polarized light with a rotation angle of up to 85°. Experimental results demonstrate excellent optical performance, with a degree of polarization (DoP) exceeding 95% across the tuning range.

We report an inline fiber-optic microcell integrated with microfluidic channels via femtosecond laser-induced selective etching. This architecture enables seamless liquid infiltration, with a dedicated space for sealing and isolating evaporation-induced bubbles away from the optical path. Utilizing field-responsive ferrofluids, the platform achieves versatile sensing, with performance tunable via geometry and field optimization.

Aerial optical cables in telecommunications infrastructure are susceptible to damage, necessitating fibre break localisation. A promising approach is to thermographically detect leakage light at break points; however, reducing the required optical input power remains a key challenge. We propose a fibre break localisation method combining distributed multi-fibre optical input with lock-in thermography. Experiments using an 8-fibre cable demonstrated our method can detect breaks at −7 dBm with simultaneous 8-fibre input, reducing power up to 3 dB compared to the conventional continuous-wave approach.

This work introduces a novel in-situ monitoring system for detecting micron-sized particles during optical coating in a vacuum chamber. By combining laser light scattering with high-resolution event-based vision, the system enables monitoring of contaminants. The event-based vision system includes an event camera, a dataset compiled from measurements and enlarged with synthetic data, a specifically trained neural network for detecting and a combination of different algorithms for tracing the particles. The reliability of these in-situ observations during optical coating processes was confirmed through ex-situ wafer inspections and comparative particle counts.

The interest in photonic crystals (PhCs) over the past decades has grown owing to their novelty exhibiting properties such as photonic band gaps, slow light effect, and high or low group velocity dispersion. Among the various PhC implementations, one-dimensional PhC nanobeams are particularly attractive because they offer strong confinement in a compact footprint and enable high spectral selectivity through engineered bandgaps and localized cavity resonances. We demonstrated, a novel concept of a band rejection filter operating at λ = 1550 nm on a polymer/TiO2 hybrid platform optimized to operate in the quasi-TM00 mode. The vertical nano-waveguide is composed of two thick and large (ca. 900 nm × 800 nm) polymer (nLOF, AZ2070) rails fabricated on an Si substrate with a 3 µm thermal oxide insulating layer. The device is further coat-ed by conformal atomic layer deposition of TiO2. By engineering the period and fill factor in a one-dimensional nanobeam array hybridized with in the core, a photonic bandgap centered at λ = 1550 nm was opened. Experiments validate the design by showing a measured transmission spectra exhibiting a slightly narrower photonic band gap than theoretically expected, but in accordance with the fabrication tolerances.

State of polarization (SOP)-based sensing is an effective approach for strain measurement, although sensitivity improvement remains important. In this work, a polarimetric strain sensor using a high-birefringence fibre loop mirror is demonstrated. A 0.45 m Hi-Bi fibre section was stretched up to 500 μm, and the sensor response was evaluated using the Stokes parameters, Poincaré sphere, polarization ellipse, and phase variation. The results show a clear SOP dependence on strain, confirming the potential of this configuration for enhanced strain sensing.

This work presents a preliminary study on the extension of the Subaquatic Laser-Induced Plasma-Assisted Ablation (SLIPAA) technique for glass processing by introducing saline aqueous media. SLIPAA has demonstrated the capability to fabricate high-aspect-ratio structures in soda-lime glass by combining plasma-induced ablation, shock waves and cavitation effects generated in a confined liquid environment. On the other hand, the shock waves generated in salt solution presents higher peak pressure and energy than in water, enhancing the metallic micromachining of the surfaces. In this contribution, we explore the influence of salt concentration in water (0.2–5 wt.%) on the ablation efficiency and surface quality of channels fabricated by SLIPAA. The outcomes will contribute to optimizing SLIPAA for advanced microfluidic and optofluidic applications.

We report a compact, all-optical fibre sensor capable of real-time monitoring at high volatile organic compound (VOC) concentrations. The device is fabricated by coating a porous cholesteric liquid crystal film (CLCF) on the end face of an optical fibre ferrule. An ultra-wideband wavelength-swept laser monitors shifts in the CLCF reflection in response

to benzene, toluene, and acetone vapors. The measured sensitivities are 6.11 pm/ppm for benzene, 4.48 pm/ppm for toluene, and 3.19 pm/ppm for acetone. The sensor additionally shows low sensitivity to temperature and humidity, operates without a battery, and is unaffected by electromagnetic interference, making it a practical sensor for the detection of flammable VOCs.

This work presents a simple characterization of a BB84 quantum classical emulation protocol implemented over a single-mode optical fiber link. A 10-bit sequence was transmitted from Alice to Bob, resulting in a final 5-bit key after basis reconciliation. The influence of external perturbations was assessed by applying strain to a 0.275 m fiber section. The results demonstrate that the SMF-28 fiber link can support BB84-based communication and can be used as a sensing element under applied strain.

In this publication a novel concept for a static optical receiver for atmospheric lidars is presented. By implementing a refractive telescope with wide field of view it is possible to cover multiple field directions with adequate usable aperture without the need of moving or rotating the whole receiving system altogether. Moreover, by coupling such wide field telescope with an adjustable field stop, it is possible to select a discrete portion of this wide field (e.g., at a time), reducing the background noise of the whole system. Thus, the here proposed static wide field receiving system offers several advantages, like decreasing the overall system complexity (omission of moving parts), enhancing robustness (higher resilience to vibrations), and reducing the overall system volume, all critical requirements for aerospace applications.

In this work, two families of sequence-based diffractive lenses are presented and comparatively analyzed: Lucas diffractive lenses and Pell–Lucas diffractive lenses. Both designs exploit the intrinsic properties of their generating sequences to produce multiple focal planes with predictable spatial relationships. Lucas diffractive lenses generate four focal planes along the optical axis with partially balanced energy distribution, where the spacing between focal positions is governed by the golden ratio. In contrast, Pell–Lucas diffractive lenses exhibit trifocal behavior, consisting of a dominant central focus and two symmetrically distributed lateral foci, whose positions follow relationships determined by the silver ratio. Numerical and experimental results show strong agreement, confirming the validity of the sequence-based design methodology. The ability to control the number, position, and relative intensity of focal planes highlights the potential of these lenses for applications in multifocal imaging, optical trapping, and advanced optical systems

Subsurface damage (SSD) in brittle optical materials degrades mechanical and optical performance. Accurate knowledge of SSD depth is essential for optimizing manufacturing processes. For this purpose, optical coherence tomography (OCT) provides a non-destructive, depth-resolved measurement approach. We present an experimental time-domain full-field OCT (TD-FF-OCT) system operating at 445 nm for imaging low-scattering SSD in glass. The setup employs a Linnik configuration with two Schwarzschild-type reflective objectives to minimize dispersion and eliminate chromatic aberrations. Imaging of SSD in ground fused silica is successfully demonstrated.

EU-funded FUELGAE-project aims to develop a novel model for the production of Advanced Liquid Fuels (ALFs) from CO2 emission streams in two industrial sectors – biorefineries and energy-intensive industries – through a microalgae pilot-scale photobioreactor (PBR) integrated into their infrastructure. As part of the project, a novel multiresolution in-line microscope, and an off-set Raman probe for on-line bioprocess monitoring were developed and validated by on-site PBR measurements.

An electrically controlled liquid crystal (LC) microlens array based on fan-shaped partitioned planar pattern electrodes is reported in this paper, which can achieve efficient light wave modulation in a block-wise manner. By jointly driving and controlling the voltages of array electrodes in different regions within the same substrate of LC microlenses, corresponding adjustable focal point-like light spots can be formed. This method will provide inspiration for the continuous development and design of LC optical components, promoting the development of applications such as light field imaging, wavefront detection/correction, and imaging enhancement systems.

This work presents the design, calibration, and validation of a suite of high speed infrared radiation thermometers (IRTs), traceable to the International Temperature Scale of 1990 (ITS-90), developed for non-contact temperature measurement in transient combustion environments. Measuring detonating fuel droplets requires an approach capable of capturing behaviour from initial room temperature conditions through ignition, self-sustained combustion, and eventual flame extinction.

The first instrument employs an InAsSb photodiode operating over the 3 to 11 µm wavelength range, enabling measurements close to room temperature. This range allows accurate tracking of droplet temperatures below the boiling point, under 300 °C for the kerosene used, making it possible to observe early stage droplet heating and the full combustion progression.

Subsequent instruments employ APD-based IRTs to extend capability into higher temperature and more dynamic regimes. Their increased temporal resolution enables observation of rapid transients, flame evolution, and combustion instabilities in both kerosene and sustainable aviation fuel (SAF). Despite differences in fuel properties, similar overall combustion trends are observed.

These optical diagnostics provide insight into ignition behaviour, flame development, and radiative characteristics, supporting comparative evaluation of alternative aviation fuels for aviation decarbonisation.

The role of researchers extends beyond scientific production and includes transferable skills that benefit both the community and society. Among these, science communication and outreach are essential for engaging diverse audiences, fostering curiosity, and promoting critical thinking in an era increasingly shaped by misinformation. With this purpose, the USCOPTICA Student Chapter and Santiago Young Minds Section were created. Since their foundation, undergraduate, master’s, and PhD students have actively participated in the dissemination of optics and photonics, gaining experience in hands-on workshops, socially oriented outreach events, and the organization of international conferences. This work presents our most relevant activities over the past two years.

Light-reconfigurable surface relief gratings (SRGs) formed on azobenzene thin films have shown great promise in the advancing of adaptive and flat optics. Tailoring these SRGs for desired light manipulation has been efficiently demonstrated using a digital holographic microscope (DHM) integrated with laser interference lithography. The robustness of this set-up enables formation of complex and intricate diffractive elements with real-time monitoring. One noteworthy photonic application of this microfabrication technique is a tunable organic thin film laser. In this study, we present a pixelated organic thin-film laser with stitched microresonators for customized lasing wavelengths. Unlike the photopatterning of an entire area with a single SRG, each small unit area, or pixel, was inscribed individually, functioning as a distinct microresonator. We demonstrate how custom photo-patterned sub-micrometer SRGs were replicated onto a PDMS substrate to serve as distributed feedback (DFB) laser resonators. An organic laser dye-based gain layer was then coated onto the structured PDMS substrate. Collective pumping of selected microresonators resulted in simultaneous lasing at multiple wavelengths, enabling tailored emission spectra.

In this presentation, we will describe the synthesis and analysis of a new series of Er3+-doped germanate glasses and glass-ceramics in the GeO2-Na2O-K2O system. We will examine how variations in glass composition influence their physical, thermal, structural, optical, and spectroscopic behavior, with the goal of developing glass-based materials with enhanced spectroscopic performance. Controlled heat treatments will be applied to induce crystal growth within the glasses, and the resulting effects of crystallization on their spectroscopic characteristics will be evaluated.

Lanthanide-doped nanocrystals enable the conversion of nearinfrared (NIR) radiation into multicolor emission in the ultraviolet (UV) and visible (vis) regions via upconversion (UC), as well as NIR emission through downshifting (DS). These properties make them promising for a wide range of applications, including biosensing, imaging, and drug delivery. However, their broader implementation is limited by low luminescence efficiency, limited morphological control, and challenges in reproducible synthesis. Thermal decomposition (TD) methods have enabled significant advances but suffer from multistep complexity and limited scalability. Microwaveassisted (MW) synthesis offers a faster and more reproducible alternative, although direct transfer of TD protocols is not straightforward. Here, we report the synthesis of LiYF₄:Yb,Er nanoparticles via a MW-assisted approach. Pure-phase nanoparticles were obtained in 30 min at 250 °C using an excess of lithium precursor. The resulting rhomboidal morphology and the well-resolved photoluminescence (PL) splitting in both UC and DS regimes are consistent with previous reports, confirming preserved spectral characteristics. To enable biomedical applications, the nanoparticles were functionalized with poly(acrylic acid) (PAA) or polyethylene glycol (PEG) using either a single-step or a sophisticated two-step protocol. The latter resulted in significantly improved colloidal stability in aqueous media while maintaining the spectral profile.

We incorporated negatively photochromic, chiral hydrazone photoswitches into polarization volume gratings to enable light-driven, reversible tuning of optical properties. UV and blue light irradiation reversibly shifts the isomer ratio, modulating diffraction efficiency and the visible spectral response of the gratings.

Diamond is a promising material in quantum and optical biosensing due to its biological compatibility and easy functionalization. NV centers can be applied for magnetic and electric fields sensing, while SiV and GeV color centers can be useful for temperature sensing. However, there are a lot of other, less well researched color centers in diamond that are interesting both for fundamental research and possible practical applications. In this work, diamond microneedles synthesized using plasma-enhanced chemical vapor deposition (PE-CVD) and thermal oxidation method were investigated using steady-state and time-resolved photoluminescence spectroscopy in the biological temperature range. 389 nm, 468 nm and NV0 color centers were identified in diamond microneedles. The observed line at 504 nm and longer fluorescence lifetimes at this emission wavelength suggest that there is one more color center, possibly H3 (NVN0). ZPL position shifts, FWHM broadening and fluorescence intensity quenching for different color centers are observed in the measured photoluminescence spectra with increasing temperature. Fluorescence lifetime dependence on temperature is observed as well. The observed temperature-dependent photoluminescence behavior could be applied for all-optical thermometry.

We report direct observation of negative optical phase accumulation

in a 100 nm free-standing carbon-nanotube film in the terahertz range. Terahertz

time-domain spectroscopy reveals a broadband negative phase shift with only

moderate attenuation and an apparent advance of the transmitted pulse peak by

about 40 fs relative to an empty aperture. The measured transmission, phase

spectra, and waveform reshaping are reproduced by a Drude model, indicating

that the effect is governed by carrier dynamics in the conductive layer.

Transparent ceramics of YAG:RE compounds prepared via solid-state sintering are promising materials for composite active laser mediums. Solid-state sintering from powders provides a flexible and cost-efficient approach to create a medium with mixed activators within a monolithic element. However, the sintering conditions of ceramics varied with different activators. In the current work, an approach to unify the sintering temperature for both Nd-doped and Sm-doped ceramics was proposed. It was found that the microstructure and optical properties of Nd³⁺:YAG ceramics doped with both Si⁴⁺ and Mg²⁺ are significantly less sensitive to the consolidation temperature compared to those doped with Si⁴⁺ alone. This occurs due to magnesium ion-induced inhibition of recrystallization during sintering. This enables production of optical ceramics with low optical losses over a relatively wide temperature range. This will enable the fabrication of YAG:Nd³⁺/YAG:Sm³⁺ composite elements within a single technological cycle.

The design of transparent conductive electrodes (TCEs)

for optoelectronic devices is fundamentally limited by a trade-off between electrical conductivity and optical transmittance, restricting device efficiency. Here, we present a significant advance in TCE technology

by introducing a novel fabrication strategy that alleviates this limitation:

a monolithic, metal-integrated high-contrast grating, termed metalMHCG. The metalMHCG architecture provides superior electrical conductivity compared to existing TCEs while maintaining excellent optical transparency and strong antireflective properties. At a wavelength of 10 µm, the structure achieves an absolute transmittance of 75% for unpolarized infrared light, corresponding to a relative transmittance of 108% compared to a bare GaAs substrate. This erformance is combined with an exceptionally low sheet resistance of 0.5–1 Ω/sq, several times lower than previously reported TCEs [1]. Additionally, a second design featuring gold stripes embedded in a GaAs grating reaches 94% transmittance at 7 µm and a relative transmittance of 135%, while maintaining a low sheet resistance of 2.8 Ω/sq [2]. These metalMHCG-based structures establish a new benchmark for mid- to far-infrared TCEs and show strong potential for high-power optoelectronic applications.

High-efficiency light emission at low temperatures is a prerequisite for implementing optical data links in cryogenic environments. Combined with the theoretical prospect of achieving >100% light-emission efficiency, leading to electroluminescent cooling, this motivates the study of LED operation at cryogenic temperatures. We have developed a cryogenic measurement setup that enables IV and spectral characterization of LEDs, and designed devices incorporating integrated resistive thermometers. Using these GaAs-based LEDs and our setup, we investigate how temperature affects efficiency and the underlying recombination mechanisms, and how the internal device temperature depends on bias and ambient temperature. Specifically, we study electroluminescence from LEDs with a resistive thermometer deposited directly on top of the device while controlling the temperature between 10 K and 300 K in a cryostat. This setup enables simultaneous measurement of the LED temperature and its electroluminescent properties. From these measurements, we estimate the temperature dependence of radiative and non-radiative recombination, and assess their impact on LED efficiency and heat generation at cryogenic temperatures. Our results provide insight into the temperature dependence of key recombination mechanisms in GaAs LEDs. This delivers data for the development of more efficient light emitters, optical coolers and cryogenic optical data links.

The photocatalytic coupling of selective phenylcarbinol oxidation with hydrogen evolution has attracted considerable attention as a promising dual-functional reaction system. Herein, a lattice-matched 2D/3D NiS/CdIn2S4 (NiS/CIS) Schottky heterojunction is rationally designed for efficient dual-functional photocatalysis under visible light. Structural analyses confirm the uniform deposition of NiS nanosheets on octahedral CIS with a lattice mismatch below 5%, ensuring coherent interfacial contact. The optimal 3% NiS/CIS composite exhibits exceptional hydrogen and benzaldehyde production rates of 2636.4 and 2717.6 μmol g-1 h-1, respectively—representing enhancements of 39.7 and 38.0 times over pristine CIS. The catalyst also demonstrates remarkable stability, retaining over >99.0% activity after six cycles. Mechanistic studies reveal that the Schottky junction facilitates spatial separation of photogenerated carriers: electrons migrate to NiS, prolonging charge carrier lifetimes and lowering the hydrogen evolution overpotential, while holes accumulate on CIS that facilitated phenylcarbinol adsorption to drive selective phenylcarbinol oxidation via a carbon-radical pathway. This work provides a viable approach for designing efficient bifunctional photocatalysts through lattice-matched interface engineering.

Augmented reality and see through displays have become a hot topic in holography and in the development of holographic recording materials. Designing holograms for these applications depends strongly on the recording material, and therefore both the behaviour and the display must be adapted to the material’s properties. In smart glasses, the photopolymer is located close to the mucous membranes—eyes, nose, and mouth—so the use of non toxic materials is highly desirable. In this work, we explore the optical characteristics of Biophotopol, a highly environmentally compatible photopolymer, for waveguide couplers used in see through applications. Biophotopol exhibits higher shrinkage, around 4%, compared to other commercial photopolymers (1.4%). However, we demonstrate that it is still possible to obtain good results in the recording of these holographic optical elements.

Beam self-cleaning in multimode fibers leads to the emergence of a stable, fundamental-mode-dominated beam from a complex input field. A reduction of shot-to-shot fluctuations with increasing power supports its interpretation as a statistically driven, i.e., thermodynamic-like, process.

We investigate polarization and cross-phase modulation

instabilities in polarization-maintaining all-normal-dispersion photonic

crystal fibers. We demonstrate their coexistence and clarify the distinct roles

of phase and group birefringence in their dynamics. We also reveal an

inverse process, in which the modulation sidebands undergo polarization

inversion due to negative group birefringence.

Embedding nitrogen-vacancy (NV) centers in diamond within optical fibres provides a compact platform for sensitive magnetic field detection. The NV centers’ spin-dependent photoluminescence allows precise measurement of magnetic fields, while integration into fibres enables remote and minimally invasive sensing. Fibre-coupled NV-diamonds maintain stable optical and spin properties, offering high spatial resolution and robustness against environmental perturbations. Different NV-diamond embedding approaches offer complementary advantages, balancing measurement precision, sensing versatility, and fabrication considerations.

Space-division multiplexing (SDM) using coupled-core multi-core fibers (CC-MCFs) has emerged as an efficient solution to the capacity limits of single-mode systems. Strong evanescent coupling between closely spaced cores redistributes optical power among supermodes, inherently reducing differential group delay and mode-dependent loss compared to weakly coupled designs. However, this same coupling introduces a fundamental challenge for amplification. In coupled-core erbium-doped fiber amplifiers (CC-MC-EDFAs), each supermode exhibits a distinct overlap with the doped region, and the excited supermode composition varies dynamically with wavelength and perturbations such as bending and twist. Consequently, the net gain per core becomes a non-separable function of wavelength and modal content, rendering conventional pump-based gain equalization ineffective.

We address this limitation using a two-stage CC-MC-EDFA architecture incorporating a wavelength-dependent filter for each core. The first stage operates at high inversion, while the inter-stage filter reshapes the spectral-spatial power distribution prior to a shorter second stage. By optimizing core-resolved attenuation profiles, we redistribute modal gain interactions and enforce simultaneous spectral flatness and spatial uniformity. Numerical results demonstrate gain equalization within ±0.5 dB across the 1550–1610 nm band in a three-core fiber, establishing a scalable pathway for uniform SDM amplification.

We report stimulated Raman scattering (SRS)-induced beam self-cleaning in a 355 nm-pumped, UV-optimized graded-index multimode fiber. At low pump power, the output exhibits a strongly multimode speckled profile. With increasing pump power, cascaded Raman Stokes components occur, accompanied by a transition toward near-Gaussian beams. Spectrally resolved measurements reveal a pronounced wavelength dependence: while all Stokes initially exhibit improved beam quality, lower-order Stokes degrade at high power, whereas higher-order Stokes maintain stable near-Gaussian profiles. These results demonstrate Raman-order-dependent modal dynamics and extend beam self-cleaning to the UV regime.

Optical fibre-based extreme learning machines with spectral phase encoding are an unconventional computing platform that yields excellent results in machine learning benchmarks. Here we present the first numerical study of the effect of nonlinear polarisation dynamics on fibre-ELM performance.

This study evaluates textile wear using RGB camera, and VIS and SWIR hyperspectral imaging on abraded cotton samples. VIS (CIELAB coordinate b*) showed the strongest correlation with wear, and RGB (local binary pattern) and SWIR (PLS model) moderate correlation. Our results demonstrate that these optical methods can assess textile wear, extending beyond traditional fibre composition identification.

We present an integrated optical deformation sensor fabricated via embedded printing. The sensor detects angular deflections up to 9° with sub-degree resolution at 2σ confidence. It operates with two parallel multi-mode waveguides, one locally functionalized by in-process injected CdSe/CdS

quantum dots. Deformation alters total internal reflection, changing the fluorescence-to-excitation ratio used for angle determination. Embedded printing provides precise spatial control of quantum-dot placement while maintaining optical transparency. Remaining challenges include optical attenuation, quantum-dot dispersion and simulation based modeling.

Two-dimensional rare-earth titanate nanosheets provide a unique platform for field-responsive optical materials due to their anisotropic geometry and rich luminescent transitions. Here, we demonstrate electric-field-induced polarization anisotropy in Eu³⁺-doped Gd1.4Eu0.6Ti3O10 nanosheets and exploit the differential responses of co-originated electric-dipole (ED) and magnetic-dipole (MD) emissions for self-referenced optical decoding. Under alternating electric fields up to 15 V mm⁻¹, nanosheet alignment selectively enhances the polarization dependence of the ED transition while the MD transition remains nearly isotropic. The normalized differential response of the ED channel reaches 42.2%, whereas the MD response remains within the experimental noise floor. By using the MD emission as an internal reference, common-mode fluctuations are effectively suppressed, improving the signal-to-noise ratio from 6.79 dB to 20.22 dB. Combining spectral self-referencing with polarization-selective readout enables reliable discrimination of field-written optical states and tunable decoding contrast. These results establish a symmetry-resolved strategy for noise-resilient optical information processing and highlight the potential of two-dimensional rare-earth luminescent materials for advanced photonic applications.