Abstracts Track 2026

Area 1 - Optics
Area 2 - Photonics

Area 1 - Optics

Nr: 26
Title:

Investigations of Organic Light-Emitting Diodes with Multilayer Exciton-Confinement Architecture Based on Benzothiadiazole-Containing Emitters Exhibiting Red-to-Near-Infrared Thermally Activated Delaye
Authors:

Lesia Volyniuk, Stepan Kutsyi, Dmytro Volyniuk, Audrius Bucinskas, Irena Kulszewicz-Bajer and Juozas Vidas Grazulevicius
Abstract: Red and near-infrared (NIR) organic light-emitting diodes (OLEDs) are preferred over inorganic ones for healthcare applications because they provide potential biocompatibility, environmentally friendly low-temperature manufacturing, and flexibility. The red and NIR OLEDs are typically characterized by low external quantum efficiency (EQE), partly because of the lack of effective narrow-band-gap organic emitters with photoluminescent quantum yields close to unity in the solid state. This limitation is fundamentally linked to the energy gap law, which means that organic semiconductors with narrow band gaps are more likely to undergo non-radiative relaxation of excited states as the energy gap decreases. This issue can be tackled by developing new device structures and red/NIR organic materials that harness singlet and triplet excitons under electrical excitation, for example, donor-acceptor-type organic emitters showing thermally activated delayed fluorescence (TADF). In this work, a quantum well (QW) structure was used to fabricate light-emitting layers for red/NIR OLEDs with a multilayer exciton-confinement architecture, using novel benzothiadiazole-containing TADF emitters [1]. Those light-emitting layers were fabricated using step-by-step deposition, doping-free narrow-band emitters and a wide-band host. The output electroluminescent parameters of QW OLEDs were compared with the parameters of doping-free and host-based red/NIR OLEDs. Before OLED development, TADF properties were truly characterized by steady-state and time-resolved spectroscopy at different temperatures. Photoluminescent intensity of both emitters was significantly increased with increasing temperatures from 110 to 300 K. They were also characterized by small singlet-triplet splitting of close to 0.02 eV. Such dependencies were attributed to the efficient TADF of the developed compounds. Partially due to triplet harvesting via TADF, the NIR-emitting emitter showed maximum EQE values of 0.19%, 0.7%, and 0.29% and emissions at 745 nm, 693 nm and 723 nm for doping-free, host-based and QW OLEDs. The red-emitting emitter showed maximum EQEs of 1.52%, 3.42%, and 2.98% and emissions at 621 nm, 621 nm, and 632 nm for doping-free, host-based, and QW OLEDs, respectively. Thus, the OLEDs with a multilayer exciton-confinement architecture exhibited red-shifted electroluminescence relative to host-based OLEDs and higher EQE values than those of doping-free OLEDs. More details can be found in the reference. [1] or in a presentation at the conference. Acknowledgements This work has received funding from the Research Council of Lithuania (LMTLT) for the dissemination of the PhD study of Lesia Volyniuk. References [1] L. Volyniuk, J. Drapala, M. Ghasemi, S. Kutsii, A. Dabuliene, A. Pron, J.V. Grazulevicius, I. Kulszewicz-Bajer, D. Volyniuk. Schubert. Highly oxygen-sensitive red to near-infrared emitting benzothiadiazole derivatives for electroluminescent devices and optical sensors operating within the biological window. Sens. actuators, B Chem. 2026, 449, 139066.
Nr: 28
Title:

Optimization of Dental Portable OCT Scanner
Authors:

Tatsuo Shiina and Seiroh Okaneya
Abstract: The current state of dental diagnosis begins with visual examination, followed by palpation using a probe, X-ray imaging devices, and has now advanced to the introduction of CT. Diagnosis of the teeth is conducted through palpation (using a probe), visual examination, and X-rays, while the gums are diagnosed for periodontal disease and gum recession also through visual and tactile examinations. The challenge lies in the variability of judgments based on the subjective diagnosis of a dentist. Additionally, there is significant variability in the diagnoses themselves, resulting in outcomes that depend on the skill and experience of the dentist [1]. Nowadays, optical devices are being introduced from the perspectives of objectivity in diagnosis and tooth measurement, and ease of judgment. There are also high expectations for Optical Coherence Tomography (OCT), starting with reports of tomographic measurements inside teeth, and widely reported applications including the measurement of caries, microcracks, and the enamel-dentin junction (EDJ) [2]-[3]. Unlike X-rays, there is no concern about exposure, and sufficient resolution for addressing the above issues is being discussed. There is a strong demand for portable OCT scanners usable in dental applications that are small, lightweight, and operate on DC battery power to enable chairside use and mobility in home medical care. We have long been developing a portable OCT scanner based on TD-OCT [4][5]. TD-OCT is characterized by a high degree of design freedom in the OCT configuration, allowing independent settings for wavelength, measurement resolution, measurement range, and so on. On the other hand, a challenge with TD-OCT compared to SD-OCT is its slower measurement speed. In this study, by using multiple rotating reflectors combined with a 3x3 fiber coupler, we achieved a measurement range of over 10 mm and a measurement speed of 1,000 scans per second. Since the waveform of TD-OCT directly obtains the interference signal along with depth information, it can be acquired directly by A/D converter without using FFT. Real-time waveform processing becomes possible even with a single board computer. We are advancing research and development aimed at the dental application of this portable OCT scanner. In particular, the dental intraoral probe was designed to ensure high accessibility, allowing free positioning within the oral cavity, with a highly compact optical system. We developed a cylindrical probe with a diameter of less than 10 mm and a length under 10 mm, enabling free probe positioning inside the oral cavity for tooth measurement. This study demonstrated the capability to measure and evaluate caries and gums, detect and visualize microcracks and the enamel-dentin junction (EDJ), and evaluate attenuation coefficients derived from material properties. This report presents the development of the optimized portable OCT scanner specialized for dental use, including the evolution of probe designs, their correspondence with measurement postures, and various measurement examples. Future prospects are also discussed.
Nr: 40
Title:

A Self-Referencing Interferometric Technique for Complete Characterization of Stokes Singularities
Authors:

Rahul Joshi, Baby Komal, P. Senthilkumaran and Sunil Kumar
Abstract: Stokes singularities are increasingly important in modern photonics, naturally appearing in applications ranging from optical manipulation and imaging to structured-light communication. However, detecting these singularities typically requires time-consuming polarization measurements and often fails to resolve degeneracies in their Stokes indices. In this work, we present a simple and robust lateral shear interferometry (LSI) approach that overcomes these limitations using only intensity measurements, offering a fast and practical alternative to traditional polarimetric techniques. An optical singularity refers to a point in space where a parameter describing the electromagnetic field becomes indeterminate. Such singularities occur either in the field's phase or in its state of polarization and are accordingly categorized as phase or polarization singularities. Stokes singularities arise when two scalar phase-singular beams of orthogonal polarizations interfere, leading to points where either the azimuth or the handedness of the polarization ellipse cannot be defined. For a Stokes field S₁₂ = S₁ + iS₂, polarization singularities correspond to the phase singularities in the Stokes phase ϕ₁₂, where the SOP is circular and ϕ₁₂ = tan^−1(S₂/S₁), with S₁ and S₂ representing the light Stokes parameters. Similarly, Poincaré singularities correspond to phase singularities in the Stokes phases ϕ₂₃ and ϕ₃₁, where the SOP is linear. These classifications provide a unified framework for understanding the complex polarization topologies in structured optical fields and highlight the need for accurate and efficient singularity detection. Stokes singularities can be generated using spatially varying waveplates, spatial light modulators, metasurfaces, or interference-based methods. For their detection, our work introduces a simple and effective new technique. This technique uses a glass wedge-plate to create controlled self-referenced interference between the front- and back-reflected components of an incident singular beam. By analysing the resulting fork-fringe patterns through projections onto six polarization eigenstates of the Pauli matrices, the underlying component topological charges of the beam can be directly retrieved. These patterns allow us to unambiguously identify polarization (C- and V-point) singularities, Poincaré singularities (ϕ₂₃, ϕ₃₁), their helicity, and their Stokes indices. We apply this method to beams represented on the higher-order Poincaré sphere (HOPS) and hybrid-order Poincaré spheres (HyOPS), demonstrating that LSI can distinguish between singularities that appear degenerate under conventional Stokes polarimetry. This includes resolving cases where different combinations of topological charges yield the same Stokes phase but generate distinct polarization distributions, which is important for beam engineering based on singular optics. Overall, this intensity-based, vibration-insensitive technique provides a fast and accessible tool for optical instrumentation and metrology, while also offering new diagnostic capabilities for structured-light photonics, optical manipulation, and mode-selective optical communication. By enabling detailed singularity analysis without complex polarization setups, it broadens the applicability of singular optics across imaging, sensing, beam shaping, and next-generation photonic systems.
Nr: 51
Title:

Development of Single-Emitter-Based White Organic Light-Emitting Diodes Using Quinoxaline Derivatives Exhibiting Efficient Room Temperature Phosphorescence
Authors:

Dmytro Volyniuk, Mohamed Hassan Saad Abdella, Matas Guzauskas, Jurate Simokaitiene, Mykhaylo Hladun, Pavlo Stakhira and Juozas Vidas Grazulevicius
Abstract: In pursuit of single-molecule white-emitting emitters, we examined four quinoxaline derivatives, encompassing both rigid and flexible molecular architectures [1]. These derivatives exhibit highly efficient room-temperature phosphorescence (RTP) that is observable in both solution and solid films. The developed RTP emitters possess potential across a variety of applications, including single-emitter white organic light-emitting diodes (OLEDs). The engineered molecular structures substantially influenced the RTP parameters, resulting in PRT colours transitioning from green to orange, RTP lifetimes ranging from 0.83 to 525 ms, and RTP quantum yields increasing to as high as 45.6%. The differences in molecular structure-property relationships were effectively elucidated through both theoretical and experimental methods. The key finding of this study is that the developed compounds, molecularly doped into the rigid polymer, exhibit room-temperature phosphorescence quantum yields that are 910 times higher than their fluorescence quantum yields. The solutions processed OLEDs with the emitting layers of the synthesized compounds showed whitish electroluminescence with the colour coordinates of (0.32, 0.31) close to those of natural white emission (0.33, 0.33). According theoretical calculations, the dual phosphorescence for quinoxaline derivatives with rigid molecular structures, versus single-peak phosphorescence for quinoxaline derivatives with flexible molecular structures, can be explained by two factors: 1) the oscillator strengths for the relevant transitions; 2) the energy gap between the molecular orbitales with the highest coefficient in the configuration interaction expansion for these transitions is smaller for compounds with rigid molecular structures compared to compounds with flexible molecular structures. Acknowledgements This work also received support from Horizon Europe, the European Union’s framework programme for research and innovation (R&I) for 2021-2027, project HELIOS, grant agreement No 101155017. References [1] M. Abdella, M. Guzauskas, J. Simokaitiene, A. Dabuliene, M. Cekaviciute, D. Volyniuk, V. E. Matulis, E.G. Ragoyja, J.V. Grazulevicius. Multifunctionality of quinoxaline derivatives with variable room temperature phosphorescence for luminescent tags, morphological imaging, single-emitter white OLEDs, and highly sensitive oxygen sensors. Results in engineering, 2026, the manuscript was submitted to the journal.
Nr: 65
Title:

Design of a Green-Light Photonic Synopsis Multiplexer Based on Multicore Polymer Optical Fiber
Authors:

Dror Malka
Abstract: The growing demand for miniaturized photonic systems in the green spectral region is accelerating the development of integrated wavelength-division multiplexing (WDM) technologies. Conventional multiplexers often rely on bulky elements that increase insertion loss and limit compact integration. In parallel, neuromorphic photonic computing motivates multifunctional devices that jointly support wavelength multiplexing and optical weighting on a single platform. This paper presents a four-channel green-wavelength photonic multiplexer implemented in multicore polymer optical fiber (MC–POF) with embedded polycarbonate (PC) cores. Passive wavelength combination is achieved via engineered coupling between adjacent cores, enabling operation over 500–560 nm without external lenses or gratings. Beam propagation method (BPM) simulations show that a 20-mm fiber segment provides low insertion loss (0.13–0.55 dB), uniform 20-nm channel spacing, and stable performance under thermal variation. A single optimized coupling region satisfies the coupling conditions for all four wavelengths simultaneously, supporting wavelength-dependent signal convergence analogous to a photonic synapse. The structure employs a symmetric hexagonal lattice with multiple PC layers embedded in a fluoropolymer background and is designed to realize four-channel multiplexing using a single switching length, thereby reducing structural complexity and improving spectral efficiency. Beyond multiplexing, tuning the switching length enables wavelength-dependent power redistribution (optical weighting), permitting passive weighted summation at the output and supporting synapse-like photonic processing. Predicted device performance includes high transmission at the target channels, narrow channel linewidths, and robust tolerance to wavelength drift and temperature variation. Experimental validation using a two-channel prototype at 500 nm and 540 nm shows far-field output patterns in good agreement with simulations, confirming effective spatial multiplexing and combination within the fiber. The proposed architecture eliminates multiple coupling sections and discrete optical components, offering a compact, scalable, and energy-efficient approach for green-band WDM and neuromorphic photonic interconnects enabled by switching-length optimization.
Nr: 33
Title:

Eu3+ Doped WO3-Containg Borosilicate Glasses for Red Emitting LED Application
Authors:

Aneliya Yordanova, Lyubomir Aleksandrov, Margarita Milanova, Reni Iordanova and Petia Petrova
Abstract: Glasses with composition 55SiO2-25B2O3-(15-x)Al2O3-xWO3-5CaO-yEu2O3 (x = 0, 5; y= 0, 2 wt%) were prepared by the conventional melt-quenching method and were investigated by infrared (IR), Raman, UV-Vis and Photoluminescence (PL) spectroscopies, as well as SEM and DSC analysis. Physical properties like density, molar volume, oxygen molar volume and oxygen packing density were also determined. The influence of WO3 on the structure and luminescent properties was established. From DSC analysis information about the thermal parameters of the samples was obtained. Glasses are characterized by a high glass transition temperature. No crystallization temperatures were observed up to 1000оС. Infrared and Raman results indicate that the glass network consists of SiO4 tetrahedra with one non-bridging oxygen, BO3 triangles, Si-O-Si, Si-O-Al and Si-O-B linkages. Tungstate ions incorporate into the base borosilicate glass as tetrahedral [WO4]2- groups, leading to an increased number of non-bridging oxygens. The glasses are characterized by good transmission in the visible region, of about 90%. A strong red emission from the 5D0 level of Eu3+ ions was registered under near UV (392 nm) excitation using the 7F0 → 5L6 transition of Eu3+. It was established that the addition of WO3 to borosilicate glasses leads to improvement of the emission properties of the active ion through the occurring non-radiative energy transfer from the tungstate groups to the europium. The integrated fluorescence intensity ratio R (5D0 → 7F2/5D0 → 7F1) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu3+ in non-centrosymmetric sites. This fact is directly related to the increased emission intensity of WO3-containg glass sample. The calculated color coordinates of the obtained glasses are very close to those of the standard red color and the emission is characterized by high color purity. The obtained results indicate the efficiency of the glass structure for the luminescence performance of doped Eu3+ samples and the potential application of these borosilicate glasses in the field of red light-emitting diodes (LEDs). Acknowledgements: This work is supported by Financing Agreement № PVU-10/12.09.2025 / BG-RRP-2.020-0001-C01 funded by the European Union - Next Generation EU (NextGenerationEU), Investment C2I2.
Nr: 39
Title:

Quantum Homodyne Tomography Application to Ultra-Narrow Linewidth Semiconductor Lasers
Authors:

Frederic Grillot
Abstract: Continuous-variable quantum communications provide a promising pathway toward practical quantum information transfer by exploiting the continuous quadratures of the electromagnetic field. Unlike discrete-variable protocols based on single-photon detection, continuous-variable approaches are compatible with standard telecommunication technologies, enabling room-temperature operation and seamless integration within existing optical-fiber networks [1]. In this context, achieving sensitivities below the shot-noise limit remains a central challenge. Squeezed states, which reduce quantum noise in one quadrature at the expense of the conjugate one, represent a key resource for enhanced communication performance, improved sensing capabilities, and scalable continuous-variable quantum information processing [2]. Although squeezed states are commonly generated through nonlinear processes such as parametric down-conversion or four-wave mixing, quiet optoelectronic sources such as semiconductor lasers have also been shown to exhibit nonclassical light under appropriate pumping conditions [3,4]. In this work, we present an experimental framework for full quantum homodyne tomography of optical fields emitted by an ultra-narrow-linewidth semiconductor laser. The setup is validated using vacuum and coherent states, which provide benchmarks for phase control, homodyne detection fidelity, and noise calibration [5]. Two complementary reconstruction techniques namely the inverse Radon transform and maximum-likelihood estimation are implemented to recover the Wigner function and evaluate the quantum properties of the measured states. This platform lays the groundwork for future investigations into quantum-noise suppression and potential nonclassical emission from semiconductor lasers, particularly in the quiet-pump regime. The approach is directly applicable to the development of continuous-variable quantum key distribution transmitters and to the broader integration of semiconductor devices into advanced quantum-optical technologies. References [1] V. C. Usenko et al., arXiv:2501.12801 (2025). [2] F. Grosshans and P. Grangier, Phys. Rev. Lett. (2002). [3] S. Machida, Y. Yamamoto, Y. Itaya, Phys. Rev. Lett. (1987). [4] S. Zhao et al., Phys. Rev. Research (2024). [5] J. Wright, Lecture 22: Introduction to Quantum Tomography (2015).
Nr: 59
Title:

MMW Imaging System Based on Glow Discharge Detector Focal Plane Array and Lock-In Camera
Authors:

Tomer Latucha, Dor Azran, Lidor Ladany, Or Kakon, Daniel Rozban, Arun Ramachandra Kurup, Yitzhak Yitzhaky, Natan S. Kopeika and Amir Abramovich
Abstract: MMW Imaging has become one of the most rapidly developing fields in applied opto-electronics and THz technology. Its unique advantages such as, non-ionizing radiation safety and deep penetration through clothes, make it ideal for security screening, biomedical diagnostics, environment research etc. Furthermore, it experiences less scattering in the atmosphere from particles such as dust compared to IR and VIS [1]. Our Focal Plan Array (FPA) is based on commercial neon lamps namely, Glow Discharge Detectors (GDDs) as pixels [2]. The neon lamp costing about 0.5$ is biased by 110-130 Volts and it is illuminated by modulated MMW radiation. As a result, the internal plasma current increases and decreases accordingly. The first detection mechanism was based on measuring the internal plasma current from each pixel (GDD) of the FPA [2] , namely Electrical Detection. The second THz detection mechanism and more advanced one we developed was an optical detection in which we measure the changes of the GDD emitted light. Using a typical VIS CCD/CMOS camera which simplifies the image acquisition [3]. The drawback of this method was the very long time to generate one MMW image since it required an accumulation of thousands of frames to generate a single MMW frame [3] In this work, a new detection mechanism is demonstrated in which a unique Lock-In camera is used to generate the MMW image. This breakthrough allows us to detect objects in quite easily and significantly faster ( three orders of magnitude better) compared to our previous experimental studies [4] [5] . First MMW images based on this innovative technology will be presented in this work. References: [1] B. Riley; “Comparison of Infrared and Millimeter-Wave Image Performance in Adverse Weather Conditions”, pages. 11, 12, 14, 30 (2019). [2] D. Rozban, A. Levanon, A. Akram, A. Abramovich, N. S. Kopeika, H. Joseph, Y. Yitzhaky, A. Belensky, O. Yadid-Pecht; “MM Wave and THz Imaging using very inexpensive neon indicator lamp detector focal-plane arrays”(2008) [3] D. Rozban, A. Aharon, L. Kahana, A. Abramovich, Y. Yitzhaky, H. Altan, N. S. Kopeika; Robust, sensitive, and inexpensive 2D focal plane array upconverting MMW imaging into the visible”(2019) [4] A. R Kurup, D. Rozban, L. Kahana, A. Abramovich, Y. Yitzhaky, N. Kopeika; “Performance Enhancement of Inexpensive Glow Discharge Detector Operating in Up-Conversion Mode in Millimeter Wave for Focal Plane Arrays” (2021). [5] A. R. Kurup, D. Rozban, A. Abramovich, Y. Yitzhaky, N. Kopeika; Fast and Enhanced MMW Imaging System Using a Simple Row Detector Circuit with GDDs as Sensor Elements and an FFT-Based Signal Acquisition System” (2023).
Nr: 69
Title:

Contaminant Localization and Environmental Analysis using Real-time Photonic Integrated Circuit Sensors
Authors:

Davey Oliver Davies-Armstrong, Sherif Ibrahim, Shirin Naserikarimv, Simon Whelan, Owen J. Guy, Francesco Masia, Anthony Bennett and John Hadden
Abstract: Contaminants in water supplies, from pathogenic microorganisms and viruses to toxic chemicals, pose significant risks to both public health and the environment. Yet current monitoring approaches remain slow, expensive, and heavily reliant on centralized laboratory facilities. To address this challenge, we are developing portable, label-free contaminant sensing platforms capable of real-time, on-site detection of pollutants. By leveraging photonic integrated circuits (PICs) functionalized with tailored surface chemistries, our approach offers highly sensitive, real-time monitoring. This technology will not only enable earlier intervention and safer water systems but also demonstrate the transformative potential of integrated photonic sensors for widespread adoption in environmental, agricultural, and healthcare applications. Recently, increasing attention is being given to the application of PIC sensors to real world problems. Silicon Nitride (SiN) on Silicon Dioxide is a photonic material system which leverages mature and scalable processing capabilities allowing fabrication of low-loss (<0.1dB/cm [1]), and temperature insensitive (~11 pm/° C) waveguide devices across its wide transparency window (300nm to beyond 8000nm [1]). This enables development of sensitive and economic PIC sensors on a 200 mm wafer scale platform. In this work, we present a proof-of-concept of a lab-on-chip bio-compatible biosensor using SiN-based photonic microring resonators and etched microfluidic channels, which can sense changes in the local environment with a mean sensitivity of 590nm/RIU. In the literature microring-based sensors achieve sensitivity values range from 120nm/RIU [2] to 585nm/RIU [3]. Using receptor-functionalized SiO2, the low loss of the SiN platform can enable ultra-sensitive detection of biomarkers in liquid around the waveguide which transduces a change in the resonant frequency of the ring via the effective refractive index [4]. We begin by detailing our work in determining an ideal ring resonator geometry that best facilitates bulk refractometric sensing. This is followed by an investigation of the sensor’s functionality under different test conditions, temperature, liquid, and optical probing parameters. The devices are probed using a C-band tunable laser with a spectral range of 1528nm-1568nm and 100KHz linewidth. PIC Sensing devices are exposed to fluids through etched microfluidic channels which are coupled with 3D printed microfluidic packaging solution enabling microfluidic testing. We will conclude by discussing routes to further enhancement of the device sensitivity, and opportunities for near term real world-applications in contaminant sensing within the water industry. References [1] Guo Xuhan, et al. “Ultra-wideband integrated photonic devices on silicon platform: from visible to mid-IR”, Nanophotonics, 12.10.1515/nanoph-2022-0575 (2023) [2] Anastasia Tsianaka, et al. “Sensitivity Enhancement of a Micro Ring Resonator-Based Photonic Sensor by Using a Gelatin Methacryloyl Functional Coating for the Detection of Metoprolol”, ACS Applied Optical Materials, 10.1021/acsaom.5c00149 (2025) [3] Huan Zhang, et al. “Highly sensitive optical biosensors based on silicon nitride sandwich-slot microring resonators for refractive index sensing”, Journal of Optics. 27. 10.1088/2040-8986/ade88c (2025)

Area 2 - Photonics

Nr: 43
Title:

Erbium Fiber Laser Wavelength Tuning by a Forward-Only Optical Mesh
Authors:

Marek Vlk, Carson Glenn Valdez, Anne Kroo, Charles Roques-Carmes, Shanhui Fan, David Miller and Olav Solgaard
Abstract: Advances in photonic integrated circuits, including low-loss waveguides and integrated phase modulators, are enabling compact tunable solid-state lasers rivaling free-space and fiber systems. Such lasers are desirable for e.g., spectroscopy and LIDAR. Widely explored approaches rely on microring resonators providing wavelength selection via high-Q resonances. Although single-ring designs suffer from limited free spectral range (FSR), Vernier configurations using two or more coupled rings extend to tens of nanometers. However, they require precise resonance mapping and alignment. We demonstrate a fundamentally different approach to tunable lasers that avoids resonant structures apart from the main laser cavity. The enabling component is a programmable intracavity filter based on recently proposed feed-forward optical meshes with an integrated delay line array. The device is a 4×4 programmable integrated photonic filter (PICF) and consists of three layers: a programmable power splitter A, a waveguide delay line array, and a programmable optical mesh M composed of three diagonal lines Ui. Layers A and M comprise arrays of Mach–Zehnder interferometers, each with two directional couplers and two thermo optic phase shifters. The 4 delay lines have a constant length increment 740 µm, yielding a 100 GHz (~0.8 nm) in 500 nm × 220 nm silicon waveguides at 1550 nm and 25 GHz channel spacing. Input/output coupling uses standard grating couplers. When A splits the power uniformly and the first diagonal U₁ is optimized for maximum transmission at frequency ωc, we implement a sinc-type filter used in wavelength division multiplexing and suited for intracavity wavelength selection. Wavelength tuning is achieved by applying a linear phase tilt across the delay lines as 2n(p−1)γ with γ ∈ [0,1). This continuously shifts the filter response within one FSR, which was confirmed around 1555 nm. The transmission was recorded with an optical spectrum analyzer (OSA) by launching spontaneous emission from an erbium-doped fiber amplifier (EDFA) into input 3 of the calibrated PICF. The PICF was then inserted into a fiber laser ring cavity using the EDFA as gain medium. An optical circulator (OC) enforces unidirectional operation, and a fiber polarization controller (FPC) aligns the polarization to the waveguide TE mode. A fixed 100 GHz WDM filter narrowed the gain bandwidth to match the PICF’s FSR. Laser output was extracted via a 90:10 beam splitter (BS). The emission wavelength followed the PICF transmission peak near 1555 nm as γ was stepped from 0 to 0.75. Tuning of ~0.5 nm was achieved while the full 0.8 nm FSR was restricted by the fixed WDM. Output power reached ~8 mW with an upper-bound linewidth of 2 GHz limited by the OSA resolution and frequency jitter due to the broad 25 GHz PICF bandpass. Round-trip loss was ~23 dB, dominated by ~12 dB from the two grating couplers and ~11 dB from waveguides, fibers, and fiber connectors. This work introduces a resonance-free, programmable filter for tunable lasers. Unlike Vernier schemes, it requires no resonance tracking or matching. Moreover, the WDM-like response is only one of many possible transfer functions. Future designs will focus on the delay line array to extend continuous tuning beyond several nanometers while narrowing linewidth below 100 MHz. Coupling loss will be reduced by improved grating couplers or edge coupling or gain medium integration.
Nr: 71
Title:

Power-Over-Fiber Driven Thermo-Optic Switches for Reconfigurable Optical Networks
Authors:

Teresa Crisci, Maurizio Casalino, Alice Gelli, Stefano Vergari, Francesca Parasecolo, Pieter Dumon and Francesco Giuseppe Della Corte
Abstract: Reconfigurable optical networks rely on fast, reliable, and remotely controllable switching elements to dynamically route optical signals. This work presents the experimental characterization of thermo-optic Mach-Zehnder interferometer (MZI) switches fabricated using standard design libraries provided by Luceda Photonics. The devices were specifically implemented to validate a previously developed Power-over-Fiber (PoF) system, enabling the delivery of a stable electrical bias to integrated heaters and demonstrating the feasibility of fully optically powered photonic circuits suitable for deployment within telecommunication cabinets. Each MZI switch consists of a 1×2 MMI input coupler and a 2×2 MMI output coupler, with light routing determined by the phase difference accumulated along the interferometer arms. Phase modulation is achieved via localized heating of tungsten resistive elements placed above both arms. The devices are realized on a silicon-on-insulator platform, with silicon waveguides embedded in a silicon dioxide cladding, ensuring CMOS compatibility and low optical losses. The operation of the switches was first investigated using two-dimensional steady-state thermal simulations. The temperature distribution induced by the heaters was computed, accounting for the thermo-optic coefficients of silicon and silicon dioxide. For a heater power of 40 W/μm, the upper waveguide reached 309.6 K, while the lower waveguide remained at 300 K, generating a refractive index difference of Δn = 1.93 × 10^-3. These thermal profiles were then incorporated into 2.5D optical simulations, which predicted transmission coefficients of 0.85/0.05 and 0.05/0.85 for the two operational states, with an excess loss below 0.6 dB. Optimization of the MZI arm length at 183 μm provided a compromise between compactness and switching performance, and simulations confirmed robustness to ambient temperature fluctuations. Experimental characterization employed a PoF system consisting of a 1310 nm laser delivering up to 69.4 mW through a single-mode fiber to a photovoltaic diode, which provided regulated voltage to the heaters via a DC-DC converter. The switches were probed using a tunable laser for TE-mode excitation, and output signals were monitored with photodiodes. The PoF system achieved a maximum efficiency of 22% with a 1.4 kΩ load, and full system operation under a ±2.5 V square-wave drive demonstrated complementary output signals, rise and fall times of 24 μs and 32 μs, and measured crosstalk of -13.5 dB. The average power dissipation per switch was approximately 6 mW, confirming the suitability of PoF powering for scalable integrated circuits. This work demonstrates the practical realization of reconfigurable optical switches operated entirely via optically supplied electrical power, providing a validated platform for future N×M switch matrices. These results highlight the potential of PoF-driven photonic devices for compact, remotely powered, and efficient optical routing in next-generation network infrastructures.
Nr: 34
Title:

Coaxial Time-of-Flight LiDAR with a Double-Clad Fiber Receiver for Blind-Zone-Free Ranging
Authors:

Jun Zhang
Abstract: LiDAR has advanced rapidly in recent years and is now a key technique for long-range, high-precision detection. As deployment moves into more intricate and confined environments, eliminating blind zones in the scan field while preserving system stability becomes critical. We present a coaxial LiDAR system with a double-clad optical-fiber receiver, in which a single-mode fiber core delivers the outgoing laser beam and a multimode inner cladding collects and guides the back-reflected light. The real-time system measures distances in both the near and far field within a single optical channel, thereby removing blind spots. Experimental results show a detection range of 0.2–70.7 m, with a distance accuracy of 3.4 cm and an angular resolution of 0.018°. Compared with conventional coaxial LiDAR implementations, the proposed architecture avoids complex free-space optical layouts and algorithmic compensations, providing a simpler structure with improved stability and high ranging accuracy.
Nr: 45
Title:

Preparation of Glass-Ceramic Materials by Controlled Crystallization of Eu2O3-doped WO3-B2O3-La2O3 Glasses for LED Application
Authors:

Lyubomir Aleksandrov, Aneliya Yordanova, Margarita Milanova, Reni Iordanova, Petar Tzvetkov, Pavel Markov and Petia Petrova
Abstract: The crystallization behavior of 52WO3:22B2O3:26La2O3:0.5Eu2O3 glass has been investigated in detail by XRD and TEM analysis. The luminescent properties of the resulting glass-ceramics were also investigated. By XRD and TEM analysis, crystallization of β-La2W2O9 and La2WO6 crystalline phases has been proved. Photoluminescent spectra showed increased emission in the resulting glass-ceramic samples compared to the parent glass sample due to higher asymmetry of Eu3+ ions in the obtained crystalline phases, where the active Eu3+ ions are incorporated. Also, in the glass-ceramics, the crystalline particles are embedded in the amorphous matrix and more of them are separated from each other which improves the light scattering intensity from the free interfaces of the nanocrystallites, resulting in the enhancement of the PL intensity. It was established that the optimum emission intensity is registered for glass-ceramic samples obtained after an 18 h heat treatment of the parent glass. After 21 h of glass crystallization, the amount of crystallite particles is high enough, and they are in close proximity to each other, and hence, the average distance between europium ions decreases, resulting in quenching of Eu3+ and a decrease in the emission intensity. Additionally, at 21 h of glass crystallization, formation of new crystalline phase—La2WO6 is established. A redistribution of Eu3+ ions in the different crystalline compounds is most likely taking place, which is also not favorable for the emission intensity.
Nr: 56
Title:

WASIMM – Water Analysis System with Integrated Microscope and Machine Learning
Authors:

Marios Sergides, Aliki Souzou, Sherife Ustuner, Nicolas Kitsios, Panagiota Loukaidou, Panagiotis Kamintzis, Andreas Papadopoulos, Grigorios Itskos and Panayiota Demosthenous
Abstract: Reliable detection of microbial contaminants in water systems requires optical technologies capable of operating with high sensitivity in complex aqueous matrices. We present recent advances from the Water Analysis System with Integrated Microscopy and Machine Learning (WASIMM), a biosensing platform combining Total Internal Reflection Fluorescence (TIRF) microscopy, antibody-based molecular recognition, and machine learning (ML) for rapid detection of pathogens in treated wastewater. The system utilizes antibody-functionalized BK7 and UV-fused silica substrates, selected following detailed chemical and optical evaluation. Functionalization reproducibility was assessed both through external photoluminescence mapping and direct experimental verification on the WASIMM optical setup, confirming uniform coverage and selective binding of labelled antibodies at the TIR interface. A fluorescence-based sandwich assay enables selective capture of target pathogens, and validation with nanometre scale fluorescent beads yielded a strong 25:1 signal-to-noise ratio, while E. coli imaging demonstrated clear morphological visibility and low background interference. A custom control software manages the acquisition pipeline, automatically switching between fluorescence and bright-field imaging modes while streaming data from the CMOS camera. In real time, the software detects and counts captured pathogens by interfacing with the ML engine, ensuring synchronized data collection and continuous monitoring. The optical module integrates TIRF illumination, CMOS-based multimodal imaging, and a photodiode for parallel emission-intensity monitoring, producing complementary datasets for robust detection. A dedicated ML pipeline evaluated on curated laboratory and open-source datasets identified YOLOv12 as the highest-performing model, with Grad-CAM providing transparent localization of features driving predictions. These combined optical, biochemical, and computational results demonstrate that WASIMM delivers sensitive, selective, and explainable microbial detection in water samples. The platform shows strong potential for future deployment as an automated, real-time water quality monitoring solution.