Introduction: The effect of cancer on health, society, and global economy makes early identification and treatment of the disease by biomarker detection in body fluids one of the biggest challenges in the modern world. Current gold-standards (PCR, flow cytometry, immunofluorescence, western blotting, ELISA, etc.) remain laborious, operator-dependent, time-consuming, and require large sample volumes. Therefore, an effective and real-time monitoring platform with clinically relevant limits of detection (LODs) for cancer diagnosis using biofluids remains urgent. To fulfil this demand, we introduce a compact biophotonic platform that integrates lossy mode resonance-based optical fiber sensors with embedded microfluidics.

Methods: The device employs a D-shaped single-mode optical fiber coated with a thin film of SnO₂ that supports the generation of lossy mode resonance (LMR), a physical phenomenon enabling high sensitivity and resolution in the detection of biomolecules, while retaining key advantages of optical fibers, such as unique light control, flexibility, electromagnetic immunity, robustness in harsh environments, and compatibility with optoelectronics. Firstly, the sensing surface is functionalized with a commercial polymer (Eudragit L100) to provide COOH groups. Afterwards, the sensor is integrated into a specially engineered microfluidic system and then the sensing surface is passivated with bovine serum albumin (BSA) to suppress nonspecific adsorption and improve assay specificity. Finally, the platform is evaluated across clinically relevant concentration ranges of transforming growth factor beta 1 (TGF-β₁) as an osteosarcoma-related biomarker.

Results: The device showcases excellent analytical performance in a standard running buffer (PBS), with a clinically relevant LOD of 5 pg/mL for TGF-β₁, demonstrating strong potential for early cancer biomarker detection.

Conclusions: These promising results lay the groundwork for the next experimental tests using clinically mimicking biofluids to assess the real performance of the biophotonic sensing device integrated with microfluidics.

Introduction: In modern vehicles, new enhancements are being sought for engine components, break discs, and valves, using light-weight materials which are applicable not only in conventional cars but also in electric vehicles. The utilization of novel additive manufacturing aims to reduce energy loss and mechanical stress, improving component longevity at a lower cost.

Method: Theeffective hardfacing of silicon carbide (SiC) over stainless steel was achieved using a Rofin Sinar Nd:YAG 2 kW robotized laser system with powder feedstock. Different Metal Matrix Composites (MMCs) were manufactured using Laser Directed Energy Deposition (DED-LB), making it possible to additively manufacture near-net-shaped parts while having the freedom to obtain variable geometries for the surface layout. Samples were prepared from teh following flat products of EN 10088: X2CrTi12(1.4512, AISI 409), Х15CrNi25-20 (1.4840, AISI 310), X5CrNi18-10 (1.4301, AISI 304), and X1CrNiMoCuN20-18-7 (1.4547, UNS: S31254). The reinforcement comprised a fine carbide powder of SiC, and the MMCs were produced after the solidification of the molten mixture. The study included an assessment of the interface zones and measurement of their microhardness, as well as microstructural analysis with visual defect evaluation focusеd on porosity and microcracking detection.

Results: In order to increase durability and heat and wear resistance, advanced MMC sample components for various vehicles applications were explored. In one layer with a thickness of 1.5 mm, composed of X1NiCrMoCuN20-18-7 and SiC, the hardness characteristic was observed to be about 25 MPA higher than that experimentally obtained for the base material. For the same MMC, the carbide–metal interface zoneswere investigated.No cracks were observed, and it displayed a porosity of ≈ 1.57 %. DED-LB MMC possess excellent thermal stability and resistance to abrasion.

Conclusion: Laser application allows various geometric applications on the surfaces of car parts. The appropriate selection of component phases can enable thedesign of parts with specific functionality, where the interaction between the microstructure and properties is complex.

Funding: The author acknowledges support from project BG16RFPR002-1.014-0005.

Laser transmission welding relies on controlled laser–matter interaction at polymer interfaces, where the optical absorbance and transmission between parts to be welded governs the local energy deposition and the subsequent melting of both materials. This work explores an absorptance-based strategy to enhance laser–matter interaction independently of the intrinsic optical properties of the material that plays the role of absorbent component. A dark masking agent was introduced at the interface of a typical overlap joint to locally increase absorbance for a wavelength of 1070 nm (a continuous-wave ytterbium fiber laser). The influence of laser power on the fusion zone morphology was evaluated. Optical microscopy and mechanical testing were employed to assess the impact of the masking agent. Overall, it significantly altered the laser–matter interaction, leading to enhanced energy absorption and clearly promoting greater material melting. Microscopic observations revealed improved interfacial continuity and polymer cell bridging, indicating more efficient conversion of optical energy into effective load-bearing material. These results demonstrate that interfacial absorbance control is a powerful optical strategy for tailoring laser energy deposition in laser transmission welding. The proposed approach broadens the applicability of laser-based polymer joining and highlights the central role of optical absorbance in governing process efficiency and joint performance.

The demonstration of single-photon emission in the near-infrared range in silicon offers an enticing perspective for developing industrial-scale silicon-based single-photon sources that emit at telecom wavelengths. Among the recently identified Si-based quantum emitters, the G center is a carbon-related point defect in silicon with an emission spectrum characterized by a zero-phonon line (ZPL) emission at 1279 nm, and with appealing features for the implementation of quantum technologies, including defect coupling with nuclear and electron spin degrees of freedom.

Theoretical studies have shown that the configuration of this complex represents a structurally metastable state [1], thereby raising the need to optimize the post-implantation thermal treatment, which is currently one of the main factors limiting the scalable manufacturing of color centers in silicon.

In this contribution, we report the activities based on two primary directives. The first one aims to understand the role of radiation damage during the ion implantation process, which is used to introduce extrinsic impurities into the silicon lattice. The emission properties of intrinsic self-interstitial W centers in high-purity and C-rich silicon substrates, following keV implantation, are investigated using single-photon-sensitive cryogenic confocal microscopy. This technique enables the identification of the effects of post-implantation thermal treatment on the formation of telecom quantum emitters.

The second experimental approach aims to explore more responsive thermal processing and implantation protocols to achieve higher creation yields. Here, we present the direct and non-destructive localized activation of G centers upon spatially resolved ns-pulsed laser annealing in keV carbon-implanted high-purity silicon substrates. Specifically, this approach involves ns heat transients during the annealing step, offering a practical off-equilibrium pathway for competitive processes in forming defective complexes and radically different possibilities for defect engineering [2].

[1] Deák, P., et al., Nat. Commun. 14, 1–6 (2023)

[2] Andrini, G. et al., Commun. Mater., 5, 47, (2024)

This study investigates the performance of stochastic and gradient descent algorithms within an active optical system for free-space optical communication applications. The primary function of the adaptive optical system in this context is to dynamically focus a laser beam through a diaphragm emulating a single-mode optical fiber input, utilizing the specified control algorithms. The efficiency of the focusing process is quantified by the proportion of total laser energy transmitted through the diaphragm. The selected algorithms offer a comparative advantage in implementation simplicity over more common alternatives such as stochastic parallel gradient descent (SPGD) or genetic algorithms.
The core objective of the study is to increase the integrated photodiode signal, which serves as the system's merit function, and to iteratively enhance this signal by applying wavefront correction. This correction aims to reshape the laser beam's wavefront to minimize transmission losses through the target aperture. A feedback control loop was established between a piezoelectric deformable mirror and the photodiode, using stochastic and gradient descent algorithms to optimize the aperture's phase profile. The fundamental goal of these optimization routines is to maximize the energy density in the far-field focal spot. This is achieved by minimizing the spot diameter toward the diffraction limit while concurrently increasing its peak intensity.
Empirical findings indicate that the stochastic algorithm, by its nature, progresses rapidly and converges in fewer iterations, albeit with lower final precision. In contrast, the gradient descent algorithm converges more slowly but yields a superior final value for the merit function. Experimental results demonstrated that a 45 mm piezoelectric mirror with 32 control channels was capable of focusing approximately 90% of the initial beam energy through diaphragms of 19 μm and 9 μm diameter, using either optimization strategy.

Introduction: Superconducting nanowire single-photon detectors (SNSPDs) are pivotal to quantum information science due to their high detection efficiency and low timing jitter. However, traditional SNSPDs are limited by a binary response, necessitating the development of photon number resolving (PNR) capabilities for advanced quantum communication and sensing. While spatial multiplexing has enabled PNR resolution up to 24 photons, scaling these architectures to 32 pixels while maintaining detection uniformity and minimizing crosstalk remains a significant technical challenge.

Methods: We report the complete development cycle of a PNR-SNSPD, from design optimization to nanofabrication. The fabrication process depositing a 6 nm superconducting thin film via DC magnetron sputtering at room temperature. A three-step electron beam lithography (EBL) process was employed: PMMA for contact pads (10 nm Ti/60 nm Au), HSQ (hydrogen silsesquioxane) for the nanowire geometry, and a final PMMA layer as a resist for AuPd resistors (5 nm Ti/85 nm Au). The nanowire pattern was transferred using hybrid reactive ion etching (RIE), whereas the contact pad and resistor patterns were defined by electron beam evaporation followed by a lift-off procedure.

Results: SEM characterization successfully verified the morphological integrity of the 32-pixel PNR-SNSPD arrays. Material optimization of NbTiN films demonstrated that the superconducting transition temperature (Tc) is highly sensitive to the nitrogen concentration ratio. We achieved a peak Tc of approximately 11.4 K for thicker films and around 9 K for thinner films at 5% nitrogen concentration, followed by a monotonic decrease in Tc as the nitrogen concentration increased toward 25%.

Conclusions: Our results demonstrate a robust fabrication pathway for high-density 32-pixel SNSPD arrays. The optimization of NbTiN deposition parameters provides a viable route to improving device performance and operational stability. These advancements contribute to the scalable production of PNR-capable detectors essential for high-fidelity quantum state characterization.

In recent years, two-dimensional materials (2DMs) have attracted considerable interest for their remarkable properties, which allow for them to be employed in many fields. In particular, 2DMs are increasingly finding application in the field of optoelectronics, with the aim of reducing manufacturing costs and device dimensions to enhance their efficiency. Furthermore, the van der Waals lattice structure of 2DMs enables them to be easily integrated with silicon technology. Unfortunately, the thin nature of these materials might result in weak light absorption. To address this issue, heterostructures of 2DMs are fabricated: combining them allows the tuning of electronic bandgaps, obtaining low-cost devices in a given range of wavelengths. Topological insulators (TIs) are 2DMs characterized by an insulating bulk gap and Dirac helical electronic surface states. Among these, Bi₂Se₃ demonstrates considerable potential in high-speed detection, due to the high mobility of surface electronic states and its 0.3 eV bandgap, which enable it to operate at telecommunications wavelengths (λ=1550 nm). On the other hand, Te is a material with a thickness-dependent bandgap which extends from 0.3 eV (bulk) to 1.2 eV (monolayer). The absorbance of Te films in the infrared range is higher than Bi₂Se₃ of the same thickness. Considering these properties, we fabricated, through a low-cost vapor–solid deposition technique, a photodetector based on a Te/Bi₂Se₃ heterostructure, deposited onto a prepatterned n-Si substrate, in order to increase performance in both the VIS and IR spectral range. Single layers of Te and Bi₂Se₃ and Te/Bi₂Se₃ heterostructures were separately characterized by XRD and SEM to investigate their structural and morphological properties. The obtained Te/Bi₂Se₃ photodetectors are sensitive to both VIS (λ=633 nm) and IR (λ=1550 nm) light, exhibiting a responsivity of 2.6 A/W and a detectivity of 2.6 x 10¹¹ Jones at λ=633 nm, and showing a linear and ultrafast response (108 ns).

Introduction: QUANTEP develops quantum-optics devices using silicon photonics. Foundry runs highlighted the need for in-house prototyping for fast iterations, often before final oxide encapsulation and before full optical testing is available. We present a SOI 220 nm workflow where a reversible polymer overcladding acts as a non-permanent photonic environment to accelerate early fabrication of nanowaveguides and grating couplers, compatible with post-processing such as metallization and local rework.

Methods: Patterns were defined by electron-beam lithography (EBL) on SOI 220 nm and transferred by reactive ion etching (RIE). In this first iteration, an Al hard mask improved pattern transfer; in parallel, the flow migrated toward high-etch-resistance resists (e.g., CSAR-class) to reduce complexity in subsequent runs. The design set included full-etch and partial-etch grating coupler (GC) variants: full-etch structures were obtained by RIE, while partial-etch regions were implemented locally by ion beam (FIB) milling and quantified by atomic force microscopy (AFM). Selected chips were coated with approximately 2 um polymethyl methacrylate (PMMA) to enable waveguide confinement; EBL-defined windows preserved access for alignment, metallization, and local rework while keeping polymer coverage on photonic areas. Etch depths and film thicknesses were obtained from AFM and tilted-stage SEM.

Results and Conclusions: SEM confirms fabrication of nanowaveguides and GC structures. AFM validates a partial-etch depth of 65 +/- 6 nm versus a 70 nm target and verifies PMMA thickness. The workflow provides a SOI 220 nm prototyping route combining RIE transfer, FIB partial-etch, and reversible polymer overcladding. While not replacing final SiO2 encapsulation, PMMA increases processing flexibility and enables access windows, metallization, and local rework that would be more complex with oxide cladding.

Optical time-domain reflectometry (OTDR) is widely used for fault detection and optical path loss characterization in optical fiber systems and networks. While long pulses are necessary for adequate signal-to-noise ratio and measurement range, they blur localized fault events, degrading both spatial resolution and the ability to detect non-reflective or weakly reflective localized losses. For short-distance optical systems that cascade multiple optical components where spatial resolution in the 10 cm to 1 m range is desired, this limitation is particularly significant. This work addresses these constraints through developing blind pulse spread function (PSF) estimation and post-processing of OTDR traces. Our method exploits localized reflection events (such as induced reference reflections at known locations) to estimate the system's impulse response without requiring hardware modifications or independent pulse characterization. The estimated PSF is then used to perform deconvolution, along with noise reduction processing, on OTDR traces acquired from commercial instruments on laboratory systems. By iteratively refining PSF estimates and applying advanced signal processing techniques adapted from image deconvolution literature, we aim to enhance spatial resolution and improve detection fidelity for discrete loss events. We will present preliminary results from OTDR trace simulations demonstrating the feasibility of blind PSF estimation using iterative optimization methods. Ongoing measurements using commercial OTDR instruments on laboratory systems will be conducted to validate the approach on real-world data.

Introduction: Integrated photonic refractive index sensors are increasingly important for chemical and biological sensing due to their high sensitivity, compact footprint, and compatibility with silicon-based fabrication technologies. Resonant photonic structures that support sharp spectral features are particularly attractive, as they enable enhanced detection of small refractive-index variations through precise wavelength tracking.

Methods: In this work, a silicon-on-insulator (SOI) refractive index sensor based on a coupled-resonator optical waveguide (CROW) architecture is presented. The design employs two inversely coupled Sagnac loop reflectors connected by a self-coupled feedback waveguide, generating Fano-type asymmetric resonances through discrete–continuum interference. Numerical simulations based on the finite-element method were used to analyze the influence of structural parameters, including loop radius, coupling gap, and feedback length. Refractive index sensing was evaluated over the range of 1.33–1.36 by monitoring resonance wavelength shifts.

Results: The ridge waveguide configuration exhibited stable asymmetric resonances with sensitivities between 106 and 120 nm/RIU. By incorporating a subwavelength-grating segment into the feedback waveguide to enhance evanescent field interaction, the sensor sensitivity was increased to 185.8–212.2 nm/RIU while preserving resonance asymmetry and spectral stability.

Conclusion: The proposed coupled Sagnac loop CROW sensor demonstrates high sensitivity, tunability, and fabrication tolerance in a compact footprint. These characteristics highlight its strong potential for integrated biochemical and environmental sensing applications.