At the current stage of development of infrared detector technology in the long-wave infrared range, the only detector arrays available on the market that operate at room temperature are thermal detectors. Among these, monolithic microbolometer arrays are the most popular with production volumes exceeding those of all other infrared array technologies combined. However, the efficiency of thermal detectors is modest; they exhibit a slow response time and are not very useful for multispectral detection. For this reason, new ideas for thermal detector designs and new materials that meet the expected performance requirements are being sought. High hopes are pinned on a new generation of thermal detectors based on low-dimensional solid (LDS) materials. It is predicted that the fundamental properties of LDS thermal detectors, driven by the quantum-size effect, enable them to overcome the performance limitations of conventional bulk detectors. This paper aims to organise existing knowledge on this subject, compile current detector performance data, and identify potential directions for further development. It focuses on several types of thermal detectors operating at room temperature: photothermoelectric, bolometric, pyroelectric, nanoelectromechanical resonator, and CMOS-compatible detectors.
The article shows that doping silicon with nickel in the temperature range of T = 1000–1250 °C makes it possible to almost completely suppress the generation of thermal donors during thermal annealing in the temperature range of T = 100–700 °C. It has been established that impurity nickel atoms form clusters and precipitates in silicon that absorb oxygen atoms. A method for producing silicon with stable electrophysical parameters has been proposed. The proposed method for gettering uncontrolled impurity atoms can be used in various electronic production. This makes it possible to obtain a silicon material with stable doping parameters containing nickel impurity atoms.
The NiO-ZnO heterostructures were fabricated using a combination of physical vapour deposition and thermal oxidation techniques. Thin films of nickel and zinc were sequentially deposited onto non-conductive substrates and subsequently oxidised to form nanostructured p–n junctions. The influence of thermal oxidation parameters on the structural, morphological, and optical properties of the resulting heterostructures was thoroughly investigated using scanning electron microscopy, high-resolution transmission microscopy, X-ray diffraction, and UV-Vis spectroscopy. The heterostructures exhibited a strong UV absorption and a band gap of 3.29 eV. Photocatalytic activity was evaluated using an aqueous solution of methylene blue under UV irradiation. The NiO-ZnO films achieved a degradation efficiency of 93% after 540 min, confirming their potential for photocatalytic water treatment applications. These preliminary findings demonstrate that even thin-film configurations with limited catalyst mass can be promising in degrading organic pollutants.
Multi-carrier signal generation techniques are important in various photonic application domains. Multi-carrier sources having stable frequency responses, narrow line width and adequate spectral flatness can be used instead of laser arrays. One of the major applications of multi-carrier sources relates to high-speed optical communication networks. Optical systems such as orthogonal frequency division multiplexed (OFDM) and dense wavelength division multiplexed (DWDM) systems transmit information using multiple carriers on a single channel to improve the spectral efficiency of the transmission system. Traditional systems use multiple laser sources to generate multi-carriers, one for each channel with minimal phase coherence. Optical frequency combs (OFCs) generate optical subcarrier/carriers from a single laser source with improved phase and space coherence using different electro-optic schemes. Contrary to standard lasers, OFCs-based optical carriers provide reduced cost, flexibility, and improved spectral efficiency. In recent years, numerous publications have reported a variety of techniques to implement OFC and have succeeded in generating a wide range of carriers. For a comprehensive understanding of OFCs, it is essential to summarise and compare the techniques from a practical perspective, emphasising their real-world applications, advantages, and limitations. This review examines the characteristics of optical multi-carrier generators, providing a detailed comparison of different techniques. Furthermore, the transmission properties of these methods are analysed with focus on key practical factors, including flexibility, cost-efficiency, and power consumption. Lastly, potential challenges and future research directions relevant to real-world implementations are highlighted in this review.
Inverse design has emerged as a powerful approach for developing high-performance photonic devices beyond the limitations of conventional geometry-based methods. In this study, we propose a compact 3 dB optical power splitter designed using a boundary-based inverse design strategy driven by the particle swarm optimisation (PSO) algorithm. The device boundary along the propagation direction is discretised into fine segments and iteratively optimised through a two-stage framework to simultaneously suppress input reflection and achieve balanced power distribution at the output ports. Over a 100 nm bandwidth, the improved structure exhibits outstanding optical performance. The excess loss stays between-0.1 and-1.1 dB, but the reflection is decreased to about-20 dB. Nearly equal power splitting is seen at the middle wavelength when the balancing factor is close to 0 dB. The device also exhibits symmetric and consistent responses when excited from either input port. With a compact footprint of approximately 6 & micro;m & times; 16 & micro;m, the proposed design is suitable for high-density photonic integrated circuits. These results confirm the effectiveness of a PSO-based boundary inverse design for realising broadband, low-loss, and compact photonic components.
Photovoltaic (PV) power generation in high-penetration renewable energy systems exhibited pronounced fluctuations and substantial uncertainty. To improve PV power forecasting accuracy, this study proposed a hybrid forecasting model, termed DA-LSTM, which integrated a dual-attention (DA) mechanism with a long short-term memory (LSTM) network. The model leveraged LSTM temporal encoding to capture key meteorological features from multidimensional input data. In addition, attention mechanisms were introduced at both the feature and temporal levels to extract task-relevant representations and identify historical time steps most similar to the current prediction target, thereby enabling the modelling of non-linear temporal dependencies. To evaluate model performance, a series of comparative experiments was conducted against multiple benchmark models. The results showed the following. First, compared with the benchmark models, DA-LSTM achieved a root mean square error (RMSE) of 795.36 kW, a mean absolute error (MAE) of 580.15 kW, and an R2 value of 0.9658. Second, ablation experiments demonstrated that removing the feature attention module increased the RMSE by 4.8%, which confirmed the effectiveness and necessity of the dual attention mechanism. Third, the proposed model exhibited superior robustness and adaptability under conditions characterised by abrupt weather variations and high-penetration power fluctuations. Overall, the experimental results demonstrated that incorporating dual attention into the LSTM framework significantly improved the forecasting accuracy of PV power generation. The proposed approach also provided a practical technical solution for enhancing prediction performance and operational stability in high-penetration renewable energy grids.
This work demonstrates polarisation-controlled millimeter-wave generation without using an optical filter. The configuration involves two lithium-niobate Mach-Zehnder modulators operating in parallel at the maximum transmission bias point (MATP). In the proposed scheme, a 5 GHz local RF signal is subjected to frequency 8-ctupling, resulting in the generation of a 40 GHz millimeter-wave signal. The system achieves sideband suppression ratios (SSRs) of 50 dB and 44 dB in the optical and RF domains, respectively, for a modulation index of 2.868. Carrier suppression is achieved using a polarisation-based control method. An analytical assessment is carried out to evaluate the variation in SSR with changes in the extinction ratio, the azimuth angle of the polarisation controller, and the amplitude of the RF drive signal.
Free-space optics (FSO) is a promising technology for meeting the high bandwidth and data rate requirements of modern wireless communications. However, atmospheric instability, such as turbulence, significantly degrades the quality of the received signal. This challenge can be effectively mitigated by integrating wavelength-division multiplexing (WDM) and multiple-input multiple-output (MIMO) techniques. This research presents a simulation-based performance analysis of a quadrature amplitude modulation frequency-shift keying (QAM-FSK) dual-modulated, linearly polarised WDM-MIMO-FSO system under various atmospheric conditions, including haze, rain, and fog. The proposed system uses eight individual wavelength channels, each carrying 200 Gbps of QAM-FSK-modulated data, which are then transmitted via four FSO-MIMO links. This configuration achieves a high net data transmission rate of 6.4 Tbps. The simulation results show that under clear weather conditions, the system can achieve a remarkable link range of up to 113 km. Furthermore, across all eight wavelength channels and under various adverse atmospheric conditions, the proposed system demonstrates a superior Q-factor, high signal-to-noise ratio (SNR), and low bit error rate (BER) when compared to prior works in the literature.
Design and femtosecond laser fabrication of high-order fibre Bragg gratings with precisely controlled absolute wavelengths and spectral separation between higher-order resonances are presented. The line-by-line inscription technique ensures relatively high and similar reflection coefficients for neighbouring harmonics. A high-order fibre Bragg grating was fabricated to operate within the SCL-band, matching the spectral range of commercially available fibre optic interrogators. The gratings were experimentally verified as an easy-to-use sensor for accurate simultaneous strain and temperature discrimination. The proposed approach addresses key limitations in dual-parameter sensing through a single compact structure, flexible spectral design, and straightforward application and compatibility with existing interrogation systems.
The growing interest in solar corona and heliospheric backscatter glow observations in the vacuum ultraviolet, along with technological advancements in the feasibility of vacuum ultraviolet optical components for such applications, underscores the need for improved metrological solutions. This work presents a detailed characterisation of a compact laser-produced plasma vacuum ultraviolet source based on a double-stream gas-puff target, relevant in the metrology of optical elements for space applications. The measurements include the source spectrum, the number of photons, and the source size for targets produced using different gases. Such a source was used to test optical components of the Lyman-alpha space-based observation systems and remains available for future metrology applications. To the best of our knowledge, this is the first application of a laser-produced plasma vacuum ultraviolet source for characterising space-relevant optical components.
This study reports the results of an investigation of a niobium-doped titania dioxide thin film fabricated via a sol-gel method and dip-coating. Niobium-doped and undoped titania films were deposited on silicon wafers and soda-lime glass slides. The niobium-doped and undoped titanium dioxide films exhibit a high refractive index of similar to 2.1 and thicknesses exceeding 110 nm. The study addresses the technological procedures, characterisation methods, and the influence of niobium doping on the optical properties of TiO2 films.
This work explores the use of atomic layer deposited (ALD) ZnO thin films as functional and aesthetic layers in monocrystalline silicon solar cells. ZnO films of varying thickness were deposited on polished silicon wafers and finished solar cells producing distinct interference colours - gold, violet, and green - while enabling precise control over optical properties. Colorimetric analyses in RGB and CIE Lab colour spaces confirmed the tunability of the perceived colour with increasing ZnO thickness. Raman spectroscopy and X-ray fluorescence verified crystalline quality and composition of the ZnO films, while spectroscopic reflectometry demonstrated thickness uniformity and growth rates consistent with ALD characteristics. The deposition of ZnO layers reduced the power conversion efficiency of the solar cells from similar to 15.2% to similar to 13.5%, highlighting a trade-off between aesthetics and photovoltaic performance. Nevertheless, the coloured ZnO coatings exhibited potential for integrating photovoltaic modules into architecturally sensitive environments where visual harmony is desired. The results underline the versatility of ALD technology in engineering both the optical and functional properties of solar cells through a controlled thinfilm deposition.
The article presents methods for synthesising nanocomposites of Cu and Zn with various crystalline structures, ranging from metallic oxides to solid solutions. Using physical vapour deposition and thermal oxidation, two types of nanocomposites were obtained: (I) Cu0.76Zn0.24 nanobrass covered with a porous ZnO nanofoam, and (II) CuO nanowires with a ZnO forming a core-shell nanostructure. The morphological and structural properties of the nanocomposites were analysed using scanning electron microscopy (SEM), transmission electron microscopy (TEM, HRTEM), and X-ray diffraction (XRD). The nanobrass with ZnO nanofoam composite exhibited strong gas-sensing activity. Its electrical resistance increased significantly when exposed to gases, showing responses of 158% for methane, 131% for hydrogen, and 91% for ammonia at 200 degrees C, with full reversibility upon air flushing. The CuO-ZnO nanowire composite demonstrated high photocatalytic efficiency. These findings highlight the potential of the developed nanocomposites for applications in gas sensing and photocatalytic environmental treatment.
This study investigates the capability of a field-programmable gate array (FPGA)-based quantum bit (QUBIT) emulator to replicate the quantum superposition state with randomness evaluation serving as the primary verification method. The QUBIT device is built on the FPGA, an integrated circuit that is a massively parallel array of independent logic elements. Using two QUBIT devices, a simple random number generator is created and statistical tests are used to verify randomness. These tests provide a quantitative measure of randomness quality, reflecting the emulator effectiveness at mimicking quantum superposition. The results offer insights into the limitations and potential of using the emulator (QUBIT) as an alternative to aphysical quantum system. Randomness of generated numbers (bit strings) was tested with the NIST Statistical Test Suite (SP 800-22), widely regarded as the standard for randomness evaluation. In total, 106 bits were generated and tested with different block lengths: 10 blocks of 105 bits and 100 blocks of 104 bits. The observed deviations indicate that while the emulator can serve as an educational tool, its statistical properties currently limit its applicability in cryptographic contexts.
To advance the development of thin-film photovoltaic (PV) technologies, current research is increasingly focused on identifying alternative materials to zinc oxide (ZnO), cadmium sulfide (CdS), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS). Among the most promising candidates are titanium oxide (TiO2) and copper oxide (Cu2O or CuO), owing to their abundance, non-toxicity, and favourable optoelectronic properties. This study presents a simulation-based investigation of a multi-junction PV structure based on n-TiO2/p-CuxO single cell using the solar cell capacitance simulator (SCAPS). The multiminimising defects associated with lattice mismatch for thinner TiO2/CuxO layers in a tandem device. Reducing interface defect density through improved fabrication techniques could substantially enhance efficiency. Furthermore, in multi-junction architectures, improved carrier extraction and reduced recombination losses increase the open-circuit voltage (Voc), thereby improving carrier transport to external contacts and enhancing cell performance.
The article examines the impact of temperature on the main lighting parameters of selected high-power LED sources. In the first stage of the research, the actual value of thermal resistance Rthj-c was determined, thereby enabling the final junction temperature Tj of the tested LED sources to be determined. Then, using a laboratory setup with a 50 cm integrating sphere and a Peltier module, the research examined the effect of temperature on the luminous flux Phi, correlated colour temperature (CCT), colour rendering index (CRI), spectral distribution, and optical efficiency eta o for three selected LED sources from various manufacturers. The tests were conducted at three forward current values, IF = 350, 700, and 1050 mA, and four Peltier module temperatures, Tp = 25, 45, 65, and 85 degrees C. The obtained research results were analysed and conclusions were formulated.
The article discusses modern single-pixel imaging techniques. Different solutions of spatial light modulators (SLMs) used in infrared imaging are presented. The focus is on image reconstruction methods, in particular on the use of a modulator based on orthogonal codes, cyclic matrices, and neural networks for image reconstruction. The potential possibilities and limitations of these new imaging methods are described, emphasizing their usefulness in different ranges of the infrared spectrum. Moreover, the experimental implementation of a single-pixel infrared camera is presented. Possible applications and future development perspectives of this technology are indicated.
This paper investigates the application of a G-Flake graphene oxide (GO) layer as an innovative coating material for optical fibre tapers, enhancing the sensor sensitivity to various volatile liquid vapours. The results confirm that this combination is effective because the formation of a monolayer of adsorbed gas alters light propagation in the tapered optical fibre. These changes are detectable across a broad wavelength spectrum, ranging from visible to infrared. In this study, three volatile liquids – trimethyl phosphate (TMP), 1,4-thioxane (THX), and ammonium hydroxide (NH4OH) – were tested using pure THX and TMP without dilution, while NH4OH was applied as a 25% solution. The gases used in the research simulate chemical warfare agents, such as sulphur mustard and sarin. The authors used the differential method to analyse the results, which revealed the formation of characteristic peak pairs around a wavelength of 795 nm. The peak heights and the distance between them varied over time in response to exposure to the selected vapours. Additionally, the amplitude of the transmitted power changes linearly in the first 30–45 min, with the highest power change rate observed for TMP (0.026 dBm/min at 789.2 nm). The greatest contrast between maximum and minimum power levels was observed for TMP, reaching 4.45 dBm. An approach was presented that demonstrates how a tapered fibre covered with GO can be used as the basis for developing a low-cost gas and vapour sensor.
Multimode interference (MMI) waveguides are favoured for their wide bandwidth, extensive fabrication tolerance, high stability, effective light confinement, and minimal transmission loss. In this study, the authors propose a numerical design of an optical power splitter based on restricted interference (RI) mechanisms using silicon-on-insulator waveguides, where the precise positioning of input pairs and subsequent adjustment of the MMI region length are essential aspects. The RI-MMI configuration facilitates the reduction of the MMI length due to the applied interference theory. The authors’ design undergoes a rigorous simulation and optimization using a highly accurate three-dimensional beam propagation method (3D-BPM) simulation method to ensure optimal performance. Simulation results confirm the authors high-performance design with low excess loss (< 2.7 dB), small relative phase difference (< 2%), negligible residual (< −18 dB), excellent coupling ratio (−0.09 dB to 0.05 dB), and high balance factor (< −17 dB) across the wide range of 100 nm (1500 nm–1600 nm). Furthermore, the authors’ optimized design exhibits a width tolerance of ± 2.1 µm and a height tolerance of ± 10 nm. Notably, the core component of the splitter is housed within an extremely compact footprint area of 6 µm × 65 µm. These exceptional characteristics position the authors’ proposed device as highly promising for large-scale integrated optical circuits, as well as photonic neural networks in ultrawideband telecom applications.
This paper introduces quantum key distribution-as-a-service (QKDaaS) to address the end-to-end security challenges posed by the involvement of multiple orchestrators in 6G networks. These networks require seamless coordination of processes from endpoints to services, with tiered components supporting data-driven and cross-layer predictive procedures. While multi-party (spanning multiple domains, tenants, and providers) enhances local security through advanced controls, it also complicates the implementation of an end-to-end security framework that is essential for mobile network operators. To address this issue, we propose QKDaaS, a secure platform that leverages a fibre transport network for credential and encryption key distribution in multi-party environments. The solution uses wavelength multiplexing to integrate quantum and classical channels within a single fibre. Both C-band and O-band quantum channels are considered, with classical communication in the C-band. The simulation results show that with the currently available experimental setup and mobile network requirements, secure keys can be generated for distances approaching 100 km in the C-band and 60 km in the O-band case. This means that QKDaaS can be deployed in mobile network operators’ current transport infrastructures.
