Search Results (814)

Rare-earth-doped microsphere cavities have attracted significant interest for applications in miniaturized photonic devices due to their unique optical properties. In this work, Yb³⁺/Er³⁺ co-doped microsphere cavities were fabricated via a melting method, which enables uniform interior doping at high and tunable rare-earth concentrations through a simpler and more cost-effective process compared with existing coating and fiber-etching approaches. Whispering gallery modes (WGMs) enhanced upconversion luminescence, which was observed using tapered fiber coupling, producing a vivid green fluorescence ring near the equatorial region of the microsphere. The luminescence characteristics of the microsphere cavity were investigated by measuring the fluorescence spectra under varying excitation powers. The results indicated that the fluorescence emission follows a two-photon absorption process, consistent with the upconversion emission mechanism of Er³⁺. A finite difference time domain (FDTD) model was employed to simulate the optical field distribution within the microsphere cavity. At a microsphere diameter of 90 μm and a coupling gap of 0 μm, both the 980 nm pump light and the emitted light were effectively confined near the equatorial region of the microsphere, forming WGM confinement patterns. These findings are expected to advance the application of rare-earth-doped microsphere cavities in fields such as biosensing, bioimaging, optical communications, and upconversion microlasers. Full article

This work presents the Smart-Reflex-Scope, a compact and accessible smartphone-based microscope with integrated reflective illumination developed for on-chip analysis of microparticle dynamics. In this work, the platform is specifically employed to characterize size-dependent microparticle motion within a microchannel. The Smart-Reflex-Scope simultaneously functions as an illumination source and imaging unit by integrating a reversed smartphone camera lens, a custom reflex module, a microfluidic chip, and a precision Z-axis translation stage for focal adjustment. The optical performance was quantitatively evaluated in terms of equivalent focal length, magnification, and object-plane spatial resolution, providing a comprehensive assessment of the system’s microscale imaging capabilities. A comparative design study was conducted between two configurations: Design-1, based on normal reflection, and Design-2, based on angular reflection. The two approaches were analyzed with respect to illumination uniformity and imaging performance to identify the optimal configuration for enhanced visualization. Experimental validation was performed using synthetic microparticles with diameters of $6\mathsf{\mu }\mathrm{m}$ and $20\mathsf{\mu }\mathrm{m}$, enabling assessment of the system’s ability to resolve and dynamically track micrometric objects of different sizes. The results demonstrate reliable detection and size-dependent dynamic characterization. A two-factor statistical ANOVA analysis confirmed the significance of the observed differences between microparticle groups under the tested experimental conditions (p-value $<0.0001$). Overall, the proposed platform represents a scalable and miniaturized microscopy solution bridging conventional benchtop instruments and portable analytical devices. Full article

In response to the demands for planetary material detection, in this study, we propose an optical system for a compact remote Raman–LIBS (CRBS, Laser-Induced Breakdown Spectroscopy) combined spectrometer based on liquid lens focusing. This system adopts a design approach incorporating liquid lens focusing, a shared pulsed excitation source, and a common optical path for both transmission and reception. Compared to existing international combined Raman–LIBS spectrometer systems, the proposed optical system is more compact and achieves integrated Raman and LIBS detection capabilities, thereby facilitating system miniaturization and enhancing detection efficiency. This system represents a promising approach for compact, robust remote surface analysis instruments for terrestrial and planetary science. This study provides a theoretical foundation for achieving stable in-orbit detection in lunar material exploration and other long-distance signal detection missions. Full article

Micro- and nanoplastic (MNP) pollution has emerged as a global environmental and health concern, driving the rapid development of sensor technologies for faster, more sensitive, and field-deployable detection. This review synthesizes recent advances in optical, electrochemical, and biosensor platforms for MNP analysis and compares their analytical performance and practical feasibility. Optical sensors, including plasmonic, spectroscopic, and colorimetric systems, enable label-free and often rapid detection with material discrimination capability, and are well-suited for screening applications, though they commonly exhibit higher detection limits and matrix interference. Electrochemical sensors demonstrate the highest analytical sensitivity overall, frequently reaching low µg L⁻¹ to ng mL⁻¹ levels, with strong potential for miniaturization and on-site deployment; performance is further enhanced by nanostructured electrodes, photoelectrochemical designs, and signal amplification strategies. Biosensors incorporating peptides, aptamers, enzymes, or engineered proteins provide improved polymer selectivity and enable targeted detection, but face challenges related to stability, cross-reactivity, and reproducibility in complex samples. Practically, portable electrochemical and simple optical colorimetric platforms are currently the most feasible for field use, while hybrid bio-electrochemical systems show the highest performance potential. Future research should prioritize robust selective recognition elements, antifouling interfaces, standardized validation protocols, mixed-polymer quantification models, and integration with machine learning to enable reliable, real-world MNP monitoring. Full article

Osteoarthritis (OA) and osteochondral degeneration present a significant clinical burden characterized by the complex interplay of extracellular matrix degradation and chronic inflammation. While biochemical profiling has matured, a critical translational gap remains in transitioning from benchtop assays to systems capable of continuous, intra-articular monitoring. This review provides a comprehensive synthesis of experimentally validated biosensing technologies, including optical, electrochemical, and piezoelectric Quartz Crystal Microbalance (QCM) platforms, evaluated through the lens of sensing architecture, biomarker specificity, and matrix compatibility. Our analysis reveals that while optical sensors offer superior sensitivity, electrochemical platforms show the greatest promise for miniaturized, implantable integration. However, a pivot in the field is identified: the primary bottleneck has shifted from analytical detection limits to operational stability within the hostile synovial environment. Current research is largely restricted to single-analyte detection in simplified media, failing to address the multifactorial nature of OA. We propose that the next generation of osteochondral diagnostics must prioritize multiplexed arrays, mechanically compliant architectures, and machine-learning-assisted signal processing. By bridging these engineering frontiers, biosensors will evolve from passive diagnostic tools into intelligent, personalized platforms for real-time disease management. Full article

Biosensors have a recognition element that detects a bioanalyte as well as a transducer that transfers the measured physicochemical properties into an electric signal, which is amplified, processed, and depicted on a user interface and usually stored in a data storage system. Such biosensors can be used in a broad range of applications, from personalized medicine to drug discovery, and from food safety to plant disease diagnosis. Portable biosensors are often based on microfluidic systems or micro-electromechanical systems (MEMS), measuring physical or chemical parameters. In spite of their importance for diverse applications, there are still several limits regarding the portability of biosensors, which is often necessary. Besides the required miniaturization of the components and the limited lifetime of some biological reagents, sample preparation and handling can be problematic. This review gives an overview of recent biosensor research, concentrating on optical measurements, and shows the possibilities and limits of the biosensors developed during the last few years. Full article

Optical tweezers (OTs) serve as a core contactless manipulation tool at the micro- and nano-scale, with wide applications in physics, biology, colloid science and other fields. However, conventional single-beam gradient force OTs are limited by diffraction, optical damage, low throughput, and system complexity. To meet the demand for large-scale particle manipulation in complex environments, speckle optical tweezers (SOTs) based on random optical fields have emerged as a promising alternative to conventional OTs that transform random speckle patterns into a controllable manipulation resource. Since their formal establishment, SOTs have developed a solid theoretical foundation and diverse implementation platforms with key breakthroughs in micro- and nanoparticle manipulation. This paper systematically reviews the origin and development of SOTs, elaborates their core principles, summarizes the statistical properties of speckle fields, and introduces typical configurations based on random media, multimode fibers, and spatial light modulators. It also highlights the unique value of SOTs in micro- and nanoparticle manipulation, active particle dynamics, and cold atom physics, with advantages of high throughput, low cost, and environmental adaptability. Finally, future development trends are discussed, including intelligent regulation of optical fields, interdisciplinary applications, system miniaturization and multi-technology integration. This review provides a comprehensive reference for the theoretical development, system optimization, and practical application of SOTs in fields such as statistical physics, biomedicine, microfluidics, and quantum science. Full article

To address the need for high electrical insulation, strong immunity to electromagnetic interference, and miniaturized AC electrical-signal detection in complex electromagnetic environments, we propose and experimentally demonstrate a fiber-optic sensor based on a piezoelectric ceramic (PZT)-driven ring tapered-fiber resonator. The applied AC excitation is converted into periodic mechanical deformation through the inverse piezoelectric effect of the PZT, and the resulting strain modulates the resonator response, enabling optical demodulation of the input frequency and amplitude. A comprehensive figure of merit was introduced to optimize the tapered-fiber geometry, yielding an optimal waist diameter of approximately 10 μm. The sensor can effectively distinguish both single- and dual-frequency AC signals. Over the range of 50–500 Hz, the demodulated frequency agrees closely with the input frequency, with a linear fitting coefficient of 0.9999. At a fixed driving frequency of 250 Hz, the amplitude of the characteristic spectral peak increases nearly linearly with the input voltage amplitude, with a fitting coefficient of 0.9945. The device also exhibits good stability over 30–150 °C and during 70 h of continuous operation. With its simple structure, low cost, and strong immunity to electromagnetic interference, this sensor provides a practical solution for AC electrical-signal detection in complex environments. Full article

To address the demand for underwater acoustic detection with hydrostatic pressure resistance, this paper proposes a fiber-optic Fabry–Perot (F-P) underwater acoustic sensor based on micro-electromechanical system (MEMS) technology. According to the F-P interference principle, the diaphragm deforms under acoustic pressure, inducing variations in the F-P cavity length which modulate the interference spectrum and enable the measurement of underwater acoustic signals. A sensing diaphragm with a composite structure consisting of a central boss and a micro-hole array is designed, which improves the optical signal quality while reducing the influence of the pressure difference between the inner and outer surfaces of the diaphragm on sensor operation. MEMS fabrication, computer numerical control (CNC) machining, and laser fusion splicing technologies are employed to achieve batch fabrication of the sensing units and adhesive-free integration of the sensor. Experimental results show that the proposed sensor exhibits a flat frequency response within ±1.5 dB over the range of 1 kHz to 10 kHz, with an average signal-to-noise ratio (SNR) of 86.35 dB. The sensitivity reaches −181.79 dB re 1 rad/μPa at 10 kHz, with a maximum nonlinearity of 0.48% F.S., a repeatability error of 0.15% F.S. and a dynamic range of 100.83 dB. The proposed sensor features miniaturization, high consistency, hydrostatic pressure self-balancing capability, and immunity to electromagnetic interference, providing a solid foundation for hydrostatic-pressure-resistant underwater acoustic measurements in deep-sea environments. Full article

This review evaluates recent progress in nanozyme-based biosensors for detecting circulating tumour cells, nucleic acids, and protein biomarkers, with particular attention to how peroxidase-, oxidase-, and catalase-like reactions enhance signal generation across electrochemical, optical, and microfluidic platforms. The roles of iron oxide–gold composites, silica nanostructures, quantum dots, and hybrid nanomaterials in improving analytical performance, enabling multiplexed detection, and facilitating assay miniaturization are critically assessed. Advances such as amplification-free detection approaches, smartphone-compatible point-of-care systems, and AI-assisted data analysis are discussed in relation to their translational potential. Key barriers, including regulatory requirements, reproducibility concerns, and manufacturing scalability, are also evaluated. By integrating mechanistic understanding with practical considerations for clinical deployment, this review outlines how next-generation nanozyme-based biosensors may strengthen early cancer detection, real-time monitoring, and precision oncology. Full article

Amplified Spontaneous Emission (ASE) sources are widely employed as highly stable broadband sources in fields such as high-precision navigation and optical detection. Erbium-doped fiber (EDF), as the core active component in ASE sources, has long been a key subject of thermal stability research. We fabricated a low-doped EDF with an 80 μm-cladding using the vapor phase doping (VPD) technique. This EDF was compared with a commercial 125 μm-cladding EDF using a double-pass forward (DPF) optical path configuration with a narrowband filter. We investigated the temperature-dependent characteristics of the ASE spectra generated by the two EDFs with different parameters. The temperature drift performance of the two EDFs was analyzed based on three critical indicators of the spectrum: mean wavelength, spectral bandwidth, and output power. In comparison with the commonly used EDF, the results show that a properly designed small-cladding EDF with an appropriate length can deliver higher ASE output power and exhibit a lower mean-wavelength temperature drift. This study provides an important guideline for promoting the miniaturization of high-precision fiber-optic sensing devices. Full article

Relaxor ferroelectric single crystals, such as Pb(In₁/₂Nb₂/₃)O₃–Pb(Mg₁/₂Nb₂/₃)O₃–PbTiO₃, possess extraordinary electro-optic (EO) coefficients, offering immense potential for next-generation integrated modulators. However, the application of PIN-PMN-PT in fiber-optic gyroscopes (FOGs) is hindered by the challenge of fabricating high-quality optical waveguides with strict mode selectivity, as conventional diffusion typically excites multi-mode propagation. Here, the fabrication of high-quality, mode-selective waveguides is achieved in rhombohedral PIN-PMN-PT via a nickel in-diffusion technique. The resulting graded-index structures exhibit a Gaussian profile with a maximum refractive index change (∆n) of 1.53% while preserving the single crystal structure. Under specific processing conditions, we achieve precise mode selectivity, enabling exclusive transverse electric (TE) mode transmission. This mode selectivity fulfills the requirements for single-mode Y-branch geometries, establishing a robust platform for ultra-compact, low driving voltage modulators and advancing the miniaturization of inertial navigation and integrated photonic systems. Full article

In the fields of atomic physics, quantum sensing, and precision measurement, 852 nm lasers are essential for the resonant excitation and manipulation of the cesium (Cs) D₂ transition ($6S_{1/2}\to 6P_{3/2}$). While significant global progress has been made in developing 852 nm laser based on distributed feedback (DFB) lasers and external cavity diode lasers (ECDL), the burgeoning demand for portable and integrated quantum instruments imposes stringent requirements on miniaturization and long-term, maintenance-free operation. To address the challenge of mode competition in Faraday lasers, this work demonstrates a frequency-stabilized semiconductor laser based on an atomic frequency-selective architecture. By utilizing a customized Faraday Anomalous Dispersion Optical Filter (FADOF) for frequency selection, the laser wavelength automatically corresponds to the Cs 852 nm D₂ transition, offering “Plug-and-play” operation. To further enhance integration, we propose and demonstrate a miniaturized Faraday laser architecture that resolves the instability caused by the mismatch between the FADOF transmission bandwidth and the free spectral range (FSR) of the external cavity. By employing a 7000 Gs magnetic field, the FADOF bandwidth is actively broadened to ∼15 GHz, while the cavity length is concurrently compressed to 30 mm to maximize FSR to effectively suppressing unstable mode competition. The resulting laser achieves a highly compact dimension of $102\times 109\times 96{\mathrm{mm}}^3$. Performance testing demonstrates a Lorentzian fitted linewidth of $16.4\mathrm{kHz}$ and a 1-s frequency stability of $3.05\times {10}^{-13}$ after modulation transfer spectroscopy (MTS)-based frequency locking. This robust and autonomous 852 nm laser source provides a critical technological foundation for the miniaturization of high-performance quantum sensors. Full article

In the far-field approximation, an object’s diffraction field can be expressed as its Fourier transform multiplied by a phase factor. Here, we present a simple method with which to directly retrieve this phase factor from a single-shot off-axis interference pattern. By exploiting and adjusting its unique two-dimensional quadratic form, the quadratic contribution from the object’s Fourier transform can generally be neglected, particularly for amplitude-only objects and slowly varying phase objects. The phase factor is extracted by fitting a quadratic surface to the unwrapped phase obtained via Fourier-transform-based phase retrieval. Removing this factor enables precise reconstruction through a straightforward inverse Fourier transform, without requiring iterative computations. Compared with conventional far-field diffraction setups, our approach reduces system length and allows the use of smaller CCD sensors. Experimental validation using a modified Mach–Zehnder interferometer demonstrates high reconstruction accuracy and robustness. Overall, this method provides an efficient, practical, and real-time solution for object reconstruction, with the potential to simplify and miniaturize optical setups, offering an alternative approach to standard coherent diffraction imaging techniques. Full article

Hyperspectral sensing allows for the capture of spatially resolved spectral data, a capability critical for applications spanning from remote sensing to biomedical diagnostics. Nevertheless, the widespread adoption of this technology is hindered by the bulk and complexity of traditional systems based on diffractive optics. To overcome these hurdles, substantial research efforts have been dedicated to system miniaturization via component scaling and computational imaging. This review outlines the technological progression of compact hyperspectral imaging, ranging from miniaturized dispersive elements and tunable filters to computational snapshot designs using optical multiplexing. Although these approaches decrease system volume, they generally treat the sensor as a passive intensity recorder requiring external encoding. Therefore, we focus here on the rising paradigm of sensor-level integration made possible by nanomanufacturing. We examine optics-free architectures where spectral discrimination is embedded directly into the pixel, distinguishing between pixel-level nanophotonic filtering and intrinsic material-based selectivity. We specifically highlight emerging platforms such as compositionally engineered and cavity-enhanced perovskites, as well as electrically tunable organic or two-dimensional (2D) material heterostructures. To conclude, this review discusses persistent challenges regarding fabrication uniformity and stability, providing an outlook on the future of scalable and fully integrated hyperspectral vision systems. Full article