Search Results (168)

This paper proposes the use of laser-assisted cutting technology to control the brittle–plastic transition of single-crystal CaF₂ through local thermal softening, thereby suppressing its processing anisotropy. Nano-scratch experiments show that heating significantly increases the critical plastic cutting depth of each crystal plane and reduces the inter-plane differences. Based on this, laser-assisted ultra-precision turning was used to fabricate CaF₂ optical microcavities with a surface roughness below 10 nm, achieving a maximum quality factor of ~7.79 × 10⁷, and significantly reducing the performance differences among different crystal orientations. The research indicates that this method can effectively promote uniform plastic flow on each crystal plane, providing an effective approach for the high-performance and consistent fabrication of anisotropic brittle optical components. Full article

Microlasers are innovative photonics devices that have recently attracted attention for their unique characteristics, including compactness, broad spectral emission, and low lasing threshold. These properties are beneficial in biophotonics as these lasers can interact with biological materials without causing damage, especially for optical biosensing applications. Among the optical materials recently used as gain media in microlasers are organic dyes, rare-earth ions, fluorescent proteins, and semiconductors, including quantum dots and perovskites. Moreover, different optical cavities and current laser configurations have increased the versatility of microlasers. Recently, digital sensing methods based on novel algorithms, machine learning, and neural networks have been combined with microlaser systems to enhance their accuracy and expand their applications. This work provides a comprehensive review of recent progress in microlasers, covering gain media, microcavity types, and their applications in biophotonics, including conventional spectral-based sensing and new digital approaches for the biomedical field. Full article

In micro-opto-electro-mechanical systems (MOEMS), the micro-optical cavity plays a pivotal role. As performance requirements for MOEMS devices continue to rise, these cavities must achieve higher performance levels while simultaneously reducing their physical footprint. However, existing high-precision micro-optical cavities face challenges such as high process sensitivity and conflicting trade-offs between dynamic range and precision. To address these issues, piezoelectric thin-film actuators present a viable solution due to their high precision, stroke flexibility, electromagnetic interference resistance, and structural scalability. This study proposes a piezoelectric thin-film actuator based on the $d_{33}$ mode. The device adopts an island-circular structure that integrates a lead zirconate titanate (PZT) piezoelectric film with metal electrodes. By employing particle swarm optimization (PSO) to enhance displacement output and anti-gravity capabilities, the actuator achieves displacement outputs below 100 nm within a compact form factor while maintaining nanometer-level resolution. Simulation and experimental results confirm a first-order natural frequency of approximately 5.8 kHz, along with a reasonable linear displacement response across a 4–6 V drive voltage range. Furthermore, the device demonstrates functionality within a Fabry–Pérot (F-P) microcavity system, enabling active optical path length modulation through precise cavity tuning. This research provides an effective approach to enhancing the dynamic performance and process compatibility of micro-optical cavity devices, advancing the development of next-generation MOEMS systems. Full article

Oxide materials represent a versatile and fundamental platform for photonics, allowing the manipulation of light through optical property engineering. This review focuses mainly on the physics and applications of simple oxides, analysing their use in the realisation of dielectric mirrors, in particular of distributed Bragg reflectors, and planar microcavities. Critical aspects regarding the design of multilayer structures, the control of optical confinement and the improvement of the quality factor in passive devices are discussed. However, to provide a complete picture of the evolution of the field, the section dedicated to oxide materials anticipates future directions dominated by complex oxides such as lithium niobate, lithium tantalate and barium titanate required for active photonics. In this context, a necessary technological paradigm shift is highlighted: the transition from the current use of film-on-insulator platforms to the direct epitaxial growth of these functional materials, an essential step for the scalability and monolithic integration of future photonic devices. Full article

We analyze the formal equivalence between the electromagnetic energy conservation law derived from Maxwell’s equations in an optical microcavity and the conservation of a probability fluid associated with the de Broglie–Bohm theory for an effective massive particle describing a photon in this cavity. This work is part of a critical analysis of recent experiments by Sharoglazova et al. carried out with a view to refuting the de Broglie–Bohm theory. Furthermore, the consequences of our analysis for microphotonics go far beyond these experiments. In particular, extensions that take into account photon spin and stochastic aspects associated with radiative or absorption losses are considered. From the point of view of symmetries and probability current, here the effective photon behaves like a spin-1/2 particle. Full article

Light–matter interactions in optical microcavities attract much attention due to their potential for controlling properties of materials. Among the various types of optical microcavities, porous silicon microcavities (pSiMCs) are of special interest because of their relatively simple fabrication procedure, tunable porosity, and large specific surface area, which make them highly suitable for a wide range of optoelectronic and sensing applications. However, the fabrication of pSiMCs with precisely controlled parameters, which is crucial for effective light–matter coupling, remains challenging due to the multiple variables involved in the process. In addition, the parameter characterizing the capacity of pSiMCs for confining light inside the cavity (the quality factor, QF) rarely exceeds 100. Here, we present advanced methods and protocols for controlled fabrication of pSiMCs at room temperature, combining theoretical and numerical simulations and experimental validation of microcavity structural parameters for enhancing light–matter interactions. This systemic approach has been used to design and fabricate pSiMCs with an about twofold increased QF and correspondingly improved optical performance; the theoretical modeling shows that its further development is expected to increase the QF even more. In addition, we fabricated hybrid fluorescencent structures with the R6G dye embedded into the optimized pSiMCs. This provided a 5.8-fold narrowing of the R6G fluorescence spectrum caused by light–matter coupling, which indicated enhancement of the fluorescence signal at the eigenmode wavelength due to an increased rate of spontaneous emission in the cavity. The proposed methodology offers precise theoretical simulation of microcavities with the parameters required for specific practical applications, which facilitates optimization of microcavity design. The controllable optical properties of pSiMCs make them promising candidates for a wide range of applications where improved spectral resolution, and increased luminescence efficiency are required. This paves the way for further innovations in photonic systems and optoelectronic devices. Full article

Achieving controllable wavelength tuning in optofluidic whispering gallery mode microcavity lasers is crucial for high-throughput, multi-sample, multiplexed biochemical sensing and multifunctional integrated photonic devices. This paper develops a bidirectionally wavelength-tunable optofluidic fiber whispering gallery mode microcavity laser driven by Rhodamine 6G co-doped with different acceptor dyes. Experimentally, a thin-walled silica ring inside a hollow-core anti-resonant fiber served as the optical microcavity, with a fixed 2.5 mM Rhodamine 6G co-doped with other dyes as the gain medium. The results revealed that when co-doped with Rhodamine B or Cy3, the single-longitudinal-mode laser emission wavelength exhibited a red shift with increasing co-dopant concentration. Conversely, when co-doped with Cy5, the laser output wavelength showed a distinct blue shift. This unique bidirectional tuning characteristic originates from the different fluorescence resonance energy transfer efficiencies between the co-dopants and Rhodamine 6G, and their competitive modulation of the system’s effective gain spectrum. The study offers a novel and flexible strategy for achieving wide-range, controllable wavelength tuning on a single laser platform, with significant potential for applications in biochemical sensing and multifunctional integrated photonic devices. Full article

We present a parallel DNA molecular analysis platform based on an array of plano-concave Fabry–Pérot (PC-FP) microcavity lasers that enables the simultaneous, sequence-specific detection of multiple DNA targets. Each PC-FP cavity is functionalized with a distinct probe DNA and integrated within a microfluidic channel, allowing localized hybridization and lasing emission upon optical pumping. When Cy3-labeled complementary targets were introduced, distinct lasing peaks emerged from corresponding cavities at ~607 nm, whereas single-base-mismatched sequences produced no measurable signal. The lasing threshold was approximately 0.6 µJ/mm², confirming highly efficient optical feedback and cavity-enhanced signal amplification. The parallel operation of three PC-FP cavities demonstrated independent, multiplexed detection without optical crosstalk. The plano-concave geometry provides mode stability, compact alignment tolerance, and a tenfold reduction in threshold compared to flat FP mirrors. These results highlight the potential of PC-FP microcavity laser arrays as a scalable alternative to fluorescence-based assays, offering rapid, high-throughput DNA hybridization and melting analysis within a miniaturized solid-state architecture. Full article

Photodetectors are critical components in a wide range of applications, including military, communications, medical, and aerospace fields. With ongoing advancements in optoelectronics, the strategy of integrating multiple optical structures with photodetectors has led to substantial improvements in detection performance. This review summarizes recent research progress in optically coupled photodetectors, providing a systematic analysis of the operational mechanisms and performance characteristics of five key coupling configurations: optical waveguides, surface plasmon resonance structures, microcavities, gratings, and integrated metasurfaces. Furthermore, the main limitations of current coupling technologies and challenges facing the development of future coupled devices are discussed. Recent studies indicate that heterogeneous integration, multi-physical field coupling, and automated fabrication processes are paving the way for high-performance photodetectors with enhanced bandwidth, sensitivity, functional integration, and spectral control capabilities. Full article

Achieving room-temperature exciton–polariton condensation represents a frontier challenge in condensed matter physics and optoelectronics. However, its mainstream approach—distributed Bragg reflector (DBR) microcavities—faces widespread application challenges due to complex fabrication and high costs. Here, we report direct observation of the interaction between exciton and microcavity photons in Sn-doped CdS microsheet without extreme fabrication conditions. In situ PL and Raman mapping demonstrate the formation of superlattice structure. Using angle-resolved photoluminescence (ARPL) spectroscopy, we obtain Rabi splitting of polaritons up to 140 meV, and the exciton-like and photon-like components in low-polariton states at different cavity–exciton detuning were revealed at room temperature. Our work demonstrates the origin of optical microcavities and the light–matter coupling in CdS/CdS:SnS₂ superlattice microwires. Full article

The exceptional surface (ES) in non-Hermitian physics has attracted much attention due to its strong robustness and enhanced frequency splitting in the sensing field. However, the detection limit of the ES-based sensing structure is still limited by the mode linewidth in the optical microcavity. In this paper, we demonstrate that Sagnac–Fizeau shift in a microcavity based on an ES separates the dark mode from the bright mode, further enhancing the frequency splitting in the transmission spectrum. Moreover, a strategy for manipulating spectral line shape is realized by the phase in the reflection loop. Compared with the traditional ES-based sensing structure, the proposed nanoparticle sensing mechanism significantly reduces the detection limit for weak perturbations. This work will contribute to the development of high-precision nanoparticle sensors. Full article

We present the design, fabrication, and optical characterization of fully polymer-based high performance Fabry-Pérot microcavities for sensing and lasing applications. Two microcavity types (Cavity A and B) were realized using polymeric Distributed Bragg Reflector (DBR) films offering distinct spectral properties. Cavity A achieved a high quality factor (Q ≈ 2.15 × 10⁵), demonstrating excellent sensitivity for bulk refractive index sensing with an ultrahigh figure of merit of 5.89 × 10⁴ and a theoretical detection limit down 3.4 × 10⁻⁷ RIU. Cavity B was optimized for lasing applications. When filled with a Rhodamine B dye solution, it exhibited clear lasing action with a low threshold (1.83 μJ/mm²) and resonant peaks consistent with its free spectral range. These results highlight the potential of cost-effective polymeric cavities for disposable photonic sensor platforms and integrated biolaser devices. Full article

The optical force exerted on a dipole particle can be divided into gradient force, scattering force, and spin–curl force, all of which can be derived from Maxwell’s stress tensor with the dipole approximation. Here, we identify an additional spin–curl force for arbitrary objects beyond the dipole approximation, which is named the generalized spin–curl force in this paper. The generalized spin–curl force originates from the Minkowski force density and depends on the imaginary parts of the permittivity, permeability, and chirality of the object. However, it remains imperceptible in conventional optical force calculations due to its exact cancellation by a compensatory surface force during MST surface integration. The study of the generalized spin–curl force provides critical insights into elucidating the mechanisms underlying optical momentum transfer and internal force distribution within complex media. Furthermore, the generalized spin–curl force offers a novel mechanism for enhancing optical sensors, enabling highly sensitive detection of absorptive or chiral perturbations in systems such as microcavities and metasurfaces. Its ability to manipulate internal force distributions also provides new pathways for advancing optical force probes and chirality-selective sensing at the nanoscale. Full article

Whispering-gallery-mode (WGM) microresonators are amongst the most promising optical sensors for detecting bio-chemical targets. A number of laser interrogation methods have been proposed and demonstrated over the last decade, based on scattering and absorption losses or resonance splitting and shift, harnessing the high-quality factor and ultra-small volume of WGMs. Actually, regardless of the sensitivity enhancement, their practical sensing operation may be hampered by the complexity of coupling devices as well as the signalprocessing required to extract the WGM response. Here, we use a silica microsphere immersed in an aqueous environment and efficiently excite optical WGMs with a free-space visible laser, thus collecting the relevant information from the transmitted and back-scattered light without any optical coupler, fiber, or waveguide. We show that a 640-nm diode laser, actively frequency-locked on resonance, provides real-time, fast sensing of dielectric nanoparticles approaching the surface with direct analog readout. Thanks to our illumination scheme, the sensor can be kept in water and operate for days without degradation or loss of sensitivity. Diverse noise contributions are carefully considered and quantified in our system, showing a minimum detectable particle size below 1 nm essentially limited by the residual laser microcavity jitter. Further analysis reveals that the inherent laserfrequency instability in the short, -mid-term operation regime sets an ultimate bound of 0.3 nm. Based on this work, we envisage the possibility to extend our method in view of developing new viable approaches for detection of nanoplastics in natural water without resorting to complex chemical laboratory methods. Full article

To improve the efficiency and stability of the system, this paper proposes a monolithic integrated optical path design for a cavity optomechanical accelerometer based on a 250 nm top silicon thickness silicon-on-insulator (SOI) wafer instead of readout through U-shape fiber coupling. Finite Element Analysis (FEA) and Finite-Difference Time-Domain (FDTD) methods are employed to systematically investigate the performance of key optical structures, including the resonant modes and bandgap characteristics of photonic crystal (PhC) microcavities, transmission loss of strip waveguides, coupling efficiency of tapered-lensed fiber-to-waveguide end-faces, coupling characteristics between strip waveguides and PhC waveguides, and the coupling mechanism between PhC waveguides and microcavities. Simulation results demonstrate that the designed PhC microcavity achieves a quality factor (Q-factor) of 2.26 × 10⁵ at a 1550 nm wavelength while the optimized strip waveguide exhibits a low loss of merely 0.2 dB over a 5000 μm transmission length. The strip waveguide to PhC waveguide coupling achieves 92% transmittance at the resonant frequency, corresponding to a loss below 0.4 dB. The optimized edge coupling structure exhibits a transmittance of 75.8% (loss < 1.2 dB), with a 30 μm coupling length scheme (60% transmittance, ~2.2 dB loss) ultimately selected based on process feasibility trade-offs. The total optical path system loss (input to output) is 5.4 dB. The paper confirms that the PhC waveguide–microcavity evanescent coupling method can effectively excite the target cavity mode, ensuring optomechanical coupling efficiency for the accelerometer. This research provides theoretical foundations and design guidelines for the fabrication of high-precision monolithic integrated cavity optomechanical accelerometers. Full article