Search Results (160)

Stimulated Brillouin scattering (SBS) in microresonators offers a unique way to develop narrow-linewidth chip-scale lasers. Yet their coherence performance is hindered by the cascaded SBS process, which clamps the output power and broadens the fundamental linewidth of the first-order Stokes wave. Resonance splitting proves to be an effective approach to suppress intracavity SBS cascading. However, precisely aligning and controlling the resonance splitting behavior remains challenging. We address these issues by proposing a piezoelectrically actuated grating-embedded tantalum pentoxide (Ta₂O₅) microring resonator. This microresonator comprises a Bragg grating segment that induces a counter-propagating wave and a ring segment that is integrated with a lead zirconate titanate (PZT) actuator. The half-circumference Bragg grating has a peak reflectivity of 31% at 1549.8 nm and a bandwidth of 88.89 pm, which is narrow enough to ignite resonance splitting in only one azimuthal mode. The PZT actuator empowers the resonator with a frequency tuning rate of 0.1726 GHz/V, particularly useful for post-fabrication compensation and splitting control. The proposed architecture offers a promising solution to breaking the intracavity cascaded SBS chain with frequency tuning capability, paving the way towards highly coherent chip-scale laser sources. Full article

Dissipative sensing in a whispering-gallery-mode (WGM) microresonator entails monitoring changes in WGM throughput dip depth or linewidth due to analyte absorption. In our earlier work, we showed that dip depth sensitivity can be two orders of magnitude greater than linewidth sensitivity for sensing the broadband absorption of a dye in methanol. Here we experimentally demonstrate enhancement of absorption sensing of methane. Its narrowband absorption lines (a few GHz linewidth) necessitate strain tuning of the WGM of our hollow bottle resonator (HBR) to bring the WGM into resonance with the absorption line. Three asymmetric tapered fibers with different nonadiabaticities were designed to excite multiple fiber modes that couple into the WGM to interact with methane inside the HBR via the internal evanescent field. Measurements were carried out for both pure and trace (in 1 atm of air) methane at 1654 and 1651 nm. Enhancement factors as large as 141 were found; the experimental results agree with theoretical calculations and with the predictions of a limiting-case model. Effective absorption path lengths as large as 273 cm, more than ten thousand times the HBR diameter, were achieved for trace methane sensing, with detection limits estimated to be in the hundreds of ppm. 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

Based on the theory of optical sensing, we propose a high-precision plasmonic refractive index nanosensor, which consists of a symmetric rectangular waveguide and a circular ring containing a rectangular cavity. The designed novel tunable micro-resonant circular cavity filter based on surface plasmon excitations is able to confine light to sub-wavelength dimensions. The data show that different geometrical factors have different effects on sensing, with the geometry of the rectangular cavity and the radius of the circular ring being the key factors affecting the Fano resonance. Furthermore, the resonance bifurcation enables the structure to achieve a tunable dual Fano resonance system. The structure was tuned to obtain optimal sensitivity (S) and figure of merit values up to 3066 nm/RIU and 78. The designed structure has excellent sensing performance with sensitivities of 0.4767 nm·(mg/d${\mathrm{L}}^{-1}$) and 0.6 nm·(mg/d${\mathrm{L}}^{-1}$) in detecting Na⁺ and K⁺ concentrations in the electrolyte solution, respectively, and can be easily achieved by the spectrometer. The wavelength accuracy of 0.001 nm can be easily achieved by a spectrum analyzer, which has a broad application prospect in the field of optical integration. Full article

Polymer-based photonic sensors are emerging as cost-effective, scalable alternatives to conventional silicon and glass photonic platforms, offering unique advantages in flexibility, functionality, and manufacturability. This review provides a comprehensive assessment of recent advances in polymer photonic sensing technologies, focusing on material systems, fabrication techniques, device architectures, and application domains. Key polymer materials, including PMMA, SU-8, polyimides, COC, and PDMS, are evaluated for their optical properties, processability, and suitability for integration into sensing platforms. High-throughput fabrication methods such as nanoimprint lithography, soft lithography, roll-to-roll processing, and additive manufacturing are examined for their role in enabling large-area, low-cost device production. Various photonic structures, including planar waveguides, Bragg gratings, photonic crystal slabs, microresonators, and interferometric configurations, are discussed concerning their sensing mechanisms and performance metrics. Practical applications are highlighted in environmental monitoring, biomedical diagnostics, and structural health monitoring. Challenges such as environmental stability, integration with electronic systems, and reproducibility in mass production are critically analyzed. This review also explores future opportunities in hybrid material systems, printable photonics, and wearable sensor arrays. Collectively, these developments position polymer photonic sensors as promising platforms for widespread deployment in smart, connected sensing environments. Full article

Miniaturized spectrometers employing photonic crystal cavity arrays in conjunction with computational reconstruction have gained attention as effective tools for spectral analysis. Nevertheless, achieving an optimal balance among spectral resolution, detection range, and device compactness remains challenging, particularly when complex nonlinear mappings, inter-pattern correlations, and noise interference are involved. In this work, we present ESTspecNet, a deep learning framework that integrates EfficientNet, the Swin Transformer, and spatial-channel attention mechanisms to improve spectral reconstruction accuracy. We reconstructed near-infrared spectra over an 80 nm range using a 144-unit photonic crystal cavity array, and achieved a single-peak resolution of $0.47$ nm and a double-peak resolution of $0.7$ nm. Compared to conventional methods, the proposed model demonstrates superior performance in both wide-range spectral reconstruction and fine-resolution tasks, thus highlighting its ability to effectively capture intricate spectral features and long-range dependencies, thereby advancing the reconstruction capabilities of miniaturized spectrometers. Full article

The high-repetition-rate dual-microcomb interferometry, characterized by its high precision, rapid measurement speed, and ease of integration, shows significant promise in applications such as precision spectroscopy and high-speed precision ranging. As dual-microcomb interferometry usually requires a specific difference in repetition rates, tuning the repetition rate of the microcomb is crucial for integrating dual-microcomb sources and enhancing the measurement performance, including the precision and the update rate. This work demonstrates a coherent dual-microcomb system driven by a single continuous-wave fiber laser at 1560.49 nm. The system employs a hybrid tuning method combing single-sideband (SSB) modulation for precision pump frequency control (enabling continuous repetition rate tuning across a 4.34 MHz range) with thermal control for coarse tuning. The linear dependence between the repetition rate and pump modulation frequency shows a measured coefficient of 143.58 kHz/GHz. This method enables dual microcombs with MHz-level repetition rate tuning, significantly relaxing the fabrication and pairing requirements for microresonators. The advancement is particularly valuable for dual-comb spectroscopy and ranging applications, including gas detection and satellite formation flying. Full article

Quartz-enhanced photoacoustic spectroscopy (QEPAS) has shown great promise for monitoring greenhouse gases and pollutants with a high measurement accuracy and limit of detection. A QEPAS sensor, which can achieve high photoacoustic signal gain without requiring the laser beam to pass through the two prongs of a quartz tuning fork (QTF), is reported. A custom QTF with a resonant frequency of 7.2 kHz and a quality factor of 8406 was employed as a sound detection element, and the parameters of the acoustic micro-resonator (AmR) in the off-beam QEPAS spectrophone were optimized. A signal-to-noise ratio (SNR) gain of 16 was achieved based on the optimal AmR dimensions compared to the bare custom QTF. Water vapor (H₂O) was detected utilizing the QEPAS sensor equipped with the off-beam spectrophone, achieving a minimum detection limit (MDL) of 4 ppm with a normalized noise equivalent absorption coefficient (NNEA) of 5.7 × 10⁻⁸ cm⁻¹·W·Hz^−1/2 at an integration time of 300 ms. Full article

In this study, we designed and experimentally demonstrated an all–optical tuning system based on the absorption effect of magnetic nanoparticles on a pump light. The all-optical tuning process induces a temperature change in the microcavity–taper coupling system, resulting in a shift in the WGM resonance spectrum. The core of the sensor involved in this study is a microcapillary resonator with a microfluidic channel, in which a magnetic fluid is filled within the channel of the microcapillary resonator. We tested the sensing sensitivity of microcapillary resonators with two sizes. The experimental results indicate that for the larger microcapillary resonator, the sensitivity is 0.0347 nm/mW when the pump light power increases, and 0.0331 nm/mW when the pump light power decreases. For the smaller microcapillary resonator, the sensitivity significantly increases, with 0.1018 nm/mW and 0.1029 nm/mW as the power increases and decreases, respectively. The demonstrated optofluidic device has the advantages of small size, good repeatability, high sensitivity, and low price, and thus shows great potential for sensing applications. Full article

A novel application of microresonators for refractometric sensing in aqueous media is presented. To carry out this approach, microspheres of different materials and sizes were fabricated and doped with Nd³⁺ ions. Under 532 nm excitation, the microspheres presented typical NIR Nd³⁺ emission bands with superimposed sharp peaks, related to the Whispering Gallery Modes (WGMs), due to the geometry of the microspheres. When the microspheres were submerged in water with increasing concentrations of glycerol, spectral shifts for the WGMs were observed as a function of the glycerol concentration. These spectral shifts were studied and calibrated for three different microspheres and validated with the theoretical shifts, obtained by solving the Helmholtz equations for the electromagnetic field, considering the geometry of the system, and also by calculating the extinction cross-section. WGM shifts strongly depend on the diameter of the microspheres and their refractive index (RI) difference compared with the external medium, and are greater for decreasing values of the diameter and lower values of RI difference. Experimental sensitivities ranging from 2.18 to 113.36 nm/RIU (refractive index unit) were obtained for different microspheres. Furthermore, reproducibility measurements were carried out, leading to a repeatability of 2.3 pm and a limit of detection of 5 × 10⁻⁴ RIU. The proposed sensors, taking advantage of confocal microscopy for excitation and detection, offer a robust, reliable, and contactless alternative for environmental water analysis. Full article

The integration of a photodetector that converts optical signals into electrical signals is essential for scalable integrated lithium niobate photonics. Two-dimensional materials provide a potential high-efficiency on-chip detection capability. Here, we demonstrate an efficient on-chip photodetector based on a few layers of MoTe₂ on a thin film lithium niobate waveguide and integrate it with a microresonator operating in an optical telecommunication band. The lithium-niobate-on-insulator waveguides and micro-ring resonator are fabricated using the femtosecond laser photolithography-assisted chemical–mechanical etching method. The lithium niobate waveguide-integrated MoTe₂ presents an absorption coefficient of 72% and a transmission loss of 0.27 dB µm⁻¹ at 1550 nm. The on-chip photodetector exhibits a responsivity of 1 mA W⁻¹ at a bias voltage of 20 V, a low dark current of 1.6 nA, and a photo–dark current ratio of 10⁸ W⁻¹. Due to effective waveguide coupling and interaction with MoTe₂, the generated photocurrent is approximately 160 times higher than that of free-space light irradiation. Furthermore, we demonstrate a wavelength-selective photonic device by integrating the photodetector and micro-ring resonator with a quality factor of 10⁴ on the same chip, suggesting potential applications in the field of on-chip spectrometers and biosensors. Full article

Integrated optical amplifiers are the building blocks of on-chip photonic systems, and they are often accompanied by a narrowband filter to limit noise. In this sense, a bandwidth-tunable optical amplifier with narrowband filtering function is crucial for on-chip optical circuits and radio frequency systems. The intrinsic loss and coupling coefficients between resonator and waveguide inherently limit the bandwidth. The parity-time symmetric coupled microresonators operating at exceptional points enable near zero bandwidth. In this study, we propose a parity-time symmetric coupled microresonators system operating near EPs to achieve a bandwidth of 46.4 MHz, significantly narrower than bandwidth of 600.0 MHz and 743.2 MHz achieved by two all-pass resonators with identical gain/loss coefficients. This system also functions as an optical bandwidth-tunable filter. The bandwidth tuning ranges from 175.7 MHz to 7.8 MHz as gain coefficient adjusts from 0.2 dB/cm to 0.4 dB/cm. Our scheme presents a unique method to obtain narrow bandwidth from two broadband resonators and serves as an optical bandwidth-tunable filter, thereby paving a new avenue for exploring non-Hermitian light manipulation in all-optical integrated devices. Full article

The rapid increase in Internet usage has led to a growing demand for bandwidth. Optical microring resonators (MRRs) are emerging as a promising solution to meet this need. MRRs generate optical frequency combs (OFCs) that provide multiple wavelengths with high phase coherence, enabling communication via wavelength division multiplexing (WDM). Spectrum allocation methods, such as the Routing, Modulation Level, and Spectrum Assignment (RMLSA) approach, play a crucial role in executing this strategy efficiently. While current algorithms have improved allocation efficiency, further development is necessary to optimize network performance. This paper presents an integer linear programming (ILP)-based method for network resource allocation, aiming to maximize the number request and the bandwidth assigned to each. The proposed approach offers a flexible cost function that prioritizes system constraints such as transmission distance and bandwidth requirements, resulting in significant improvements to the bandwidth blocking rate (BBR). By integrating multilevel modulation and using wavelengths generated by MRRs, this method efficiently handles up to 1075 requests, achieving a BBR of zero. This dynamic and adaptable allocation strategy ensures optimal resource utilization, enhancing overall network performance. Full article

The reliable generation of dissipative Kerr solitons (DKSs) enables applications in communications, metrology, optical clocks, and, more recently, artificial intelligence. We show how single DKS can be generated by Si₃N₄ dual-coupled microring resonators (DCMs). We modeled this coupled structure using the Lugiato–Lefever equation (LLE), including mode interactions in the dispersion profile. We also characterized the pump power and detuning parameter space for several mode interaction strengths and frequencies, and we found parameters for which a DKS could be deterministically obtained using a single, adiabatic frequency sweep with a constant pump power. We demonstrated deterministic single DKS generation for this path by simulating 200 times with different random noise inputs. This result paves the way for reliable, inexpensive, and deterministic single DKS generation in a simple setup. Full article

Optical microresonators supporting whispering-gallery modes (WGMs) have become a versatile platform for achieving electromagnetically induced transparency-like (EIT-like) phenomena. We theoretically and experimentally demonstrated the tunable coupled-mode induced transparency based on the surface nanoscale axial photonics (SNAP) microresonator. Single-EIT-like and double-EIT-like (DEIT-like) effects with one or more transparent windows are achieved due to dense mode families and tunable resonant frequencies. The experimental results can be well-fitted by the coupled mode theory. An automatically adjustable EIT-like effect is discovered by immersing the sensing region of the SNAP microresonator into an aqueous environment. The sharp lineshape and high slope of the transparent window allow us to achieve a liquid refractive index sensitivity of 2058.8 pm/RIU. Furthermore, we investigated a displacement sensing phenomenon by monitoring changes in the slope of the transparent window. We believe that the above results pave the way for multi-channel all-optical switching devices, multi-channel optical communications, and biochemical sensing processing. Full article