This paper proposes a continuously tunable random lasers (RLs) based on the gain system of cellulose nanocrystals (CNCs)-doped hydrogels and the laser dye made of Rhodamine B (Rh B). Between them, the prepared CNCs-doped hydrogels have not only a weak scattering structure that can provide excellent multiple scattering, thus yielding a large gain, but also good mechanical properties that can provide great advantages in the tuning of RL. The experimental results indicate that the RL emission wavelength blue shifts with an increase in the stretching length. The continuous tuning range reaches up to 7.1 nm when the CNCs-doped hydrogels are stretched to 400%. In addition, the proposed CNCs-doped hydrogels effectively solve the problem of the structures of traditional hydrogels, which are easily destroyed during repeated stretching and ensure good stability of RL output and tuning. The RL error is tested and found to be less than 0.5 nm, when the same length is stretched during repeated stretching. Our results provide a new approach to obtain tunable and stable RLs. Simultaneously, in combination with the good biocompatibility of CNCs-doped hydrogels, the proposed RLs demonstrated great importance in the biological field.

Heavy metal ions have drawn enough attention due to their harm to both humans and environments, and there has been an urgent need for stable and quick detection of them. Besides, the manganese ion is one of the most abundant ions in urban water systems, which needs to be monitored carefully. Hereby, a carbon dots (CDs) (the microwave method) based surface plasmon resonance (SPR) Mn²⁺ sensor has been proposed and discussed, which could achieve high detection sensitivity of 6.383 nm/lg(ppb) in the range of 0 ppb–200 ppb on manganese ions, with the detection limit of 0.3462 ppb. The proposed sensor also possesses high stability upon time and temperature, and it also has great ion selectivity against 9 other ions. Practical usage scenarios have been tested on the human serum, tap water, lake water, and river water, which confirm that the proposed sensor holds great potential for both blood tests and environmental monitoring.

We have numerically and experimentally investigated the flow rate measurement of the pipeline based on the optical fiber. Employing the large eddy simulation (LES) model, we have quantitatively analyzed the pressure fluctuation of the pipe wall caused by the turbulent flow in the pipeline. The simulation results have shown that the standard deviation of pressure fluctuation was quadratic with the flow rate. We have verified the theoretical model by using a distributed optical fiber acoustic sensing (DAS) system in the flow rate range from 0.61 m/s to 2.42 m/s. The experimental results were consistent with the simulation results very well. Furthermore, to improve the measuring error at the low flow rate, we have employed the composite adaptive denoising algorithm to eliminate the background noise and system noise. The final results have shown that the minimum goodness of fit was improved from 0.962 to 0.997, and the variation of the quadratic coefficient significantly decreased by 93.25%. The measured flow rate difference was only 0.84% between different sensing points in repeated experiments.

To improve the sensitivity measurement of temperature sensors, a fiber optic temperature sensor structure based on the harmonic Vernier effect with two parallel fiber Sagnac interferometers (FSIs) is designed, and theoretical analysis and experimental testing are conducted. The FSI consisting of two polarization maintaining fibers (PMFs) with lengths of 13.62 m and 15.05 m respectively is used to achieve the basic Vernier effect. Then by changing the length of one PMF to approximately i times that of the others, the FSI composed of two PMFs of 7.1 m and 15.05 m is used to achieve the first-order harmonic Vernier effect. Afterward, temperature sensing tests are conducted to observe the wavelength drift during temperature changes and ultimately achieve high sensitivity. The experimental results show that the temperature sensitivity of the sensor based on the first-order harmonic Vernier effect is −28.89 nm/°C, which is 17.09 times that of a single FSI structure (−1.69 nm/°C) and 1.84 times that of the sensitivity generated by the structure based on the basic Vernier effect (−15.69 nm/°C). The experimental results are consistent with the theoretical analysis. The structure proposed in this paper achieves drift measurement of 0.1 °C variation based on 1 °C drift, making the fiber optic temperature sensor applicable to related fields that require high precision temperature. The proposed temperature sensor has the simple structure, low production cost, high sensitivity, and broad application prospects.

The surge in demand for cost-effective, lightweight, and rapidly responsive sensors has propelled research in various fields, and traditional sensors face limitations in performing up to the mark due to their intrinsic properties and a lack of innovative fabrication techniques. Consequently, over the last decade, a notable shift has been toward harnessing naturally existing nanostructures to develop efficient and versatile sensing devices. One such nanostructure in morpho butterfly wings has attracted attention because of its vibrant uniqueness and diverse sensing properties. This review will explore recent interdisciplinary research endeavors on the nanostructure, including chemical, vapor, and acoustic detection. Furthermore, its potential as an infrared sensor, considerations related to heat transfer properties, and a brief overview of various replication techniques and challenges encountered in reproducing the intricate nanostructure are discussed.

We study that the different-mode (waveguide-connected) power splitter [(W)PS] can provide different-mode testing points for the optical testing. With the PS or WPS providing two different-mode testing points, the measured insertion losses (ILs) of the three-channel and dual-mode waveguide crossing (WC) for both the fundamental transverse electric (TE₀) and TE₁ modes are less than 1.8 dB or 1.9 dB from 1540 nm to 1560 nm. At the same time, the crosstalks (CTs) are lower than −17.4 dB or −18.2 dB. The consistent test results indicate the accuracy of the (W)PS-based testing circuit. Additionally, combining the tunable tap couplers, the (W)PS can provide multiple testing points with different modes and different transmittances.

In this paper, a dual Mach-Zehnder interferometer for measuring both temperature and strain is proposed and verified by experiments. The sensor configuration involves cascading a four-core fiber and a double-clad fiber between two single-mode fibers. By exploiting the different responses of the two Mach-Zehnder interferometers to temperature and strain, we construct a matrix using two selected resonance dips from the transmission spectra, so that both temperature and strain can be measured simultaneously. The experimental results show the sensor’s remarkable performance, with the maximum temperature sensitivity of −94.2 pm/°C and the maximum strain sensitivity of 2.68 pm/µε. The maximum temperature error and strain error are found to be ±0.35 °C and ±4.8 µε, respectively. Compared with other optical fiber sensors, the sensor has high sensitivity, a simple structure, and ease to manufacture and implement, making it a structure choice for applications in quality inspection of materials.

We developed an all optic-fiber waveguide-coupled surface plasmon resonance (SPR) sensor using zirconium disulfide (ZrS₂) and poly-dopamine (PDA) as the dielectric layer and biological cross-linker, respectively. This sensor can be employed to monitor the entire process of the C-reactive protein (CRP) sensing, including antibody modification and antigen detection. The design and the optimization of the optical fiber waveguide-coupled SPR sensor were realized, based on the transfer matrix method and first-principles calculations. The sensor was fabricated and characterized according to the optimized parameters. The experimental setup was implemented to measure the entire process of antibody modification and antigen detection for CRP with the detection limit of 3.21 pmol·mL⁻¹, and the specificity tests were also carried out.

Due to the stimulated emission amplification, lasers with excellent characteristics, including the high energy density, ultra-narrow spectral linewidth, and high directionality, are extremely favorable for sensing, detection, and imaging. Bringing these merits into the micro/nano scale, micro/nano lasers with miniaturized device sizes further enable outstanding spatial and temporal confinement, greatly boosting the light-matter interaction and bridging the size mismatch between light and biomolecules. Thanks to these advantages, micro/nano lasers have drawn widespread attention and opened new opportunities for a variety of biomedical and biochemical applications. In this paper, we review recent developments in biomolecular sensing and cellular analysis based on micro/nano lasers. We first describe the fundamental building blocks of micro/nano lasers, with discussions on gain material considerations, cavity structures, and pumping. We then review recent applications using micro/nano lasers as biosensors and bioprobes, including biomolecule (mainly proteins and DNAs) sensing, wavelength-multiplexed cell labeling/tracking/probing, and high-resolution cellular/tissue bioimaging. Finally, an outlook of the challenges and potential developments of micro/nano lasers for biological sensing and clinical applications is provided.

We study here the response of photonic hydrogels (PHs), made of photonic crystals of homogeneous silica particles in polyacrylamide hydrogels (SPHs), to the uranyl ions UO₂ ²⁺ in aqueous solutions. It is found that the reflection spectra of the SPH show a peak due to the Bragg diffraction, which exhibits a blue shift in the presence of UO₂ ²⁺. Upon exposure to the SPH, UO₂ ²⁺ gets adsorbed on the SPH and forms complex coordinate bonds with multiple ligands on the SPH, which causes shrinking of hydrogel and leads to the blue shift in the diffraction peak. The amount of the blue shift in the diffraction peak increases monotonically up to UO₂ ²⁺ concentrations as high as 2300µM. The equilibration time for the shift in the Bragg peak upon exposure to UO₂ ²⁺ is found to be ~30 min. These results are in contrast to the earlier reports on photonic hydrogels of inhomogeneous microgel particles hydrogel (MPH), which shows the threshold UO₂ ²⁺ concentration of ~600 µM, below which the diffraction peak exhibits a blue shift and a change to a red shift above it. The equilibration time for MPH is ~300min. The observed monotonic blue shift and the faster time response of the SPH to UO₂ ²⁺ as compared to the MPH are explained in terms of homogeneous nature of silica particles in the SPH, against the porous and polymeric nature of microgels in the MPH. We also study the extraction of UO₂ ²⁺ from aqueous solutions using the SPH. The extraction capacity estimated by the arsenazo-III analysis is found to be 112 mM/kg.

Micro-gyroscopes using micro-electro-mechanical system (MEMS) and micro-opto-electro-mechanical system (MOEMS) are the new-generation and recently well-developed gyroscopes produced by the combinations of the traditional gyroscope technology and MEMS/MOEMS technologies. According to the working principle and used materials, the newly-reported micro-gyroscopes in recent years include the silicon-based micromechanical vibratory gyroscope, hemispherical resonant gyroscope, piezoelectric vibratory gyroscope, suspended rotor gyroscope, microfluidic gyroscope, optical gyroscope, and atomic gyroscope. According to different sensitive structures, the silicon-based micromechanical vibratory gyroscope can also be divided into double frame type, tuning fork type, vibrating ring type, and nested ring type. For those micro-gyroscopes, in recent years, many emerging techniques are proposed and developed to enhance different aspects of performances, such as the sensitivity, angle random walk (ARW), bias instability (BI), and bandwidth. Therefore, this paper will firstly review the main performances and applications of those newly-developed MEMS/MOEMS gyroscopes, then comprehensively summarize and analyze the latest research progress of the micro-gyroscopes mentioned above, and finally discuss the future development trends of MEMS/MOEMS gyroscopes.

A corrugated surface long period grating (LPG) was fabricated on a flat-shaped plastic optical fiber (POF) as a refractive index (RI) sensor by a simple pressing with the heat pressure and mechanical die press print method. The light propagation characteristics of an LPG imprinted on a multi-mode POF were analyzed by the method of geometrical optics. Theoretical and experimental results showed that the structural parameters of the sensor affected the RI sensing performance, and the sensor with a thinner flat thickness, a deeper groove depth of the corrugated surface LPG, and a longer LPG exhibited better RI sensing performance. When the POF with a diameter of 1 mm was pressed with the heat pressure to a flat shape with a thickness of 600 µm, an LPG with a period of 300 µm, a groove depth of 200 µm, and a length of 6 cm was fabricated on it, and the RI sensitivity of 1447%/RIU was obtained with a resolution of 5.494×10⁻⁶ RIU. In addition, the influences of the POF cladding, tilting of LPG, and bending of the sensing structure were investigated. The results demonstrated that after removing the cladding and tilting or bending the LPG, the RI sensing performance was improved. When the LPG imprinted on the flat-shaped POF was bent with a curvature radius of 6/π cm, the highest sensitivity of 6 563%/RIU was achieved with a resolution of 2.487×10⁻⁹ RIU in the RI range of 1.3330–1.4230. The proposed sensor is a low-cost solution for RI measurement with the features of easy fabrication, high sensitivity, and intensity modulation at the visible wavelengths.

Photodetectors operating at the wavelength in the visible spectrum are key components in high-performance optoelectronic systems. In this work, massive nonlinearities in amorphous silicon p-i-n photodiodes enabled by the photogating are presented, resulting in responsivities up to 744 mA/W at blue wavelengths. The detectors exhibit significant responsivity gains at optical modulation frequencies exceeding MHz and a more than 60-fold enhanced spectral response compared to the non-gated state. The detection limits down to 10.4 nW/mm² and mean signal-to-noise ratio enhancements of 8.5 dB are demonstrated by illuminating the sensor with an additional 6.6 µW/mm² red wavelength. Electro-optical simulations verify photocarrier modulation due to defect-induced field screening to be the origin of such high responsivity gains. The experimental results validate the theory and enable the development of commercially viable and complementary metal oxide semiconductor (CMOS) compatible high responsivity photodetectors operating in the visible range for low-light level imaging and detection.

In this study, the multi-peak terahertz metamaterials sensors are designed and fabricated, whose structures are the asymmetrical single split ring (SSR) and three split rings (TSR). The resonant formation and sensing mechanism of the two structures are investigated by using the finite-difference time-domain (FDTD) method. Vitamin B₆ (VB₆) and its reactants with bovine serum protein (BSA) are tested as the medium, and the sensing experiments of the SSR and TSR are carried out. The experimental and simulation results indicate the consistent law, which is the sensitivity of the resonance in the transverse magnetic (TM) mode is much greater than that in the transverse electric (TE) mode. According to the weighted average method and the law for unequal precision measuring, the quality factor of the resonance is used as the weighting coefficient to calculate the comprehensive evaluation parameter (CEP) of the multi-peak metamaterials sensors in the TE and TM modes based on the experimental data. When the CEP and frequency shifts are as the evaluation parameter in experiments, the law’s variation of the CEP is consistent with that of the frequency shift, indicating that it is feasible to characterize the sensing characteristics of metamaterials with the CEP, which presents simplified characteristics of multi-peak metamaterials at different polarization modes. The method implies that the different influencing factors may be integrated into the CEP with the idea of weight, which promotes the practical application of the metamaterials sensor. The revelation of the sensing law also provides a method for the design of the terahertz metamaterials sensor with the high sensitivity.

In recent years, levitated particles of optical traps in vacuum have shown the enormous potential for precision sensor development and new physics exploration. However, the accuracy of the sensor is still hampered by the uncertainty of the calibration factor relating the detected signal to the absolute displacement of the trapped particle. In this paper, we suggest and experimentally demonstrate a novel calibration method for optical tweezers based on free-falling particles in vacuum, where the gravitational acceleration is introduced as an absolute reference. Our work provides a calibration protocol with a great certainty and traceability, which is significant in improving the accuracy of precision sensing based on levitated optomechanical systems.