Three interferometers (the Sagnac sensor, the linear polarization interferometer, and the reflecting polarization interferometer) incorporated with the bow tie fiber are proposed to detect the seawater temperature. Bow tie fiber, a kind of polarization maintaining fiber, has stress induced birefringence. The three interferometers are categorized as transmission and reflection types to analyze the sensing principles. Related experiments are performed to explore the influence of the wavelength and length of the bow tie fiber on the sensitivity and free spectral range (FSR). The sensitivity and FSR both increase with the wavelength increasing. The sensitivity fluctuates in a small range and FSR decreases with the length increasing. The reflecting polarization interferometer has the bigger sensitivity of −1.19nm/°C than the other two. And it has the advantages of easy fabrication, simple operation, and good stability, so it is applicable in real ocean exploration. Our work can provide a reference to researchers who do oceanographic research.
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.
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.
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.
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.
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.
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.