查看更多>>摘要：Responding to the urgency of remote sensing for monitoring large concentrations of methane leakage,a high-speed modu-lation continuous laser methane leakage remote methodology based on a near-infrared single-photon avalanche diode detector[SPAD]and a lower power distributed feedback laser was developed.Based on the proposed laser modulation and time-correlated single-photon counting method,the method could simultaneously detect the methane concentration and background target distance.The effects of SPAD dead time and after-pulse probability on the intensity of methane spectra were investigated.The proposed ranging and methane sensing method was also demonstrated by conducting out-field observation through the verification system.The measured methane absorption spectral intensity was verified and consistent with theoretical value.The initial validation results provide a new scheme for subsequent single-photon gas detection,and reference for subsequent methane monitoring equipment development.
查看更多>>摘要：An ultrasonic phase extraction method is proposed for co-cable identification without modifying transceivers in coherent optical transmission systems.To extract the ultrasonic phase,we apply an improved residual frequency offset compen-sation algorithm,an optimized unwrapping algorithm for mitigating phase noise induced by phase ambiguity between digital signal processing[DSP]blocks,and an averaging operation for improving the phase sensitivity.In a 64-GBaud dual-polarization quadrature phase shift keying[DP-QPSK]simulation system,the phase sensitivity of the proposed method reaches 0.03 rad using lasers with 100-kHz linewidth and a 60-kHz ultrasonic source,with only 400 k-points[kpts]stored data.Also verified by an experiment under the same transmission conditions,the sensitivity reaches 0.39 rad,with 3 kpts of data stored and no averaging due to the equipment limitation.The results have shown this method provides a better choice for low-cost and real-time co-cable identification in integrated sensing and communication optical networks.
查看更多>>摘要：A high-birefringence fiber,Tb:YAG crystal-derived silica fiber[TYDSF],was fabricated by CO2 laser-heating drawing tech-nique.Its linear birefringence was 2.99 × 10-5,and it was used to fabricate an all-fiber quarter-wave plate[QWP]device.The polarization extinction ratio[PER]of the device was 0.29 dB,and its ellipticity was 44.26° at 25℃.In the temperature range of-5℃ to 200℃,its PER was always less than 0.80 dB,and the fluctuation of PER and ellipticity was also small.Compared with QWPs fabricated with PANDA-type polarization-maintaining fiber[PMF]and elliptical-core PMF,the performance of TYDSF QWP was least sensitive to temperature.Furthermore,the TYDSF QWP was used in a high-power laser system,still main-taining good circular polarization state,and the nonlinear effects were suppressed in the system.The experimental results are of great significance to high-power lasers,fiber-optic current sensors,etc.,in harsh environments.
查看更多>>摘要：We propose a photonic frequency-multiplied vector millimeter-wave[mmW]signal generation scheme based on constant-envelope delta-sigma modulation[CE-DSM].The CE characteristic of phase modulation can easily avoid intensity-dependent nonlinear distortion caused by photonic frequency multiplication.Additionally,combined with one-bit DSM,the in-band signal-to-noise ratio can be dramatically improved,enabling high-order quadrature amplitude modulation[QAM]vector mmW signal generation with high spectral efficiency.Experimental results indicate that a 40 GHz four-fold frequency-multi-plied 4096-QAM vector mmW signal generation system is successfully accomplished with 15-km standard single-mode fiber[SSMF]and 1-m wireless transmission,and the bit error ratio[BER]reaches the threshold of 3.8 × 10-3.
查看更多>>摘要：We have prepared kilometer-scale low-loss hollow-core nested anti-resonant nodeless fibers by improving their structural design,which reduces the difficulty of fabricating low-loss hollow-core fibers over long distances.The lowest loss is 2.7 dB/km at 1506 nm,and this loss is less than 5 dB/km at 1417-1620 nm.High-precision frequency transfer is achieved using the fabricated 1050 m hollow-core fiber by locking the repetition frequency of the optical frequency comb to a rubid-ium atomic clock.The frequency stability is 1.67 × 10-12/s and 5.66 × 10-14/1000 s when the temperature is changed,and no phase compensation device is used.It is an order of magnitude lower compared to that of the conventional single-mode fiber.
查看更多>>摘要：Motion blur restoration is essential for the imaging of moving objects,especially for single-pixel imaging[SPI],which requires multiple measurements.To reconstruct the image of a moving object with multiple motion modes,we propose a novel motion blur restoration method of SPI using geometric moment patterns.We design a novel localization method that uses normalized differential first-order moments and central moment patterns to determine the object's translational posi-tion and rotation angle information.Then,we perform motion compensation by using shifting Hadamard patterns.Our method effectively improves the detection accuracy of multiple motion modes and enhances the quality of the recon-structed image.We perform simulations and experiments,and the results validate the effectiveness of the proposed method.
查看更多>>摘要：The high-sensitivity three-axis detection of magnetic fields is widely used in various applications.Our study demonstrates an atomic magnetometer detecting vector magnetic field,of which the core components are one glass cell and two ellip-tically polarized laser beams.The light-intensity noise is suppressed by differential detection technology,so a higher sen-sitivity is obtained compared with our previous work.The three-axis average sensitivities of the atomic magnetometer simultaneously reached 14 fT/Hz1/2 along the x axis,11 fT/Hz1/2 along the y axis,and 25 fT/Hz1/2 along the z axis.Furthermore,the atomic magnetometer's dynamic range was further improved to 150 nT,and its bandwidth was increased to over 200 Hz using a closed-loop control system.The proposed three-axis atomic magnetometer with a large dynamic range and a wide bandwidth holds great promise for biomagnetic measurement in a more challenging environment.
查看更多>>摘要：Micromagnets,as a promising technology for microscale manipulation and detection,have been the subject of extensive study.However,providing real-time,noninvasive feedback on the position and temperature of micromagnets in complex operational environments continues to pose a significant challenge.This paper presents a quantum imaging device utilizing diamond nitrogen-vacancy[NV]centers capable of providing simultaneous feedback on both the position and temperature of a micromagnet.The device achieves a temporal resolution of 2 s and a spatial resolution of 1.3 pm.Through flux locali-zation analysis,we have determined a positioning accuracy within 50 pm and a temperature accuracy within 0.4 K.
查看更多>>摘要：A broadband gas sensing technology is reported.The measurement principle relies on Fourier transform photoacoustic spectroscopy[FT-PAS]using a differential photoacoustic cell,in which both phase modulation and amplitude modulation are simultaneously applied to the broadband light sources.The thermal light source and supercontinuum source are employed sequentially.The performance of the FT-PAS is demonstrated by measuring the spectra of methane in the 2-10 μm range and acetylene in the 1-2 μm range.By leveraging the wavelength-independent nature of the photoacoustic effect,this system holds promise for comprehensive full-spectrum spectral detection.
查看更多>>摘要：We theoretically and experimentally demonstrate a cylinder-shaped hole array with a small depth and an appropriate period integrated on a silicon-on-insulator substrate can enhance infrared absorption due to more bending of light and a higher back reflection.The Si metal-semiconductor-metal[MSM]photodiode with an hole array,whose depth is 250 nm,exhibits a 4-fold improved external quantum efficiency[EQE]of 81％,and an ultra-fast impulse response speed of 22 ps enabling a 3 dB bandwidth of up to 23.9 GHz.PbSe film with a thickness of 80 nm is integrated to broaden the response wavelength.A more than 500％EQE enhancement of the Si-based PbSe photodiode with 150-nm-deep photon-trapping holes is achieved at 1550 nm compared to the device without hole structures.
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