查看更多>>摘要：In this paper,we present a fast mode decomposition method for few-mode fibers,utilizing a lightweight neural network called MobileNetV3-Light.This method can quickly and accurately predict the amplitude and phase information of different modes,enabling us to fully characterize the optical field without the need for expensive experimental equipment.We train the MobileNetV3-Light using simulated near-field optical field maps,and evaluate its performance using both simulated and reconstructed near-field optical field maps.To validate the effectiveness of this method,we conduct mode decomposition experiments on a few-mode fiber supporting six linear polarization[LP]modes[LP01,LP11e,LP11o,LP21e,LP21o,LP02].The results demonstrate a remarkable average correlation of 0.9995 between our simulated and reconstructed near-field light-field maps.And the mode decomposition speed is about 6 ms per frame,indicating its powerful real-time processing capability.In addition,the proposed network model is compact,with a size of only 6.5 MB,making it well suited for deploy-ment on portable mobile devices.
查看更多>>摘要：Lens-free on-chip microscopy with RGB LEDs[LFOCM-RGB]provides a portable,cost-effective,and high-throughput imaging tool for resource-limited environments.However,the weak coherence of LEDs limits the high-resolution imaging,and the luminous surfaces of the LED chips on the RGB LED do not overlap,making the coherence-enhanced executions tend to undermine the portable and cost-effective implementation.Here,we propose a specially designed pinhole array to enhance coherence in a portable and cost-effective implementation.It modulates the three-color beams from the RGB LED sepa-rately so that the three-color beams effectively overlap on the sample plane while reducing the effective light-emitting area for better spatial coherence.The separate modulation of the spatial coherence allows the temporal coherence to be modu-lated separately by single spectral filters rather than by expensive triple spectral filters.Based on the pinhole array,the LFOCM-RGB simply and effectively realizes the high-resolution imaging in a portable and cost-effective implementation,offering much flexibility for various applications in resource-limited environments.
查看更多>>摘要：The pandemic of respiratory diseases enlightened people that monitoring respiration has promising prospects in averting many fatalities by tracking the development of diseases.However,the response speed of current optical fiber sensors is still insufficient to meet the requirements of high-frequency respiratory detection during respiratory failure.Here,a scheme for a fast and stable tachypnea monitor is proposed utilizing a water-soluble C60-Lys ion compound as functional material for the tracking of humidity change in the progression of breath.The polarization of C60-Lys can be tuned by the ambient relative humidity change,and an apparent refractive index alteration can be detected due to the small size effect.In our experiments,C60-Lys is conformally and uniformly deposited on the surface of a tilted fiber Bragg grating[TFBG]to fabricate an ultra-fast-response,high-sensitivity,and long-term stable optical fiber humidity sensor.A relative humidity[RH]detecting sensitivity of 0.080 dB/％RH and the equilibrium response time and recovery time of 1.85 s and 1.58 s are observed,respectively.Also,a linear relation is detected between the resonance intensity of the TFBG and the environment RH.In a practical breath monitoring experiment,the instantaneous response time and recovery time are measured as 40 ms and 41 ms,respectively,during a 1.5 Hz fast breath process.Furthermore,an excellent time stability and high repeatability are exhibited in experiments conducted over a range of 7 days.
查看更多>>摘要：The compact,sensitive,and multidimensional displacement measurement device plays a crucial role in semiconductor manufacture and high-resolution optical imaging.The metasurface offers a promising solution to develop high-precision displacement metrology.In this work,we proposed and experimentally demonstrated a two-dimensional displacement[XZ]measurement device by a dielectric metasurface.Both transversal and longitudinal displacements of the metasurface can be obtained by the analysis of the interference optical intensity that is generated by the deflected light beams while the metasurface is under linearly polarized incidence.We experimentally demonstrated that displacements down to 5.4 nm along the x-axis and 0.12 μm along the z-axis can be resolved with a 900 μm × 900 μm metasurface.Our work opens up new possibilities to develop a compact high-precision multidimensional displacement sensor.
查看更多>>摘要：We demonstrate a high power,Er∶LuAG single-longitudinal-mode laser in an anti-misaligned resonator.Based on the Faraday effect,a 1.61 W single-longitudinal-mode[SLM]laser is obtained with the double corner-cube-retroreflector[CCR]structure,and the tunable wavelength is 1649.2-1650.3 nm.Additionally,we investigate the anti-misalignment char-acteristics when the CCR moves and rotates along the optical axis.Furthermore,by utilizing the Er∶LuAG amplifier,the maximum 2.32 W single-longitudinal-mode laser at 1649.6 nm is achieved.The beam quality factorsM2of the 2.32 W Er∶LuAG single-longitudinal-mode laser are 1.23 and 1.25 along the horizontal[x]and vertical[y]directions,respectively.
查看更多>>摘要：The high-power mode-programmable orbital angular momentum[OAM]beam has attracted significant attention in a wide range of applications,such as long-distance optical communication,nonlinear frequency conversion,and beam shaping.Coherent beam combining[CBC]of an optical phased array[OPA]can offer a promising solution for both generating the high-power OAM beam and rapidly switching the OAM modes.However,achieving real-time phase noise locking and for-mation of desired phase structures in a high-power CBC system faces significant challenges.Here,an internal phase-sens-ing technique was utilized to generate the high-power OAM beam,which effectively mitigated thermal effects and eliminated the need for large optical devices.An OPA with six elements was employed for experimental demonstration.The first effective generation of over 1.5 kW mode-programmable OAM beam in a continuous-wave domain was presented.Moreover,the results demonstrated that the generated OAM beam could be modulated with multiple dimensions.The topo-logical charge can be switched in real time from-1 to-2.Notably,this OAM beam emitter could function as an OAM beam copier by easily transforming a single OAM beam into an OAM beam array.More importantly,a comprehensive analysis was conducted on power scaling,mode switching speed,and expansion of OAM modes.Additionally,the system's compact design enabled it to function as a packageable OAM beam emitter.Owing to the advantages of having high power and programmable modes with multiple dimension modulation in phase structures and intensity distribution,this work can pave the way for producing high-power structured light beams and advancing their applications.
查看更多>>摘要：The dynamic gain of a few-mode erbium-doped fiber amplifier[FM-EDFA]is vital for the long-haul mode division multiplexing[MDM]transmission.Here,we investigate the mode-dependent dynamic gain of an FM-EDFA under various manipulations of the pump mode.First,we numerically calculate the gain variation with respect to the input signal power,where a mode-dependent saturation input power occurs under different pump modes.Even under the fixed intensity profile of the pump laser,the saturation input power of each spatial mode is different.Moreover,high-order mode pumping leads to a com-pression of the linear amplification region,even though it is beneficial for the mitigation of the differential modal gain[DMG]arising in all guided modes.Then,we develop an all-fiber 3-mode EDFA,where the fundamental mode of the pump laser can be efficiently converted to the LP11 mode using the all-fiber mode-selective coupler[MSC].In comparison with the traditional LP01 pumping scheme,the DMG at 1550 nm can be mitigated from 1.61 dB to 0.97 dB under the LP11 mode pumping,while both an average gain of 19.93 dB and a DMG of less than 1 dB can be achieved from 1530 nm to 1560 nm.However,the corre-sponding signal input saturation powers are reduced by 0.3 dB for the LP01 mode and 1.6 dB for the LP11 mode,respectively.Both theoretical and experimental results indicate that a trade-off occurs between the DMG mitigation and the extension of the linear amplification range when the intensity profile of pump laser is manipulated.
查看更多>>摘要：Curvature sensing plays an important role in structural health monitoring,damage detection,real-time shape control,modi-fication,etc.Developing curvature sensors with large measurement ranges,high sensitivity,and linearity remains a major chal-lenge.In this study,a curvature sensor based on flexible one-dimensional photonic crystal[1D-PC]films was proposed.The flexible 1D-PC films composed of dense chalcogenide glass and water-soluble polymer materials were fabricated by solution processing.The flexible 1D-PC film curvature sensor has a wide measurement range of 33-133 m-1 and a maximum sensitivity of 0.26 nm/m-1.The shift of the transmission peak varies approximately linearly with the curvature in the entire measurement range.This kind of 1D-PC film curvature sensor provides a new idea for curvature sensing and measurement.
查看更多>>摘要：Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of sponta-neous parametric downconversion[SPDC],we can generate these photon pairs using bulk nonlinear crystals.Traditionally,the crystal is designed to satisfy a specific type of phase-matching condition.Here,we report controllable transitions among different types of phase matching in a single periodically poled potassium titanyl phosphate crystal.By carefully selecting pump conditions,we can satisfy different phase-matching conditions.This allows us to observe first-order Type-11,fifth-order Type-1,third-order Type-0,and fifth-order Type-Ⅱ SPDCs.The temperature-dependent spectra of our source were also analyzed in detail.Finally,we discussed the possibility of observing more than nine SPDCs in this crystal.Our work not only deepens the understanding of the physics behind phase-matching conditions,but also offers the potential for a highly versatile entangled biphoton source for quantum information research.
查看更多>>摘要：AlGaN-based light-emitting diodes[LEDs]on offcut substrates enhance radiative emission via forming carrier localization centers in multiple quantum wells[MQWs].This study introduces the carrier transport barrier concept,accessing its impact on the quantum efficiency of LEDs grown on different offcut sapphire substrates.A significantly enhanced internal quantum efficiency[1QE]of 83.1％is obtained from MQWs on the 1° offcut sapphire,almost twice that of the controlled 0.2° offcut sample.Yet,1° offcut LEDs have higher turn-on voltage and weaker electroluminescence than 0.2° ones.Theoretical calculations demonstrate the existence of a potential barrier on the current path around the step-induced Ga-rich stripes.Ga-rich stripes reduce the turn-on voltage but restrict sufficient driving current,impacting LED performance.
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