查看更多>>摘要：Cholesteric liquid crystal[CLC]has been widely used in flat optical elements due to the Pancharatnam-Berry[PB]phase modulation.In order to achieve PB phase modulation for both circular polarizations,it is natural to come up with stacking CLCs with opposite chirality.Here,various optical properties of diverse CLC stacking structures are systematically inves-tigated by numerical calculations.With the thickness of the CLC sublayers becoming smaller,the reflection bandgap splits into three main parts,and the rotatory dispersion gradually becomes negligible.Vector beams provide a more intuitive verification.These results provide theoretical guidance for future studies on stacked chiral anisotropic media.
查看更多>>摘要：Wide-field second-harmonic generation[SHG]was used to obtain the second-harmonic signal from the entire image area for rapid imaging,despite the fact that conventional Gaussian beam illumination has low energy utilization efficiency,which makes it easy to overexpose the intensity of the image center area.However,flat-top beam illumination has uniform spatial distribution,thereby improving the photon excitation efficiency in the entire image region and reducing laser damage and thermal effect.By combining flat-top beam illumination and wide-field SHG polarization measurement,we can calculate more myosin fibril symmetrical axis orientations through polarization analysis of 16 images at a fast imaging speed while expanding the field of view.More importantly,the application of a flat-top beam can further improve the capability of polarization measurement in SHG microscopy.
查看更多>>摘要：Using an identical monolithic InGaN/GaN light emitting diode[LED]array as the sensing module and a well-designed data processing module,we demonstrate a small-size concentration sensing prototype.Overlap between the emission and the response spectra of the InGaN/GaN LED makes each pair of LEDs in the arrayed chip form a sensing channel.The changes in liquid concentration can be transformed into variation of photocurrent.The system's sensing properties are further opti-mized by varying the position,number of receivers,and packaging reflectors.With methyl orange as a tracer agent,the sensing system's resolution is 0.286 μmol/L with a linear measurement region below 40 μmol/L.
查看更多>>摘要：Coherent optical emission of free induction decay[FID]excited by the multiple-photon resonance has been recently observed in nitrogen ions produced by intense femtosecond laser pulses.Here we report that orbit angular momentum[OAM]of the pump laser pulses can be transferred to the much longer pulsed free induction decay emission with the OAM conserved.It was found that when the pump laser frequency approaches the fraction of the 391.4 nm emission[p0/5],an FID emission is emitted whereas its topological charge was identified to be 5 times of the pump laser.Due to the reduced laser intensity with a vortex pump compared to the conventional Gaussian beam,the resonant pump laser wavelength presents a redshift,and the FID signal is significantly weaker.
查看更多>>摘要：In this work,we propose a novel approach that combines a bidirectional deep neural network[BDNN]with a multifunctional metasurface absorber[MMA]for inverse design,which can effectively address the challenge of on-demand customization for absorbers.The inverse design of absorption peak frequencies can be achieved from 0.5 to 10 terahertz[THz],covering the quasi-entire THz band.Based on this,the BDNN is extended to broadband absorption,and the inverse design yields an MMA at the desired frequency.This work provides a broadly applicable approach to the custom design of multifunctional devices that can facilitate the evaluation and design of metasurfaces in electromagnetic absorption.
查看更多>>摘要：In the field of long-wave infrared[LWIR]thermal imaging,vital for applications such as military surveillance and medical diagnostics,metalenses show immense potential for compact,lightweight,and low-power optical systems.However,to date,the development of LWIR broadband achromatic metalenses with dynamic tunable focus,which are suitable for both coaxial and off-axis applications,remains a large unexplored area.Herein,we have developed an extensive database of broadband achromatic all-As2Se3 microstructure units for the LWIR range.Utilizing this database with the particle swarm optimization[PSO]algorithm,we have designed and demonstrated LWIR broadband achromatic metalenses capable of coaxial and off-axis focusing with three dynamic tunable states.This research may have potential applications for the design of compact,high-performance optical devices,including those with extreme depth-of-field and wide-angle imaging capabilities.
查看更多>>摘要：Photonic microwave harmonic down-converters[PMHDCs]based on self-oscillation optical frequency combs[OFCs]are interesting because of their broad bandwidth compared with plain optoelectronic oscillators.In this paper,a high-efficiency and flexible PMHDC is proposed and demonstrated.The properties of the OFC,such as the carrier-to-noise ratio[CNR],bandwidth and free spectral range[FSR],and the influence of optical injection,are investigated.The broadband OFC pro-vides a frequency tunable and high-quality local oscillation[L0],which guarantees flexible down-conversion for the radio frequency[RF]signal.The sideband selective amplification[SSA]effect not only improves the conversion efficiency but also promotes single-sideband modulation.The conversion range can reach 100 GHz.The 12-40 GHz RF signal can be down-converted to intermediate frequency[IF]signals with a high conversion efficiency of 14.9 dB.The fixed 40-GHz RF signal is flexibly down-converted to an IF signal with the frequency from 55.4 to 2129.4 MHz.The phase noise of an IF signal at a frequency offset of 10 kHz is the same as that of the input RF signal.The PMHDC shows great performance and will find applications in radio-over-fiber[RoF]networks,electronic warfare receivers,avionics,and wireless communication systems.
查看更多>>摘要：This paper reports a photonics-assisted millimeter-wave[mm-wave]joint radar jamming and secure communication sys-tem constructed through a photonic upconversion technique.In the experiments,a 30 GHz constant envelope linear frequency-modulated orthogonal frequency division modulation[CE-LFM-OFDM]signal with an instantaneous bandwidth of 1 GHz is synthesized by encoding 1 GBaud encrypted 16-quadrature amplitude modulation[16-QAM]OFDM signal.The velocity deception jamming is achieved with a spurious suppression ratio over 30 dB.Furthermore,we efficiently execute range deception jamming with a time shift of 10 ns.Simultaneously,the encrypted 16-QAM OFDM signal is successfully transmitted over a 1.2 m wireless link,with a data rate of 4 Gbit/s.
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