查看更多>>摘要：A 3D nonlinear photonic crystal containing four parallel segments of periodic x[2]grating structure is fabricated employing the femtosecond laser poling of ferroelectric Ca0.28Bao.72Nb2O6 crystal.The second harmonic generation from this four-segment structure is studied with a fundamental Gaussian wave.By tuning the wavelength of the fundamental wave,the second harmonic varies from the Laguerre-Gaussian beam[topological charge lc=1]to the higher-order Hermite-Gaussian beam and Laguerre-Gaussian again[lc=-1].This effect is caused by the wavelength-dependent phase delays introduced by the four-grating structure.Our study contributes to a deeper understanding of nonlinear wave interactions in 3D nonlinear photonic crystals.It also offers new possibilities for special beam generation at new frequencies and their control.
查看更多>>摘要：Stimulated Brillouin scattering in planar integrated circuits promises to realize compact and highly coherent lasers.Here we report efficient Brillouin lasing at telecommunication wavelength from a planar Ge25Sb10S65 chalcogenide[ChG]resonator with a high quality factor above 106.A low lasing threshold of 24.8 mW is achieved with a slope efficiency of 8.3％.An 8-kHz linewidth is measured for 1.56-mW on-chip output power.This work offers a good opportunity to enrich the versatility and functionality of the ChG photonics on account of their intrinsic advantages of low loss,high third-order nonlinearity,and potential capacity for wafer-scale fabrication.
查看更多>>摘要：We use a broad Gaussian beam with perturbations to motivate rogue waves[RWs]in a two-dimensional optical-induced lattice.In a linear situation,we fail to observe RWs.Nevertheless,under a nonlinear condition,the probability of RWs in the lattice is less than that in a homogeneous medium.Additionally,we obtain a shorter long-tail distribution of probability density function in an optical lattice.
查看更多>>摘要：The generation of high-power laser pulses using a compact hetero-integrated assembly based on a semiconductor laser with a dual-element composite 2 pm x 100 pm aperture and a compact heterothyristor switch is demonstrated.The achieved peak optical power was 33 W with a pulse duration of 3 ns at a thyristor operating voltage of 55 V.The leading edge of the laser pulse turn-on was 50 ps to a power level of 24.7 W,and the turn-on delay between the elements of the composite aperture was 160 ps.
查看更多>>摘要：In this work,we introduce a kind of new structured radial grating,which is named the even-type sinusoidal amplitude radial[ETASR]grating.Based on diffraction theory and the principle of stationary phase,a comprehensive theoretical investi-gation on the diffraction patterns of ETASR gratings is conducted.Theoretical results show that novel carpet beams with beautiful optical structures and distinctive characteristics have been constructed on the basics of the ETASR grating.Their diffraction patterns are independent of propagation distance,that is,the new carpet beams have diffraction-free propa-gating characteristics.The non-diffracting carpet beams are divided into two types by beam characteristics:non-diffracting integer-order and half-integer-order carpet beams.Subsequently,we experimentally generate these carpet beams using the ETASR grating.Finally,their particularly interesting optical morphology and features are explored through numerical simulations and experiments.
查看更多>>摘要：Frequency-modulated continuous-wave[FMCW]Lidar has the characteristics of high-ranging accuracy,noise immunity,and synchronous speed measurement,which makes it a candidate for the next generation of vehicle Lidar.In this work,an FMCW Lidar working at the single-photon level is demonstrated based on quantum compressed sensing,and the target distance is recovered from the sparse photon detection,in which the detection sensitivity,bandwidth,and compression ratio are improved significantly.Our Lidar system can achieve 3 GHz bandwidth detection at photon count rates of a few thousand,making ultra-long-distance FMCW Lidar possible.
查看更多>>摘要：We demonstrate a resolution enhancement scheme of radio-frequency signals by tailoring a phase-squeezed state.The echo radio-frequency signals collected by photonic radar give rise to displacements in the phase quadrature of a probe laser and are estimated by the balanced homodyne detector.In contrast to the conventional coherent state,the noise variances for radio-frequency estimation with a squeezed state are reduced by approximately 6.9 dB.According to the Rayleigh criterion that defines the resolution limit,the minimum resolvable displacement Δa with a squeezed state is reduced to 45％compared to that with a coherent state,demonstrating the quantum advantage.The squeezing-enhanced technique has extensive applications for multitarget recognition and tracking in contemporary photonic radar systems.
查看更多>>摘要：A highly sensitive carbon dioxide[CO2]sensor based on light-induced thermoelastic spectroscopy[LITES]utilizing a self-designed low-frequency quartz tuning fork[QTF]and a fiber-coupled multipass cell[MPC]is reported in this paper.The QTF with a low resonant frequency of 8675 Hz and a high Q factor of 11,675.64 was used to improve its energy accumulation time and the sensor's signal level.The MPC with the fiber-coupled structure and optical length of 40 m was adopted to signifi-cantly increase the gas absorbance and reduce the optical alignment difficulty as well as improve the robustness of the sensor system.A distributed feedback[DFB],near-infrared diode laser with an emission wavelength of 1.57 μm was used as an excitation source.The experimental results showed that this CO2-LITES sensor had an excellent linear response to CO2 concentrations.The minimum detection limitation[MDL]of this CO2-LITES sensor was obtained to be 445.91 ppm,and it could be improved to 47.70 ppm[parts per million]when the integration time of the system reached 500 s.Further improvement methods for the detection performance of such sensors were also discussed.
查看更多>>摘要：We present a tunable terahertz[THz]spectrum analyzer with hyperspectral resolution formed from electrically tunable metamaterial and plasmonic structures.As few as eight encoders based on four detectors are needed to recover 396 spectral bands.The incident spectra in the range of 1-5 THz can be reconstructed with a localization precision of 0.3 GHz and a minimum average mean squared error[MSE]of 6.9 x 10-5.Our proposed analyzers are faster and more portable than those based on frequency combs and power meters,and more accurate than existing Fourier transform techniques,showing promising applications in pathology,biomedical imaging,and many other areas.
查看更多>>摘要：In this work,a simple fabrication method of germanium-based metasurfaces is proposed,where the deposited Al2O3 layer with high selectivity is chosen as the hard mask and retained after the dry etching process.The simulation and experimental characterization results verify the feasibility of the fabrication method.The experimental study on the fabrication methods of germanium-based metasurfaces is very significant as the meta-atoms with a higher refractive index can achieve O to 2πtransmission phase variation with a smaller period under the same thickness-to-period ratio,which is consistent with the requirement of the period miniaturization in some cases.
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