查看更多>>摘要：Aiming for suppressing side-mode and spectrum broadening,a slit beam-shaping method and super-Gaussian apodization processing for femtosecond laser point-by-point[PbP]inscription technology of fiber Bragg gratings[FBGs]are reported here.High-quality FBGs,featuring narrow bandwidth of less than 0.3 nm,high reflectivity above 85％,low insertion loss[0.21 dB],and low cladding loss[0.82 dB],were obtained successfully.By a semi-automatic PbP inscription process,an array consisting of six FBGs,exhibiting almost no side-mode peaks with high suppression ability and narrow bandwidth,was fabricated along three independently developed single-mode fibers with an interval of 20 mm.
查看更多>>摘要：We experimentally transmit eight wavelength-division-multiplexing[WDM]channels,16 quadratic-amplitude-modulation[QAM]signals at 32-GBaud,over 1000 km few mode fiber[FMF].In this experiment,we use WDM,mode division multiplexing,and polarization multiplexing for signal transmission.Through the multiple-input-multiple-output[MIMO]equalization algo-rithms,we achieve the total line transmission rate of 4.096 Tbit/s.The results prove that the bit error rates[BERs]for the 16QAM signals after 1000 km FMF transmission are below the soft-decision forward-error-correction[SD-FEC]threshold of 2.4 × 10-2,and the net rate reaches 3.413 Tbit/s.Our proposed system provides a reference for the future development of high-capacity communication.
查看更多>>摘要：A concept of divergence angle of light beams[DALB]is proposed to analyze the depth of field[DOF]of a 3D light-field display system.The mathematical model between DOF and DALB is established,and the conclusion that DOF and DALB are inversely proportional is drawn.To reduce DALB and generate clear depth perception,a triple composite aspheric lens structure with a viewing angle of 100° is designed and experimentally demonstrated.The DALB-constrained 3D light-field display system significantly improves the clarity of 3D images and also performs well in imaging at a 3D scene with a DOF over 30 cm.
查看更多>>摘要：Edge detection for low-contrast phase objects cannot be performed directly by the spatial difference of intensity distri-bution.In this work,an all-optical diffractive neural network[DPENet]based on the differential interference contrast prin-ciple to detect the edges of phase objects in an all-optical manner is proposed.Edge information is encoded into an interference light field by dual Wollaston prisms without lenses and light-speed processed by the diffractive neural network to obtain the scale-adjustable edges.Simulation results show that DPENet achieves F-scores of 0.9308[MNIST]and 0.9352[NIST]and enables real-time edge detection of biological cells,achieving an F-score of 0.7462.
查看更多>>摘要：We demonstrate a simultaneous transmission of time-frequency and data over a 160-km urban business network in Shanghai.The signals are transmitted through a cascaded optical link consisting of 48 km and 32 km,which are connected by an optical relay.The metrological signals are inserted into the communication network using dense wavelength division multiplexing.The influence of the interference between different signals has been discussed.The experimental results demonstrate that the radio frequency[RF]instability can reach 2.1 × 10-14 at 1 s and 2.3 × 10-17 at 10,000 s,and the time interval transfer of one pulse per second[1PPS]signal with less than 10 ps at 1 s is obtained.This work paves the way for the widespread dissemination of ultra-stable time and frequency signals over the communication networks.
查看更多>>摘要：A new electronic speckle pattern interferometry method is proposed to realize in situ deformation measurements.The feature of the method is the combination of a high-speed camera and multiple laser Doppler vibrometers[LDVs]for syn-chronous measurements.The high-speed camera is used to record and select effective interferograms,while the LDVs are used to measure the rigid body displacement caused by vibrations.A series of effective interferograms with known shifted phase values are obtained to calculate the deformation phase.The experimental results show that the method performs well in measuring static and dynamic deformations with high accuracy in vibrating environments.
查看更多>>摘要：Optical coherence tomography[OCT]allows a direct and precise measurement of laser welding depth by coaxially meas-uring the keyhole depth and can be used for process monitoring and control.When OCT measurement was taken during single-beam laser welding,the keyhole instability of aluminum welding resulted in highly scattered OCT data and compli-cated the welding depth extraction methods.As a combination of an inner core beam and an outer ring beam,a novel adjustable ring mode[ARM]laser for producing a stable keyhole was applied to the OCT measurement.Different ARM laser power arrangements were conducted on aluminum and copper.The results indicated that the ring beam greatly improved the stability of the core beam-induced keyhole,and smooth welding depth can be extracted from the concen-trated OCT data.
查看更多>>摘要：We propose an absolute distance measurement method that employs heterodyne and superheterodyne combined inter-ferometers to achieve synchronous detection and demodulation of multiwavelengths.Coarse and fine synthetic wave-lengths are generated by a dual-longitudinal-mode He-Ne laser and four acoustic optical frequency shifters.Further,to improve phase synchronization measurement for multiwavelengths,we analyze the demodulation characteristics of coarse and fine measurement signals and adopt a demodulation method suitable for both signals.Experimental results demonstrate that the proposed method can achieve high-precision synchronous demodulation of multiwavelengths,and standard deviation is 1.7 × 10-5 m in a range of 2 m.
查看更多>>摘要：A flexible-grid 1 ×(2 × 3)mode-and wavelength-selective switch which comprises counter-tapered couplers and silicon microring resonators has been proposed,optimized,and demonstrated experimentally in this work.By carefully thermally tuning phase shifters and silicon microring resonators,mode and wavelength signals can be independently and flexibly conveyed to any one of the output ports,and different bandwidths can be generated as desired.The particle swarm opti-mization algorithm and finite difference time-domain method are employed to optimize structural parameters of the two-mode[de]multiplexer and crossing waveguide.The bandwidth-tunable wavelength-selective optical router composed of 12 microring resonators is studied by taking advantage of the transfer matrix method.Measurement results show that,for the fabricated module,cross talk less than-10.18 dB,an extinction ratio larger than 17.41 dB,an in-band ripple lower than 0.79 dB,and a 3-dB bandwidth changing from 0.38 to 1.05 nm are obtained,as the wavelength-channel spacing is 0.40 nm.The corresponding response time is measured to be 13.64 μs.
查看更多>>摘要：Mode splitters that directly separate modes without changing their orders are highly promising to improve the flexibility of the mode-division multiplexing systems.In this paper,we design a high-performance mode splitter on the silicon-on-insulator platform with a compact footprint of 14 μm× 2.5 μm using an inverse design method based on shape optimization.The fabrication of this mode splitter requires only a single lithography step and exhibits good fabrication tolerances.The experimental results show that the proposed device exhibits state-of-the-art insertion loss[＜0.9 dB]and cross talk[＜-16 dB]over a broad bandwidth[1500-1600 nm].Furthermore,the shape optimization method used is implemented to design a dual-mode[de]multiplexer,and the experimental results fulfill the design objective,demonstrating the excellent generality of the design method in this paper.
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