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Coarse wavelength division multiplexing (CWDM) technology has been widely used in short-reach optical communication systems. By using the same technology in a solid-state photonics-based Lidar, one can achieve significant cost reduction. Beam steering is realized through diffraction of light wave upon grating couplers. However, current design has a small viewing angle and a low angular resolution. We propose a configuration based on Silicon-on-Insulator (SOI) waveguide grating coupler. The viewing angle is increased by 2.5 times with light signals propagating bidirectionally. The angular resolution is doubled through interleaving beams with trans-electrical (TE) polarization and beams with trans-magnetic (TM) polarization. By optimizing the design of a single grating coupler, the output beams are evenly distributed and the transmittance is improved. With 4 CWDM lasers being the source, a 34° beam angle of view and an angular resolution of 1.9° are demonstrated.

In this work, we design and numerically investigate a silica-cladded Germania-doped ring-core fiber (RCF) that supports orbital angular momentum (OAM) modes with all-normal dispersion. By optimizing the structure parameters of the designed RCF, an all-normal and flat dispersion with a total variation of 1,1 mode. A 1.3-octave supercontinuum spectrum of the OAM1,1 mode is generated numerically after launching a 40-fs 200-kW chirp-free hyperbolic secant pulse train centered at 1700 nm into a 2-cm long designed fiber with 50 mol% Ge-doped ring-core, covering 1290-nm bandwidth from 885 nm to 2175 nm at −40 dB power level. The coherence of the generated supercontinuum of the OAM1,1 mode depicts nearly perfect property over the whole spectral range. This design can serve as an efficient way to extend the spectral coverage of beams carrying OAM modes in various applications.

The flexibility of producing two dispersive waves (DWs) in silicon nitride (Si3N4) slot waveguide is demonstrated, by tailoring the slot features and the corresponding phase-matching condition. DWs are generated at visible and mid-infrared (mid-IR) wavelength regions, respectively. We obtain a broadband low normal dispersion region from 2 to $5.25~\mu \text{m}$ , which offers particular advantages for DW generation at mid-IR wavelength region. The long-wave dispersive wave (LWDW) can cover beyond $4~\mu \text{m}$ . This is the first time to illustrate the freedom of Si3N4 slot waveguide for DWs generation ever reported. A broadband spectrum can be extended from 0.5 to $4.5~\mu \text{m}$ at −30 dB level by launching a 1-kW 1550-nm hyperbolic secant input pump pulse to a 1-cm proposed waveguide. The newly formed spectrum has a high degree of coherence. This approach provides more flexibility for frequency conversion, and has the advantages for biophotonics, optical sensing, chip-integrated spectroscopy, health and environmental monitoring.

Many visual simultaneous localization and mapping (SLAM) systems have been shown to be accurate and robust, and have real-time performance capabilities on both indoor and ground datasets. However, these methods can be problematic when dealing with aerial frames captured by a camera mounted on an unmanned aerial vehicle (UAV) because the flight height of the UAV can be difficult to control and is easily affected by the environment. For example, the UAV may be shaken or experience a rapid drop in height due to sudden strong wind, which may in turn lead to lost tracking. What is more, when photographing a large area, the UAV flight path is usually planned in advance and the UAV does not generally return to the previously covered areas, so if the tracking fails during the flight, many areas of the map will be missing. To cope with the case of lost tracking, we present a method of reconstructing a complete global map of UAV datasets by sequentially merging the submaps via the corresponding undirected connected graph. Specifically, submaps are repeatedly generated, from the initialization process to the place where the tracking is lost, and a corresponding undirected connected graph is built by considering these submaps as nodes and the common map points within two submaps as edges. The common map points are then determined by the bag-of-words (BoW) method, and the submaps are merged if they are found to be connected with the online map in the undirect connected graph. To demonstrate the performance of the proposed method, we first investigated the performance on a UAV dataset, and the experimental results showed that, in the case of several tracking failures, the integrity of the mapping was significantly better than that of the current mainstream SLAM method. We also tested the proposed method on both ground and indoor datasets, where it again showed a superior performance.

We propose and design a hollow As2S3 ring-core photonic crystal fiber (PCF) with 514 radially fundamental orbital angular momentum (OAM) modes over 360 nm communications bandwidth across all the O, E, S, C, and L bands. The designed PCF with 40 $\mu \text{m}$ -radius air core and 150 nm-width As2S3 ring can support eigenmodes up to HE130,1 and EH128,1. The numerical analysis shows that the designed ring PCF has large effective refractive index contrast, and can transmit up to 874 OAM modes near 1.55 $\mu \text{m}$ . Simulation results show that in the C and L bands, the PCF with a hollow-core radius of 40 $\mu \text{m}$ and a ring width of 0.15 $\mu \text{m}$ can retain an $2.5\times 10 ^{-3}$ effective refractive index difference between the two highest order OAM modes, which achieves effective mode separation, thereby achieving stable OAM mode transmission. The $n_{eff}$ difference between the even and odd fiber eigenmodes and the intra-mode walk-off are also carefully studied under different bending radii. The results show that higher-order OAM modes has better tolerance to the fiber bending, compared with the lower-order modes. The fiber has the potential to support ultra-high capacity OAM mode division multiplexing in the optical fiber communication systems.

In this paper, we propose and design a Ge-doped air-core ring fiber, which can support a large amount of OAM modes for mode-division multiplexing (MDM) in optical fiber communications. By varying the mole fraction of GeO2 and adjusting the structure parameter, including the air-core radius and the GeO2-doped ring width, we investigate the influence of different fiber parameters on the total supported OAM mode number. The hollow silica fiber with a 50- $\mu \text{m}$ air core and a 1.5- $\mu \text{m}$ thickness of Ge-doped ring is designed in simulation to support fiber eigenmodes up to HE112,1 and EH107,1. This provides 436 OAM modes at 1550 nm while maintaining radially single mode condition. Moreover, it can support more than 400 radially fundamental OAM modes for the wavelength from 1460 nm to 1625 nm, covering entire S, C and L bands. The optical parameters of the guided OAM modes in the fiber are also numerically analyzed, including effect of material loss, optical field distribution, effective refractive index profile and chromatic dispersion, etc. The simulation results show that the higher-order OAM modes have longer $2\pi $ and 10-ps walk-off length in the air-core ring fiber with ellipticity or bending compared with low-order modes.

It is well-known now that orbital angular momentum (OAM) modes can be a potential technology to take full advantages of the space resources in the fiber-based optical communication system because of its infinite states. However, the corresponding fiber design for OAM modes to meet various requirements in the fiber-based communication system is still not enough. For the dispersion property, there are various attributes given in the standard of ITU-T series, which has not yet been proposed for the OAM modes. In this paper, we propose and design a non-zero dispersion-shifted air-core ring fiber for OAM mode, which can offer more options on dispersion values. A negative dispersion of −1.246 ps/(nm $\cdot $ km) or a positive dispersion of 1.541 ps/(nm $\cdot $ km) at 1550 nm with < 1.5 ps/(nm $\cdot $ km) dispersion variation across the C band or < 4 ps/(nm $\cdot $ km) dispersion variation across the C and L bands for OAM $_{1,1}$ mode is achieved in the numerical simulation.

In human-machine-interface study, recognition of conscious human motion by contactless passive magnetic marked method can provide abundant information, such as PM marked tongue-machine-interface (TMI). However, solution of this nonlinear magnetic inverse problem heavily relies on initialization. This paper takes advantage of the motion characteristics constrained by physiological structure, and develops an enhanced algorithm for real-time full-pose passive magnetic localization in TMI application. In the proposed algorithm, a predetermined-discretized database is introduced, and provides reliable initializations for the nonlinear magnetic localization problem. This database presents the connotative relationships between the location and orientation of passive magnetic source, termed location-orientation mapping database (LOMD). The influence of initialization and LOMD constitution on solving the nonlinear inverse magnetic problem are studied through extensive simulations. Test bench evaluations are conducted on the designed experiment system. The experiment results show that about 38.5 % localization improvement can be achieved with a real-time tracking frequency up to 56.5 Hz.

High-baud-rate coherent optical system is essential to support the ever-increasing demand for high-speed applications. Owing to the recent progress in advanced modulation formats, over 1 Tb/s single-carrier data transmission has been achieved in the laboratory, and its commercial application is envisioned in the near future. This paper presented the trend of increasing baud rate and utilizing high-order quadrature-amplitude modulation (QAM), and several enabling technologies in the coherent optical communication systems. We first discussed recent progress of high-order QAM system and digital signal processing technology. Furthermore, we compared the transmission performance of three different ultrahigh-order QAM formats. The paper then reviewed the commonly used methods of achieving over 100 GBaud optically modulated signals. Besides, five attractive modulators and their corresponding modulation structures are illustrated. Key performance parameters including electrode length, 3-dB bandwidth, half-wave voltage, extinction ratio and optical loss are also compared. Finally, the trade-off between the baud rate and QAM orders in implementing high-speed systems are investigated in simulations. The results show that for the coming 800 GbE or 1.6 TbE, PDM-64-QAM might be an idea choice by considering the trade-off between the link reach and required system bandwidth. By adopting the latest probabilistic shaping technology, higher-order QAM signals, such as PS PDM-256-QAM, could be favorable for long reach applications while using extra system bandwidth.

In this work, we designed and simulated a novel air-core As2S3 ring fiber that supports orbital angular momentum (OAM) modes. By optimizing the structure parameters of the designed fiber to effectively tailor its chromatic dispersion, a near-zero flat dispersion profile with a total of 1,1 mode. After launching a 100-fs 70-kW hyperbolic secant pulse into an 8-mm air-core As2S3 ring fiber, a light-carrying OAM supercontinuum is numerically formed beyond two-octave range, covering 5717nm bandwidth from 1182 nm to 6897 nm at -30dB. Furthermore, the generated supercontinuum is highly coherent across the whole spectral range. This can serve as an effective manner to expand the spectral coverage of the OAM beams for various applications.

In this work, we design and simulate an air-core As2S3 ring fiber for high-order orbital angular momentum (OAM) supercontinuum generation. We show that the chromatic dispersion of the ring fiber can be substantially tailored by proper optimization of the air-core radius. Two-octave supercontinuum carrying OAM17,1 mode, spanning from 1560 to 6250 nm, is obtained by pumping a 50-fs 100-kW secant hyperbolic pulse centered at the wavelength of 3800 nm into the designed fiber with 50-μm air-core radius and 1-μm ring width. We further engineer the chromatic dispersion of some other OAM modes and perform simulations of supercontinuum spectra using different kilowatt-level peak power, which indicates that the fiber we design represents a promising avenue for supercontinuum generation of all the OAMl,1 modes (|l| ≤17). The proposed fiber is suitable for the transmission of OAM beams in infrared wavelength range and it could promote the development and application of high-order OAM beams.

In this work, an air-core ring fiber is designed with a record high 1322 orbital angular momentum (OAM) modes at 1550 nm while maintaining radially single-mode condition. Moreover, it can support over 1004 OAM modes across all O, E, S, C, and L bands, exploiting to our knowledge the highest number of OAM modes ever supported in the optical fiber within a wide wavelength range. Simulations show that, across the C and L bands, the fiber with 55-μm air-core radius and 0.45-μm ring width can preserve 3.3 × 10-3 effective refraction index difference between the two highest-order OAM modes HE340,1 and EH271,1. This enables efficient mode separation, and thus achieving stable OAM modes transmission. The effective refractive index differences between the even and odd fiber eigenmodes are also analyzed in the elliptical and bent fibers. We note that higher-order OAM modes are more tolerant to the fiber ellipticity and bending. This ring fiber design has the potential to increase the spectral efficiency and the overall capacity in fiber-based communications system.

We design and simulate an all-normal dispersion arsenic trisulfide (As2S3) photonic crystal fiber (PCF) with high nonlinearity to enable a flat and coherent orbital angular momentum (OAM) supercontinuum (SC) generation. The photonic crystal fiber features a near-zero and flat negative dispersion with variation between -96.5 and -36.5 ps/(nm·km) over a 940-nm wavelength range from 1740 to 2680 nm. A 1946-nm supercontinuum forms from 959 to 2905 nm at -20 dB level which covers a 1.6-octave bandwidth, by launching a 100-fs 5-kW chirp-free hyperbolic secant pulse with wavelength at 2000 nm into a 1.0-cm designed fiber. The generated supercontinuum of the other two vortex modes (TE01 and TM01) can cover more than two octaves by optimizing the proposed fiber structures. The coherence of the generated supercontinuum of the three modes all shows nearly perfect property over the whole bandwidth. In general, we found that the designed ring-core As2S3 PCF with all-normal dispersion could be used for broadband coherent supercontinuum generation of various vortex modes.

A silicon nitride horizontal slot waveguide with silicon dioxide cladding is designed to achieve flat negative dispersion (-3 W. After passing through another ideal positive dispersion element, we find that the output pulse peak power can be recompressed close to 1 W in the case of different input pulse widths. Moreover, for the input pulse with a much higher peak power, the pulse width of the output pulse can be compressed to a much narrower level because of the spectral broadening introduced by optical nonlinearity. A 100-fs input pulse with 10-kW peak power can be compressed to 12.5 fs with a peak power of 63 kW. Considering the time-domain broadening and the peak power reduction, such a slot waveguide with a flat negative dispersion could be used as a time stretcher for 10-fs level pulse in on-chip chirped pulse amplification (CPA) system.

Joint estimation of human body in point cloud is a key step for tracking human movements. In this work, we present a geometric method to achieve detection of the joints from a single-frame point cloud captured using a Time-of-Flight (ToF) camera. Three-dimensional (3D) human silhouette, as global feature of the single-frame point cloud, is extracted based on the pre-processed data, the angle and aspect ratio of the silhouette are subsequently utilized to perform pose recognition, and then 14 joints of human body are derived via geometric features of 3D silhouette. To verify this method, we test on an in-house captured 3D dataset containing 1200-frame depth images, which can be categorized into four different poses (upright, raising hands, parallel arms, and akimbo). Furthermore, we test on a subset of the G3D dataset. By hand-labelling the joints of each human body as the ground truth for validation and benchmarks, the average normalized error of our geometric method is less than 5.8 cm. When the distance threshold from the ground truth is 10 cm, the results demonstrate that our proposed method delivers improved performance with an average accuracy in the range of 90%.

Nowadays, the object detection techniques have been developed rapidly for different applications, ranging from remote sensing to autonomous vehicles. We demonstrate identification of object open angle and direction using machine learning (ML) algorithms based on received light beam's intensity profiles. Compared with previous optical orbital-angular-momentum (OAM) spectrum system and other related works, our proposed technique only uses a single-shot image, and can efficiently reduce the complexity of hardware implementation. Specifically, we verify the reliability of the simulation results experimentally for 14 open angles and 32 directions. Experimental result shows that convolutional neural network (CNN) outperforms the other traditional ML algorithms, such as decision tree (DT), k-nearest neighbor algorithm (KNN), and support vector machine (SVM). As one of the variant of CNN, MobileNet (MN) has relatively simplified iteration algorithm than VGG-like net. It reduces the computational power, while still maintaining high accuracy for identification issues.

We simulate and analyze the mode properties and propagation effects of orbital angular momentum (OAM) modes in a ring fiber. A ring fiber with 0.05 up-doping is designed in simulation to support up to 10 OAM modes while maintaining single-mode condition radially. With a multiple-ring fiber, tens of OAM modes can be potentially multiplexed to greatly enhance the system capacity and spectral efficiency. The mode index difference can be maintained above 10-4 over hundreds of nanometers optical bandwidth. Higher order OAM modes' azimuthal intensity and odd-order OAM modes' azimuthal phase show better tolerance to the fiber ellipticity. Moreover, higher order OAM modes also have longer 2π and 10-ps walk-off length. After 600-km propagation, OAM0,4 mode shows

The proposed silicon-on-nitride (SON) waveguide exhibits an ultrabroadband (4200 nm), low chromatic dispersion in the mid-infrared (MIR) wavelength region from 2430 to 6630 nm. It has two zero-dispersion wavelengths within the span. Even at 6 , the nonlinear coefficients of the SON waveguides are still comparable with the ones of integrated waveguides around 1550 nm, which are widely used for octave-spanning nonlinear process. This enables a potential nonlinear optical platform for broadband signal processing across the over-one-octave MIR bandwidth.

A 3-D chirped high-contrast grating hollow-core waveguide (HCG-HW) exhibits highly efficient 2-D (transverse and lateral) light confinement. Compared with step-index ones, laterally chirped HCG-HWs (graded index) can pronouncedly reduce the propagation loss (>; 10×) without compromising the lateral index contrast. Simulation results show that a propagation loss as low as 0.04 dB/cm can be achieved. For a chirped HCG-HW with a 6-μm core height, it exhibits 30and 141-nm spectral widths for 0.1and 1-dB/cm loss requirements. The chirped HCG-HW also shows an ultralow nonlinear coefficient, which is on the order of 10-5 /W/m.