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Diffractive optical element (DOE) array promises compact shape for full-parallax integral imaging three-dimensional (3D) display. However, DOEs suffer from large chromatic aberration due to the strong wavelength-dependent nature of diffraction phenomena that degrade the quality of reconstructed 3D images. An end-to-end DOE optimization approach is proposed to reduce chromatic aberration for integral imaging. The end-to-end optimization framework includes RGB pre-processing convolutional neural networks and achromatic optics optimization design of rotationally symmetric DOE. An optical display model based on diffractive optics is proposed to analyze the integral imaging 3D display process for achromatic optical optimization design. The pre-processed elemental image arrays are modulated by an optimized DOE array to reconstruct the achromatic 3D images. A 3D artifacts scene without chromatic aberration is reconstructed in different views with the proposed method, and both peak signal to noise ratio (PSNR) and structural similarity (SSIM) are improved compared to the conventional Fresnel lens DOE.

The morphing aircraft is a promising solution to achieve an optimal flight performance according to various mission scenarios. To apply the morphing technology in hypersonic vehicles, a variable-sweep-wing morphing waverider was proposed in previous studies, and its aerodynamic performance and dynamic model were presented. In this paper, this morphing waverider is assumed to perform a long-range unpowered glide mission over a wide speed range from hypersonic to subsonic speed. First, the accurate longitudinal dynamic model for the morphing waverider is presented, with all the additional forces and moments that stem from morphing. And a control-oriented longitudinal dynamic model is proposed and it separates the additional morphing forces and moments from derivatives of state variables. Then, an adaptive super twisting sliding mode controller is applied for this morphing waverider to track the optimized trajectory during the entire morphing process. Finally, the overall performance of this controller is examined by nominal condition simulations and Monte Carlo runs. Under the nominal condition simulations, the adaptive super twisting algorithm based sliding mode controller reduces mean tracking error of the pitch angle by 25% compared with the traditional sliding mode controller. In the 500 Monte Carlo runs, the ASTA controller reduces maximum tracking error of the pitch angle by 47% compared with the SMC controller.

The variable-sweep-wing morphing waverider is a promising solution for the wide speed range flight with adaptability to various mission requirements. However, it is a highly nonlinear system with inherent uncertainties and complex internal couplings due to the alteration of its configuration. In this paper, a dynamic and kinematical model with explicit expression of nonlinear/coupled forces and moments caused by morphing is proposed in a six degree of freedom flight. However, the above morphing forces and moments are difficult to measure and they can be estimated by the designed nonlinear disturbance observer. Then, a nonlinear model predictive controller is developed based on the state space model considering estimated disturbances. The global asymptotic stability of the composite controller can be guaranteed through stability analysis. Lateral weaving numerical simulation cases of the morphing waverider are carried out to investigate lateral maneuverability and overall controller performance.

With phase-sensitive optical time-domain reflectometry (Φ-OTDR), an optic fiber can be used as a distributed vibration sensor to perceive the external disturbance along the fiber through the phase variation of the Rayleigh backscatter light. However, due to the inevitable interference fading phenomenon, the signal-to-noise ratio (SNR) of Rayleigh backscatter light at certain points is insufficient, thus affecting the fidelity of vibration sensing. In this paper, we propose the spectrum extraction and the rotated-vector-sum (SERVS) method to suppress the interference fading in the pulse-intensity-coding Φ-OTDR, which applies Golay complementary sequence through acousto-optic modulator (AOM). Benefited from the easier implementation, the experimental results demonstrate that the percentage of fading points can be reduced from 2.98% to 0.33% significantly and the standard deviation of differential phase is also decreased from 0.6556 rad to 0.2901 rad. Also the minimum level of averaged power spectral density (PSD) of the differential phase at whole locations along the fiber is reduced about 6 dB/Hz effectively. For the demodulated disturbance signal, no influence on the SNR is observed thus it maintains a SNR improvement of 8.6 dB compared to the traditional single pulse Φ-OTDR system, achieving a noise floor of 2.38 pϵ/√Hz.

In previous studies, a variable-sweep-wing morphing waverider was proposed and its aerodynamic performance and dynamic model were provided. This morphing waverider can change sweep angle according to different flight scenario in order to achieve an optimal flight performance. For the traditional fixed-geometry waverider, the main objective of the trajectory planning problem is to find an optimal trajectory consisting of time-dependent variables including the angle of attack, the velocity, the altitude, the flight path angle and so on. As for this morphing waverider, an optimal morphing wing changing strategy is also required to be calculated together with an optimal trajectory. At first, to alleviate computational cost and improve trajectory-planning efficiency, aerodynamic coefficients of the morphing waverider are approximated and modeled as polynomial functions of multiple variables including the Mach number, the angle of attack and the sweep angle. Thereafter, an offline integrated optimization problem of both wing morphing strategy and trajectory based on the Gauss pseudo-spectral method is investigated, which can fulfill actual task requirements and variable constraints. Compared with four specific fixed-wing waverider configurations, this morphing waverider has a larger downrange distance and a lower angle of attack. However, the real flight trajectory of the morphing waverider may deviate from the nominal condition due to multiple uncertainties and this morphing waverider is required to have an intelligent online optimization ability. Therefore, an online optimization method based on the neural network is proposed for both wing morphing strategy and trajectory optimization. Finally, the overall performance of this method is examined by comparisons and Monte Carlo runs.

In this paper, passive generation of the multi-wavelength parabolic pulses (PPs) in tapered silicon nanowires (TSNs) is numerically investigated. The coupled inhomogeneous nonlinear Schrödinger equation (INLSE) is derived in the context of TSN to model the multi-wavelength PP generation. The TSN is designed based on the well-known self-similar theory that the group-velocity dispersion is decreased while the nonlinear coefficient is unchanged along the propagative direction. While the pump wavelengths for three input pulses are specially set with equal intervals of 18, 12, and 6 nm, the time-domain profiles are aligned at the same position. Simulation results show that except for wavelength interval, the waveguide length is also a critical factor that influences the quality of generated PP. Both of them reshape the pulse profile by the means of walk-off effect which depends on the cross-phase modulation between multiple pulses. By properly optimizing the input parameters of Gaussian pulses as well as the center wavelength interval and TSN length, we prove that the generation of two- even three-wavelength PPs with high-quality is feasible.

Due to physical limitation in resolution of display device, it is usually very difficult to achieve a high spatial resolution and a high angular resolution simultaneously for a three-dimensional (3D) light field display. Here, a computational super-resolution full-parallax 3D light field display is demonstrated, which can achieve both high spatial resolution and angular resolution. The proposed display consists of a specially designed backlight unit with controlled scattering angle, two cascadedly arranged LCDs with a resolution of 3840 × 2160, an aberration-suppressed compound lens array, and a holographic functional screen. The optical image formation processing of the display is analyzed and modeled as a whole process, and the superresolution light field synthesis method is presented. By co-designing the optical elements with computation processing, our proposed display architecture can improve the spatial resolution and angular resolution with a factor of 2× in both horizontal and vertical directions, comparing with these of the conventional light field display with single LCD and standard lens array. Finally, a super-resolution full-parallax 3D light field display with a designed spatial resolution of about 640 × 360 in a display area of 21.5 inches and an angular resolution of 166 × 166 in a viewing angle of 45 × 45 degrees is constructed, and an excellent 3D visual experience with improved image quality can be perceived.

Supercontinuum (SC) with broad bandwidth and high coherence is crucial in the SC-based frequency comb source generation. In this paper, we numerically investigate the mid-infrared (MIR) SC generations with the three optical modes (TE00, TE10, and TE20) in a multimode chalcogenide (As2Se3) strip waveguide. The waveguide structure is carefully engineered to ensure that the pump pulses are propagated in the normal dispersion regions of the considered three optical modes. Highly coherent and octave-spanning MIR SCs are generated when the optimized pump pulse with 80-fs pulse duration, 3-kW peak power, and 3-μm center wavelength is used. Moreover, the nonlinear dynamics of the SC generation are numerically analyzed. Finally, the SC-based frequency combs are numerically demonstrated when a pulse train with a repetition rate of 50 MHz is used as the pump source and launched into the multimode As2Se3-based strip waveguide. It is believed that the generated MIR SC and SC-based frequency comb sources have important applications in biophotonics, metrology, and sensing.

The small unmanned aerial vehicles are susceptible to wind disturbances due to the turbulent environment at their low operational altitude. Compared to conventional IMU output, the phase-advanced information provided by angular acceleration measurement is more beneficial for flight stability. This paper presents a general and systematic approach to enhance the attitude stability of small fixed-wing unmanned aerial vehicles. The methodology begins by designing a virtual angular accelerometer (VAA), which is based on 4 MEMS IMUs measurement fusion. Then, the angular acceleration is exploited to estimate and compensate disturbances. Finally, an enhanced attitude control scheme is developed to improve attitude tracking performance, where linear or nonlinear control approaches can be adopted. A VAA-based backstepping controller (BS) is designed and its stability is analyzed via Lyapunov function. Three simulation cases are carried out to verify the performance of tracking accuracy, robustness, and disturbance rejection. PID and backstepping methods are applied to the scheme. As a comparison, a widely used nonlinear disturbance observer (NDO)-based robust controller (RC) is studied. The simulation results show the excellent performance of the sensor-based VAA to observe the fast time-varying disturbance, where the NDO causes the time delay and phase lag. The tracking accuracy of the enhanced controllers (PID+VAA, BS+VAA, and RC+VAA), compared to the basic controllers, are improved by 14.3%-93.7% and the closed-loop control systems gain notable robustness.

Spectral compression (SPC) can be used for generating narrow bandwidth and wavelength-tunable light sources, which have important applications in optical communication system, spectroscopy, and nonlinear microscopy. In this paper, we numerically demonstrate the high-degree SPC of the chirp-free femtosecond pulse at wavelength 2.4 μm in a 6-cm long adiabatically suspended silicon waveguide taper. The silicon waveguide taper is designed with a dispersion-increasing profile along the propagation distance z. Simulation results show that the SPC factor can be up to 10.9, along with the brightness-enhanced factor of 8.0 and negligible sidelobe. The impacts of the higher order dispersion, higher order nonlinearity, losses (including linear and nonlinear loss), and variation of Kerr nonlinear coefficient along z on the SPC are also investigated. It is found that variation of Kerr nonlinear coefficient γ(z) and linear loss are the dominant perturbation to the degradation of the SPC performance.

A real-time computer-generated integral imaging (CGII) display rendering method based on depth-image-based multiple reference viewpoints (MDIBR) is presented, and good three-dimensional (3D) image quality with the high frame rate can be achieved. The traditional rasterization pipeline and 3D image warping are used to accelerate CGII, and the proposed method is suitable for dynamic and complex 3D content generation for the 3D display. Qualitative and quantitative experiments are carried out to evaluate the feasibility of the proposed method. Experimental results show that the MDIBR method can achieve realtime integral imaging display with 80 × 80 viewpoints based on large-scale 3D data with a million points.

In this paper, we numerically demonstrate efficient spectral compression (SPC) of wavelength-shifting soliton in a chalcogenide strip waveguide. It is found that the profiles of group-velocity dispersion (GVD) and Kerr nonlinearity play key roles in determining SPC. After calculating the dispersion of Kerr nonlinearity and Raman spectrum for three kinds of chalcogenide materials, Ge11.5As24Se64.5 is chosen as the material for designing the chalcogenide strip waveguide (CSW). The geometric parameters of CSW are optimized to obtain the desired GVD and Kerr nonlinearity. Simulation results show that in the designed CSW, an input spectrum width of 52.04 nm can be compressed to 7.23 nm along with wavelength shift of 17 nm when the input peak power is 25 W. With the input peak power increasing to 75 W, the SPC is slightly weakened, but wavelength shift can be up to 190 nm. The proposed CSW is applied to integrated all-optical quantization and an effective quantization number of 3.66-bit is achieved. It is expected that our research results can find important applications in on-chip integrated spectroscopy, all-optical signal processing, etc.

In this paper, we propose a microdisk resonator with negative thermal optical coefficient (TOC) polymer for refractive index (RI) sensing with thermal stability. The transmission characteristics and sensing performances by using quasi-TE01 and quasi-TM01 modes are simulated by a three-dimensional finite element method. The influences of the TOC, RI, and thickness of the polymer on the sensing performances are also investigated. The simulation results show that the RI sensitivity Sn and temperature sensitivity ST with different polymers are in the ranges of 25.1-26 nm/RIU and 67.3-75.2 pm/K for the quasi-TE01 mode, and 94.5-110.6 nm/RIU and 1.2-51.3 pm/K for the quasi-TM01 mode, respectively. Moreover, figure-of-merit of the temperature sensing for the quasi-TM01 mode is in the range of 2 × 10-4-8 × 10-3, which can find important application in the implementation of the adiabatic devices.

In this paper, a microdisk resonator with two whispering-gallery modes (WGMs) is proposed for label-free biochemical sensing. According to the transmission responses of the two WGMs with different coupling gaps, there is the critical coupling status for the WGM (0, 36) while there is no critical coupling status for the WGM (1, 28). For the WGMs (0, 36) and (1, 28), the refractive index (RI) sensitivities of 45.8821 and 72.9402 nm/RIU are obtained, and the corresponding RI detection limits (DLs) of 8.5902 × 10-4 and 1.9228 × 10-3 RIU are achieved, respectively. Moreover, the proposed sensor also has the temperature sensitivities of 0.0730 and 0.0703 nm/K, which correspond to the temperature DLs of 0.1631 and 0.6263 K, respectively. By constructing a characteristic matrix, it is demonstrated that simultaneous measurement of the RI and temperature can be achieved.

The humidity and temperature responses of a microfiber coupler (MFC) coated with silica gel are investigated. Two MFC structures with different waist diameters of 2.5 and 3.5 μm were fabricated by fusing and tapering two single-mode fibers using a microheater brushing technique. The influences of the coating thickness and tapered waist diameter on the sensing performance are analyzed. For the proposed sensor with a waist diameter of 2.5 μm and 8-layers thick coating, the change in the relative humidity (RH) results in an exponential blueshift with a maximum sensitivity of 1.6 nm/% RH in the range from 70 to 86% RH. In response to the temperature change, the sensor's transmission spectrum redshifts in a linear fashion with an average sensitivity of 0.55 nm/°C in the range from 20 to 40 °C. The study is important for the development of the proposed fiber structure as a humidity or temperature sensor.

In this paper, we investigate the strong modulation instability (MI) at telecommunication band in a silicon-organic hybrid slot waveguide. The organic material of polymer poly (bis para-toluene sulfonate) of 2, 4-hexadiyne 1, 6 diol (PTS), which has high third-order nonlinear refractive index and very low two-photon absorption, is used to fill the slot of the waveguide. The optical gain can be up to ~3600 m-1 with a low pump peak power of 300 mW. By using Gaussian pulses with width of 10 ps and peak power of 250 mW, deep modulation of the pump is achieved, and the ultrashort pulse trains with the periods of 27 and 24 fs are obtained in the anomalous and normal group-velocity dispersion regions, respectively.