Research on optical simulation of dim target based on passive detection link analysis.

In order to meet the ground calibration requirements of optical detection equipment to identify optical characteristics of dim targets, an optical simulation method of dim targets based on passive detection link analysis and bidirectional scattering distribution function model is proposed. The off-axis collimation system for long focal length, the simulated energy transmission model of dim targets and the simplified model of bidirectional scattering distribution function are established. An internal stray light suppression baffle was designed to effectively suppress secondary scattering, and an optical simulation system for dim targets was built. The experimental results show that the system can simulate +7 Mv∼+20 Mv, and the simulation accuracy is better than 0.07 Mv. At the same time, the detection ability of the camera is tested by using the +15 Mv point simulated by the system. The signal-to-noise of the star point target reaches 6.7, which meets the requirements of detection rate and false alarm rate, and realizes the ground test of the camera's detection ability of the dim target.

Experimental demonstration of a free space optical wireless video transmission system based on image compression sensing algorithm.

The wireless transmission of video data mainly entails addressing the massive video stream data and ensuring the quality of image frame transmission. To reduce the amount of data and ensure an optimal data transmission rate and quality, we propose a free-space optical video transmission system that applies compressed sensing (CS) algorithms to wireless optical communication systems. Based on the Artix-7 series field programmable gate array (FPGA) chip, we completed the hardware design of the optical wireless video transceiver board; the CS image is transmitted online to the FPGA through Gigabit Ethernet, and the video data is encoded by gigabit transceiver with low power (GTP) and converted into an optical signal, which is relayed to the atmospheric turbulence simulation channel through an attenuator and a collimating mirror. After the optical signal is decoded by photoelectric conversion at the receiving end, the Camera-Link frame grabber is d; thus, the image is collected, and it is reconstructed offline. Herein, the link transmission conditions of different algorithm sampling rates, optical power at the receiving end, and atmospheric coherence length are measured. The experimental results indicate that the encrypt-then-compress (ETC) type algorithm exhibits a more optimal image compression transmission reconstruction performance, and that the 2D compressed sensing (2DCS) algorithm exhibits superior performance. Under the condition that the optical power satisfies the link connectivity, the PSNR value of the reconstructed image is 3-7 dB higher than that of the comparison algorithm. In a strong atmosphere turbulence environment, the peak signal-to-noise ratio (PSNR) of the corresponding reconstructed image under different transmission rates at the receiving end can still exceed 30 dB, ensuring the complete reconstruction of the image.

Optical adaptive power control based on atmospheric channel reciprocity for mitigating turbulence disturbances in free-space optics communication.

A continuous time-domain adaptive power model of transmitter optical and control algorithm based on atmospheric turbulence channel reciprocity are explored for mitigating the free-space optical communication (FSOC) receiver optical intensity scintillation and bit error rate (BER) deterioration. First, a transmitter optical adaptive power control (OAPC) system architecture using four wavelength optical signals based on atmospheric turbulence channel reciprocity is proposed, and electronically variable optical attenuator (EVOA) and erbium-doped fiber amplifier (EDFA) are employed as the main OAPC units for power adaptation. Moreover, a reciprocity evaluation model for gamma-gamma (G-G) continuous-time signals is generated using the autoregressive moving average (ARMA) stochastic process, which takes into account the delay time and system noise, and a reciprocity-based OPAC algorithm is proposed. Numerical simulations were also performed to analyze the signal reciprocity characteristics under different turbulence, noise, and sampling time mismatch at both ends, as well as the scintillation index (SI) performance under OAPC system operation. Simultaneously, the time-domain signals of continuous quadrature amplitude modulation -16 (QAM-16) and QAM-32 real states are fused with the gamma-gamma (G-G) reciprocal turbulence continuous signals to analyze the probability density function (PDF) and bit error ratio (BER) performance after OAPC correction. Finally, a 64 Gpbs QAM-16 OPAC communication experiment was successfully executed based on an atmospheric turbulence simulator. It is shown that the OAPC correction is carried out using reciprocity at millisecond sampling delay, the light intensity scintillation of the communication signal can be well suppressed, the signal-to-noise ratio (SNR) is greatly improved, the suppression is more obvious under strong turbulence, the overall BER reduction is greater than 2.8 orders of magnitude with the OAPC system, and this trend becomes more pronounced as the received power increases, even reach 6 orders of magnitude in some places. This work provides real time-domain continuous signal samples for real signal generation of communication signals in real turbulence environments, adaptive coding modulation using reciprocity, channel estimation, and optical wavefront adaptive suppression, which are the basis of advanced adaptive signal processing algorithms.

Line-scanning technique using a PDMS grating in a microscope configuration.

We report the concept of a 1550 nm laser line scanning microscope based on a polydimethylsiloxane (PDMS) grating with scanning by stretching the PDMS grating to improve the scanning speed and enable low-cost scanning. Zemax is used to verify the possibility of realizing the system by simulating the illumination light path and the emission light path. The scanning field of view is 0.11m m×0.11m m, and the modulation transfer function (MTF) data of the 0th, ±1st, and ±2 nd diffraction orders in the illumination light path and the emission light path, respectively, meet the requirements of the diffraction limit resolution at the cutoff frequencies.

Generation of temporal fading envelope sequences for the FSOC channel based on atmospheric turbulence optical parameters.

The temporal characteristics of the free space optical communication (FSOC) turbulence fading channel are essential for analyzing the bit error rate (BER) performances and compiling the rationale of adaptive signal processing algorithms. However, the investigation is still limited since the majority of temporal sequence generation fails to combine the autocorrelation function (ACF) of the FSOC system parameters, and using the simplified formula results in the loss of detailed information for turbulence disturbances. In this paper, considering the ACF of engineering measurable atmospheric parameters, we propose a continuous-time FSOC channel fading sequence generation model that obeys the Gamma-Gamma (G-G) probability density function (PDF). First, under the influence of parameters such as transmission distance, optical wavelength, scintillation index, and atmospheric structural constant, the normalized channel fading models of ACF and PSD are established, and the numerical solution of the time-domain Gaussian correlation sequence is derived. Moreover, the light intensity generation model obeying the time-domain correlation with statistical distribution information is derived after employing the rank mapping, taking into account the association between the G-G PDF parameters and the large and small scales turbulence fading channels. Finally, the Monte Carlo numerical method is used to analyze the performances of the ACF, PDF, and PSD parameters, as well as the temporal characteristics of the generated sequence, and the matching relationships between these parameters and theory, under various turbulence intensities, propagation distances, and transverse wind speeds. Numerical results show that the proposed temporal sequence generation model highly restores the disturbance information in different frequency bands for the turbulence fading channels, and the agreement with the theoretical solution is 0.999. This study presents essential numerical simulation methods for analyzing and evaluating the temporal properties of modulated signals. When sophisticated algorithms are used to handle FSOC signals, our proposed temporal sequence model can provide communication signal experimental sample data generating techniques under various FSOC parameters, which is a crucial theoretical basis for evaluating algorithm performances.

Tunable peak power square-wave pulse based on an all-PM thulium-doped mode-locked fiber laser.

Nanosecond dissipative soliton resonance pulse is a demonstration of an all polarization-maintaining (PM) thulium-doped fiber laser in a nonlinear amplifying loop mirror (NALM)-based figure-eight configuration. Each loop of the apparatus includes a controllable power amplifier. With increased amplifier power, pulse width broadens linearly from 3.6 to 13.5 ns, and maximum single pulse energy can reach 27.5 nJ. Interestingly, the output peak power presents two completely opposite proportional effects in terms of the variation of settings for two amplifiers, respectively. The experimental results show that the NALM loop plays an important role for tunable pulse duration, and the unidirectional ring part makes a significant contribution for power scaling.

Decentralized stabilizability and formation control of multi-agent systems with antagonistic interactions.

This paper studies the stabilizability and formation control problems of multi-agent systems with antagonistic interactions. The agents run a bipartite consensus protocol using a signed Laplacian which is different from the conventional one. By taking advantage of the proposed structurally balanced independent strongly connected components(SBiSCCs) of the signed graph, a sufficient and necessary condition is presented to solve the decentralized stabilizability problem of multi-agent systems with antagonistic interactions. Besides, formation control is considered and the sufficient and necessary condition is provided by applying the proposed results. Several simulations are given to illustrate the theoretical results.