Conventional semi-active laser guidance (SAL) systems take advantage of the laser designator to illuminate precisely and form a laser spot on the target. The seeker collects reflected light by a quadrant detector and converts to relative position information to guide the missile to the target accurately. Computational ghost imaging (CGI) provides new promising scheme for semi-active laser guidance in virtue of the similarity in the system composition. As with traditional optical imaging processes, scattering and turbulence in atmospheric medium interfere with the final imaging result. In this work, a mathematical model of entire imaging process is established basing on principles of Mie scattering of colloidal particles and scintillation of turbulence. Analysis of the SNR of the reconstructed image to different environment parameters or system parameters indicates that both scattering and turbulence lead to a decrease in imaging quality. In the mechanism of action, turbulence introduces a random multiplicative noise while scattering highlights the interference of the inherent additive noise to the imaging system.
Single-pixle detector based computational ghost imaging (CGI) reconstructs an image by measuring the correlations between the scene and a series of masks. Recently, multi-pixels detector and parallel encoding is used to reduce modulation times and improve imaging speed. Due to the separate characteristics of encoding and detection in CGI system, detector defocus will not lead to image blurring in this single-pixel detector based CGI. However, detector defocus in multi-pixels detector based CGI is different to single-pixle detector based system. In this paper, based on the principle of CGI and the model of detector defocus, the influence of detector defocus in CGI is theoretically analyzed. Simulation and experiment results indicate that the multi-pixels detector based CGI inherits characteristics of antidefocus. The quality of reconstructed image is mainly affected by the degree of defocus and the array size of the detector.
Optical waveguide phased array can realize high-speed beam scanning without mechanical deflection, which is a research hotspot of new system LiDAR. Limited by the manufacturing error of the device, the theoretical value of the modulation phase cannot achieve precise beam steering. The most commonly used SPGD algorithm achieves accurate beam deflection without pre-wavefront phase detection by optimizing the phase modulation voltages of the array elements, avoiding cumbersome parameter error calibration. However, in some cases, the SPGD algorithm converges slowly and is prone to local extremum. To achieve fast adaptive phase correction, a chaotic stochastic parallel gradient descent (CSPGD) algorithm combining chaos theory and SPGD is proposed in this paper. The neighborhood chaotic search is centered on the wave control voltages obtained by SPGD optimization. The ergodicity of chaotic sequences is employed to improve the fine search performance of the algorithm, thereby speeding up the correction and improving the correction accuracy. Plus, a phase-correcting optical system is built using a one-dimentional eight-element (1×8) lithium niobate (LiNbO3) optical waveguide phased array to verify the convergence performance of the new algorithm. The random phase modulation OPA is used to simulate a large phase error scenario. Simulation and experimental results show that the CSPGD phase correction algorithm can deflect the beam to the target direction more quickly and improve the beam quality effectively within the same iteration scale, compared with the classical SPGD algorithm.
A novel scheme of optical phase array(OPA) based on wave-guide is represented in this paper. Fiber paths is main design of system, the single mode fibers are used as transmission paths, photonic crystal fibers(PCF) are adopted as the output array, LiNbO3 wave-guide is used as the phase modulator. The system configuration have been given in the paper, performance of main device such as LiNbO3 wave-guide and PCF array are analyzed. According to the theory of OPA and electro-optical effect of LiNbO3 wave-guide, the feasibility of system have been demonstrated. By adjusting the phase shift of each LiNbO3 wave-guide, the beam deflection have been observed. Simulation experiments have been implemented to study the influence of its structure parameter on output diffraction characteristics. The results show that the inter-elements distance, the quantity of fiber core and arrangement of fiber core affect the beam steering quality including full width at half-maximum(FWHM), output intensity distribution and normalized amplitude distribution. The grating lobes can be suppressed by smaller distance, the beam scanning accuracy is improved by more units of fiber core. Then two-dimension arrangements of fiber core is analyzed. By adjusting the arrangements of the fiber core, the coupling coefficient and the coupling length between two fiber core in the PCF array are changed, which conduct the different output amplitude distribution. So the structure parameter of PCF array is main factor to the beam steering. With the development of craft for PCF, the research result will provide assistance for the design of OPA in the future.
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