Peipei Hou

Optical image processing for synthetic-aperture imaging ladar based on two-dimensional Fourier transform

A two-dimensional (2D) Fourier transform algorithm for the image reconstruction of synthetic-aperture imaging ladar (SAIL) collected data is suggested. This algorithm consists of quadratic phase compensation in azimuth direction and 2D fast Fourier transform. Based on this algorithm and the parallel 2D Fourier transform capability of spherical lens, an optical principle scheme that processes the SAIL data is proposed. The basic principle, design equations, and necessary analysis are presented. To verify this principle scheme, an experimental optical SAIL processor setup is constructed. The imaging results of SAIL data obtained by our SAIL demonstrator are presented. The optical processor is compact, lightweight, and consumes low power. This optical processor can also provide inherent parallel and speed-of-light computing capability, and thus has potential applications in on-board and satellite-borne SAIL systems.

Continuous angle steering of an optically- controlled phased array antenna based on differential true time delay constituted by micro-optical components.

We propose an optically controlled phased array antenna (PAA) based on differential true time delay constructed optical beamforming network (OBFN). Differential true time delay is realized by stack integrated micro-optical components. Optically-controlled angle steering of radio frequency (RF) beams are realized and demonstrated by this configuration. Experimental results demonstrate that OBFN based PAA can accomplish RF-independent broadband beam steering without beam squint effect and can achieve continuous angle steering. In addition, multi-beams for different steering angles are acquired synchronously.

Performance analysis of pupil-matching optical differential receivers in space-to-ground laser communication

In the paper, the principle and structure of a pupil-matching optical differential receiver consisting of double 4f confocal lens groups is introduced to overcome atmosphere turbulences in space-to-ground laser communication. Using the scalar diffraction theory, a systematic analysis of 4f lens groups is formulated mathematically. Based on Seidel aberration, lens aberrations produced by the inherent unideal lens and mutual alignment errors of double 4f lens groups primarily caused by relative axial displacement of the foci and vertical position change of the optical axes are studied mathematically and detailed. Under the effects of varying aberrations on the double 4f lens groups, we evaluate the performance of this receiving system by the model of power penalty for a given 10(-9) bit error ratio. Simulated results of the relationship between power penalty and the different root-mean-square errors are concluded in order to put forward the requirement of machining precision of individual components. That will be helpful in optimizing the design of these groups in the optical receiver.

Design and sub-beam phase measurement of Dammann grating with three-phase array output

An improved type of Dammann grating (DG) that could generate an equal-intensity spot array which has only three phases is proposed. Numerical solutions of 1×4 and 1×5 such DGs are given. A 4×4 two-phase DG manufactured by very-large-scale integration (VLSI) techniques is presented. A phase-shift-interferometry-based technique that measures the intensity and sub-beam phases of beam splitting gratings is proposed. The performance measurements of the manufactured 4×4 two-phase DG using the proposed technique is carried out.

3D coherent imaging ladar based on FMCW technology

3D coherent imaging ladar based on frequency modulated continuous wave (FMCW) technology is proposed. The triangle wave is used to modulate chirped laser. The distance information is detected by optical heterodyne technique. Meanwhile, the beam scanning is realized by rotation double-prism. And the 3D target image is obtained. The 3D coherent imaging ladar has advantages of anti-background interference, high sensitivity and long-detected distance. Under the condition of the strongly sunlight background, the targets outdoor are scanned and high resolution images are achieved. This technique has a great potential for applications in extensive imaging ladar fields.

Multiple wavelength spectral system simulating background light noise environment in satellite laser communications

Performance of satellite laser communications between GEO and LEO satellites can be influenced by background light noise appeared in the field of view due to sunlight or planets and some comets. Such influences should be studied on the ground testing platform before the space application. In this paper, we introduce a simulator that can simulate the real case of background light noise in space environment during the data talking via laser beam between two lonely satellites. This simulator can not only simulate the effect of multi-wavelength spectrum, but also the effects of adjustable angles of field-of-view, large range of adjustable optical power and adjustable deflection speeds of light noise in space environment. We integrate these functions into a device with small and compact size for easily mobile use. Software control function is also achieved via personal computer to adjust these functions arbitrarily. Keywords:

Lensless optical image processing based on two-dimensional Fresnel diffraction for synthetic-aperture imaging ladar

A principle scheme of a lensless optical processor for synthetic-aperture imaging ladar (SAIL) is proposed. The collected data from SAIL is initially digitally added with a quadratic phase in the range direction. These data are then uploaded on a liquid crystal spatial light modulator to modulate the incident light. The target image is obtained through two-dimensional (2D) free-space Fresnel diffraction. The imaging process is mathematically analyzed using a 2D data-collection equation of strip-mode side-looking SAIL. The design equation, imaging resolutions, and target-image compression ratios are presented. Based on this principle scheme, we construct an experimental optical SAIL processor and present the imaging result of data obtained from one SAIL demonstrator. The optical processor is found to exhibit the flexible property of digital processing, as well as the fast processing capability of optical means, because this optical processor is a lensless system.

New coherent laser communication detection scheme based on channel-switching method

A new coherent laser communication detection scheme based on the channel-switching method is proposed. The detection front end of this scheme comprises a 90° optical hybrid and two balanced photodetectors which outputs the in-phase (I) channel and quadrature-phase (Q) channel signal current, respectively. With this method, the ultrahigh speed analog/digital transform of the signal of the I or Q channel is not required. The phase error between the signal and local lasers is obtained by simple analog circuit. Using the phase error signal, the signals of the I/Q channel are switched alternately. The principle of this detection scheme is presented. Moreover, the comparison of the sensitivity of this scheme with that of homodyne detection with an optical phase-locked loop is discussed. An experimental setup was constructed to verify the proposed detection scheme. The offline processing procedure and results are presented. This scheme could be realized through simple structure and has potential applications in cost-effective high-speed laser communication.