Yapeng Wu

A synthetic aperture imaging ladar demonstrator with Ø300mm antenna and changeable footprint

A demonstrator of synthetic aperture imaging ladar (SAIL) is constructed with the maximum aperture Ø300mm of antenna telescope. This demonstrator can be set with a rectangular aperture to produce a rectangular footprint suitable for scanning format with a high resolution and a wide strip. Particularly, the demonstrator is designed not only for the farfield application but also for the verifying and testing in the near-field in the laboratory space. And a 90 degree optical hybrid is used to mitigate the external phase errors caused by turbulence and vibration along line of sight direction and the internal phase errors caused by local fiber delay line. This paper gives the details of the systematic design, and the progresses of the experiment at a target distance around 130m.

The location of laser beam cutting based on the computer vision

Based on the computer vision theory, this article researched the algorithm for the location of laser beam cutting. This article combines Canny operator and thresheolding image. It overcomes the inaccuracy of edge detection and clutter jamming problem which are caused by the poor quality of acquired images. Collecting the key points of target edge, making B-spline curves fitting, it solved the problem that target edge is jagged. And it uses interpolation algorithm to locate the point for laser beam cutting. At last, we developed corresponding and prefessional software system which is based on Visual Stdio2003 and C#.

Phase-space analysis of laser beam propagation within atmospheric turbulence

The phase-space description of signals is a joint space-spatial frequency representation in local domain. It employ the phase-space representation functions to describe the property of optical signals between two variables that form a Fourier transform pair and provide a valuable analysis tool for signals when this new mathematical analysis tool applied to an optical system. This method can also be applied to the analysis of propagation of laser beam within free space or atmosphere condition. In this paper, we give the analytical formula of optical field distribution of laser beam after propagation within turbulence in the domain of phase-space. The results show an instructing aspect of optical signal propagation and are helpful to the future application of phase-space method to the laser communications.

Polarization Phase-shifting Cyclic Jamin Shearing Interferometer

In the inter-satellite laser communication, the laser beam transmitted from the optical terminals is required to be highly collimated and its divergence approaches diffraction-limit. For testing the diffraction-limit wavefront, a polarization phase-shifting cyclic Jamin shearing interferometer is proposed. It is composed of a Jamin plate with a PBS film coated on its front surface, a right-angle prism reflecting beams two times, a shearing plate shearing beams by its rotation and a polarization phase shifter. The laser beam to be test is incident on the Jamin plate and gives rise to two interference beams with mutually perpendicular polarization directions by the PBS film. The two beams falls on the right-angle prism before or after passing through the shearing plate. With reflection of the right-angle prism, a cyclic Jamin shearing interferometric light path is formed. Two emitted beams go into the polarization phase shifter to obtain phase-shifting interferograms. In this interferometer, the cyclic interferometric light path can eliminate error of the surface profile of the optical element and the effect of environment. The interferometer has polarization phase shifting function and its fringe visibility is high. Therefore the interferometer can obtain high accuracy with variable shearing amount. In experiments, phase-shifting interferograms are obtained and the usefulness of the interferometer is verified.

The simulation of space-time speckle and impact based on synthetic aperture imaging ladar

In synthetic aperture imaging ladar (SAIL), spatially and temporally varied speckles are resulted from the linear wavelength chirped laser signal. The random phase and amplitude of space-time speckle is imported to heterodyne beat signal by antenna aperture integration. The numerical evolution for such an effect is presented. Our research indicates the random phase and amplitude is closely related to the ratio of antenna aperture and speckle scale. According to computer simulation results, the scale design of optical antenna aperture to reduce the image degradation is proposed.

Control analysis of acquirement and locking in inter-satellite laser communications

Process of acquirement and locking-up of compound axis system in inter-satellite laser communication has been studied. The effect of different condition parameters on the process of acquirement and locking-up have also been researched and simulated. Simulation results show that when the system with appropriate bandwidth has been adopted, both fine pointing system and coarse pointing system can satisfy three requirements of step response, stability criterion and dwell time and then finish the acquirement and locking-up of beacon laser beam. The simulation results provide the suited condition parameters for both fine pointing system and coarse pointing system, which is very helpful to the subsequent point and tracking processes.

A new method for acquiring the complex hologram in optical scanning holography

In this paper, we propose a new method that can acquire the complex hologram of a 3D object for optical scanning holography (OSH) by using polarized optical elements and a 90 degrees 2×4 optical hybrid. The 3D object is scanned by a wave front combined by a plane and spherical wave with orthogonal polarization. The transmitted/reflected signal light is divided into two beams by a polarized beamsplitter (PBS). Then after the polarization control, the two separated beams are heterodyne detected by a 90 degrees 2×4 optical hybrid with two balanced detectors. The 3D object can be reconstructed from the complex hologram acquired from the balanced detectors. Compared with the conventional OSH, the acousto-optic modulator and complex electronic system are not needed in this method. Another advantage of this method lies in its high efficiency since there is almost no energy loss in the generation of the scanning beam by using the polarized optical elements. This method should be used for 3D holographic microscopy and 3D holographic television.

Laboratory demonstration of Fresnel telescope imaging ladar

In this paper, we present a laboratory demonstration of Fresnel telescope imaging ladar system for imaging the faraway objects with high resolution. Two concentric and coaxial quadratic wavefront with orthogonal polarization are used as scanning beams to illuminate the target. The scattered light from the target is heterodyne detected by a 90 degree 2×4 optical hybrid with two balanced receivers. The target image can be reconstructed by digital processing of the output signals of the balanced receivers. Point targets 4.3m away are reconstructed with high resolution in experiments.

Control loop analysis of the complex axis in satellite laser communications

Satellite laser communication involves communications between GEO satellites and LEO satellites. The optical link can be built by the accurate pointing and tracking, which often employs the combination effect of coarse pointing assembly and fine pointing assembly. In order to achieve this goal with ratable wedged-plate lenses, the mathematic model of transfer function of control loop is obtained by analyzing the total control loop for such complex axis. One can also get the optimized programs between coarse and fine pointing assembly.

Design and development of control software in the experiment system of synthetic aperture laser imaging radar

A control software experiment system of synthetic aperture imaging ladar is developed based on multithreading parallel mechanism of Labview8.6 and SCPI (standard commands for programmable instruments) protocol. Firstly, hardware composition and software function requirement of the system are analyzed. Then, the control module of the laser and stepper motor and the data communication module of oscillograph are developed separately and the three modules are integrated to realize the gather and compute of the return signal. Finally, by the result of experiment, the control software worked steady and real timely and it can operate the laser, stepper motor and oscillograph successfully.