It is necessary, on the ground in a laboratory, to test the technical parameters and to verify the working performance for
the optical pointing, acquisition and tracking (PAT) of an inter-satellite lasercom terminal. In this paper, we report a
completed PAT test-bed for this aim. The test-bed works in a fully physical way and is an integration of a 2D optical
scanner of two rotating prisms, a 2D fine beam deflector of two tilting optical wedges and a double-focus laser
collimator, the overall aperture is about Φ440mm.
The optical scanner is designed to scan the beam in the range of 30° with an accuracy of 100μrad and used to simulate
the mutual movement between two satellites. The fine beam deflector has the maximum beam deviation of about 1mrad
with a step of 0.5μrad and is used to measure the tracking error of a terminal. The collimator has the double focal
lengths, respectively, of 1.5m and 10m, the former provides a wide view of field for the use in the acquisition process of
the terminal and the latter a narrow view of field for the use in the tracking process. In this paper, the design and
fabrication considerations of the PAT test-bed as well as the main specifications of the completed integrated test-bad are given.
The original scanner of tilting orthogonal double prisms is studied for testing the tracking performance in inter-satellite
laser communications. Two prisms respectively rotate around the horizontal axle and the vertical one within the
admissible range to determine the corresponding orientation and position of the passing beam, therefore the high
accuracy deviation angle of passing beam can be performed. The test experiments performed with autocollimator and
interferometer, as well as the theoretical analysis, indicates that the scanner can meet the requirements of the deviation
accuracy superior to 0.5 μrad with the deviation range greater than 500 μrad, which accords to our design requirements.
Recent successful demonstrations of laser communications have demonstrated the feasibility of some of the key aspects
of this technology. The demonstrations can not success without the full-up ground test and validation. So an integrate
test-bed was build in build to test the technical parameters and to verify the working performance for the optical
pointing, acquisition and tracking (PAT) of various inter-satellite lasercom terminals.
In this paper, we detail the test technical scheme (TTS) and the corresponding experiments. The integrate test-bed is a
high quality optical system that will measure the key characteristics of lasercom terminals, such as point error, tracking
error, acquisition possibility etc.. The test-bed can operate over the relative wavelength range.
Through quantitative tests, the terminal could be optimized base on the test results.
Two-run-times-two-frame phase shift method is reviewed and a new phase retrieval algorithm is proposed. The properties
of two phase retrieval algorithms are discussed from the point of view of Fourier analysis. Analysis shows that the two
algorithms are equivalently sensitive to phase-shifter miscalibration and irreproducibility, and the amplitude of phase
error depends on the average phase-step error. The influences of the signal harmonics on phase measurement rely on the
phase shift of the object beam. The effects of random noise on the two algorithms are generally different, but the same
only when the phase step of the reference beam is equal to Π/2.
The scanner of orthogonally tilting double prisms is researched for testing the performance of tracking performance in inter-satellite laser communications for the first time. With the reduction ratio of more than a hundred times from the change rate of deviation angle of beam to that of tilting angle of each prism, the scanner can reach the scanning accuracy of sub-microradian order but facilitates the mechanical structure design. The theoretical analysis performed, as well as the validation experiment, indicates the scanner can meet the requirements of the scanning accuracy superior to 0.5 μrad with the scanning range greater than 500 μrad.
We have proposed an improved regularized phase-tracking (RPT) technique for unwrapping two-dimensional principal phase maps. Simulated annealing (SA) algorithm is applied to RPT technique for finding the global optimum values. Further, the size of the neighborhood selected for plane approximation at each pixel is adjustable according to local noise quantity. In the area of low noise, the size of neighborhood is small to improve processing speed. On the contrary, a neighborhood with large size is selected to enhance the noise-reduced ability in the high-noisy area. Numerical simulation proves that this technique is highly robust to noise and experimental results show the feasibility of this technique.
The modulation transfer function (MTF) has been used to evaluate the image quality of the optical system. There are no papers discussing the MTF of the endoscope system. This paper discusses the image quality of the fiber endoscope system by MTF. We found that the defocus error and the discrete pixel structure of the image fiber bundle are the two main factors of influencing the system resolution. The theoretical MTF values of the fiber endoscope system at the different working distances were calculated. The highest spatial frequencies that can be distinguished by the system at the different working distances were gotten through the MTF. The theoretical results were compared with the system resolutions that were measured experimentally. We found that the agreement between theory and experiment was excellent. Finally, we suggest that the system resolutions are determined by different factors in different cases.
The fiber-endoscope has been widely used in medicine. The image fiber bundle usually has pixels from several thousands to tens of thousand. Because of the non-transparent wall cladding of individual fibers, the images putout by the image fiber bundle present honeycomb pattern (noise). It will influence the image visual effect, so it is very important to find methods to remove these honeycomb noise and improve the image quality. In this paper, three methods were used to process the fiber-endoscopic images for removing the honeycomb noise. First, low-pass spatial filtering mask was used to process the image. Secondly, the image special frequency was gotten by Fourier transform, and the honeycomb pattern frequency is separated from the image message. It's possible to remove these honeycomb pattern frequency without degrading the image quality. Finally, the linear interpolation method was used to process the image. We compared the processing results of these methods. These methods can be used in real color images as well as gray level images.