A test system including light path system and software system is built for measuring the refractive index of fiber by using the digital holographic tomography technology. Based on the phase distribution curve of object wave the optimal hologram is recorded. The spectral range corresponding to the object wave is selected accurately based on the optimization of the spectrum. The phase distribution information of object wave is extracted with the angular spectrum reconstraction. The accuracy of extracted phase information has been verified through the simulation holograms of optical fiber. Combined with the multilayers model of fiber, the refractive index distribution along the diameter direction of fiber tomogram is recovered from a single hologram. Single-mode and multi-mode optical fiber are tested as samples. The experiment results are consistent with the results of S14 refractive index profiler, the precision is 10-4. The compare result shows that our method is simple, fast and accurate for the measurement of the refractive index of fibers. We have also studied the measurement of the refractive index distribution of the special optical fiber.
A new array processing system that performs high-resolution imaging in turbulent ocean media is introduced. It exploits information contained in higher-order spatial spectra and images to a resolution which is limited by the array aperture rather than the medium. Precise a priori knowledge of the turbulence’s spatial coherence structure is not needed. Furthermore, the signal processing is straightforward to implement, the system is self-calibrating, and the computational demands are reasonable. Initial tests of the imager have been conducted and several representative examples are presented. It is found that precise bispectrum estimates are required for good image quality. Since this requires large data sets, in essence this algorithm trades data requirements for resolution. In addition, the direction of arrival information, contained in phase terms that are processed with the bispectrum, is lost in the averaging process. Nevertheless, the system provides very good quality images, even in severe environments.
Hartmann-Shack method is widely used in adaptive optics system for wavefront sensing.A data processing system i employed in the sensor for computing wavefront gradient,wavefront reconstruction and control.To get a wide control bandwidth,the system should reach the processing needs in real time.In this paper,a parallel processing architecture called pipeling multiple SIMD(PMSIMD) architecture is presented.In the system,image acqusltion,wavefront gradient computation(WFGC) and wavefront reconstruction computation(WFRC) are conducted in pipeline,at the same time,the SIMD architecture is employed in both of the WFGC and WFRC.The computer simulation experiment shows the system based on the PMSIMD architecture is capable of processing video images of l2SXl28 pixels at 1000 frames per second and the time delay is less than 1/4 of frame period.
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