Research On Real-time Partially Coherent Beam Parallel Generation Algorithms Based On GPU

The high coherent optical is susceptible to environment, which reduces the performance of the communication system. However, the latest theoretical results show that the partially coherent beams are less affected by turbulence, so the coherence of the beam is optimized. In order to generate partially coherent with different coherence width in real-time and conveniently, a partially coherent beam real-time generation method accelerated by graphic processing unit(GPU) is proposed. The main contents include five parts:Firstly, the hardware architecture, memory organization model, thread structure, software architecture and programming model of CUDA architecture GPU are analyzed.Secondly, the basic partially coherent theory is introduced from both space-time domain and space-frequency domain. The two different methods to generate partially coherent beam are introduced, one utilizes the frosted glass, and other make use of the liquid crystal(LC) spatial light modulator(SLM) device.Thirdly, the calculation of two-dimensional convolution are needed when generate a random phase map by using a SLM. It is necessary to study the parallel optimization design of the two-dimensional convolution in CUDA architecture. In order to compare the performance of GPU parallel accelerated, two algorithms are also implemented on CPU. The experimental results show that the performance of the convolution based on FFT can be improved from 30 to 45 times after GPU acceleration, and the performance of separation convolution can be improved from 12 to 24 times.Fourthly, the application of separable convolution and convolution based on FFT is analyzed. The experimental system platform is designed and the method is testified. Experimental results show that: to a spatial light modulator with a resolution of 256 × 256, the total time to generate a random phase map with a coherence width 0.15 mm, 0.9mm and 1.5mm by GPU are 0.95 ms, 2.2ms and 2.8ms. Adding up time that CPU reading and sending to liquid-crystal spatial light modulator and the response time of the liquid-crystal spatial light modulator, the real-time partially coherent beam generation frequency of our liquid-crystal partially coherent beam generation is up to 150 Hz. For generating a partially coherent laser beam with coherence width are 0.15 mm and 1.5mm respectively, the root-mean-square error are 0.021306 and 0.020883, the peak-to-valley are 0.073576 and 0.072998. So this method meets the requirements of real-time and accurately generates partially coherent beam with specific coherence length.