Owing to the requirement of high resolution of imaging system, such as the infrared imaging system, the imaging laser radar, the compressive sensing is used in the imaging system with low resolution sensors to obtain high quality image information. In this paper, compressive sensing is applied in an imaging system. A random phase mask is placed on the lens of the optical system. The optical wave propagation process of light field from the object plane to the lens, then to the image plane is analyzed and theoretical formula of the propagation with the form of the Fourier transform expression is deduced, thus the reconstruction speed is high by using the fast Fourier transform. The orthogonal wavelet transform and the orthogonal matching pursuit algorithm are employed in the reconstruction. The simulation results prove the good performance of the reconstruction quality and speed.
Diffractive optical elements (DOEs) can realize beam shaping with higher light efficiency, strong flexibility of diffraction pattern, and is suitable to be used in optical interconnections to split beams. In order to increase the intensity uniformity of the split beams, a hybrid algorithm merging Gerchberg-Saxton (GS) algorithm with gradient method is presented based on the sampling rule different from the existing optimization algorithms. By controlling N extra points with zero amplitude besides the original N sampling points on the input plane, and finally the sampling pitch on the Fourier plane is half of that of the conventional sampling rule. Then the N extra points on the Fourier plane will be controlled. Finally spot array with high intensity uniformity can be realized with the proposed algorithm. Simulation results demonstrate the good performance of the proposed algorithm.
Focusing elements are usually employed in the flow cytometry to focus the input laser beam into elliptically shaped Gaussian beam in order to increase power for excitation of fluorescence for high signal-to-noise ratio (SNR). While in order to ensure repeatable and reliable signal generation for accurate population discrimination - despite slight deviations of the cell from the flow centre, the shaped beam should be a cubic diffraction region with uniform power intensity across the cell flow stream. However, it is hard for beam shaping with refractive optical elements. In this paper, we present a beam shaping system in flow cytometry with diffractive optical elements (DOEs) to shape the input laser beam to a cubic diffraction region with uniform power intensity. The phase distribution of the DOE is obtained by using the inverse Fresnel diffraction based layered holographic stereogram, and the cubic diffraction region with uniform power intensity within the cell flow channel is well reconstructed. Simulation results demonstrate the good performance of the new beam shaping system.
Many kinds of optimization algorithm have been applied to design diffractive optical elements (DOEs) for beam shaping. However, only the selected sampling points are controlled by these optimization algorithms, the intensity distribution of other points on the output plane is always far away from the ideal distribution. In our previous research, the non-selected points were well controlled by using a hybrid algorithm merging hill-climbing with simulated annealing, but this hybrid algorithm is time-consuming. In this paper, a new hybrid algorithm merging Gerchberg-Saxton algorithm with gradient method is presented. Because of the use of iterative algorithm, the optimization time is largely reduced. The intensity distribution of the non-selected points as well as that of the selected points is well controlled, and good performance of beam shaping is obtained. Finally the experimental results demonstrate the good performance of this algorithm.
Fast optimization algorithms of the design of diffractive optical elements (DOEs) for beam shaping are often based on
fast Fourier transform (FFT), and the demand of the sampling theorem must be met when FFT is used to calculate the
light intensity. Limited by the fabricating technology, the pixel size of a DOE cannot be too small. For beam shaping in
Fresnel diffraction domain, given that the sampling interval of a DOE is fixed, if the diffraction distance is too short, all
FFT algorithms would not meet the demand of the sampling theorem, and then the results of beam shaping would
become worse. In this paper, the disadvantages of the FFT algorithms in near Fresnel diffraction domain are discussed,
and an area division method is proposed for the DOEs design. The simulation and experimental results show the validity
of the proposed area division method.