Wavefront Sensing Based On Mode Mode Modulation And Filter

Wavefront sensing is an art for measuring the incident wavefront aberration.It acquires the wavefront information of the incident light beam by sampling,modulating and measuring intensity information.It plays a key role in adaptive optics(AO)system and providing the real-time measurement of the incident wavfront.Compared with the optical testing,AO has much harsher requirements on wavefront sensing.Wavefront sensing is required to realizing the real-time measurement for stochastic and fast-changing wavefront in AO systems.At present,the common wavefront sensing techniques measure the incident wavefront quality by acquiring and analyzing the two-dimensional light intensity distribution information.The acquisition of the two-dimensional information depends on array detector.The array detector is a kind of device with complex manufacturing process and high production cost,particularly when the application system has high requirements for speed,bandwidth,quantum efficiency and so on.Meanwhile,the wavefront sensing methods which use array detector to acquiring light intensity distribution leads to the beam energy dispersion.The sampling of light intensity distribution generates huge data respectively.The huge data leads to the high requirements of transmission bandwidth and operational speed.So the array detector works as the detector of wavefront and has become one of the main limitation factors in the performance of wavefront sensing method.For solving this problem,the wavefront sensing based on single detector arises in response to it.Compared with the wavefront sensing method acquiring wavefront information with array detector,the method sensing wavefront realize wavefront information sampling with single detector.Single detector usually also has mature manufacture process and outstanding performance in practice.The method modulates the incident light beam with spatial light modulator,focuses and filters the modulated light beam,detects the light intensity of the focus and reconstructs the wavefront based on the light intensity.It foucus the full aperture and detects the light intensity,which makes the method work better in sensing wavefront with weak light.Presently,the research of the method is still in the theoretical stage and focuses on studying the establishment and solution of the equations between wavefront and the focus light intensity.But because of the complex relationship between them,it is hard to solve the functions established based on the relationship rapidly.Only approximate solutions or iterative solutions can be determined,which limits the application of the method severely.In order to acquire simple analytic relationship and relize wavfront reconstruction quickly,a wavefront sensing method based on mode modulation and filter is proposed.The method builds the relationship between the coefficients of the optical field modes and the light intensity of the far field.The relationship is much more explicit and easier and it realizes the fast solution of the optical field modes.Meanwhile,the action of the optical field sparse is researched and the wavefront sensing based on compressed sening is introduced.The main contents of the paper are as follows:Firstly,the function between the wavefront expansion coefficients and the the far field focus light intensity is nonlinear.Its solution is complex and difficult which limits the accuracy and speed of the wavefront reconstruction.The wavefront sensing method based on binary mode modulation filtering is proposed.The method builds the relationship between the expansion coefficients of the light field and the intensity of the far field focus.Through designing and generating the corresponding modulation function,the expansion coefficients of the light field are determined quickly.The phase which is extracted directly from the light field is the wrapped phase which is different with the incident wavefront.Therefore,the phase unwrapping and smoothing techniques are introduced to deal with the wrapped phase and improve the wavefront reconstruction accuracy.Numerical simulation and experiment are presented to and and the feasibility of the algorithom is demonstrated.The research provides a kind of wavefront reconstruction method which can reconstruct wavefront quickly and accurately.Secondly,considering that the sparsity of the real part of the optical field under the Walsh functions,the wavefront restoration based on the compressed modulation modes is carried out.The sparsity of the real part of the light field is statistically analyzed and the Walsh functions are selected based on the analysis results.The wavefront is rebuilt with the selected Walsh funcions.Numerical simulations and experiments are used to validate the feasibility of the method.The study compresses the number of the modulation mode used in the wavefront reconstruction and improves the sampling frequency.Finally,the wavefront sensing method based on compressed sensing is studied.In view of the single pixel imaging,compression sensing is introduced into the reconstruction of the light field,and the sparsity of the real part of the light field is explored and its application in the reconstruction of the optical field.The reconstruction of the real part of the optical field is transformed into the solution of the sparse coefficients.Meanwhile,the block optimization is introduced to optimize the symbol of the imaginary part of the light field.The feasibility of the method is verified by numerical simulation and experiment.The research provides a method which makes wavefront “imaging” possible.