二值编码相位掩模交替迭代优化的无干涉非相干全息术

Interferenceless Incoherent Holography Optimized by Alternate Iteration of Binary Coded Phase Mask

提出基于交替策略的随机轨迹直接二进制搜索法。数值仿真结果表明,该方法有效抑制了迭代过程中直流偏置的增加并提高迭代速度。实验结果证明,在同样的迭代次数下,该方法显著降低了重建图像的相关重建噪声。该方法推动了无干涉编码孔径相关全息术(I-COACH)系统在可见光范围外成像的应用。

Objective Interferenceless coded aperture correlation holography(I-COACH)employs incoherent illumination,distinct from other coherent holography techniques.In I-COACH,phase information is redundant,and only the intensity pattern of the three-dimensional observation scene is required to recover object information.Owing to its interference-free nature,it offers the advantages of a simpler optical path and more convenient processing,transmission,and storage of data.This has led to the development of an even more simplified,lensless I-COACH(LI-COACH)system.Utilizing a coded phase mask(CPM),the object intensity is encoded into a specific speckle pattern.The object’s speckle hologram and the corresponding point spread hologram(PSH)are used for object reconstruction through cross-correlation,but this reconstruction method is associated with considerable background noise.I-COACH system based on binary coded phase mask significantly reduces reconstruction noise while expanding the imaging spectral range.In this approach,the peak-tobackground ratio of the PSH is enhanced using a direct binary search method to reduce the system’s reconstruction noise.However,this method increases the bias value of the PSH during the iteration process,leading to unstable iteration effects,and the use of dictionary order scanning results in slower iteration speeds.This paper proposes a direct binary search method based on an alternate strategy with random trajectories.Numerical simulations demonstrate that this method effectively suppresses the increase in the bias value during the iteration process and enhances the iteration speed.Experimental results confirm that,with the same number of iterations,this method significantly reduces the correlation reconstruction noise.This method advances the application of the I-COACH system in imaging beyond the visible light range,offering broad application prospects in fields such as astronomy and the military.Methods Our design is based on the principle of DBSA and employs a variant known as binary search with random trajectory(DBSRT)to alternately iterate two binary coded phase masks(bCPMs).Initially,two independent CPMs are generated using the Gerchberg-Saxton(G-S)algorithm,which are then binarized to serve as the initial values for the DBSA.The peak-to-background ratio(PBR)is used as an indirect metric to evaluate the reconstruction effect of the PSH,and the DBSRT is utilized to optimize the PBR of the PSH to reduce reconstruction noise.To ensure the bias value is a constant during the iteration process,the improved DBSA selects bCPM1 for iteration when the number of iterations is odd,and bCPM2 when it is even.To further increase the iteration speed,a random unscanned pixel on the bCPM is selected,and its phase is inverted.The PSH and its PBR of the altered bCPMs are calculated in the meantime.If the PBR increases,the change is retained;otherwise,it is reverted to its original state.This process is continued until convergence is reached or a threshold is met.Finally,the iterated bCPMs are used as the random phase masks in the I-COACH system.Results and Discussions In the experiment,Element 2 of Group 1 from the USAF1951 resolution test chart is chosen as the target.Significant changes are observed in the PSH and object intensity response generated by both the initial bCPMs and those optimized using DBSA(Fig.8).The experimental data is synthesized into PSH and object holograms,followed by reconstruction using POF.This method demonstrates a substantial improvement in imaging quality compared to the original method(Fig.8).The images reconstructed from the initial bCPMs and the original DBSA-optimized bCPMs have PSNRs of 15.6 dB and 17.5 dB respectively,while the image from the bCPMs optimized by our method has a PSNR of 19.5 dB,indicating a better reconstruction effect.However,the reconstruction of the target object from bCPMs optimized by DBSA for only bCPM1 yielded a PSNR of 9.6 dB.This shows that sequential iteration by DBSA needs to complete iterations of both bCPM1 and bCPM2 to effectively reduce reconstruction noise.This is attributed to the variation in the bias value of the PSH when only one of the bCPMs is iterated,with the bias value being a contributing factor to noise in the reconstructed light field of the I-COACH system.Conclusions We propose an alternating strategy for iteratively optimizing bCPMs,which offers improved stability and increased speed in iterations.Through theoretical analysis and numerical simulations,it has been demonstrated that changes in the bias value during DBSA iterations are one of the crucial factors affecting the optimization results.Iterating with an alternating strategy effectively constrains the bias value of the PSH and employing random trajectory scanning significantly enhances the iteration speed of DBSA.This method has notably improved the stability and speed of DBSA.Experimental results show that this approach further enhances the system’s reconstruction performance with the same number of iterations.The alternating strategy in DBSRT effectively reduces the number of iterations required by DBSA,thereby improving the reconstruction quality of the system.This provides a straightforward and effective method for fast,high-quality reconstruction in I-COACH systems based on bCPM.