دانلود رایگان مقاله انگلیسی بازپس گیری فاز بر اساس مدلاسیون کدگذاری شکافنده - وایلی 2017

Summary

A new coded splitting imaging technique is proposed to reconstruct the complex amplitude of a light field iteratively using a single-shot measurement. In this technique, a specially designed coded splitting plate is adopted to diffract the illuminating beam into multiple beams of different orders and code their wavefronts independently and differently. From the diffraction pattern array recorded on the detector plane, both the modulus and phase distributions of the illuminating beam can be reconstructed iteratively using known transmission functions of different orders of the coded splitting plate. The feasibility of the proposed technique is verified both numerically and experimentally.

Resolution

In order to estimate the resolution of the coded splitting method, the maximum (the cutoff) spatial frequency νmax of the sample that can be detected by the diffraction pattern array is calculated. The coordinate transform is described as ν = x/λL, where ν is the spatial frequency of the sample, x is the coordinate on detector plane, and L is the distance between the sample and CCD. The width of region occupied by each diffraction pattern in the detector plane is d. So, the cutoff frequency is νmax = d/2λL. This indicates that the resolution is determined by the light splitting ability of the CSP, and in some spectral regions (for example, visible light), the resolution of the coded splitting method can be close to the order of wavelength by using a CSP with small grating period. We also quantified the resolution by measuring a United State Air Force (USAF) 1951 resolution target using the experimental setupmentioned above. Further, the reconstructed image is shown in Figure 6, where we can observe that the second elements in group 4 can be distinguish, so the resolution achievable is 27.8 µm (17.95 lp mm−1). The resolution of the above experiment can be calculated using the relationship νmax = d/2λL, where d is (2672/3 × 9) µm, L is (60.193 + 289.03) mm, and λ is 0.6328 µm. Further, νmax is calculated to be 0.0181 µm−1, such that the theoretical resolution x = 1/2νmax is 27.55 µm, which is consistent with the measured resolution. As we discussed above, the achievable resolution is determined by the beam splitting ability of the CSP. In the experiment mentioned above, the generated CSP was displayed on the SLM, so its minimum grating period needs to be at least two times larger than the pixel size of the SLM to accurately realize the beam splitting function. Higher resolution can be obtained by using a SLM with smaller period size or manufacturing CSP with smaller grating period using photoetching technique.