| With the advent of the big data era,the secure storage of massive data are facing great challenges.At present,the mainstream data storage technologies such as magnetic storage and traditional optical storage have the problems of high maintenance cost,high energy consumption and low recording density,which are difficult to meet the requirements of the big data era.Holographic data storage technology adopts three-dimensional volume storage mode,which has the advantages of high data redundancy,high recording density and high transfer rate.It is a research hotspot of new generation storage technology.This paper introduces the development of holographic data storage technology,analyzes the limitations,low code rate and low signal-to-noise ratio(SNR),of traditional amplitude-modulated holographic data storage.In contrast,phase-modulated holographic data storage has obvious advantages in improving coding rate and SNR with its rich phase modulation,and it has broad research prospects.Therefore,the phase-modulated holographic data storage is studied in this paper.There is a problem that the phase information cannot be obtained by the detector directly,so we can solve this problem by interferometric method or non-interferometric method.However,interferometry is easily affected by the external influence and usually needs multiple operations,and its reading results are unstable.Thus,the system of non-interferometric method with simpler,compact and stable is used for phase retrieval.In this paper,a dynamic sampling method for the single Fourier spectrum taken by the detector is proposed to improve the efficiency of non-interferometric phase retrieval.In the Fourier spectrum,the low frequency component and high frequency component respectively own energy information with high intensity and detail information with low intensity.In the first few iterations,low frequency component is dominant.So,we keep relatively low frequency component of Fourier spectrum at the beginning of iteration,and then gradually released more high frequency component at the subsequent iterations.In simulation and experiments,it is proved that the dynamic sampling method can provide a better convergence path for phase retrieval,to shorten the iterative number by 1 times and reduce the phase error rate to some extent.The combination of dynamic sampling method and frequency expanded method is proposed,the efficient phase retrieval can be realized by using only 1 time Nyquist spectrum.It is determined that the SNR is the highest when the expanded Fourier spectrum from 1 times Nyquist frequency to 4 times Nyquist frequency.Then the new expanded spectrum is dynamically sampled to speed up the phase retrieval rate.This scheme can reduce the area of the required recording spectrum by 4 times,and can better retrieve the phase by only half the number of iterations of the traditional method.The phase data error rate was reduced from 6.84% to 1.95%,which improves the efficiency of phase retrieval.Therefore,the scheme can achieve higher storage density and more efficient phase retrieval of phase-modulated holographic data storage system.Its significance is to prove the possibility of integration of multiple approaches on the Fourier plane. |
