Study On Phase Encoding And Decoding In Phasemodulated Holographic Data Storage

With the development of information technology,the amount of data is generating in the exploding way.The demand for data storage density and data transfer rate has increased dramatically.The traditional data storage technology has been difficult to meet the needs of data growth,and a new generation storage technology needs to be developed.As a threedimensional volume storage technology,holographic storage technology is considered as a powerful contender for the new generation of storage technology due to its high theoretical storage density and ultra-fast data transfer rate.This dissertation proposes a more efficient phase-modulated holographic storage technology to overcome the shortcomings of low signal-noise-ratio(SNR)and low code rate in the current amplitude-modulated holographic storage technology.The dissertation proceeds to theoretical and applied researches from the aspects of phase encoding and phase decoding.In the phase encoding part,the role of phase modulation is investigated firstly.On the one hand,an effective phase modulation range is proposed.In this range,phase modulation uniforms recording central intensity in the material and improves the SNR.On the other hand,it proposes to use phase modulation of adjacent positions of signal to reduce inter-crosstalk in the shifting multiplexing.Secondly,the phase encoding method of the code pair is proposed,solving the problem of phase confusion and making it possible to read the phase accurately with a single interference,which increases the data transfer rate.In the phase decoding part,a new non-interferometric phase retrieval method is proposed.Compared with the traditional interferometric method,the non-interfering system is simpler,more compact and stable.The non-interferometric phase retrieval method can reduce the requirement for the diffraction efficiency of the material,greatly increase the multiplexing number of holograms and increase the storage density.At the same time,proposed method increases the data recording speed by 14 times in the experiment.By adding embedded data to the encoding,the convergence speed of the phase retrieval is greatly increased,from the hundreds of iterations originally required to about 10 iterations.All parameters related to non-interferometric phase retrieval are calculated and analyzed,and the relationship between each parameter and phase retrieval is established.After adding noise,the most appropriate parameter values under the experimental conditions are got.In the experiment,we successfully used the 4-order phase to encode,record,read,and noninterfere-decode the real data.The non-interferometric phase retrieval method is optimized.The combination of interference and non-interference is proposed where the partial correct phase of the interferometric decoding is used to replace the required embedded data.In this way,the code rate is nearly doubled.A super-resolution scheme for non-interferometric phase retrieval using only one Nyquist spectrum is proposed,which can reduce the area of the required recording spectrum in the material by at least 4 times,reduce the material consumption by35%,and increase the storage density by 1.5 times at least.In summary,this article mainly has three major innovations.First,a phase encoding scheme for code pair is proposed to achieve a single-interference accurate phase readout which can increase the data transfer rate.Secondly,a non-interferometric phase retrieval method is proposed,and a stable and practical phase-modulated holographic storage system is established.The code rate and storage density are increased by about 4 times,and the data recording speed is greatly increased.Third,a non-interferometric phase retrieval scheme with only one Nyquist spectrum recording is proposed,which can increase the storage density by at least 1.5 times.