Photorefractive Time-Domain Differential Detection Method for High-Precision Distinction of Phase-Modulated Signals in Holographic Data Storage

We develop a photorefractive time-domain differential detection (PR-TDDD) method in holographic data storage systems with considering the temporal response of photorefractive two-wave mixing (PR-TWM). Optimizing the parameters of PR-TDDD method provides high-precision distinction of phase-modulated signals, i.e. distinction of small phase difference. In PR-TDDD method, the phase information can be sequentially-distinguished by monitoring the output intensity of PR-TWM. This is because the output intensity of PR-TWM is changed when the signal phase is changed. In addition, the changing rate of the output intensity corresponds to that of the signal phase. The advantages of our method are high energy efficiency, alignment-free optics and the distinction of multi-valued phase-modulated signals. Especially, we focus attention on applying to phase-based holographic data storage systems, which can achieve homogeneous intensity distribution on recording plane, i.e. Fourier transform plane, in general, and high energy efficiency because of 100% white rate. More noteworthy is that multi-valued phase-based holographic data storage can be realized by using PR-TDDD method. In this work, we consider the important parameters in PR-TDDD method; signal-to-pump beam intensity ratio, photorefractive coupling strength, and photorefractive time constant. The balance between these parameters is important for realizing the high-precision distinction of phase-modulated signal.