Novel phase detection method for a holographic data storage system using two interferograms

Data page phase modulation is attracting interest as an alternative to amplitude modulation in holographic data storage for a homogenized Fourier spectrum. The problem with phase modulation is in the reconstruction of the pure phase information. This paper proposes a simple yet effective phase detection method for a phase-modulated holographic data storage system. An extra detection beam is introduced to interfere with the reconstructed signal beam at the CCD plane for phase detection. To eliminate the stationary noise and beam non-uniformity in the holographic data storage system, a new algorithm using two interferograms is proposed to obtain clear detection results. This detection method is suitable for a holographic data storage system because the detection beam does not penetrate the recording medium and therefore does not limit storage capacity compared with other detection methods. Simulation and experimental results are presented to confirm this method.