Phase-encoded multi-valued signal has advantages of the simultaneous increase of storage density and data transfer rate. However, to acquire the phase information, it is usually required that the diffracted image interferes with another plane wave because the imaging device cannot obtain the phase information directly. Such an additional process leads to complication of the optical system, and lowering the transfer rate due to the plurality of detection.
To address this issue, we proposed a simple method of extracting phase-encoded signal by one image acquisition without using any other plane wave. This method utilizes inter-pixel crosstalk to retrieve the recorded phase. In the holographic data storage system, the rectangular aperture is usually inserted in the Fourier plane of the input image in order to limit the exposure area of the recording medium. Since this aperture is also acting as a low-pass filter, transmitted image is blurred and inter-pixel crosstalk occurs. At the boundary of pixels, the light waves of adjacent pixels interfere with each other, and its resultant intensity is determined by the relative phase between adjacent pixels. Therefore, if the known-phase pixels are properly arranged in the input image, we can determine the unknown phase from the intensity at the boundary.
In order to estimate the reconstruction ability of our proposed method, we have numerically investigated the pixel error rate of 4-level phase encoded signal as a function of aperture size and detecting area at the boundary. We also confirmed the validity of our proposed method experimentally.
Ryushi Fujimura, Yuki Kunii, and Tsutomu Shimura, "Single-shot signal detection in phase-encoded holographic data storage (Conference Presentation)," Proc. SPIE 10943, Ultra-High-Definition Imaging Systems II, 1094304 (Presented at SPIE OPTO: February 02, 2019; Published: 4 March 2019); https://doi.org/10.1117/12.2515392.6009915555001.
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