Abstract:In this paper, we present a study of observation of phase error of a volume holographic storage disc during the reading process when the disc is rotated or displaced in the theoretical calculation and the corresponding experiment. This additional phase error will dramatically decrease the bit error rate of a phase-only signal, even applying double-frequency shearing interferometry to retrieve the stored phase signal. Then we propose a novel approach to solve the problem. The stored signal is pre-processed by p… Show more
“…As illustrated in Fig. 1 b, we derive the irradiance (I) on the CMOS image sensor 53 , 57 where Δz is the distance between the front Fourier plane and DFG, θ is the bending angle between the optical axis of the Lens 1 and the Lens 2, θ 1 and θ 2 are the first-order diffracted lights, ξ and η are the coordinates in the image-sensor plane, f 1 and f 2 are the focal lengths of lens 1 and lens 2, respectively; Δϕ 0 is the initial phase difference between the two diffracted waves induced by the phase relation of the two gratings, Δϕ x is the relative phase shift induced by the DFG displacement (Δx) along the x-axis, and can be expressed as, where λ is the wavelength. Figure 1 (a) The light path for the DFGSI, (b) the geometry, (c) the simulation of the interferogram by the two diffracted lights on the CMOS image sensor, and (d) the corresponding experimental observation.…”
Section: Principlementioning
confidence: 99%
“…Figure 3 shows the simulations of the readout signals upon displacement of the disc (Δu). The displacement of the disc induces a slow-varying phase error across the signal plane 57 . The slow-varying phase error can be alleviated through the inherent characteristics of the shearing interferometry.…”
Section: Characteristicsmentioning
confidence: 99%
“…The simulation is based on the same condition as stated in the previous section, and it is used to examine whether the proposed pre-integral-DFGSI-PSI is a superior interferometer in 2D phase retrieval 57 . In the following, PSI means that a general 4-step phase-shifting algorithm is applied.…”
Section: Simulation and Experimentsmentioning
confidence: 99%
“…Thus, if phase errors occur at a certain location, the phase error will accrue at all pixels along the shearing direction, along with the post integral. By contrast, a pre-integral approach aimed at compensating for these two shortcomings has been proposed and demonstrated in a holographic data storage system 57 . This paper proposes and demonstrates a novel and powerful DFGSI with several unique advantages: (1) the self-reference shearing interferometer is robust in dynamic circumstances; (2) the shearing interferometer eliminates slow-varying phase errors; (3) the utilization of a built-in phase-shifting function combined can retrieve multi-level phase signals; (4) the pre-integral signal processing makes the DFGSI free from error accumulation and is more robust to retrieve multi-level phase signals.…”
In this paper, we propose and demonstrate a novel interferometer and signal process to retrieve two-dimensional signals with multilevel phases. The interferometer is based on a shearing interferometry with double-frequency grating, and phase-shifting interferometry is derived as a built-in function of the lateral displacement of the grating. The interferometer not only retrieves the multilevel phase signals but also eliminates slow-varying phase errors wherever they occur. Owing to the common path algorithm, the new interferometer is more robust in dynamic circumstances for optical testing and data processing. We propose a pre-integral signal process for two-dimensional (2D) data processing to prevent post-phase-integral due to shearing interferometry. The simulation and experiment showed that the proposed interferometer with a pre-integral process has various advantages in signal processing for multilevel phase retrieval, and will be useful for higher data rates in optical data storage and free-space communication.
“…As illustrated in Fig. 1 b, we derive the irradiance (I) on the CMOS image sensor 53 , 57 where Δz is the distance between the front Fourier plane and DFG, θ is the bending angle between the optical axis of the Lens 1 and the Lens 2, θ 1 and θ 2 are the first-order diffracted lights, ξ and η are the coordinates in the image-sensor plane, f 1 and f 2 are the focal lengths of lens 1 and lens 2, respectively; Δϕ 0 is the initial phase difference between the two diffracted waves induced by the phase relation of the two gratings, Δϕ x is the relative phase shift induced by the DFG displacement (Δx) along the x-axis, and can be expressed as, where λ is the wavelength. Figure 1 (a) The light path for the DFGSI, (b) the geometry, (c) the simulation of the interferogram by the two diffracted lights on the CMOS image sensor, and (d) the corresponding experimental observation.…”
Section: Principlementioning
confidence: 99%
“…Figure 3 shows the simulations of the readout signals upon displacement of the disc (Δu). The displacement of the disc induces a slow-varying phase error across the signal plane 57 . The slow-varying phase error can be alleviated through the inherent characteristics of the shearing interferometry.…”
Section: Characteristicsmentioning
confidence: 99%
“…The simulation is based on the same condition as stated in the previous section, and it is used to examine whether the proposed pre-integral-DFGSI-PSI is a superior interferometer in 2D phase retrieval 57 . In the following, PSI means that a general 4-step phase-shifting algorithm is applied.…”
Section: Simulation and Experimentsmentioning
confidence: 99%
“…Thus, if phase errors occur at a certain location, the phase error will accrue at all pixels along the shearing direction, along with the post integral. By contrast, a pre-integral approach aimed at compensating for these two shortcomings has been proposed and demonstrated in a holographic data storage system 57 . This paper proposes and demonstrates a novel and powerful DFGSI with several unique advantages: (1) the self-reference shearing interferometer is robust in dynamic circumstances; (2) the shearing interferometer eliminates slow-varying phase errors; (3) the utilization of a built-in phase-shifting function combined can retrieve multi-level phase signals; (4) the pre-integral signal processing makes the DFGSI free from error accumulation and is more robust to retrieve multi-level phase signals.…”
In this paper, we propose and demonstrate a novel interferometer and signal process to retrieve two-dimensional signals with multilevel phases. The interferometer is based on a shearing interferometry with double-frequency grating, and phase-shifting interferometry is derived as a built-in function of the lateral displacement of the grating. The interferometer not only retrieves the multilevel phase signals but also eliminates slow-varying phase errors wherever they occur. Owing to the common path algorithm, the new interferometer is more robust in dynamic circumstances for optical testing and data processing. We propose a pre-integral signal process for two-dimensional (2D) data processing to prevent post-phase-integral due to shearing interferometry. The simulation and experiment showed that the proposed interferometer with a pre-integral process has various advantages in signal processing for multilevel phase retrieval, and will be useful for higher data rates in optical data storage and free-space communication.
“…Volume holographic recording is a type of three-dimensional storage technology [ 1 , 2 , 3 ]. Compared to traditional two-dimensional storage, such as magnetic storage [ 4 ], optical storage [ 5 ] and semiconductor storage [ 6 ], holographic storage exhibits the excellent properties of a high transmission rate, high storage density and simultaneous reading/writing ability [ 7 , 8 ].…”
The dark diffusion enhancement process (DDEP) caused by photopolymerization during the pre-exposure of TI/PMMA (titanocene dispersed methyl methacrylate matrix) polymers was theoretically analyzed and experimentally investigated, revealing the holographic grating enhancement of TI/PMMA polymers in the post-exposure process without additional operations. The diffusion of photo-initiators and photoproducts dominated the grating enhancement process after exposure. We adopted two pre-exposure methods, long-time (second level) and short-time (millisecond level) laser exposure, at 532 nm, to investigate the DDEP during the post-exposure process. A five-fold enhancement in grating strength was achieved in consecutive long-time pre-exposures, while a two-fold grating development was examined after short-time exposure. Additionally, the exposure durations and repetition rates influenced the grating increment of the DDEP. This study provided a basis for the feasibility of holographic application in TI/PMMA photopolymers via the dark diffusion effect.
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