Homodyne detection of holographic memory systems

The spatially coupled low-density parity-check (SC-LDPC) was considered for holographic data storage. The superiority of SC-LDPC was studied by simulation. The simulations show that the performance of SC-LDPC depends on the lifting number, and when the lifting number is over 100, SC-LDPC shows better error correctability compared with irregular LDPC. SC-LDPC is applied to the 5:9 modulation code, which is one of the differential codes. The error-free point is near 2.8 dB and over 10−1 can be corrected in simulation. From these simulation results, this error correction code can be applied to actual holographic data storage test equipment. Results showed that 8 × 10−2 can be corrected, furthermore it works effectively and shows good error correctability.

Section: Correctability Of Spatially Coupled Ldpcmentioning

confidence: 99%

Spatially coupled low-density parity-check error correction for holographic data storage

Ishii¹,

Katano²,

Muroi³

et al. 2017

“…11,[28][29][30] Multiphase levels, for example, 0, π=2, π, and 3π=2, are used for recording and they are retrieved by being interfered by the local oscillator and diffraction beams. 29,30) The interpixel crosstalk cancellation technique based on the phase difference cannot be applied to multiphase level recording because the phase level difference itself is used for encoding.…”

Section: Compatibility With Other High-density Recording Methodsmentioning

confidence: 99%

Interpixel crosstalk cancellation on holographic memory

Ishii

Fujimura

2017

In holographic memory systems, there have been no practical techniques to minimize interpixel crosstalk thus far. We developed an interpixel crosstalk cancellation technique using a checkerboard phase pattern with a phase difference of π/2, which can decrease the size of the spatial filter along the Fourier plane with the signal-to-noise ratio (SNR) kept high. This interpixel crosstalk cancellation technique is simple because it requires only one phase plate in the signal beam path. We verified the effect of such a cancellation technique by simulation. The improvement of SNR is maximized to 6.5 dB when the filter size specified in the Nyquist areal ratio is approximately 1.05 in ideal optical systems with no other fixed noise. The proposed technique can improve SNR by 0.85 in an assumed monocular architecture at an actual noise intensity. This improvement of SNR is very useful for realizing high-density recording or enhancing system robustness.

“…Therefore, the phase information of the reproduced beam is detected by homodyne detection, in which the oscillator beam interferes with the reproduced beam, and performance is further improved via the signal amplification effect. [23][24][25] Then, when the oscillator beam is defined as The intensity I is expressed as follows:…”

Section: Signal Degradation In Wddmentioning

confidence: 99%

Wavelength diversity detection for phase-modulation holographic data storage system

Nakamura

Fujimura

2020

The wavelength diversity detection (WDD) method for a holographic data storage system (HDSS) actively utilizes scattering from the media to suppress speckle noise with a finite bandwidth light source. In this study, we analytically and numerically revealed signal degradation in the case of a phase-modulation HDSS under WDD in practical conditions, e.g. recording medium position shift; and we proposed an oscillator page recording method to suppress such degradation. Using phase modulation, an oscillator beam must retrieve the recorded phase from interference between the oscillator beam and the reproduced signal beam. The proposed method also records the oscillator beam as a hologram, and simultaneously reproduces the two beams. Simulation results indicate that the proposed method can compensate the degradation and drastically improve the signal-to-noise ratio from 6.5 to 39.1 dB at the largest possible media shift. Therefore, we confirmed feasibility to utilize WDD in PSK under the practical condition.