Mitsuru Toishi

High-brightness single photon source from a quantum dot in a directional-emission nanocavity

We analyze a single photon source consisting of an InAs quantum dot coupled to a directional-emission photonic crystal (PC) cavity implemented in GaAs. On resonance, the dots lifetime is reduced by more than 10 times, to 45 ps. Compared to the standard three-hole defect cavity, the perturbed PC cavity design improves the collection efficiency into an objective lens (NA = 0.75) by factor 4.5, and improves the coupling efficiency of the collected light into a single mode fiber by factor 1.9. The emission frequency is determined by the cavity mode, which is antibunched to g((2))(0) = 0.05. The cavity design also enables efficient coupling to a higher-order cavity mode for local optical excitation of cavity-coupled quantum dots.

Improvement in Temperature Tolerance of Holographic Data Storage Using Wavelength Tunable Laser

In this paper, we report a new method of increasing the temperature tolerance of holographic recording media using a wavelength tunable laser. Of all holographic media, photopolymer media are particularly sensitive to temperature, thus some methods are required to maintain a low bit-error ratio (BER) as temperature changes. We demonstrate here how to maintain a high signal-to-noise ratio (SNR) as temperature changes using a wavelength tunable blue external cavity laser diode (ECLD) currently under development. For comparison, we analyze the temperature tolerance by a angle-tuning method and a wavelength-tuning method. We have focused that a hybrid of wavelength-tuning and angle-tuning method, we can read out the full of the image at 60°C, which is +30°C above the recording temperature. Moreover, we propose a recording method that allows the wavelength to be adjusted to the temperature changes. By adjusting the wavelength linearly to the temperature changes during recording, we can read out the holograms recorded at different temperatures using the wavelength corresponding to the readout temperature.

Littrow-type external-cavity blue laser for holographic data storage

An external-cavity laser with a wavelength of 405 nm and an output of 80 mW has been developed for holographic data storage. The laser has three states: the first is a perfect single mode, whose coherent length is 14 m; the second is a three-mode state with a coherent length of 3 mm; and the third is a six-mode state with a coherent length of 0.3 mm. The first and second states are available for angular-multiplexing recording; all states are available for coaxial multiplexing recording. Due to its short wavelength, the recording density is higher than that of a 532 nm laser.

Two-dimensional simulation of holographic data storage medium for multiplexed recording

In this paper, we propose a new analysis model for photopolymer recording processes that calculate the two-dimensional refractive index distribution of multiplexed holograms. For the simulation of the photopolymer medium, time evolution of monomer diffusion and polymerization need to be calculated simultaneously. The distribution of the refractive index inside the medium is induced by these processes. By evaluating the refractive index pattern on each layer, the diffraction beams from the multiplexed hologram can be read out by beam propagation method (BPM). This is the first paper to determine the diffraction beam from a multiplexed hologram in a simulated photopolymer medium process. We analyze the time response of the multiplexed hologram recording processes in the photopolymer, and estimate the degradation of diffraction efficiency with multiplexed recording. This work can greatly contribute to understanding the process of hologram recording.

Analysis of Photopolymer Media of Holographic Data Storage Using Non-local Polymerization Driven Diffusion Model

In this paper, we propose a new model taking account of polymer reaction length and a dark reaction, and we develop a simulator using the finite-difference time-domain (FDTD) method. To consider the polymer reaction length, we revise the non-local polymerization-driven diffusion (NPPD) model by considering the dark reaction and the multiple hologram process. We analyze some physical parameters of the photopolymer medium for data storage, such as the polymer reaction length, the diffusion coefficient, and the refractive indices of the binder, polymer, and monomer. We also estimate the important physical parameters of the photopolymer medium by fitting the experimental results using a least square approximation with non-linear parameters.

Novel encryption method using multi reference patterns in coaxial holographic data storage

In this paper, we propose an encryption method, in which a multi reference pattern is used in coaxial holographic data storage. The signal data patterns are multiplexed at one spot with multi reference patterns, which are the key code for secure readout. This method is easy to implement in coaxial holographic storage drives, and provides higher security against unauthorized readout and copying of the hologram disk. We experimentally demonstrate the encryption and decryption process with the proper and improper keys. Next, we analyze the degree of security provided by this method, and demonstrate a method of increasing the security further by recording more than 10 holograms at one spot. Finally, we record multiplexed holograms to reach 50 and 100 Gbit/in.2 with this encryption method, and analyze the degradation of the error rate.

Linear Reproduction of a Holographic Storage Channel using Coherent Addition of Optical DC Components

A holographic data storage channel is normally a nonlinear channel; however, it can be made linear. Using coherent addition of DC components in the reproduction process and calculating the square root of intensity, we can retrieve a linearly reproduced signal. Our simulation results revealed that a conventional equalizer works well to suppress interpixel interference so that a higher recording density can be achieved.

Tunable blue laser compensates for thermal expansion of the medium in holographic data storage

A tunable laser optical source equipped with wavelength and mode-hop monitors was developed to compensate for thermal expansion of the medium in holographic data storage. The lasers tunable range is 402-409 nm, and supplying 90 mA of laser diode current provides an output power greater than 40 mW. The aberration of output light is less than 0.05 lambdarms. The temperature range within which the laser can compensate for thermal expansion of the medium is estimated based on the tunable range, which is +/-13.5 degrees C for glass substrates and +/-17.5 degrees C for amorphous polyolefin substrates.

Experimental analysis in recording transmission and reflection holograms at the same time and location

Holographic recording media with a reflection layer are useful because they make it possible to maintain backward compatibility with CDs and DVDs, and a conventional servo system is easily attachable. The incident beam is fed back to the recording layer by the reflection layer, so there are four beam pairs to record the transmission and reflection holograms. We analyze the basic property of the transmission and reflection holograms and evaluate the problem when the transmission and reflection holograms are recorded at the same time. It is shown that the shrinkage in the photopolymer medium has a different effect on each hologram, so the readout image from the two holograms is misaligned. Those diffraction beams make the interference pattern, and the signal-to-noise ratio (SNR) of the output image decreased. Taking into account the difference in wavelength selectivity between the transmission and the reflection holograms, we propose a way to select one hologram to get the diffraction beam and eliminate the interference pattern using the tuning readout wavelength. By using this method, we can eliminate the diffraction beam from the reflection hologram and keep a high SNR.

Photopolymer Media Simulator for Holographic Data Storage using FDTD Method and Non-Local Polymerization Driven Diffusion Model

We simulated the holographic data storage process using a photopolymer medium taking account of the polymerization and diffusion of the monomer. We used the FDTD method to construct our simulation, which adopts a new model which includes consideration of the polymer chain length and dark reaction. We analyze the dependency of physical mameters of the photopolymer medium, such as polymer chain length and diffusion coefficient, on holographic recording. We also estimate critical physical parameters of the photopolymer medium by fitting with expimental results. 1. Introduction Holographic data storage (HDS) has application to high density archival data storage and next generation consumer optical storage (I). Recent advances of HDS are supported by the progrss of photopolymer materials 121. We should consider monomer diffision and the process of polymerizing a holographic medium which has three stages, namely, initiation, propagation, and termhation and also the, so the temporal behavior of hologram recording is relatively complicated. To simulate the holographic recording process, various simulation methods taking account of monomer diffi~sion and polymmization have been proposed (2, 31. In this paper we propose a new model to simulate the holographc recordmg of a photopolymer and construct the simulator using the fink-difference time-domain (FDTD) method. We analyze difiaction efficiency as a function of the polymer chain length, the diffusion coefficient, and the difference between the refractive indices of monomer and polymer. We also estimate various physical parameters of the photopolymer medium by fitting the theoretical model to the experimental data. 2. Numerid model of the photopolymer simulator We adopt the non-local polymerization driven diffusion model (3,4) as the polymerization model, and revise this model by consi-g he dark rwcLion and kmhaion process LLner the beam illurnhalion. The 1-~enuioml non-local diffision equation considering the dark reactim is written as n(q,t,) = Cp@p(%,t,)+Cm@m(%,t,)~~~# 3 (6)