Diffraction Focal Position and Vector Diffraction Theory for Micro Holographic Storage Systems

Cheol-Ki Min,Young-Pil Park,No-Cheol Park,Hyungbae Moon,Kyoung-Su Park,Do-Hyung Kim

doi:10.3390/app4010057

Abstract

In this study, we proposed a method to determine the optimal focal position for micro-holographic storage systems, using vector diffraction theory; the theory provides exact solutions when the numerical aperture (NA) exceeds 0.6. The best diffraction focus was determined by the position and wavelength corresponding to minimal spherical aberration. The calculated refractive index modulation, polarization illumination, and boundary conditions at the interface of different media were analyzed. From the results of our analysis, we could confirm the size of micrograting as a function of NA and wavelength, based on vector diffraction theory, compared with scalar diffraction theory which defines the micrograting by . To demonstrate our analysis, we adapted an optical alignment method using a Twyman-Green interferometer, and could obtain good agreement between analysis and experimental results.

Highlights

A micro holographic storage system (MHSS) is one of the best candidates for next-generation high density optical memories [1,2]
To calculate the electric field in the photopolymer, we introduce vector diffraction theory which accounts for polarization illumination and the boundary conditions of multi-layer system such as lens-air-photopolymer configuration [12].Vector diffraction theory approaches the limits of the validity of scalar theory used to describe the illumination; this theory provides an exact solution when the numerical aperture (NA) exceeds 0.6 [12,13,14,15]
The micrograting was modulated by 532 nm wavelength, objective lens (OL) of

Summary

Introduction

A micro holographic storage system (MHSS) is one of the best candidates for next-generation high density optical memories [1,2]. Data bits are represented by microscopic-size holograms formed by the interference of two tightly focused counter-propagating beams, with each bit consuming a small amount of the entire volume [3,4]. Each recorded hologram bit size should be reduced for high density recording To satisfy this requirement, the optical system is required to short wavelength and high numerical aperture (NA) lenses. The micrograting created in a photopolymer is commonly analyzed by two counter-propagating beams using scalar diffraction theory [1,7,8]. We propose a method to determine the optimal focal position using vector diffraction theory for MHSS;the method provides exact solutions when the NA exceeds 0.6.

Vector Diffraction Theory for Micrograting

Numerical Results for Micrograting

Experimental Section

Conclusions