Optical data encryption using time-dependent dynamics of refractive index changes in LiNbO_3

Esa Jaatinen,Daniel Sando

doi:10.1364/oe.21.019510

Abstract

We present a method for optical encryption of information, based on the time-dependent dynamics of writing and erasure of refractive index changes in a bulk lithium niobate medium. Information is written into the photorefractive crystal with a spatially amplitude-modulated laser beam which when overexposed significantly degrades the stored data making it unrecognizable. We show that the degradation can be reversed and that a one-to-one relationship exists between the degradation and recovery rates. It is shown that this simple relationship can be used to determine the erasure time required for decrypting the scrambled index patterns. In addition, this method could be used as a straightforward general technique for determining characteristic writing and erasure rates in photorefractive media.

Highlights

The photorefractive (PR) effect is a nonlinear optical phenomenon whereby the refractive index of a medium is modified by exposure to light of the appropriate wavelength and intensity
We present a method for optical encryption of information, based on the time-dependent dynamics of writing and erasure of refractive index changes in a bulk lithium niobate medium
Information is written into the photorefractive crystal with a spatially amplitude-modulated laser beam which when overexposed significantly degrades the stored data making it unrecognizable

Summary

Introduction

The photorefractive (PR) effect is a nonlinear optical phenomenon whereby the refractive index of a medium is modified by exposure to light of the appropriate wavelength and intensity. The PR effect in inorganic crystals has been employed for applications in data storage (holographic [1] or otherwise [2, 3]), photorefractive solitons [4,5,6], and optically-induced waveguides [7, 8] In such applications, a laser beam with a specific intensity distribution is used to induce the desired refractive index changes in the medium. For PR inorganic crystals (e.g. lithium niobate – LiNbO3, barium titanate – BaTiO3), the refractive index changes induced in these media can be erased and rewritten This property enables a level of functionality that is important for random access memories and lightcontrolling-light devices.

Experiment and analysis methods

Results and discussion

Conclusion