空间光调制器的应用

DOI 10.1007/s11141-015-9547-8

Radiophysics and Quantum Electronics,Vol.57,Nos.8–9,January,2015

(Russian Original Vol.57,Nos.8–9,August–September,2014)

APPLICATION OF THE PHASE LIGHT MODULATOR IN THE IMAGE OPTICAL ENCRYPTION SCHEME WITH SPATIALLY INCOHERENT ILLUMINATION

A.P.Bondareva,N.N.Evtikhiev,V.V.Krasnov,∗

and S.N.Starikov UDC004.932.4+004.942

+535.42+535.8

We describe application of the phase liquid-crystal spatial light modulator HoloEyePLUTOVIS

as an encoding element in the image optical encryption scheme with spatially incoherent illumi-

nation.Optical encryption and numerical decryption of test images were conducted.The results

of experiments demonstrate the efficiency of the constructed optical encryption scheme.

1.INTRODUCTION

Currently,we are witnessing the existence and intense development of the optical encryption meth-ods characterized by a high speed,simultaneous multichannel processing,and the absence of concomitant radiation in the radio-frequency band.Encryption systems in spatially coherent monochromatic light are widespread.One of the best-known systems uses the double random-phase encryption[1–5].In this case, encryption is performed in monochromatic spatially coherent light using two random phase masks.Appli-cation of random phase masks as two-dimensional encoding keys leads to the fact that such systems have a high cryptographic strength.However,because of the need to record phase,such systems require holo-graphic methods of recording and,correspondingly,complex optical schemes.Moreover,the use of random phase masks leads to a poor-quality encryption of images.

To simplify the encryption schemes and improve the decryption quality,one can pass from spatially coherent to spatially incoherent radiation.In this case,recording of the encrypted image is no longer required and the holographic recording scheme becomes unnecessary.The encryption is performed by transmission of monochromatic spatially incoherent radiation from the encrypted object through a diffractive optical element,resulting in the formation of an intensity distribution described by the object image convolution with a point spread function,namely,an impulse response of the diffractive optical element in intensity[6, 7].This intensity distribution is the encrypted image recorded by a matrix photosensor.

The fundamental possibility of optical encryption in incoherent light was demonstrated in[8],but using a random phase mask as the encoding diffractive optical element precluded the achievement of an acceptable decryption quality.This is because the point spread function of a random phase mask is virtually unlimited in space and significantly exceeds the size of the encrypted image.As a result,the photosensor records only the central part of the encrypted image,which leads to distortions of the decrypted image.To solve this problem,we suggest that the encoding element is not used as a random phase mask,but as a diffractive optical element having a given spatially limited point spread function,with length smaller than the size of the encrypted image.

∗vitally.krasnov@mail.ru

National Nuclear Research University(NNRU),Moscow,Russia.Translated from Izvestiya Vysshikh Ucheb-nykh Zavedenii,Radiofizika,Vol.57,No.8–9,pp.693–701,August–September2014.Original article submitted November11,2013;accepted March31,2014.

0033-8443/15/5708-0619c 2015Springer Science+Business Media New York619