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Journal of the Optical Society of America A

Journal of the Optical Society of America A


  • Editor: Stephen A. Burns
  • Vol. 26, Iss. 9 — Sep. 1, 2009
  • pp: 2033–2042

Statistical investigation of the double random phase encoding technique

David S. Monaghan, Unnikrishnan Gopinathan, Guohai Situ, Thomas J. Naughton, and John T. Sheridan  »View Author Affiliations

JOSA A, Vol. 26, Issue 9, pp. 2033-2042 (2009)

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The amplitude-encoding case of the double random phase encoding technique is examined by defining a cost function as a metric to compare an attempted decryption against the corresponding original input image. For the case when a cipher–text pair has been obtained and the correct decryption key is unknown, an iterative attack technique can be employed to ascertain the key. During such an attack the noise in the output field for an attempted decryption can be used as a measure of a possible decryption key’s correctness. For relatively small systems, i.e., systems involving fewer than 5 × 5   pixels , the output decryption of every possible key can be examined to evaluate the distribution of the keys in key space in relation to their relative performance when carrying out decryption. However, in order to do this for large systems, checking every single key is currently impractical. One metric used to quantify the correctness of a decryption key is the normalized root mean squared (NRMS) error. The NRMS is a measure of the cumulative intensity difference between the input and decrypted images. We identify a core term in the NRMS, which we refer to as the difference parameter, d. Expressions for the expected value (or mean) and variance of d are derived in terms of the mean and variance of the output field noise, which is shown to be circular Gaussian. These expressions assume a large sample set (number of pixels and keys). We show that as we increase the number of samples used, the decryption error obeys the statistically predicted characteristic values. Finally, we corroborate previously reported simulations in the literature by using the statistically derived expressions.

© 2009 Optical Society of America

OCIS Codes
(030.6600) Coherence and statistical optics : Statistical optics
(070.2580) Fourier optics and signal processing : Paraxial wave optics
(100.2000) Image processing : Digital image processing
(200.4740) Optics in computing : Optical processing

ToC Category:
Optics in Computing

Original Manuscript: February 27, 2009
Revised Manuscript: July 3, 2009
Manuscript Accepted: July 26, 2009
Published: August 24, 2009

David S. Monaghan, Unnikrishnan Gopinathan, Guohai Situ, Thomas J. Naughton, and John T. Sheridan, "Statistical investigation of the double random phase encoding technique," J. Opt. Soc. Am. A 26, 2033-2042 (2009)

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