Experimental imaging coding system using three-dimensional subjective speckle structures

Abstract

We propose, and experimentally demonstrate, an optical encoding system employing a three-dimensional subjective speckle distribution as a secure information carrier. An image mask (containing the information to be sent) is illuminated by randomly distributed light. The outgoing wavefront reaches a lens, and thus three-dimensional subjective speckle distributions are generated in the normal direction of the scattering plane. These speckle structures are sampled by registering consecutive planes along the optical axis with a complementary metal-oxide semiconductor camera. Along with the optical parameters (keys), these intensity patterns are sent through independent channels to a receiver. By replicating the original system with the keys and implementing a single-beam multiple-intensity reconstruction, we show that the message recipient needs a minimum set of speckle images to successfully recover the original information. Moreover, intercepting a partial set of speckle images with the keys may not result in a successful interception.

Single-random phase encoding architecture using a focus tunable lens

“…matches experimental results previously reported in [24,25] for the phase. Moreover, we studied the robustness of the system simulating information loss by partially occluding some of the image set composing the delocalized cyphertext.…”

“…There exists an equivalence between the speckle patterns produced by the focus tunable lens at the plane of the CCD sensor and those registered at different positions in a free-space propagation. Therefore, the resistance to brute-force attacks of this architecture is analogous to the one appearing in [24]. Otherwise, the security will be compromised, like in other conventional systems [11][12][13][14][15][16][17][18], if an intruder has access to a subset of images belonging to the cyphertext and the optical parameters sent by different transmission channels as discussed in [24,25].…”

“…They verified these architectures by numerical simulations. Lately, in Mosso et al [24], we have proposed an optical encoding system employing a three-dimensional subjective speckle distribution as a secure information carrier. In this system, the ciphertext is sampled by registering consecutive planes along the optical axis with a CMOS camera.…”

“…Our previous proposals [24,25] have been oriented towards the design of compact optical architectures capable of encrypting data through a secure process, with minimal optical components and employing delocalized recordings of encrypted information. In these works a mobile platform is used to capture diffracted intensity recordings planes of speckle patterns (delocalized ciphertexts) either in a freespace propagating architecture or with a single-lens imaging system.…”

“…This change presents three important advantages: avoids positioning errors, achieves faster acquisition times, and further reduces the size of the encryption system. In this work, condensed versions of the architectures reported in [24,25] are discussed by the introduction of a focus tunable lens. To our knowledge, this is the first discussion of such setup; furthermore, the introduction of a variable focal length requires a new iterative phase retrieval algorithm.…”