Rodrigo Henao

Noise-free recovery of optodigital encrypted and multiplexed images.

We present a method that allows storing multiple encrypted data using digital holography and a joint transform correlator architecture with a controllable angle reference wave. In this method, the information is multiplexed by using a key and a different reference wave angle for each object. In the recovering process, the use of different reference wave angles prevents noise produced by the nonrecovered objects from being superimposed on the recovered object; moreover, the position of the recovered object in the exit plane can be fully controlled. We present the theoretical analysis and the experimental results that show the potential and applicability of the method.

Digital speckle pattern shearing interferometry using diffraction gratings

A digital speckle pattern shearing interferometer with the aid of a diffraction grating as shearing element, is presented. A brief theoretical approach for qualitative purposes is outlined. A comparison with Michelson shearing and phase stepping measurements are presented to show the validity of the proposal. Real time visualization, compactness of the setup and good quality fringes are main advantages.

Fully digital encryption technique

We propose an alternative fully digital encryption technique based on using the Fourier transform of the original object to be processed and a speckled reference wave as encryption mask. Once encrypted, the Fourier transform spectrum of the object is holographically stored. The original-data recovering is performed by digital reconstruction using the same encryption mask, which is also holographically stored. Quality of reconstructed data is evaluated as a function of the sensed encrypted data. Computer simulations and experimental results are presented to demonstrate the method.

Lateral shift multiplexing with a modified random mask in a joint transform correlator encrypting architecture

The joint transform correlator JTC is a classical optical ar- chitecture, recently associated with interesting applications in optical se- curity. In addition, multiplexing is a tactic associated with optical encrypt- ing mechanisms that provide security for multiple users. However, experimental constraints arise when we intend to reproduce a diffuser shifting multiplexing option. This is due to the invariance to lateral shifts under a JTC setup. To overcome this problem, we propose a setup modi- fication that allows its use under a multiplexing approach. Instead of placing the encrypting mask in contact with the input JTC plane, we use the actual optical Fourier transform of a diffuser projected over the en- trance plane of the JTC. We present a theoretical explanation, along with computer simulations and experimental results, that support our proposal.

Phase stepping in Lau interferometry

The implementation of phase shifting interferometry to analyze the Lau interferometric fringe patterns is proposed. The fundamentals of this application are theoretically discussed and the basis of the phase map interpretation is outlined. The three steps algorithm is used to depict the phase maps of lens-like test objects and an application for measuring focal lengths of lenses is reported. Experimental results are presented.

Measuring velocity of speckle fields with digital speckle pattern interferometry

Abstract We investigate a digital method for detecting the velocity of a diffusing object. The technique is based on Digital Speckle Pattern Interferometry (DSPI). A set of reference fringes is generated externally through the reference beam in a digital interferometer. As the object moves, subsequent frames are acquired and subtracted according to the normal DSPI procedure and stored. By means of the theory of first order speckle statistics applied to speckle intensity correlation, we relate the visibility variations in the reference fringes with the object velocity. Thus, by measuring the fringe visibility variation in the resulting DSPI stored frames the mean object velocity can be obtained. The theoretical results are experimentally verified.

Three-dimensional speckle measurements with a diffraction grating.

A method to measure three-dimensional displacements through a speckle technique is proposed. This measurement is possible by adding a diffraction grating to the classical bidimensional Burch experimental setup. The principle is described and results are discussed.

The Talbot array illuminator: imaging properties and a new interpretation

The paper presents a new interpretation of the Talbot array illuminator (TAIL). According to our description the TAIL is equivalent to a sum of mutually shifted lenses modified by generalized pupil functions. The interpretation underlines the imaging abilities of TAILs and makes it possible to characterize an imaging process in a way based on the theory of the thin lens. The paper analyses the impulse response and the transfer functions corresponding to the image formation in spatially coherent and incoherent cases of illumination. Additionally we discuss the resolution of images created by the TAIL. The obtained theoretical results are verified experimentally.

DIGITAL POLARIZATION-ENCODING TECHNIQUE FOR OPTICAL LOGIC OPERATIONS

We implement optical logic operations, using a polarization-encoding architecture based on digital speckle pattern interferometry (DSPI). The method is based on the intensity dependence of DSPI on the rotation of the polarization direction in the paths of the interferometer between acquisition of frames. The 16 two-input logic operations can be achieved and stored in a host computer. This scheme also offers the possibility of creating dynamic logic gates.

Equilateral hyperbolic moiré zone plates with variable focus obtained by rotations.

We present equilateral hyperbolic zone plates with variable focal length, which are formed as moiré patterns by a mutual rotation of two identical basic grids. Among others, all principal zone plates, except of the spherical one, can be used as these basic transmittances. Three most important advantages of the proposed moiré zone plates are: a constant aperture of the created element during the mutual movement of basic grids, lack of aberrations due to their undesired mutual lateral displacements and high diffraction efficiency of the binary phase version. To obtain clearer moiré fringe pattern, a radial carrier frequency can be added additionally to the transmittances of basic grids. The destructive interference between both arms of the focal cross of the equilateral hyperbolic moiré zone plate can be obtained by a constant phase shift introduced in the transmittances of the basic grids. Potential applications of discussed elements are indicated, including the most promising one in the three-point alignment technique.