Roger Chiu-Zarate

Secure Computer Communication Based on Chaotic Rössler Oscillators

We describe a communication scheme based on chaotic Rossler oscillators for transmission of secure messages via computers. The computers are synchronized through one of the channels via one of the variables of the Rossler sys- tem, while an information signal is transmitted through another channel by adding the message to another system variable. This scheme provides more stable communication because the information signal does not enter to the receiver and hence does not cause an error in synchronization. The method is tested with different types of information signals: audio, text, and image.

The Ronchi test using a liquid crystal display as a phase grating

The Ronchi test with a Liquid Crystal Display (LCD) phase grating is used for testing convergent optical systems. The rulings are computer-generated and displayed on the LCD. We prove that it is possible to make a variable electronically phase grating by using an LCD. By displaying various phase-shifted rulings and capturing the corresponding ronchigrams, the phase is obtained with the conventional phase-shifting algorithms. Experimental results are shown.

Discretization of quasi-sinusoidal diffraction gratings printed on acetates

The aim of this work is to propose the use of printed acetate sheets as quasi-sinusoidal diffraction gratings, as low-cost alternative gratings for application in non-invasive optical tests. Gratings were generated with Matlab® software and made with various models of laser printers. A study of the discretization effects that depend on the symmetry in the sample was included, gratings were placed in the entrance pupil of a positive lens (illuminated by a collimated plane wave) to observe their Fourier transforms. It was found that diffraction patterns of various types of semi-sinusoidal profiles were very close to that of sinusoidal gratings. Gradual change in the size of printed ink spots was observed in more detail through a magnification of 40x. Additionally, an atomic force microscope was used to measure the roughness average of the impressions as to observe the behavior of the ink on the acetate.

Composed filter for attenuating bi-frequential noise on LCD-generated ronchigrams

This work aims to design a filter to attenuate high- and medium- frequency noise in optical test images without changing the edges and original characteristics of the test image, generated by traditional filters (spatial or frequential). The noise produced by the LCD pixels (used as a diffraction grating in the Ronchi test) was analyzed. The diffraction is modulated by the spherical wavefront of the mirror under test, generating at least two frequency band noise levels. To reduce this bi-frequential noise, we propose to use an array of filters with the following structure: a low-pass frequential filter LPFF, a band- pass frequential filter BPFF and a circular mask spatial filter CMSF; thus obtaining the composed filter CF=LPFF-(BPFF)(CMSF). Various sizes of filters were used to compare their signal-to-noise ratio against simple filters (low-pass and band-stop).

Image Processing for Optical Metrology

Optical measurements offer the desirable characteristics of being noninvasive and nondestructive techniques that are able to analyze in real time objects and phenomena in a remote sense. Science areas that involve optical characterization include physics, biology, chemistry and varied fields of engineering. The use of digital cameras to record objects or a specific phenomenon permits the exploitation of the potential of that the associated images can be processed to determine one or several parameter or characteristics of what is being recorded. These images need to be processed and securely there will be a model associated with the optical metrology that will provide an insight or a comprehensive understanding of the image being analyzed. Matlab® is the suitable platform to implement image processing algorithms due to its ability to perform the whole processing techniques and procedures to analyze and image. At the same time it provides a flexible and a fast programming language for user constructing algorithms. In the present chapter we provide some fundamentals about image acquisition, filtering and processing, and some applications. Some applications are well-know techniques while others offer the state of the art in the field under study. All authors agree that Matlab® is a powerful tool for image processing and optical metrology. All algorithms and/or sentences used in this chapter are made in such manner so that they work in the Matlab® R2007b platform or superior. Matlab® is a trade mark of Mathworks Inc., from here on we will refer it as Matlab only. Also the Matlab functions and parameters used along the chapter are typed in italics and in apostrophes, respectively. Algorithms in present chapter are presented in two formats depending on the algorithm extension: 1) Image titles and/or figure captions for low algorithms extension; 2) Subsection ends for larger algorithms.

Comparison between quasi-sinusoidal and quasi-triangular profiles for diffraction gratings printed on acetates

The aim of this work is to propose the use of printed acetate sheets as quasi-sinusoidal and quasi-triangular diffraction gratings, as low-cost alternative gratings for application in non-invasive optical tests. Gratings were generated with Matlab® software and made with various models of laser and inkjet printers. A study of the profile gratings that depend on the symmetry in the sample was included, gratings were placed in the entrance pupil of a positive lens (illuminated by a collimated plane wave) to observe their Fourier transforms. It was found that diffraction patterns of various types of quasi-sinusoidal and quasi-triangular profiles were very close to that of sinusoidal gratings. Gradual change in the size of printed ink spots was observed in more detail through a magnification of 40x. Additionally, an atomic force microscope was used to measure the average superficial roughness of the impressions as to observe the behavior of the ink on the acetate.