Showing papers by "Javier Garcia published in 2005"

Synthetic aperture superresolution by speckle pattern projection

Abstract: We propose a method for increasing the resolution of an aperture limited optical system by illuminating the input with a speckle pattern. The high resolution of the projected speckle pattern demodulates the high frequencies of the sample and permits its passage through the system aperture. A decoding provides the superresolved image. The speckle pattern can be generated in a simple manner in contrast with other structured light superresolution methods. The method is demonstrated in microscopy test images.

Controlled observation of a nonequilibrium Ising-Bloch transition in a nonlinear optical cavity.

Abstract: We report the controlled observation of the nonequilibrium Ising-Bloch transition in a broad area nonlinear optical cavity (a quasi-1D single longitudinal-mode photorefractive oscillator in a degenerate four-wave mixing configuration). Our experimental technique allows for the controlled injection of the domain walls. We use cavity detuning as control parameter and find that both Ising and Bloch walls can exist for the same detuning values within a certain interval of detunings; i.e., the Ising-Bloch transition is hysteretic in our case. A complex Ginzburg-Landau model is used for supporting the observations.

Spatial information transmission using orthogonal mutual coherence coding.

Abstract: We use the coherence of a light beam to encode spatial information. We apply this principle to obtain spatial superresolution in a limited aperture system. The method is based on shaping the mutual intensity function of the illumination beam in a set of orthogonal distributions, each one carrying the information for a different frequency bandpass or spatial region of the input object. The coherence coding is analogous to time multiplexing but with multiplexing time slots that are given by the coherence time of the illumination beam. Most images are static during times much longer than this coherence time, and thus the increase of resolution in our system is obtained without any noticeable cost.

Experimental research on the dynamics and steering of optical domain walls

Abstract: This paper presents experimental research on the formation, dynamics, and steering of domain walls (DWs) in a phase-sensitive nonlinear optical cavity, such as a photorefractive oscillator in a degenerate four-wave mixing configuration. A main feature of the system is its transverse one-dimensionality, which avoids curvature effects that affect DW behaviour. Two aspects are discussed, namely, the experimental observation of the nonequilibrium Ising-Bloch transition in optics, and the steering of individual DWs, either isolated or arranged in a stable linear array.

Super resolution by using tilted wave illumination

Abstract: Temporally restricted objects may be superresolved using the moving of two masks such as pinholes or gratings. The first one performs the encoding process of the input object and the second one is responsible for the decoding operation. This approach is efficient for exceeding the resolving capability beyond Abbes's limit of resolution but several problems exist in the system matching. We propose superresolution techniques based on the use of tilted wave illumination. In a first approach, the second grating used for the decoding operation is removed and substituted by a digital post-processing stage. In a second approach, the two masks are replaced by the use of a Vertical Cavity Surface Emitting Lasers (VCSEL) array. This VCSEL array provides a set of tilted waves at different angles and incoherent one to each other. By means of an interferometric recording process we ensure the transmission of several spatial frequency bands of the object's spectrum in parallel. After a reconstruction process, the resolution of any optical system can approach the natural λ/2 resolution limit. Unlike other interferometric superresolution techniques for this approach the exact reconstruction of the input object is obtained. Moreover, any desired synthetic coherent transfer function can be realized at ultra fast rates changing the electrical driving of the VCSEL array.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Método de calibración en tiempo real para moduladores de cristal líquido.

Abstract: espanolEn el siguiente trabajo se expone un metodo sencillo para calibrar, en tiempo real la transmision en intensidad de las pantallas de cristal liquido nematico. La metodologia experimental esta basada en el estudio de una imagen test obtenida a la salida del modulador. A partir del procesado de dichas imagenes, se puede conseguir, en tiempo real, una visualizacion de las curvas de la transmision en intensidad, lo que nos permitira el ajuste correcto de los parametros de control del dispositivo (brillo, contraste, gamma, etc.) para que el modulador trabaje en regimen lineal de transmision en intensidad con los niveles de gris. EnglishWe present a simple technique for real time liquid crystal panel intensity transmission calibration. The experimental method is based on studying a test image displayed on the modulator. Using those images, we can display different calibration curves. The visualization of the intensity transmission curves in real time allows to adjust the correct control parameters (brightness, contrast, gamma, etc.) that gives a linear response of the intensity transmission with the graylevels