María del Mar Sánchez-López

Jones matrix method for predicting and optimizing the optical modulation properties of a liquid-crystal display

We present a simple technique for the calibration, prediction, and optimization of the optical modulation properties of a liquid-crystal display (LCD). The method is useful when there is no information about the internal fabrication parameters of the device (the orientation of liquid-crystal molecules, the twist angle, or the birefringence of the material). A complete determination of the LCD Jones matrix is accomplished by means of seven irradiance measurements for a single wavelength. This technique only requires two linear polarizers and one quarter-wave plate. Once the Jones matrix has been calibrated, the amplitude, phase, and polarization modulation response can be predicted. Therefore, it can be optimized through the control of the polarization configuration. The validity of the proposed method is experimentally probed. Finally, we present a particular application to produce phase-only modulation.

Interference birefringent filters fabricated with low cost commercial polymers

We discuss a simple method for fabricating interference birefringent filters using common cellophane tape layers. Cellophane tape layers can be superimposed with different orientations to generate different spectral responses. We demonstrate this behavior with a portable spectrophotometer. This technique is a simple and inexpensive way of investigating the optical properties of birefringent filters.

Analysis of a segmented q-plate tunable retarder for the generation of first-order vector beams.

In this work we study a prototype q-plate segmented tunable liquid crystal retarder device. It shows a large modulation range (5π rad for a wavelength of 633 nm and near 2π for 1550 nm) and a large clear aperture of one inch diameter. We analyze the operation of the q-plate in terms of Jones matrices and provide different matrix decompositions useful for its analysis, including the polarization transformations, the effect of the tunable phase shift, and the effect of quantization levels (the device is segmented in 12 angular sectors). We also show a very simple and robust optical system capable of generating all polarization states on the first-order Poincaré sphere. An optical polarization rotator and a linear retarder are used in a geometry that allows the generation of all states in the zero-order Poincaré sphere simply by tuning two retardance parameters. We then use this system with the q-plate device to directly map an input arbitrary state of polarization to a corresponding first-order vectorial beam. This optical system would be more practical for high speed and programmable generation of vector beams than other systems reported so far. Experimental results are presented.

Nondiffracting Bessel beams with polarization state that varies with propagation distance.

We generate nondiffracting Bessel beams whose polarization state varies with propagation distance. We use a reflective geometry where a single parallel-aligned spatial light modulator device is used to spatially modulate two orthogonal linear polarizations with two axicon phase profiles. Then, by adding an extra phase retardation radial profile between these linear states, we are able to modulate the state of polarization along the line focus of the axicon. We provide experimental results that demonstrate the polarization axial control with zero-order and higher order Bessel beams.

Generation of integer and fractional vector beams with q-plates encoded onto a spatial light modulator.

We generate programmable vector beams with arbitrary q-plates encoded using a spatial light modulator system. Consequently, we can analyze new and exotic q-plate designs without the difficulty of fabricating individual plates. We show experimental results for positive and negative integer and new fractional vector beam values.

Performance of a q-plate tunable retarder in reflection for the switchable generation of both first- and second-order vector beams

We examine the performance of a tunable liquid crystal q-plate in a reflective geometry. When the device is tuned to a half-wave retardance, it operates as a q-plate with twice the value (2q) by adding a quarter-wave retarder between the mirror and the q-plate. However, when the device is tuned to a quarter-wave retardance, it acts as the original q-plate without the retarder. Experimental results are shown. Using an input tunable polarization state generator, the system allows the switchable production of all states on both the first- and second-order Poincaré spheres.

Generation of Bessel beam arrays through Dammann gratings

In this work we apply the Dammann grating concept to generate an equal-intensity square array of Bessel quasi-free diffraction beams that diverge from a common center. We generate a binary phase mask that combines the axicon phase with the phase of a Dammann grating. The procedure can be extended to include vortex spiral phases that generate an array of optical pipes. Experimental results are provided by means of a twisted nematic liquid crystal display operating as a binary π phase spatial light modulator.

Nondiffracting vector beams where the charge and the polarization state vary with propagation distance.

We generate nondiffracting vector beams where the charge and the polarization state vary with the propagation distance. We use reflective geometry where a parallel-aligned spatial light modulator is used to spatially modulate two orthogonal linear polarizations. We encode spiral phases with equal charge but with opposite signs onto the two polarization directions to encode a vector beam and add two axicon phases. Both the charge and the phase shift between the two axicons can be varied along the focus line. We provide experimental results that demonstrate both features.

Ray matrix analysis of anamorphic fractional Fourier systems

In this work we extend the application of the ray matrix approach to analyse anamorphic fractional Fourier systems, i.e., fractional Fourier optical systems where the fractional power is different for two orthogonal directions. The application of the ray matrix approach allows for easily obtaining the properties of the optical system, and it is therefore a powerful tool to design and simplify complicated systems. For simplicity we consider fractional Fourier systems with real orders and systems without apertures. We start by presenting the analysis of some previously reported anamorphic Fourier and fractional Fourier systems, and we end by proposing a simple optical system with tunable anamorphic fractional orders that can be varied continuously without changing the input and output planes.

Coaxial cable analogs of multilayer dielectric optical coatings

We study the properties of periodic coaxial cable structures (coaxial photonic crystals), where the periodicity consists of alternating cables with low and high impedance. We show that the electrical signal that propagates through these structures leads to similar phenomena as the light propagating through the corresponding multilayer dielectric optical coating structures. In this way, Bragg reflectors, optical thin-film filters, and Fabry–Perot resonators are reproduced in the megahertz frequency range. This represents an inexpensive way of experimentally investigating wave propagation in locally periodic media.