Gouy phase effects on propagation of pure and hybrid vector beams

The robustness of the polarization spatial distribution of vector beams upon propagation is crucial for a number of applications, including optical communications and materials processing. This study has been commonly centered on Gouy phase effects on focused vector beams. In this work, we present a theoretical and experimental analysis of the Gouy phase’s effects on the propagation of pure and hybrid vector beams. Experimental results at various axial planes, before and past the focus, are obtained by using a simplified liquid-crystal spatial light modulator-based optical system that allows the easy generation of these beams. Furthermore, a new alternative optical set-up that is devoid of moving elements is demonstrated, which simplifies this study. We experimentally verify the differences between pure and hybrid vector beams upon propagation. While the first ones remain stable, hybrid vector beams show Gouy phase effects that demonstrate an optical activity where the local polarization states rotate by an angle that depends on the propagation distance. Experimental results agree with the theory

Dual polarization split lenses

We report the realization of polarization sensitive split lens configurations. While split lenses can be used to easily generate different types of controlled structured light patterns, their realization has been limited so far to scalar beams. Here we propose and experimentally demonstrate their generalization to vectorial split lenses, leading to light patterns with customized intensity and state of polarization. We demonstrate how these polarization split lenses can be experimentally implemented by means of an optical system using two liquid crystal spatial light modulators, each one phase modulating one orthogonal polarization component. As a result, we demonstrate the experimental generation of vectorial beams with different shapes generated with these dual polarization split lenses. Excellent experimental results are provided in each case. The proposed technique is a simple method to generate structured light beams with polarization diversity, with potential applications in polarimetry, customized illuminators or quantum optics

Desarrollo de sistemas difractivos avanzados para la generación de vórtices ópticos y haces de polarización estructurada

Esta Tesis Doctoral presenta en la modalidad de compendio de artículos el desarrollo de diferentes sistemas ópticos para la realización de óptica difractiva avanzada con control del estado de polarización. El primer sistema emplea un modulador espacial de luz nemático con giro (TN-SLM), que es previamente calibrado siguiendo una propuesta basada en la determinación precisa de sus parámetros físicos. Con esta calibración se pueden identificar estados elípticos de polarización para operar el dispositivo en dos regímenes de modulación pura de fase, un régimen binario y un régimen continúo basado en un perfil de fase triplicador. Los resultados permitieron generar redes de difracción, lentes difractivas y vórtices ópticos. El segundo sistema óptico desarrollado está basado en dos moduladores de cristal líquido sobre silicio (LCoS-SLM) dispuestos un montaje óptico que denominamos “en Z”. Este sistema permite controlar de forma independiente dos componentes de la polarización lineales ortogonales, y es útil para generar elementos difractivos con variación espacial de la polarización. La primera aplicación de este sistema es el desarrollo de un polarímetro completo, puntual e instantáneo, basado en redes de difracción de polarización. Estas redes de polarización se generan mediante dos redes puras de fase que se implementan en cada modulador. Su combinación crea diferentes órdenes de difracción que actúan como analizadores de la polarización. La segunda aplicación del sistema en Z es la generación de haces vectoriales y elementos de luz estructurada. Empleando lentes de multifocalización implementadas en los moduladores espaciales de luz y un analizador es posible elegir distintos patrones de focalización. Además, combinando una focalización anular con fases espirales se obtuvieron haces vectoriales. Finalmente, se ha desarrollado un tercer sistema basado en una lente de fase geométrica y láminas-q. Estos son novedosos elementos ópticos de fase geométrica que se emplearon para realizar un divisor longitudinal de polarización circular. Este sistema nos ha permitido visualizar fácilmente vórtices ópticos y haces vectoriales y determinar sus características. En conjunto, estas cuatro publicaciones constituyen un avance en la investigación en los métodos para generar o detectar haces de luz con control estructurado del estado de polarización.This Doctoral Thesis presents, in the form of a compendium of articles, the development of different optical systems for the realization of advanced diffractive optics with polarization control. The first system uses a twisted nematic spatial light modulator (TN-SLM), which is previously calibrated following a proposal based on the precise determination of its physical parameters. This calibration allows identifying elliptical polarization states that provide two pure phase modulation regimes, a binary regime and a continuous regime based on a triplicator phase profile. The results allowed to generate diffraction gratings, diffractive lenses and optical vortices. The second optical system is based on two liquid crystal in silicon spatial light modulators (LCoS-SLM) arranged in a “Z” configuration. This system allows the independent control of two orthogonal linear polarization components, and it is useful to generate diffractive elements with spatial variation of state of polarization. The first application of this system is the development of a complete, punctual and instantaneous polarimeter, based on polarization diffraction gratings. These polarization diffraction gratings are generated by the combination of two pure phase gratings implemented in each modulator. Their combination creates different diffraction orders that act as different polarization analyzers. The second application of the "Z" system is the generation of vector beams and elements of structured light. Using multifocalization lenses implemented in the spatial light modulators and an analyzer it is possible to choose different targeting patterns. In addition, by combining an annular focus with spiral phases, different vector beams were obtained. Finally, a third system was created based on a geometric phase lens and q-plates. These novel optical elements were used to create a longitudinal circular polarization split system, useful to analyze optical vortices and vector beams. In summary, these four papers constitute an advance in the field of methods for the generation or detection of light beams with structured polarization control

Programmable Supercontinuum Laser Spectrum Generator Based on a Liquid-Crystal on Silicon Spatial Light Modulator

Supercontinuum (SC) lasers combine a broadband light spectrum with the unique properties of single-mode lasers. In this work we present an optical system to spectrally filter a SC laser source using liquid-crystal on silicon (LCoS) spatial light modulators (SLM). The proposed optical system disperses the input laser and the spectrally separated components are projected onto the LCoS-SLM, where the state of polarization of each wavelength is separately modulated. Finally, recombining the modulated spectral components results in an output laser source where the spectrum can be controlled dynamically from a computer. The system incorporates two branches to independently control the visible (VIS) and the near infrared (NIR) spectral content, thus providing a SC laser source from 450 to 1,600 nm with programmable spectrum. This new ability for controlling at will the wide spectra of the SC laser sources can be extremely useful for biological imaging applications

Phase Retrieval by Designed Hadamard Complementary Coded Apertures.

Phase retrieval (PR) is a challenging problem with applications in various fields, ranging from microscopy to astronomy. Currently, novel computational imaging systems for PR exploit the modulation of the optical field through \acrfull{rcca} to recover the amplitude and phase from a distorted beam without prior knowledge, solving an ill-posed optimization problem using the conventional phaseLift algorithm. However, these conventional approaches recover the phase and amplitude by using at least 20 coded apertures, which poses a great challenge for performing real-time acquisition and estimation of varying optical fields. To overcome this issue, in this work, we design eight binary Hadamard complementary coded apertures that reduce the acquisition time and enhance the amplitude and phase recovery quality. Through simulations, we compare our approach against traditional random complementary coded aperture using peak-signal-to-noise ratio as spatial fidelity metrics; we use 23 images from the Kodak dataset, PhaseLift as the phase retrieval reconstruction algorithm, and Fresnel as a light propagator in the near field. Extensive simulations using different noise levels prove that our approach Hadamard complementary coded aperture, outperforms conventional methods random complementary coded aperture in reducing the number of masks. Moreover, experimental results using our optical test bed demonstrate that our approach recovers the phase with a significantly improved visual quality

2880984.mp4

Visualization of different d values between 0.1 mm to 1.0 mm in steps of 0.1 mm

2880986.mp4

Visualization of different orientations of analyzer between 0° to 135°