Showing papers by "Ignacio Moreno published in 2018"

Polarimetric imaging of biological tissues based on the indices of polarimetric purity.

Abstract: We highlight the interest of using the indices of polarimetric purity (IPPs) to the inspection of biological tissues. The IPPs were recently proposed in the literature and they result in a further synthetization of the depolarizing properties of samples. Compared with standard polarimetric images of biological samples, IPP-based images lead to larger image contrast of some biological structures and to a further physical interpretation of the depolarizing mechanisms inherent to the samples. In addition, unlike other methods, their calculation do not require advanced algebraic operations (as is the case of polar decompositions), and they result in 3 indicators of easy implementation. We also propose a pseudo-colored encoding of the IPP information that leads to an improved visualization of samples. This last technique opens the possibility of tailored adjustment of tissues contrast by using customized pseudo-colored images. The potential of the IPP approach is experimentally highlighted along the manuscript by studying 3 different ex-vivo samples. A significant image contrast enhancement is obtained by using the IPP-based methods, compared to standard polarimetric images.

Random technique to encode complex valued holograms with on axis reconstruction onto phase-only displays.

Abstract: A new technique for encoding the amplitude and phase of diffracted fields in digital holography is proposed. It is based on a random spatial multiplexing of two phase-only diffractive patterns. The first one is the phase information of the intended pattern, while the second one is a diverging optical element whose purpose is the control of the amplitude. A random number determines the choice between these two diffractive patterns at each pixel, and the amplitude information of the desired field governs its discrimination threshold. This proposed technique is computationally fast and does not require iterative methods, and the complex field reconstruction appears on axis. We experimentally demonstrate this new encoding technique with holograms implemented onto a flicker-free phase-only spatial light modulator (SLM), which allows the axial generation of such holograms. The experimental verification includes the phase measurement of generated patterns with a phase-shifting polarization interferometer implemented in the same experimental setup.

Achromatic linear retarder with tunable retardance

Abstract: We present a universal design and proof-of-concept of a tunable linear retarder of uniform wavelength response in a broad spectral range. It consists of two half-wave retarders (HWR) between two quarter-wave retarders (QWRs), where the uniform retardance can be tuned continuously by simply rotating one of the HWRs. A proof-of-concept of this design is built by using commercially available Fresnel rhomb retarders that provide retardation with almost wavelength uniformity in the visible and near infrared from 450 to 1550 nm. The design is universal, since other achromatic QWRs and HWRs could also be employed. The system is experimentally demonstrated to control the state of polarization of a supercontinuum laser.

Spectral performance of a zero-order liquid-crystal polymer commercial q-plate for the generation of vector beams at different wavelengths

Abstract: Liquid-crystal polymer q-plates are commercial devices for generating vector beams at the design wavelength where the device exhibits half-wave (HW) retardance. Since they are not voltage addressable, the operational wavelength remains fixed. In this work we perform a broadband spectral characterization of the q-plate retardance as a function of wavelength, ϕ(λ), and identify the wavelengths with retardance values relevant for vector beam generation (π, π/2, and 3π/2). The wavelength is then used as a tuning parameter to change the device performance from a HW q-plate to a positive-QW or a negative-QW q-plate. These performances are analyzed using the Jones matrix formalism. We present a simple procedure to derive the polarization distribution of the vector beams expected at these QW wavelengths, as a superposition of the input polarization state and the output state of a HW q-plate. Experimental results using the red and blue lines of an Ar-Kr laser and an IR laser diode of 980 nm confirm the theoretical predictions. We show that for input linearly polarized light of 980 nm and 488 nm the device generates hybrid vector beams (where the ellipticity varies with the azimuthal angle), while for 647 nm pure radial vector beams with constant ellipticity are obtained. These results could extend the use of commercial q-plates for multicolour vector beam applications.

Programmable Zoom Lens System with Two Spatial Light Modulators: Limits Imposed by the Spatial Resolution

Abstract: In this work we present an experimental proof of concept of a programmable optical zoom lens system with no moving parts that can form images with both positive and negative magnifications. Our system uses two programmable liquid crystal spatial light modulators to form the lenses composing the zoom system. The results included show that images can be formed with both positive and negative magnifications. Experimental results match the theory. We discuss the size limitations of this system caused by the limited spatial resolution and discuss how newer devices would shrink the size of the system.

Q-plates with a nonlinear azimuthal distribution of the principal axis: application to encoding binary data

Abstract: We encode q-plates where the angular orientation of the principal axis is varied spatially with a nonstandard distribution. In the usual q-plate design, the orientation of the optical axis depends linearly on the azimuthal angle. In this work, we examine cases where this azimuthal dependence is nonlinear. We consider two cases: first, where the principal axis distribution is like an inverse-tangent function of the azimuth; and second, where it displays linear and flat segments. This last case is proposed as a new method for encoding binary data into the azimuthal lobes of the vector beam. We encode these patterns using a spatial light modulator system that allows new and exotic q-plate designs without the difficulty of fabricating individual plates. Experimental results are presented.

Extending the use of commercial Q-plates for the generation of high-order and hybrid vector beams

Abstract: Commercial non-tunable q-plates have become popular optical elements to generate vector beams at the design wavelength where the device exhibits half-wave (HW) retardance. However, their use is restricted since both the topological charge and the operating wavelength are set in fabrication. In this work, we report how to make such commercial q-plates more versatile for generating vector beams of higher topological charge and in different wavelength ranges. First, we show how to add, subtract or change the sign of the charge, by combining q-plates with HW plates. Second, we perform a broadband spectral characterization of the q-plate retardance, and identify the wavelengths with retardance values relevant for vector beam generation π, ±π/2). The wavelength is then used as a tuning parameter to change the device performance from a HW q-plate to a QW q-plate. The vector beams expected at these QW wavelengths are obtained as a superposition of the input polarization state and the output state of a HW q-plate. Experimental results are shown using the red and blue lines of an Ar-Kr laser. For input linearly polarized light of 488 nm the device generates hybrid vector beams (where the ellipticity varies with the azimuthal angle), while for 647 nm pure radial vector beams with constant ellipticity are obtained. These results could extend the use of commercial q-plates for multicolor vector beam applications.

Indices of polarimetric purity for biological tissues inspection

Abstract: We highlight the interest of using the Indices of Polarimetric Purity (IPPs) for the biological tissue inspection. These are three polarimetric metrics focused on the study of the depolarizing behaviour of the sample. The IPPs have been recently proposed in the literature and provide different and synthetized information than the commonly used depolarizing indices, as depolarization index (PΔ) or depolarization power (Δ). Compared with the standard polarimetric images of biological samples, IPPs enhance the contrast between different tissues of the sample and show differences between similar tissues which are not observed using the other standard techniques. Moreover, they present further physical information related to the depolarization mechanisms inherent to different tissues. In addition, the algorithm does not require advanced calculations (as in the case of polar decompositions), being the indices of polarimetric purity fast and easy to implement. We also propose a pseudo-coloured image method which encodes the sample information as a function of the different indices weights. These images allow us to customize the visualization of samples and to highlight certain of their constitutive structures. The interest and potential of the IPP approach are experimentally illustrated throughout the manuscript by comparing polarimetric images of different ex-vivo samples obtained with standard polarimetric methods with those obtained from the IPPs analysis. Enhanced contrast and retrieval of new information are experimentally obtained from the different IPP based images.

Holographic projection system with programmable control of state of polarization, focus plane, and size of the reconstruction

Abstract: A holographic projection system based on the encoding of computer-generated holograms onto a spatial light modulator is discussed. We show how the size, location, and polarization state of the output can be controlled completely electronically, without physically moving any element in the system. It is finally shown that the system is capable to produce optical logical operations by superimposing two different images encoded onto orthogonal polarization states. We show how these images can be added or subtracted, giving a polarization-based logic system. Experimental results are included in all cases.

Hereditary breast and ovarian cancer in Andalusian families: a genetic population study

Abstract: The BRCA1/2 mutation profile varies in Spain according to the geographical area studied. The mutational profile of BRCA1/2 in families at risk for hereditary breast and ovarian cancer has not so far been reported in Andalusia (southern Spain). We analysed BRCA1/2 germline mutations in 562 high-risk cases with breast and/or ovarian cancer from Andalusian families from 2010 to 2015. Among the 562 cases, 120 (21.4%) carried a germline pathogenic mutation in BRCA1/2; 50 in BRCA1 (41.7%) and 70 in BRCA2 (58.3%). We detected 67 distinct mutations (29 in BRCA1 and 38 in BRCA2), of which 3 in BRCA1 (c.845C > A, c.1222_1223delAC, c.2527delA) and 5 in BRCA2 (c.293 T > G, c.5558_5559delGT, c.6034delT, c.6650_6654delAAGAT, c.6652delG) had not been previously described. The most frequent mutations in BRCA1 were c.5078_5080delCTG (10%) and c.5123C > A (10%), and in BRCA2 they were c.9018C > A (14%) and c.5720_5723delCTCT (8%). We identified 5 variants of unknown significance (VUS), all in BRCA2 (c.5836 T > C, c.6323G > T, c.9501 + 3A > T, c.8022_8030delGATAATGGA, c.10186A > C). We detected 76 polymorphisms (31 in BRCA1, 45 in BRCA2) not associated with breast cancer risk. This is the first study reporting the mutational profile of BRCA1/2 in Andalusia. We identified 21.4% of patients harbouring BRCA1/2 mutations, 58.3% of them in BRCA2. We also characterized the clinical data, mutational profile, VUS and haplotype profile.

Indices of polarimetric purity to enhance the image quality in biophotonics applications

Abstract: Recently, a set of polarimetric indicators, the Indices of Polarimetric Purity (IPPs), were described in the literature. These indicators allow synthesize depolarization content of samples, and provide further analysis of depolarizers than other existing polarimetric indicators. We demonstrate the potential of the IPPs as a criterion to characterize and classify depolarizing samples. In particular, the method is firstly analyzed through a series of basic polarization experiments, and we prove how differences in the depolarizing capability of samples, concealed from the commonly used depolarization index PΔ, are identified with the IPPs. In the second part of this work, the method is experimentally highlighted by studying a rabbit leg ex-vivo sample. The obtained images of the ex-vivo sample illustrate how IPPs provide a significant enhancement in the image contrast of some biological tissues and, in some cases, present new information hidden in the usual polarimetric channels. Moreover, new physical interpretation of the sample can be derived from the IPPs which allow us to synthesize the depolarization behavior. Finally, we also propose a pseudo-colored encoding of the IPPs information that provides an improved visualization of the samples. This last technique opens the possibility to highlight a specific tissue structure by properly adjusting the pseudo-colored formula.

The first International Day of Light in Spain

Abstract: In this work, we review the main activities related to the International Day of Light (IDL) in Spain. We describe the actions of the Spanish Committee for IDL that has been created in Spain, reactivating the Spanish Committee for the International Year of Light created in 2015. The Spanish Committee of the IDL has been very active in promoting the realization of events, and providing tools for the IDL related information dissemination, as the specific related webpage for the IDL in Spain. The Spanish Committee also was the Spanish contact with the International Secretariat of the IDL. We describe the flagship IDL event in Spain that was organized in the Faculty of Physics Sciences of Universidad Complutense de Madrid on May 16th 2018. And we report on many other activities that have been developed in different places in Spain. These activities of the IDL in Spain are intended to make the society aware of the importance of the light and the light based technologies for the progress and well-being of the humankind. They have also been oriented to attract young talent to the studies of science and engineering.

Dynamic microparticle manipulation through light structures generated by a self-calibrated Liquid Crystal on Silicon display

Abstract: This paper is devoted to investigating the application of different dynamic light structures generated by a self-calibrated Liquid Crystal on Silicon (LCoS) display for microparticle manipulation. Two major studies based on implementing different DOEs, to thoroughly characterize the LCoS display and to achieve optical-inspired particle manipulation, are proposed, respectively. On the one hand, we dynamically introduced two diffractive lens based patterns (the Billet-lens configuration and the micro-lens array pattern) on the LCoS display, from which the self-calibration of the studied device is implemented. In this case, both the phase-voltage relation and the surface profile were determined and optimized to the optimal performance for microparticle manipulation. On the other hand, we performed the optical manipulation of microparticles by addressing configurable three-dimensional light structures obtained from different phase driven split-lens configurations initiated by the same but optimized LCoS display. Experimental results demonstrated that, by addressing certain phase distributions on the LCoS display, the microparticle can be trapped in the light cones and manipulated by providing certain continuous split-lens configurations.

Polarization state vector beam spectrum analyzer using q-plates encoded onto a spatial light modulator

Abstract: Vector beams where the polarization state is spatially dependent are being examined as new optical communication channels. We demonstrate a vector beam spectrum analyzer capable of simultaneously determining the topological charge and the state of polarization of an input vector beam. We encode a two-dimensional polarization diffraction grating that generates six different q-plate channels from -3 to +3 in the horizontal direction, and each is split in the vertical direction into the six polarization channels at the cardinal points of the corresponding higher-order Poincare sphere. The horizontal q-plate grating is a optimized phase-only grating that produces harmonics of a given input q-plate having a charge of +1 all of which have equal strengths. The vertical polarization grating is specially designed to produce 6 orders where the amplitude and phase of each order can be independently controlled. Different gratings are required for the horizontal and vertical polarizations to create the desired polarization states in each diffracted order. Consequently, we generate 36 different channels in parallel. We demonstrate this polarization diffraction element using a single phase-only liquid-crystal spatial light modulator in a reflective optical architecture. Details are given regarding experimental details on this process. Finally, we demonstrate that this system can act as a vector beam polarization state spectrum analyzer allowing both the topological charge and the polarization state of the input vector beam to be simultaneously determined in a single experiment.

Self-addressed diffractive lens schemes for the characterization of LCoS displays

Abstract: We proposed a self-calibration method to calibrate both the phase-voltage look-up table and the screen phase distribution of Liquid Crystal on Silicon (LCoS) displays by implementing different lens configurations on the studied device within a same optical scheme. On the one hand, the phase-voltage relation is determined from interferometric measurements, which are obtained by addressing split-lens phase distributions on the LCoS display. On the other hand, the surface profile is retrieved by self-addressing a diffractive micro-lens array to the LCoS display, in a way that we configure a Shack-Hartmann wavefront sensor that self-determines the screen spatial variations. Moreover, both the phase-voltage response and the surface phase inhomogeneity of the LCoS are measured within the same experimental set-up, without the necessity of further adjustments. Experimental results prove the usefulness of the above-mentioned technique for LCoS displays characterization.