Showing papers by "Ignacio Moreno published in 2005"
TL;DR: In this article, a simple method for fabricating interference birefringent filters using common cellophane tape layers is discussed, which can be superimposed with different orientations to generate different spectral responses.
Abstract: 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.
44 citations
TL;DR: This work presents experimental evidence of an anamorphic and spatial frequency dependent phase modulation in commercially available twisted nematic liquid crystal spatial light modulators and presents an algorithm to correct this effect and more efficiently display a diffractive optical element.
Abstract: In this work we present experimental evidence of an anamorphic and spatial frequency dependent phase modulation in commercially available twisted nematic liquid crystal spatial light modulators. We have found that the phase modulation depth depends on the magnitude of the local spatial frequency component along the horizontal direction. Along the vertical direction the phase modulation depth does not depend on the spatial frequency. This phenomenon is related with the electronics driving the device and in no way related to liquid crystal physics. It causes a reduction of the optical efficiency of a diffractive optical element displayed onto this type of modulator. We present an algorithm to correct this effect and more efficiently display a diffractive optical element. We apply it to the particular case of a Fresnel lens. Experimental results that confirm the improvements in the efficiency of the displayed diffractive lens are presented.
36 citations
TL;DR: Experimental results for programmable polarization multiplexing of diffractive optical elements (DOEs) onto two liquid-crystal displays (LCDs) show that the DOE's and polarization angles are fully programmable.
Abstract: We show experimental results for programmable polarization multiplexing of diffractive optical elements (DOEs) onto two liquid-crystal displays (LCDs). The first LCD encodes the two multiplexed phase-only diffractive optical elements. The second LCD acts as a pixelated polarization rotator to change the polarization state for each of these two DOEs. Although the system requires precise alignment, the DOE’s and polarization angles are fully programmable.
27 citations
TL;DR: In this paper, a simple analysis of the physical meaning of the elements of the ray matrix provides a fast derivation of the conditions to obtain the optical Fourier transform, which is a complementary tool useful to simplify many aspects of Fourier optics.
Abstract: In this work we examine the use of ray-transfer matrices for teaching and for deriving some topics in a Fourier optics course, exploiting the mathematical simplicity of ray matrices compared to diffraction integrals. A simple analysis of the physical meaning of the elements of the ray matrix provides a fast derivation of the conditions to obtain the optical Fourier transform. We extend this derivation to fractional Fourier transform optical systems, and derive the order of the transform from the ray matrix. Some examples are provided to stress this point of view, both with classical and with graded index lenses. This formulation cannot replace the complete explanation of Fourier optics provided by the wave theory, but it is a complementary tool useful to simplify many aspects of Fourier optics and to relate them to geometrical optics.
13 citations
TL;DR: An analytical calculation based on the Fourier-transform method is used to study the transmission spectra of multilayer dielectric optical structures as a function of the relative widths of the layers that constitute the unit cell to provide a more intuitive understanding of the transmission spectrum.
Abstract: We use an analytical calculation based on the Fourier-transform method to study the transmission spectra of multilayer dielectric optical structures as a function of the relative widths of the layers that constitute the unit cell. We can select which harmonics of the fundamental design frequency are transmitted. The results of this Fourier-transform approach are compared with the exact transmission calculated by means of the transfer matrix method and provide a more intuitive understanding of the transmission spectrum. A simple phasor diagram is derived from this Fourier-transform analysis for this purpose. Inasmuch as it is difficult for us to perform experiments in the optical region, we fabricate rf analogs of these structures, using coaxial cables that have different impedances. Experimental results agree with theory.
7 citations
TL;DR: In this paper, the performance of nonlinear optical correlations using a joint transform correlator that operates in phase-only spatial light modulation at input joint transform plane was investigated, and phase morphological correlation and orthogonal nonlinear generalized correlation were implemented optically.
4 citations
TL;DR: In this paper, a new concept of the fabrication process for glass microlenses (external diameter ED < 1 mm, focal length a few millimeters), based on the silicon master maskless anisotropic wet etching in KOH, vacuum anodic bonding and re-flow of borosilicate glass, followed by the precise wafer-scale polishing and DRIE has been presented.
Abstract: A new concept of the fabrication process for glass microlenses (external diameter ED<1 mm, focal length a few millimeters), based on the silicon master mask-less anisotropic wet etching in KOH, vacuum anodic bonding and re-flow of borosilicate glass, followed by the precise wafer-scale polishing and DRIE has been presented. A single spherical microlens as well as an array of spherical microlenses with focal length between 44.8 and 8.6 mm and external diameter 0.35 to 0.985 mm have been repeatable manufactured.
3 citations
TL;DR: In this article, a Fourier transform of the logarithmic derivate of the refraction index profile of one-dimensional photonic crystals is used to calculate the transmittance of the photonic crystal.
Abstract: In this work, we present an analysis of harmonic frequency transmission filters based on one-dimensional photonic crystals using a Fourier transform approach. This approach relates the photonic crystal transmittance with the Fourier transform of the logarithmic derivate of their refraction index profile. We compare this Fourier approach with the exact transmission calculated by means of the transfer matrix method. We study the accuracy of different functions proposed in the literature that relate the Fourier transform of the index profile with the transmittance. This Fourier approach provides a more intuitive understanding of the transmission properties of one-dimensional photonic crystals. We experimentally demonstrate these properties by using coaxial cables of different impedances. This kind of electrical system is easier to perform experimentally and reproduces, in the radiofrequency range, the properties of one-dimensional photonic crystals.
2 citations
TL;DR: In this article, the operation of twisted and parallel aligned nematic liquid-crystal displays (LCD's) for applications in optical computing, image processing, pattern recognition and diffractive optical elements is reviewed.
Abstract: We review the operation of both twisted and parallel-aligned nematic liquid-crystal displays (LCD's) for applications in optical computing, image processing, pattern recognition and diffractive optical elements. For these applications, three spatial modulation characteristics are of interest: phase-only, amplitude-only, and combined full amplitude and phase. We review how to achieve these three operating conditions. We begin with a discussion of the Jones matrix model for the twisted-nematic LCD displays. We examine optical configurations for achieving amplitude-only modulation and polarization eigenvectors for achieving phase-only modulation. Then we review an extremely successful technique for obtaining combined full amplitude and phase modulation with a single LCD by spatially modulating the maximum phase depth. Finally we discuss new advances in achieving 2D polarization modulation.
2 citations
24 Oct 2005
TL;DR: In this article, a method to fabricate interference multilayer birefringent filters was proposed and demonstrated with the aid of a portable spectrophotometer, which represents a simple and inexpensive way of experimentally investigating the optical properties of BIFs.
Abstract: In this work we propose and demonstrate a very simple method to fabricate interference multilayer birefringent filters. We employ the birefringence properties of common cellophane. Cellophane tape layers can be very easily superimposed with different orientations in order to generate different spectral responses. We experimentally demonstrate this behaviour with the aid of a portable spectrophotometer. This technique represents a simple and inexpensive way of experimentally investigating the optical properties of birefringent filters.
1 citations
24 Oct 2005
TL;DR: In this paper, the analogies between a system of coaxial cables with periodicity in the impedance and a set of dielectric stacks with periodic index of refraction were explored, and a simple phasor analysis was used to describe the transmission properties of optical multilayers.
Abstract: We explore the analogies between a system of coaxial cables with periodicity in the impedance, and a system of dielectric stacks with periodicity in the index of refraction The latter is a photonic crystal with wave propagation control in the optical range, while the former can be regarded as a "coaxial" photonic crystal for radiofrequency control We reproduce electrical analogs of widely used thin-film optical devices, such as Bragg reflectors, Fabry-Perot resonators and harmonic transmission filters Coaxial crystals represent an inexpensive way of teaching multilayer optical coatings We show also that a simple phasor analysis provides an intuitive technique to describe the transmission properties of optical multilayers
24 Oct 2005
TL;DR: In this article, the use of a liquid crystal spatial light modulator (LC-SLM) is proposed as a useful tool to teach and experience diffraction and signal processing.
Abstract: In this work we propose the use of a liquid crystal spatial light modulator (LC-SLM) as a useful tool to teach and experience diffraction and signal processing The LC-SLM acts as a programmable pixelated diffractive mask The Fourier spectra of the image displayed in the LC-SLM is visualized through a simple free propagation diffraction experiment This optical system allows easily testing different diffractive elements and performing several signal processing experiments As a demonstration we include experimental results with diffraction gratings, computer generated holograms, diffractive lenses and axicons