There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Wave propagation and group velocity

Emerging applications based on optical beams carrying orbital angular momentum (OAM) will probably require photonic integrated devices and circuits for miniaturization, improved performance, and enhanced functionality. We demonstrate silicon-integrated optical vortex emitters, using angular gratings to extract light confined in whispering gallery modes with high OAM into free-space beams with well-controlled amounts of OAM. The smallest device has a radius of 3.9 micrometers. Experimental characterization confirms the theoretical prediction that the emitted beams carry exactly defined and adjustable OAM. Fabrication of integrated arrays and demonstration of simultaneous emission of multiple identical optical vortices provide the potential for large-scale integration of optical vortex emitters on complementary metal-oxide–semiconductor compatible silicon chips for wide-ranging applications.

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Integrated Compact Optical Vortex Beam Emitters

Space-variant Pancharatnam-Berry phase optical elements based on computer-generated subwavelength gratings are presented. By continuously controlling the local orientation and period of the grating we can achieve any desired phase element. We present a theoretical analysis and experimentally demonstrate a Pancharatnam-Berry phase-based diffraction grating for laser radiation at a wavelength of 10.6microm.

Space-variant Pancharatnam-Berry phase optical elements with computer-generated subwavelength gratings.

Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.

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Roadmap on structured light

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.

/pdf/self-addressed-diffractive-lens-schemes-for-the-2ln9rrmhzh.pdf

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

In this paper we present the research line that we develop in pattern recognition of multichannel images, centered in the application of color images. Pattern recognition is performed through a multichannel correlation process. The correlation is applied to each channel, red, green and blue of the color image. The final recognition result is obtained by a combination of the information of the three monochromatic correlations. Two different approaches are proposed in order to improve the discrimination capability of the multichannel process. First, element-wise transformations over the multichannel images are used in order to enhance differences between channels. Then, the information in each channel is independent and the autocorrelation is enhanced with respect to the cross- correlations. The second approach involves the optimization of the matched phase-only filters used in every channel. This optimization is performed by means of a region of support. They are two complementary techniques that increase the discrimination capability and eliminate false alarms. The result is a better performance of the multichannel correlator for pattern recognition.

Multichannel pattern recognition of color images

In this work we summarize some of the work of our team in the last years, devoted to the use of spatial light modulators (SLM) in optical correlators and optical image processors. We have built an optical processor that uses two liquid crystal SLMs, one to implement the image to be processed and a second one to implement a Fourier filter. We analyzed the advantages of the use of SLMs, but also the restrictions they impose. We proposed several architectures and filters design to take profit of this SLM based optical processor.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical architectures for real-time image processing and pattern recognition

This work presents a novel optical system for polarization image processing using geometric-phase (Pancharatnam-Berry) lenses. Such lenses are half-wave plates where the orientation of the fast (slow) axis follows a quadratic relation with the radial coordinate, and they present the same focal length but opposite sign for left and right circular polarizations. Therefore, they split an input collimated beam in a converging beam and a diverging beam with opposite circular polarizations. This coaxial polarization selectivity introduces a new degree of freedom in optical processing systems and makes it interesting for imaging and filtering applications that require polarization sensitivity. Here we profit from these properties to build an optical Fourier filter system with polarization sensitivity. A telescopic system is used to have access to two real Fourier transform planes, one for each circular polarization. A second symmetric optical system is used to recombine the two beams onto a single final image. As a result, polarization sensitive optical Fourier filtering can be applied, as demonstrated with simple bandpass filters.

Dual polarization Fourier transform processor using geometric-phase lenses.

A polychromatic object recognition based on a circular decomposition preprocessing of RGB components and a multichannel matched filtering is described. Computer simulation results are provided to recognize a color target among objects of similar shape but with different color contents.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Ignacio Moreno

Papers

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

Multichannel pattern recognition of color images

Optical architectures for real-time image processing and pattern recognition

Dual polarization Fourier transform processor using geometric-phase lenses.

Whitening preprocessing of color components for pattern recognition