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.

/pdf/integrated-compact-optical-vortex-beam-emitters-1443e933nn.pdf

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.

/pdf/roadmap-on-structured-light-3r840pnxka.pdf

Roadmap on structured light

Arbitrary polarized vector beam modes are efficiently generated. We use two flicker-free liquid-crystal on silicon (LCOS) spatial light modulators (SLM) in an on-axis common path architecture. Different superpositions of vector modes are obtained with high light efficiency.

Vector modes generation using efficient on-axis system

In this contribution we present a method for the determination of the twist angle of an arbitrary twisted nematic liquid crystal spatial light modulator.

Twist-angle determination in nematic liquid-crystal spatial light modulators by polarimetric analysis

We present the application of a simple physical model to accurately predict the broadband spectral transmittance and
colorimetric properties of a twisted-nematic liquid crystal display (TNLCD). We spectroscopically calibrate the
retardance parameters to evaluate the spectrum of the light transmitted by a TNLCD sandwiched between two linear
polarizers. When the TNLCD is illuminated with a broadband light source, the full spectrum can be predicted as a
function of the addressed grey level for any arbitrary orientation of the polarizers. Experimental results confirming the
validity of the proposed systems are presented, both on the measured spectral responses as well as on the trajectories at
different chromatic diagrams. The presented results can be useful for optoelectronic systems requiring an accurate
control of the spectral characteristics of the light.

Accurate colour control by means of liquid crystal modulators

In this work we demonstrate a proof-of-concept depolarization emulator that generates customized spatial patterns of the polarization state (SoP) and degree of polarization (DoP). It is based on a pixelated LCOS-SLM addressed with a spatially time-varying retardance function. Three different cases featuring spatial control of the DoP are realized to show the potential of the method, including a spirally-shaped depolarization pattern. The polarization properties of the output light beam are verified by imaging the SLM screen onto a polarizing camera and performing Mueller matrix imaging polarimetry. We obtain the time-averaged Mueller matrix of the SLM and show that the output effective polarization state is governed by the averaged retardance, while the degree of polarization is governed by the retardance semidifference. An intuitive explanation of this performance is provided in the Poincaré sphere. The proposed technique could be useful in testing imaging polarimeters, in laser beam manipulation and in biomedical imaging, where emulating depolarization effects with controlled precision can help understand the physical mechanisms that cause depolarization.

Spatial depolarization patterns generated with dynamic retardance functions

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

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9664/96640Q/Teaching-multilayer-optical-coatings-with-coaxial-cables/10.1117/12.2207780.pdf

Ignacio Moreno

Papers

Vector modes generation using efficient on-axis system

Twist-angle determination in nematic liquid-crystal spatial light modulators by polarimetric analysis

Accurate colour control by means of liquid crystal modulators

Spatial depolarization patterns generated with dynamic retardance functions

Teaching multilayer optical coatings with coaxial cables