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

Spatial light modulators (SLM) are currently used in many applications in optical microscopy and imaging. One of the most promising methods is the use of liquid crystal displays (LCD) as programmable phase diffractive optical elements (DOE) placed in the Fourier plane giving access to the spatial frequencies which can be phased shifted individually, allowing to emulate a wealth of contrast enhancing methods for both amplitude and phase samples. We use phase and polarization modulation of LCD to implement an on-axis microscope optical system. The LCD used are Hamamatsu liquid crystal on silicon (LCOS) SLM free of flicker, thus showing a full profit of the SLM space bandwidth, as opposed to optical systems in the literature forced to work off-axis due to the strong zero-order component. Taking benefits of the phase modulation of the LCOS we have implemented different microscopic imaging operations, such as high-pass and low-pass filtering in parallel using programmable blazed gratings. Moreover, we are able to control polarization modulation to display two orthogonal linear state of polarization images than can be subtracted or added by changing the period of the blazed grating. In that sense, Differential Interference Contrast (DIC) microscopy can be easily done by generating two images exploiting the polarization splitting properties when a blazed grating is displayed in the SLM. Biological microscopy samples are also used.

On-axis programmable microscope using liquid crystal spatial light modulator

https://www.uv.es/gpoei/articulos/(2000)_OC_183_Graphical_representation_of_non-absorbing_polariza.pdf

Graphical representation of non-absorbing polarization devices

This work presents a complete polarimetric study of a twisted-nematic (TN) liquid–crystal (LC) cell. We review the physical models that describe the cell and analyze the different modulation regimes. We extend the usual Jones matrix approach, where these microscopic physical models were developed, to the corresponding Mueller matrix approach. This polarimetric analysis is then used to obtain the effective linear and circular retardance components of the cell and to characterize its physical parameters like the twist angle, the orientation of the LC director axis and the maximum retardance. The technique simplifies previous approaches with the advantage of employing a single wavelength. Noteworthy, it also resolves the ambiguities in the determination of the physical parameters. Experimental evidence of the effectiveness in predicting the optical modulation is shown for a single-pixel TN-LC cell. Finally, a simplified procedure is presented under the assumption that the TN-LC cell is a pure retarder component, which is useful to perform a rapid calibration of the device. 

Mueller matrix polarimetric analysis applied to characterize the physical parameters of a twisted-nematic liquid–crystal modulator

A polarimeter architecture is presented based on a birefringent grating displayed onto a parallel-aligned liquid crystal (LC) on silicon display (PAL-LCoS). The system is compact and flexible, since the size of the image can be adjusted by means of the period of the grating. The LCoS grating permits simultaneously measuring two orthogonal states of polarization (SOPs). By adding a wave plate, different couples of orthogonal SOPs can be detected. First, a basic proof of concept is presented using one quarter-wave and one half-wave plate with fixed retardances, which permit measuring the six SOPs classically used in polarimetry (linear states at 0°, 45°, 90°, and 135°, and R and L circular states). Next, the system is made fully programmable by incorporating a variable LC retarder (LCR). The LCR orientation and retardance values are optimized by means of the condition number indicator, in order to provide equivalent optimal accuracy. Experimental results of calibration images and test images are presented, showing the potentials of this architecture.

http://tecnopto.edu.umh.es/wp-content/uploads/sites/605/2014/05/ao-53-25-5585.pdf

Ignacio Moreno

Papers

On-axis programmable microscope using liquid crystal spatial light modulator

Graphical representation of non-absorbing polarization devices

Mueller matrix polarimetric analysis applied to characterize the physical parameters of a twisted-nematic liquid–crystal modulator

Flexible polarimeter architecture based on a birefringent grating

Cirugia de las complicaciones mecanicas del infarto agudo de miocardio