Multifunctional light beam control device by stimuli-responsive liquid crystal micro-grating structures.

There is an increasing need to control light phase with tailored precision via simple means in both fundamental science and industry. One of the best candidates to achieve this goal are electro-optical materials. In this work, a novel technique to modulate the spatial phase profile of a propagating light beam by means of liquid crystals (LC), electro-optically addressed by indium-tin oxide (ITO) grating microstructures, is proposed and experimentally demonstrated. A planar LC cell is assembled between two perpendicularly placed ITO gratings based on microstructured electrodes. By properly selecting only four voltage sources, we modulate the LC-induced phase profile such that non-diffractive Bessel beams, laser stretching, beam steering, and 2D tunable diffraction gratings are generated. In such a way, the proposed LC-tunable component performs as an all-in-one device with unprecedented characteristics and multiple functionalities. The operation voltages are very low and the aperture is large. Moreover, the device operates with a very simple voltage control scheme and it is lightweight and compact. Apart from the demonstrated functionalities, the proposed technique could open further venues of research in optical phase spatial modulation formats based on electro-optical materials.

Positive-negative tunable liquid crystal lenses based on a microstructured transmission line.

In this work, a novel technique to create positive-negative tunable liquid crystal lenses is proposed and experimentally demonstrated. This structure is based on two main elements, a transmission line acting as a voltage divider and concentric electrodes that distribute the voltage homogeneously across the active area. This proposal avoids all disadvantages of previous techniques, involving much simpler fabrication process (a single lithographic step) and voltage control (one or two sources). In addition, low voltage signals are required. Lenses with switchable positive and negative focal lengths and a simple, low voltage control are demonstrated. Moreover, by using this technique other optical devices could be engineered, e.g. axicons, Powell lenses, cylindrical lenses, Fresnel lenses, beam steerers, optical vortex generators, etc. For this reason, the proposed technique could open new venues of research in optical phase modulation based on liquid crystal materials.

Absorption, fluorescence and second harmonic generation in Cr³âº-doped BiB3O6 glasses.

Synthesis, spectral properties and photoinduced nonlinear optical effects of chromium-doped BiB3O6 glass are studied in the present paper. Absorption, excitation and time resolved luminescence spectra are presented and luminescence decay behavior is discussed. Detailed analysis of the obtained spectra (assignment of the most prominent spectral features in terms of the corresponding Cr(3+) energy levels, crystal field strength Dq, Racah parameters B and C) was performed. A weak photostimulated second harmonic generation signal was found to increase drastically due to poling by proton implantation in the investigated sample.

Second-order susceptibility spectra for δ-BiB3O6 polymer nanocomposites deposited on the chalcogenide crystals.

The optimized conditions for the enhancement of the second harmonic generation in the composites of the orthorhombic δ-BiB3O6:Pr(3+) nanoparticles embedded in polyvinyl alcohol films and deposited on the AgGaGe2Se6, AgGaGe2.7Si0.3Se8 (90 mol.% AgGaGe3Se8 - 10 mol.% AgGaSi3Se8), and AgGaGe3Se8:Cu substrates were established. The highest second-order susceptibility was achieved during the Ag-Ga-Ge-Se crystalline substrates photo-illumination by nanosecond laser pulses of about 2900 nm wavelength. The effect was found to be completely reversible after the interruption of the photo-inducing stimulation. Complementary studies of Atomic Force Microscopy, AFM, X-ray Diffraction, XRD, and Fourier-Transform Infrared Spectroscopy, and DFT simulations of spectral dependences of the corresponding second-order nonlinear optical susceptibilities, were performed.

Fiber Bragg gratings in hole-assisted multicore fiber for space division multiplexing.

In this Letter we present, for the first time to our knowledge, the results of fiber Bragg grating (FBG) inscription in a novel microstructured multicore fiber characterized by seven single-mode isolated cores. A clear Bragg reflection peak can be observed in all of the 7 cores after one inscription process with a KrF nanosecond laser in a Talbot interferometer set up. We furthermore perform a numerical analysis of the effective refractive indices of the particular modes and compare it with the FBG inscription results. An experimental analysis of the strain and temperature sensitivities of all of the Bragg peaks is also included.