scholarly journals Electrically Tunable Diffraction Grating Based on Liquid Crystals

2018 ◽  
Vol 2018 ◽  
pp. 1-4 ◽  
Author(s):  
Chuen-Lin Tien ◽  
Rong-Ji Lin ◽  
Shu-Hui Su ◽  
Chi-Ting Horng
Keyword(s):  
Liquid Crystals ◽  
Diffraction Efficiency ◽  
Probe Beam ◽  
Diffraction Grating ◽  
First Order ◽  
Periodic Distribution ◽  
Order Diffraction ◽  
Periodic Electric Field ◽  
Linearly Polarized ◽  
Small Voltage

A periodic electric field is generated in the grating-like electrodes cell by an applied voltage and results in the reorientation of liquid crystals. The linearly polarized probe beam experienced periodic distribution of refractive index and formed a phase grating. He-Ne laser was used as the probe beam to detect the zeroth-order (o) and first-order (+1) diffraction intensities. The experimental results showed that the diffraction grating can be switched on by applying a small voltage. The optimal first-order diffraction efficiency is about 12%. The dependence of the first-order diffraction efficiency on the polarization of the probed beam is also discussed herein.

Fabrication of Phase Mask for Optical Fiber Grating

2007 ◽  
Vol 364-366 ◽  
pp. 719-723
Author(s):  
Quan Liu ◽  
Jian Hong Wu ◽  
Ling Ling Fang ◽  
Chao Ming Li
Keyword(s):  
Diffraction Efficiency ◽  
Ion Beam ◽  
Fused Silica ◽  
Phase Mask ◽  
Fiber Grating ◽  
Ion Beam Etching ◽  
First Order ◽  
Silica Substrate ◽  
Order Diffraction ◽  
A New Technique

A fused silica phase mask with the period of 1069nm, and ruled area 50×50mm2 has been fabricated by a new technique, which combines holographic-ion beam etching and reactive ion beam etching. This involves several steps: coating of substrates with controlled thickness of photoresist, formation of a grating mask by holograph interference exposure and development, and finally transferring etching of this mask into the fused silica substrate to form a permanent phase mask. Experimental measurements have shown that the zero order diffraction efficiency is less than 4% and the plus and minus first-order diffraction efficiency is more than 35%. Theoretical analysis has shown that these phase masks can be used for fabricating UV written Fiber Bragg Gratings.

scholarly journals Localized Conical Edge Modes of Higher Orders in Photonic Liquid Crystals

Crystals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 542 ◽  
Author(s):  
Vladimir A. Belyakov ◽  
Sergei V. Semenov
Keyword(s):  
Liquid Crystals ◽  
Maxwell Equations ◽  
Analytic Solution ◽  
Second Order ◽  
Experimental Results ◽  
Analytical Theory ◽  
Exact Analytic Solution ◽  
Localized Modes ◽  
First Order ◽  
Order Diffraction

Most studies of the localized edge (EM) and defect (DM) modes in cholesteric liquid crystals (CLC) are related to the localized modes in a collinear geometry, i.e., for the case of light propagation along the spiral axis. It is due to the fact that all photonic effects in CLC are most pronounced just for a collinear geometry, and also partially due to the fact that a simple exact analytic solution of the Maxwell equations is known for a collinear geometry, whereas for a non-collinear geometry, there is no exact analytic solution of the Maxwell equations and a theoretical description of the experimental data becomes more complicated. It is why in papers related to the localized modes in CLC for a non-collinear geometry and observing phenomena similar to the case of a collinear geometry, their interpretation is not so clear. Recently, an analytical theory of the conical modes (CEM) related to a first order of light diffraction was developed in the framework of the two-wave dynamic diffraction theory approximation ensuring the results accuracy of order of δ, the CLC dielectric anisotropy. The corresponding experimental results are reasonably well described by this theory, however, some numerical problems related to the CEM polarization properties remain. In the present paper, an analytical theory of a second order diffraction CEM is presented with results that are qualitatively similar to the results for a first order diffraction order CEM and have the accuracy of order of δ2, i.e., practically exact. In particular, second order diffraction CEM polarization properties are related to the linear σ and π polarizations. The known experimental results on the CEM are discussed and optimal conditions for the second order diffraction CEM observations are formulated.

scholarly journals An Ultra-High-SMSR External-Cavity Diode Laser with a Wide Tunable Range around 1550 nm

2019 ◽  
Vol 9 (20) ◽  
pp. 4390
Author(s):  
Yan Wang ◽  
Hao Wu ◽  
Chao Chen ◽  
Yinli Zhou ◽  
Yubing Wang ◽  
...  
Keyword(s):  
Diode Laser ◽  
Diffraction Efficiency ◽  
Laser System ◽  
External Cavity ◽  
External Cavity Diode Laser ◽  
External Cavity Laser ◽  
First Order ◽  
Mode Suppression ◽  
Tunable Range ◽  
Order Diffraction

In this paper, a widely tunable external cavity diode laser (ECDL) with an ultra-high side mode suppression ratio (SMSR) was fabricated. Three configurations were constructed to investigate the relationship between the grating features and the SMSR. When a 1200 grooves/mm grating with a first order diffraction efficiency of 91% is utilized in the external-cavity laser system, a maximum SMSR of 65 dB can be achieved. In addition, the tunable range reaches 209.9 nm. The results show that the laser performance can be improved by proper high grating groove number and first-order diffraction efficiency.

The morphology of moth and butterfly wing scales which exhibit reflective diffraction phenomena

1992 ◽  
Vol 50 (2) ◽  
pp. 1010-1011
Author(s):  
M.E. Lee ◽  
E.O. de Neijs
Keyword(s):  
Thin Film ◽  
Diffraction Grating ◽  
Grating Period ◽  
Butterfly Wing ◽  
First Order ◽  
Transmission Grating ◽  
Order Diffraction ◽  
Layer Structures ◽  
Optical Effects ◽  
Wing Scales

The butterfly and moth families illustrate how nature has used diffractive micro-relief structures to achieve unique optical effects. Whereas the majority of insects use pigments (absorption) or occasionally thin film multi-layer structures (interference) to create colour, the wings of many families of butterfly and moth have complex 2-D or 3-D arrangements of submicron grating structures which produce zero and higher order diffraction conditions.The special properties of a diffraction grating can be understood by light incident perpendicularly on a transmission grating. The light is diffracted into a number of grating orders at angles θn given by the grating equation sin θn = n λ/d where λ is the wavelength of the light, n = 0, ± 1, --- and d is the grating period. The same conditions are valid for reflective diffraction structures. If the grating period is finer than the wavelength ie. d < λ, no first order diffraction exists for normal illumination.

Narrowband Optical Coupler Using Fano Interference in First Order Diffraction

ACS Photonics ◽  
2021 ◽  
Author(s):  
Giorgio Quaranta ◽  
Fabian Lütolf ◽  
Olivier J. F. Martin ◽  
Benjamin Gallinet
Keyword(s):  
Optical Coupler ◽  
First Order ◽  
Order Diffraction ◽  
Fano Interference

HIGH RESOLUTION CALORIMETRIC STUDIES AT PHASE TRANSITIONS OF ALKYLCYANOBIPHENYL LIQUID CRYSTALS CONFINED TO SUBMICRON SIZE CYLINDRICAL CAVITIES

1995 ◽  
Vol 09 (18n19) ◽  
pp. 2247-2283 ◽  
Author(s):  
DANIELE FINOTELLO ◽  
GERMANO S. IANNACCHIONE
Keyword(s):  
Phase Transitions ◽  
Liquid Crystals ◽  
High Resolution ◽  
Specific Heat ◽  
Pore Wall ◽  
Isotropic Phase ◽  
First Order ◽  
Smectic A ◽  
Nematic Director ◽  
Scalar Order Parameter

We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphenyl liquid crystals confined to the 0.2µm diameter cylindrical pores Anopore membranes. The nematic director alignment at the pore wall is varied from homeotropic to tangential by pore surface treatment. Several phenomena are uncovered by these studies which probed the weakly first order nematic to isotropic, the continuous smectic-A to nematic and the first order smectic-A to isotropic phase transitions. The specific heat is strongly dependent on the nematic director configuration, and confinement effects are remarkably distinct according to the order of the phase transition. The influence of elastic distortions and surface ordering and disordering effects are evident. Despite considerable departures from bulk behavior with regards to specific heat peaks size, rounding and width, and transition temperature shifts, a bulk-like critical behavior appears to be retained. The formation of smectic translational order within the pores is hindered for those liquid crystals that also possess a nematic phase. The average scalar order parameter temperature dependence is extracted from the specific heat results using a simplified Landau-de Gennes type of model, and is shown to be consistent with nuclear magnetic resonance results.

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