1,721,028 research outputs found
All-optical switching and filtering based on liquid crystals and photosensitive composite organic materials
No full textIntegrated optic devices using low driving power are crucial to develop new photonic systems
both for optical communications and for sensing. The large electro-optic effect and nonlinear
optical properties of liquid crystals (LC) and doped LC novel materials allow the realization of low
cost optoelectronic devices. We present our recent experimental and theoretical results on optical
channel waveguides based on LC made on both glass and silicon substrates. Devices made of
waveguides using a LC core can operate both in linear [1] and nonlinear optical regime at 1550 nm
wavelength spectral region [2]. As linear waveguides they can behave both as variable optical
attenuators and as optical switches by exploiting the electrooptic effect in a nematic LC (NLC). An
applied voltage lower than just 5 V was required to drive an electro-optic switch with an on-off
contrast of more than 40 dB. Optical Freedericks transition was also experimentally observed when
an input optical power of just 25 mW was fiber coupled to the same NLC waveguide. Modelling of
the waveguide was obtained by minimizing the LC total free energy, including the dielectric energy
at optical frequencies by using finite elements. Preliminary simulations of waveguides using azodye
doped LC indicate that a further reduction of driving power is possible. All-optical tunable
filters can also be obtained by using photosensitive composite materials.
Recent experimental findings will be presented on an integrated optic filter, which combines the
simple and low cost ion-exchange waveguide technology with a composite LC methyl red (MR)
azo-dye photosensitive compound to obtain full optical tuneability. The structure of the integrated
optical filter recalls a previous POLICRYPS based electro-optic tuneable filter [3]. The prototype
showed a pass-band with more than 20 dB signal suppression at the Bragg wavelength with a
bandwidth of the transmitted notch of about 3 nm. A tuning range of 6.6 nm was observed by
applying a pump signal of 45 mW [4]. Full consistency between experiment and simulation results
was found. The measured shift is nearly double from previous results achieved in electro-optically
tunable POLICRYPS based filters, because of the nematic liquid crystals methyl red properties.
These devices can trigger the development of a new generation of low power, compact and low cost
all-optical components for next generation fiber optic telecom and sensor systems.
References
[1] D. Donisi, B. Bellini, R. Beccherelli, R. Asquini, G. Gilardi, M. Trotta, and A. d’Alessandro, “A switchable liquidcrystal
optical channel waveguide on silicon”, IEEE J. Quantum Electron. 46, 762–768 (2010).
[2] A. d’Alessandro, R. Asquini, M. Trotta, G. Gilardi, R. Beccherelli and I. C. Khoo, “All optical intensity modulation
of near infrared light in a liquid crystal channel waveguide”, Appl. Phys. Lett. 97, 093302 (2010).
[3] A. d’Alessandro, D. Donisi, L. De Sio, R. Beccherelli, R. Asquini, R. Caputo, and C. Umeton, “Tunable integrated
optical filter made of a glass ion-exchanged waveguide and an electro-optic composite holographic grating”, Opt.
Express 16, 9254–9260 (2008), Patent US 7925124 B2 (2011).
[4] G. Gilardi, L. De Sio, R. Beccherelli, R. Asquini, A. d’Alessandro, and C. Umeton, “Observation of tunable optical
filtering in photosensitive composite structures containing liquid crystals”, Opt. Lett. 36, 4755–4757 (2011)
Waveguided optical reflectors using liquid crystals and composites
No full textWe review several approaches to filter optical signals confined in waveguides by using either electro-optical or nonlinear optical effects in liquid crystals (LC) and composites
Miglioramenti costruttivi e di pilotaggio di un display a gradazione a cristallo liquido ferroelettric
No full textWe describe the improvement of a fabrication solution for a ferroelectric liquid crystal display. Moreover a novel addressing technique is employed to drive the display at video rate by using voltages compatible with commercial circuitry.We describe the improvement of a fabrication solution for a ferroelectric liquid crystal display. Moreover a novel addressing technique is employed to drive the display at video rate by using voltages compatible with commercial circuitry
INFM Rome Group research activities
No full textOral presentation at the Meeting SAMPA “Synclinic and Anticlinic Mesophases for Photonic Applications
Integrated optical devices obtained by using LC and various waveguide technologies
No full textOral presentation at the Meeting SAMPA “Synclinic and Anticlinic Mesophases for Photonic Applications
A novel machine to deposit thin PTFE films for LC alignment
No full textA novel dust-free machine is presented for single step deposition of oriented PTFE and other polymer films, suitable as alignment jayers in LC displays. Deposition conditions can be adjusted to optimize the alignment capabilities of the film. Films are more thin, uniform nd oriented than those obtained by spinning and rubbing
Passive matrix SSFLC display with analogue grey levels using PTFE alignment films
No full textFabrication and performance of a surface stabilised ferroelectric liquid crystal display are reported. Grey shades are obtained by modulating the width of switched FLC microdomains by means of an electric field gradient distributed over the pixel, between adjacent metal columns. Such a gradient, depending on the data voltages, is achieved through a high resistance film deposited on the column glass plate. The choice of PTFE (Poly-tetra-fluoro-ethylene) alignment layers, easily deposited by friction, provides very low hysteresis and sticking effect. Morphology of alignment layers, carried out by AFM, is briefly described and evaluated. Addressing mode voltage waveforms to obtain grey shades are also reported. (C) 1999 Elsevier Science B.V. All rights reserved
Dispositivi elettroottici a cristallo liquido ferroelettrico
No full textA discussion on the basic working principles of ferroelectric liquid crystal devices is presented. The most recent advances in fabrication technology and design rules for addressing ferroelectric liquid crystal flat panel matrix displays will be reported. Moreover novel applications such as photonic devices will be mentioned
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