We demonstrate a highly tunable photonic bandgap fiber, which has a core diameter of 25 mm, and a bandgap tuning sensitivity of 27 nm/degC at room temperature. The insertion loss is estimated to be less than 0.5 dB.

An all-optical modulator is demonstrated, which utilizes a pulsed 532 nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid crystal. In order to investigate the time response of the LCPBG fiber device, a low-power CW probe laser was coupled into the fiber together with the pulsed pump laser of 2.3 mW and we have demonstrated a modulation frequency of up to 2 kHz.

We describe a new class of hybrid photonic crystal fibers, which are liquid crystal infiltrated fibers. Using these fibers, we demonstrate 'distributed' tunable filter and switching functionalities operating by the photonic bandgap effect.

Photonic crystal fibers (PCFs) have attracted significant attention during the last years and much research has been devoted to develop fiber designs for various applications, hereunder tunable fiber devices. Recently, thermally and electrically tunable PCF devices based on liquid crystals (LCs) have been demonstrated. However, optical tuning of the LC PCF has until now not been demonstrated. Here we demonstrate an all-optical modulator, which utilizes a pulsed 532nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid crystal. We demonstrate a modulation frequency of 2kHz for a moderate pump power of 2-3mW and describe two pump pulse regimes in which there is an order of magnitude difference between the decay times.

Photonic Crystal Fibers (PCFs) have appeared as a new class of optical waveguides, which have attracted large scientific and commercial interest during the last years. PCFs are microstructured waveguides, usually in silica, with a large number of air holes located in the cladding region of the fiber. The size and location of these air holes opens up for a large degree of design freedom within optical waveguide design. Further, the existence of air holes in the PCF gives access close to the fiber core and by introducing new materials into the air holes, a high interaction between light and hole material can be obtained, while maintaining the microstructure of the waveguide. In this paper, we describe what we call Liquid Crystal Photonic Bandgap Fibers, which are PCFs infiltrated with Liquid Crystals (LCs) in order to obtain increased fiber functionality. We describe a thermo-optic fiber switch with an extinction ratio of 60dB and tunable PBGs using thermo-optic tuning of the LC. These devices operate by the PBG effect and are therefore highly sensitive to the refractive index distributions in the holes.

A new type of hybrid photonic crystal fibres, which are infiltrated with liquid crystals, are demonstrated. Thermo-optic fibre switching, which utilises the phase transitions of a thermochromic liquid crystal inside a photonic crystal fibre, is demonstrated.

A new thermo-optic fibre switch is demonstrated, which utilizes the phase transitions of a thermochromic liquid crystal inside a photonic crystal fibre. We report an extinction ratio of 60 dB and an insertion loss of 1 dB.

The optical properties of an antiferroelectric liquid crystal (AFLC) cell slightly deviating from the ideal orthoconic condition, i.e., 45° tilt angle and fully horizontal surface stabilization (the molecular tilt plane parallel to the glass plates), have been investigated using the fully leaky guided mode (FLGM) technique. In contrast to standard optical investigative methods, such as polarization microscopy, the FLGM data give information about the orientation of the index ellipsoid or the molecular tilt plane, not only in the plane of the cell but in three dimensions. The sensitivity of the FLGM technique thus allows a detailed optical characterization on a mesoscopic scale and, in particular, has allowed us to discriminate, in the investigated cell, a tilt out of the substrate plane in the anticlinic state, thus a deviation from the horizontal surface stabilization condition. Orthoconic surface-stabilized AFLCs are, in the ideal case, uniaxial negative with the optic axis perpendicular to the glass plates and therefore provide a perfect dark state between crossed polarizers even if the direction of the smectic layer normal is not homogeneous in the plane of the cell. Small deviations from the ideal case lead to the appearance of a very small birefringence in the cell plane which, however, should not compromise the attractive optical properties of this class of AFLCs. Using laser diffraction we have verified that, even with the deviation from the horizontal surface stabilization detected by the FLGM study, a horizontal chevron geometry, clearly visible in the synclinic state, is not optically detectable in the anticlinic state of orthoconic AFLCs. We conclude that the attractive optical properties are preserved in a reasonably large interval around the ideal orthoconic conditions allowing for the practical exploitation of these materials as key components in liquid crystal displays and other electro-optic devices.

We report the preparation and characterization of novel isotropic polymer slab waveguides made by photochemical crosslinking, and their integration with a ferroelectric liquid crystal in an integrated electro-optic modulator. The refractive index of the passive copolymer material in the device was controlled by the copolymer composition, and good agreement between measured and calculated effective indices for the guided modes of polymer films was obtained. The active ferroelectric liquid crystal exhibited a refractive index change of Deltan approximate to0.10 upon application of an ac voltage of +/- 30 V, giving an electro-optic modulation of the input TE0-mode with a contrast ratio of 11:1 and only a small polarization conversion into TM output light. (C) 2001 Society of Photo-Optical Instrumentation Engineers.

We present electro-optic switching from a planar waveguide with a ferroelectric liquid crystal overlayer and discuss the operating principle and the parameters significant for the operation of the device. We have found electro-optic response times of about 20 mus at best as well as a high (5.7%) transmittance in the ON-state of the device. The contrast ratio was 4:1 ON to OFF state.

Highly oriented pyroelectric liquid-crystalline polymers were prepared by photopolymerization under the influence of a static electric field from binary mixtures of two acrylate monomers exhibiting chiral smectic C mesomorphism. Both monomers contained nitro groups to yield second order nonlinear optical properties (second harmonic generation) and one of the monomers had two functional groups to yield a crosslinked polymer. The room temperature second order nonlinear susceptibility of the polymers showed during the first two hours a 10 % decrease after which it remained constant during the next 48 days. At elevated temperatures there was a significant difference in the nonlinear optical properties over time between crosslinked and uncrosslinked polymers. The uncrosslinked polymer showed a pronounced loss of second order nonlinear optical activity with time at greater than or equal to 38 degrees C. The crosslinked polymer showed a much smaller and basically a temperature independent decrease rare in the second order nonlinear optical properties at all the ageing temperatures (23-130 degrees C). Both the loss in mesogen order parameter, very evident for the uncrosslinked polymer, and conformational changes occurring within the mesogens (beta mechanism), may account for the observations made.

Second-harmonic generation (SHG) was observed in a homogeneously aligned smectic C*-like liquid crystal (LC) cell showing V-shaped switching during the application of a triangular wave. At normal incidence of light, abnormally strong SHG signals were observed at about zero electric field. It was confirmed that this phenomenon is characteristic in LCs showing the V-shaped switching, and is not observable in typical ferroelectric and antiferroelectric LCs. The dynamic response of SHG was successfully simulated using the two-dimensional Langevin type potential model.

The preferred direction of alignment of the liquid crystal molecules in nematics with two-fold degenerate alignment can be affected substantially by changing the temperature or by applying an electric field. As a result, an almost in-plane switching of the molecules occurs. Here, we report an opto-thermal reorientation effect in a nematic with two-fold degenerate alignment due to a local heating of the liquid crystal by a high power laser beam. The mechanism of this phenomenon is discussed. The opto-thermal reorientation of the molecules makes it possible to visualize the temperature distribution in the illuminated cell and some applications can be foreseen.

Pyroelectric Liquid-crystal polymers were prepared by photopolymerization of binary mixtures of two monomers that exhibit a smectic C* phase: A2c, 4"-{(R)-(-)-2-[(10-acryloyloxy)decyl]oxy}-3-nitrophenyl 4-{4'-[(11-acryloyloxy)undecyloxy]phenyl}benzoate and A1b, 4"-((R)-(+)-2-octyloxy)-3"-nitro phenyl 4-(4'-[(11-acryloyloxy)undecyloxy]phenyl) benzoate. Both liquid-crystal monomers have a NO2 substituent to enhance the nonlinear optical properties, and one of the monomers, A2c, permits polymerization to a cross-linked polymer. During the polymerization an electric field of approximately 25-50 V/mu m was applied over the ferroelectric liquid-crystal cells. All cases of polymers formed from the chiral smectic C* phase showed a second-harmonic-generated signal with no external field present, indicating that polar order became fixed. The orientation dependence of the second-harmonic-generated intensity was similar to that of the ferroelectric Liquid-crystal monomer; however, some changes were observed that might be due to changes in the dielectric axes of the system. The highest d(16) and d(23) coefficients were found to be in the range 0.65-0.8 pm/V and differed depending on the detailed preparation of the sample. Experimental results of several polarization combinations of the pump and frequency-doubled light are presented and discussed. (C) 1998 Optical Society of America.

M-line measurements have been performed on thin films of pyroelectric liquid crystalline polymers (PLCP), in order to determine the magnitude and anisotropy of the refractive index. The films, polymerized under various conditions, are based on materials exhibiting a chiral smectic C (S-C*) phase. The results of the measurements were analyzed and compared with a new numerical method to model the optical properties of anisotropic multilayered thin films. In the model, which is an extension of the analytical approach of Berreman, the eigenmodes and boundary conditions of refracted light waves are handled and solved by numerical matrix manipulations. Model calculations of total reflection measurements for various multi-layered systems were used to investigate the effect of ITO and polyimide aligning layers to the apparent effective index of m-lines.

Pyroelectric Liquid Crystal Polymers (PLCP), a novel class of material with intrinsic polar order developed in our laboratory, are discussed. Thin films (2-4µm) of PLCP were prepared by photopolymerization of ferroelectric liquid crystalline monomers in the chiral smectic C (SmC*) phase. The poly(acrylate) materials have been structurally modified in order to improve their nonlinear optical and thermal properties. Further are their longterm nonlinear optical properties discussed based on results from second harmonic generation (SHG), spontaneous polarization (Ps), and dielectric spectroscopy.

Second harmonic generation in novel pyroelectric liquid crystal polymers (PLCP) made from a series binary mixtures, was studied using 1100 nm as the fundamental wavelength. The PLCPs were prepared by photo-polymerization of binary mixtures of two monomers which exhibit a smectic C∗ phase, A2c (4″-(R)-(−)-2-[(10-acrylo-yloxy)decyl]oxy-3-nitrophenyl 4-{4′-[(11-acryloyloxy)-undecyloxy]phenyl}benzoate) and Alb (4″-((R)-(+)-2-octyloxy)-3″-nitrophenyl 4-(4′-(11-acryloyloxy)undecyloxy)-phenyl)-benzoate). The highest d16 and d23 coefficients were found to be in the range 0.65–0.8 pm/V, and differed depending on the detailed preparation of the sample. All cases of polymers formed from the chiral smectic C∗ phase showed an SHG-signal with no external field present, indicating that polar order became fixed. The SHG-signal was found to increase with the tilt angle of the FLC molecules.