We report the analyses of the photo induced anisotropy generated by a mesogenic azobenzene dye complex that is doped
in isotropic and anisotropic matrices. By using time resolved polarized spectroscopy and photo induced dichroism
studies, we show that this specific dye composition undergoes photo isomerization process, but has very limited angular
mobility in all tested matrices.
We present a waveguide with in-core Bragg grating and electro-optic liquid crystal cladding. The electric field induced
reorientation of liquid crystal allows the reflection of guided light of desired wavelengths and polarizations at desired
spatial positions.
The variable optical attenuator (VOA) is an important part of agile optical telecommunication systems. VOAs built on so called free space technologies carry important drawbacks in terms of mechanical reliability, size and optical loss. Evanescent field approach have been used to design VOAs with very low insertion loss. Thermo-optic modulation mechanism was mainly used to control the attenuation level, which unfortunately requires from 10 to 100 times more electrical power compared to above mentioned free space architectures. This power consumption issue may be very challenging in high count arrays of VOAs.
At the same time, liquid crystals (LC) have been proved to require very low electrical power for operation.
In the present work, we report the creation of evanescent field modulation based VOA with extremely low insertion loss (below 0.1dB) and low electrical power consumption by removing a portion of the original fiber's cladding and replacing it by a specifically synthesized composite LC material, which have an ordinary refractive index lower than the glass one. The initial orientation of LC molecules provides an effective refractive index of the electro-optic cladding that is equal to the refractive index of the original silica cladding. We then create a LC molecule reorientation by the so-called Fredericksz effect by applying to the LC material an electrical voltage. This reorientation changes the refractive index around the depressed cladding area and brings to the partial leakage of the guided radiation into the cladding area, achieving thus attenuation levels above 50dB. Measured maximum electrical power consumption of the VOA is in the microwatt range.
We present the optical performances of a compact variable optical attenuator (VOA) developed at Photintech. The presented VOA’s operation principle is based on the guided wave evanescent field manipulation. This approach allows the cost effective fabrication of VOAs with extremely low insertion loss, below 0.1 dB. The access to the evanescent portion of the guided radiation is achieved by removing a portion of the original waveguide’s cladding and replacing it by a thermo-optic composite polymer material. By changing the temperature of the thermo-optic material we create a partial leakage of the guided radiation into the replaced cladding area, attenuating thus the guided radiation. It is well known however, that the application of polymer materials for optical component fabrication creates significant birefringence due to the shrinkage and thermal stresses. As a result, the polarisation dependence of such devices is relatively high.
We apply a specific cladding geometry and heating electrode (pending patent of Photintech inc), which ensures axial compensation of the birefringence, providing thus very small polarisation dependence. The design provides also a high dynamic range operation (above 50dB). An in-house designed electronic board allow the VOA operation in three different regimes: direct driving, constant output power or constant attenuation coefficient with a precision as better as 0.1dB. The developed VOA device can be used in agile optical networks, for such applications as dynamic gain equalisation, dynamic channel equalisation, optical transmitter power control and receivers protection in the telecommunication systems.
We report 3D photonic crystals of polystyrene micro-spheres and air spheres in Barium titanate Background with diameters between 220 and 1100 nm by filling the voids (between the polystyrene micro-spheres) with Barium titanate. The BaTiO3 was synthesized from a sol gel solution. The polystyrene is then removed by calcination. The pyrolysis at 550°C enables to make the right phase of BaTiO3. Scanning electron microscope and optical microscope confirm the quality of the samples. The structure strongly diffracts light and can be a step to photonic band gap materials.
A three-dimensional (3D) colloidal crystal have been grown from an aqueous colloidal solution of highly monodisperse submicrometer-sized polystyrene spheres using a self-assembly processing technique. The electromagnetic waves diffracted by this crystal can interfere and give rise to a photonic band-gap. However, due to the low refractive index contrast within this material the band-gap is incomplete. By filling the voids between the spheres of the colloidal crystal with titania and removing the polystyrene beads by sublimation, we obtained an inverse-opal structure with an increased refractive index contrast showing strong opalescence.
Currently organic photochromic compounds have been considered as materials of growing importance for use in optical memory applications. They have been characterized by a set of unique characteristics, and could be easily fabricated in different formats and at low-cost. We studied a new class of photochromic composites consisting of carbazole-contained polymeric hosts with spiropyran-substituted dyes. These composites have been synthesized and experimentally characterized as holographic material for direct high-resolution holographic recording in whole visible spectra. We concluded some general principles of photochromic media design for achievement of high sensitivity and diffraction efficiency while hologram records.
The photoinduced reversible color change and holographic recording in Fulgide (Aberchrome 670) doped photopolymers was investigated. The rate constants KUV and KVIS for respectively the coloring and bleaching process, photochemical fatigue resistance and real time holographic recording in fulgide doped photopolymer film was investigated.
Photochemical characterization and holographic recording of fulgide Aberchrome 670 and 540-doped polymethyl methacrylate (PMMA) were investigated. Upon UV and visible exposure, closed-form absorbency followed first-order kinetic. The real time holographic recording in fulgides doped PMMA films were studied. The effect of dye concentration, thickness of the film and the recording intensity on diffraction efficiency was reported. We used the Langmuir-Blodgett (LB) technique in order to transferring a compact multilayer of fulgide spread on water surface between two thin films of cellulose acetate (CA). The preliminary results of the surface pressure-area isotherms obtained by LB show the transfer of the fulgide between two CA thin films. Finally, the photochromic reaction of fulgide in LB films was investigated.
We report the synthesis of polycrystalline barium titanate BaTiO3 thin films on silicon substrate prepared by sol- gel technique. The structure and composition of ferroelectric film ms have been analyzed by using x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. These methods provide information on the core level electronic states and the film composition. The results indicate the films have no distinctive deviation from the stoichiometry within the accuracy of both spectroscopic methods. Thus, this study of surface structure and composition of ferroelectric films could lead to a better understanding of the observed change of electrical and optical properties and to the design of improved devices such as dynamic random access memories.
We report a new photochromic composite polymer consisting of poly-N-epoxypropylcarbazole (PEPC) polymeric matrix with a nitro-brome-substituted spiropyran (BNSP) photochromic dye. The PEPC + BNSP films can be considered as negative photochromic recording media. They are colored in the initial state and bleached upon irradiation within the visible spectra. When we placed the bleached samples to the darkness, they slowly revert to the colored form. This process has strong temperature dependence, so one can either 'freeze'' or accelerate changing of the current coloration state in the PEPC + BNSP. The experimental measurements are evaluated in conjunction with its potential applications for optical holographic recording in the visible spectral range. The real-time holographic recording procedure in PEPC + BNSP films was studied. The diffraction efficiency values reached the maximum of 23 percent at spatial frequency of 1600 line pairs per mm, during direct hologram recording with the 532 nm Coherent VERDI laser irradiation. Light exposures were ranged from 70 to 280 mJ/cm2. The investigated compounds have good perspectives for use in holography, two-photon optical data storage, electro-optics, and optical-limiting applications due to coupling of some unique properties such as high optical non-linearity, well charge transport, short response times, no-limiting resolution ability, etc.
The photo excitations of Spiropyran-doped polymer films were studied. Cellulose acetate (CA), commercial ploy(methyl
methacrylate) (PMMA) and PMMA prepared by radical polymerisation of MMA, were used as host polymer matrices. The
open form of SP presents a maximum of absorption cantered at about 600 nm upon UV irradiation. We have determined the
photoreaction rate constants, kuv and k15, for the coloring and bleaching processes. Reversible holographic recording in
SPIPMMA films was studied and photochemical fatigue resistance was evaluated upon repeated UVfVisible irradiation cycles.
We found a loss of 42, 53 and 74% respectively in PMMA by gravity deposition, PMMA (by polymerisation of MMA) and
cellulose acetate films.
By means of real-time holographic recording, two important classes of photochromic compounds (spiropyrans and
fulgides) have been characterized. For spiropyran molecules, important thickness and writing intensity effects were
observed.
Concerning fulgides molecules, photochemical fatigue resistance in different polymer hosts was investigated. After 10
irradiation cycles, the closed form lost 9, 1 1 , 13 and 35% of its initial absorbance respectively in PS, CA, PMMA and
PVK. For the holographic study, diffraction efficiency in fulgide doped PMMA films was strongly dependent on the
writing intensity: the rise time 'r takes values 25and 7s for respectively 2 and 8 mW/cm2. Optimum fulgide concentration
and writing exposure have been obtained: diffraction efficiency is maximum with a concentration of 2% and an intensity
of 4mW/cm2.
Keywords:Photochromism, photosensitive materials, fulgides, spiropyrans, polymethylmetacrylate, polyvinylcarbazole,
real-time spectrometry, photochemical fatigue resistance, holographic recording.
The characteristics of thin BaTiO3 films deposited on Si and MgO substrates by employing the metal-organic deposition
technique are studied. In the experiment, the commercial barium 2-ethyihexanoate and the synthesized titanium dimethoxy
dineodecanoate are used as precursors for the formation of BaTiO3 films. The film characterization is performed by X-ray
diffraction and the scanning electron microscopy. The obtained results show that the prepared films have nearly good
stoichiometry and the obtained tetragonal structure properties of BaTiO3 indicates that these may fmd some possible
optical/electrical applications in the field ofintegrated optics technology.
The photoinduced reversible color change and in-situ recording of fulgide Aberchrome 670 doped polymethyl methacrylate (PMMA), cellulose acetate (CA) and polystyrene (PS) were investigated. Upon UV and visible exposure, closed-form absorbency followed first-order kinetic. The rate constants KUV and KVIS for respectively the coloring and bleaching process were determined. In PMMA matrix KUV equals 1.2 * 10-3 s-1 and KVIS equals 11.1 8 10-3 s-1, in CA matrix kUV equals 2.7 * 10-3 s-1 and kVIS equals 6.4 8 10-3 s-1 and in the case of PS film kUV equals 2.1 * 10-3 s-1 and kVIS equals 11.9 * 10-3 s-1 were obtained. These results show that, KVIS is much larger than KUV for all matrices. Photochemical fatigue resistance in different polymer matrices was investigated. We found a loss of 9, 11 and 13 percent in PS, CA and PMMA respectively, after 10 repeated UV and visible cycles. The real time holographic recording in fulgide doped PMMA films were studied. We have analyzed the effect of the photochromic concentration, the thickness of the film and the recording intensity on the diffraction efficiency. The highest diffraction efficiency is obtained for the concentration of 5 percent of the fulgide dye in PMMA film with an exposure energy of 10 mw/cm2. For the same sample we have not observed any diffraction beam when the sample was illuminated by an intensity of 3 mw/cm2.
Photochromism and real-time holographic recording were characterized for two principal classes of photochromic compounds: spiropyrans and fulgides. For spiropyran molecules, important thickness and writing intensity effects were observed. Concerning fulgide, in PMMA matrix, the closed form presents a maximum of absorption centered at 525 nm upon irradiation at 365 nm. We have determined the photoreaction rate constants kUV and kvis respectively for the coloring and bleaching process: kUV equals 1.2 X 10-3 s-1 and kVIS equals 11.1 X 10-3 s-1. Photochemical fatigue resistance in different polymer matrices was investigated. We found a loss of 9, 11, 13 and 35 percent respectively in PS, CA, PMMA and PVK. Concerning holographic recording, we obtained diffraction efficiency (eta) equals 0.65 percent in PMMA films 30 micrometers thick.
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