The existence of optical amplification at 1.55 micrometers wavelength in channel waveguides using Erbium dopent and 980 nm laser pump involves an OH and CH₃ groups quantity as low as possible. Moreover, a high refractive index variation between the guide and the cladding is necessary to induce a maximum confinement and then increase the dopent efficiency. In this way, we propose a study of different routes we explored to reach this goal: use of F catalysis (to enhance condensation), hybrophobic precursors to reduce the OH quantity, and a diacrylate monomer whose reactivity allows a high refractive index change under UV light exposure.

Transparent porous matrices made by the sol-gel method are ideal as hosts for active photoactive or electroactive organic dopants. Sol-gel optics applications are related to an adequate and precise control of the compositional and pore surface variations in the cage of trapped molecules, which is necessary to the preparation of novel optical and electrooptical gel-glasses. Gel-glass dispersed liquid crystal (GDLC) with electrooptical properties shall be presented as an application of the sol-gel process for trapping microdroplets of nematogenic organic compounds (i.e., liquid crystals, LCs). GDLC films may be used as electrooptical devices. Upon application of an external electric field, unaltered GDLCs were made to switch from white opaque to colorless transparent states. The different electrooptic features of GDLCs, including GDLC performances for color display applications are reviewed.

We report the synthesis of sol-gel materials based on highly efficient heterocycle-based push-pull chromophores showing second- and third-order nonlinear optical activity. We show the proper functionalization of the best performing chromophores and their incorporation into a hybrid organic- inorganic sol-gel matrix. Different types of functionalization of the active molecule have been considered, including hydroxyl and alkoxysilyl end-groups. The functionalization strategy responded to different criteria such as stability and synthetic availability of the final molecular precursors, their solubility, and the used synthetic approach to the sol-gel material. The synthesis of the sol-gel materials has been tuned in order to preserve molecular properties and control important factors such as final concentration of the active dye in the matrix. Both acid- and base-catalyzed sol-gel synthesis has been taken into account. 3-Glycidoxypropyltrimethoxysilane and 3- aminopropyltriethoxysilane have been used as the organically modified alkoxides to prepare the hybrid organic-inorganic matrix. Characterization of the spectroscopic properties of the sol-gel materials is presented.

The orientational ordering of liquid crystal (LC) materials directly determines their optical properties. Controlling the orientational order allows the optical properties to be engineered for display and switching applications. Recent advances in LC ordering with LCs embedded in porous networks have resulted in materials with exciting new properties, enabling new display and switching technologies. A new technique called Glancing Angle Deposition (GLAD), based on conventional thin film fabrication, allows engineering of porous structures of inorganic materials in three dimensions on a nanometer scale. By impregnating the void spaces in these porous inorganics with various polymers and LCs, we have created a new type of hybrid material where the orientational order of the impregnate is controlled by the inorganic backbone structure. Optical measurements of GLAD materials with various impregnates demonstrate that simple rodlike liquid crystalline materials (nematics) are oriented by a helical inorganic backbone to form a phase similar to the chiral nematic phase seen in other (cholesteric) liquid crystals. This new hybrid material appears promising for optical switching and display applications.

With higher complexity of optical networks there is an increasing demand for components which allow to manipulate the optical signals without conversion to the electronic domain. Besides modulation the key functions needed for advanced telecom applications are multiplexing and demultiplexing in the time and frequency domains, wavelength filtering, routing, switching, dispersion equalizing. This paper describes the state-of-the-art of planar guided wave circuits (integrated optical devices) made from SiO₂, InP, LiNbO₃ and polymers, which are going to replace discrete components based on fibers, thin film technologies and bulk optics. Special emphasis will be put on scalability and the capability for higher monolithic or hybrid integration. As wafer scale integration, i.e. one circuit occupies a whole wafer, has been reached for specific components such as high channel count arrayed waveguide grating devices (Phasars) and switch matrices, new device structures which consume less real estate have to be elaborated.

The development of photonic devices for the next generation of optical networks is dependent on advances in ultrafast materials and in the success of waveguide devices comprised of these materials. This includes new methods of producing integrated-optical devices by innovative growth techniques or novel hybridization schemes. We describe aspects of the ultra-fast optical communications program at Georgia Tech that involve the development of hybridized and integrated- optical devices and devices for use in ultrafast optical data links. Two major components are under development: (1) a tapered rib electro-absorption modulator that includes an integrated spot-size converter for hybridization with a passive silica-waveguide tapped delay line. This unique hybridized semiconductor/glass waveguide provides the basic building block of the transmitter multiplexer. (2) a quasi- phase matched multilayer AlGaAs waveguide designed for surface-emitted second-harmonic generation. This device provides an all-optical serial-to-parallel converter and thereby demultiplexes ultrafast optical data streams. We describe our recent advances in materials growth and waveguide design and the impact on the performance of these devices.

PHASARs or Arrayed Waveguide Grating (AWG) multiplexers for application in Dense Wavelength Division Multiplexing optical networks have been realized using silica-waveguide technology. Using waveguide tapers, a flat-top passband characteristic is obtained. Using Fourier transform spectroscopy employing a low coherence interferometer, the power-distribution coefficients and the phase error distribution in such components is evaluated. Because of the coherence length of the used light source being smaller than the optical path length difference in the PHASAR, it is possible to resolve individual waveguides of the array. Thus, the transfer functions of the individual optical paths are accessible to the measurement, enabling the full simulation of the PHASAR transmission spectrum. It is demonstrated that the measured phase error distribution in tapered PHASAR devices consists of contributions from both tapered waveguides and arrayed waveguide grating regions. An evaluation method suitable for investigating both contributions separately is developed. Phase shift introduced by the waveguide tapers is in good agreement with simulation calculations based on the Beam Propagation Method. An analytic transmission calculation based on measured phase and power-distribution coefficients enables a full simulation of PHASARs including insertion loss, bandwidth and crosstalk performance. Excellent agreement with transmission measurements is performed.

An organic-inorganic materials associated with a direct printing by UV exposure was used to make MMI couplers. A 1 X 32 splitter and a 4 X 4 splitter/combiner were designed and achieved for working at 1.55 micrometers wavelength. The 4 X 4 splitter/combiner was then used to design a 2 nm selective MMI-Phasar working around 1.55 micrometers .

As other acousto-optic devices, acousto-optic tunable filters (AOTF) deal with information processing and transmission. However, in major cases, AOTF transmits information in a specific form--the data are contained in output light spectrum or wavelength. The estimation of possible amount of information which can be processed and transmitted by AOTF, requires to define the resolving power of a device by wavelength. The wavelength resolving power criterion has been elaborated in the presented paper. It proceeds from the condition of the necessary probability of one bit of information recognition. Taking into consideration this criterion as well as the need to distinguish gray scales in a pattern of wavelengths, the information transmission capability of AOTF has ben calculated. Along with that, it has been shown that such parameter as information capacity of AOTF represents a significant importance while analyzing the spectral composition of light transmitted through media to be studied. Some features of tellurium dioxide single crystals influencing the AOTF information possibilities, have been discussed.

A hybrid organic-inorganic material derived 3- (glycidoxypropyl)-trimethoxysilane (GPTMS) and fullerene derivatives has been developed for optical limiting applications. The control of the final material has been achieved by engineering the matrix-fullerene solid-state system. Different Lewis acids (Zr(OBu^t)₄, Ti(OBu^t)₄, BF₃, SiCl₄, and TiCl₄) have been used as the catalysts of the epoxy ring opening of (GPTMS) and the polyethylene oxide formation, in three different syntheses, to control and optimize the matrix- fullerene interaction and the optical limiting properties. The microstructure of the hybrid matrix has been studied by Fourier Transform Infra-Red Spectroscopy. UV-vis spectra and optical limiting measurements of the doped materials showed that in the Zr(OBu^t)₄, TiCl₄, BF₃ derived matrices clustering of fulleropyrrolidine molecules is avoided and optical limiting is obtained. In the Ti(OBu^t)₄, SiCl₄, and not epoxy catalyzed derived matrices, instead, the aggregation of fulleropyrrolidines degraded the optical limiting properties. The laser damage threshold in the Zr(OBu^t)₄, TiCl₄ and especially BF₃ derived matrices was larger than in the other matrices. Moreover, a multilayer system has been fabricated to develop an optical limiting device.

In this paper, the properties and applications of both inorganic and organic modified silica films achieved on InP substrates are discussed based on experimental results. The fabrication of inorganic silica film is done using multiple spin coatings and rapid thermal processing at a temperature of 450 degree(s)C. The organic modified silica film is made also by multiple-spin coatings with a baking temperature of 200 degree(s)C. The surface quality, the crack-free critical thickness and the processing conditions of the two kinds of films are compared. The suitable applications for both types of films are discussed, based upon their different properties. From our experiments, we strongly believe that monolithic integration of active and passive devices could be obtained by means of hybridizing sol-gel derived materials and InP based III-V compounds.

Nd³⁺-doped LiTaO₃ is successfully derived by the sol-gel method. The host solution is prepared by mixing LiOC₂H₅ and Ta(OC₂H₅)₅ and different concentrations of 1.0, 2.0, and 3.0 mol% of Nd³⁺ are introduced. The films are deposited on SiO₂/Si substrate by spin coating and the powders are prepared by sintering the precipitation of the solution. XRD and micro-Raman studies show that the material displays good crystallization of pure trigonal phase of LiTaO₃. AFM and SEM studies reveal that the crystalline size is about several tens of nanometers for the films and a few hundred nanometers for the powders after an annealing at 600 degree(s)C. Using the 488 nm line of an Ar⁺ laser as an excitation source, photoluminescence of the powders is observed at 1.06 micrometers , corresponding to the ⁴F_3/2 yields ⁴I_11/2 transition of Nd³⁺. The full width at half maximum is about 40 nm.

The acoustooptic (AO) phase modulation properties of coaxially deposited zinc oxide (ZnO) transducers on single mode optical fibers have been experimentally and theoretically investigated at several laboratories over the past 15 years. Maximum phase shifts are observed at distinct frequencies, corresponding to bulk acoustic waves in the fiber, over the transducer operating range of 200 MHz to 1.0 GHz. Phase shift values have been measured with both cw and pulsed signal inputs to the transducers from milliwatts to above 1 Watt. Transducer lengths have been varied from 30 mm to 2 mm to determine the effects of AO phase shift on the length of the interaction. Modulation efficiencies in the range of 0.2 to 0.3 radians per square root of input power (in mW) per centimeter, for 2 to 6 mm interaction lengths, have been observed at frequencies in the 200 to 400 MHz region corresponding to acoustic wavelengths on the order of the core dimensions of the optical fiber. The characteristics and capabilities of AO modulation in optical fibers with deposited coaxial ZnO transducers is discussed using examples from experimental work.

To confirm the credibility of the integrated optical circuits based on organic-inorganic materials, the problem of connection with an optical fiber, but also between inter and intra-cards or with a matrix of laser diodes such as VCSEL have to be resolved. In this work, we propose to integrate in an optical device some `objects' which could simplify the alignment procedure in the both last cases. We fabricated a 45 degree(s) tilted mirror made by EBID method. This mirror was placed right in front of an optical waveguide output.

The paper discusses the mechanism of cross-produce component generation connected with the acoustic parameters of the medium and acoustic power density for the fundamental frequencies. The expressions for the spatial distribution of harmonic components for the fundamental and cross-produce frequencies are given. The paper presents some experimental results of spatial distributions for the fundamental and higher acoustic harmonics for several widely used acousto- optic crystals under different power density levels of fundamental harmonic. Basing on these experimental data, are analyzed the variations of the spectrum spread function for the space-integrating acousto-optic spectrum analyzer and spatial optical distribution of cross-product components.

In order to describe acousto-optical spectrum analyzers (AOSA) it is necessary to take into consideration not only spatial resolving power defining the amount of the spectrum intervals to be distinguished (which is usually considered) but also data temporal resolving power for temporally variable spectra. These parameters are intercepted, and changing of one influences both on variation of the others and on the AOSA total information efficiency (amount of useful information extracted by the device from the variable signal of certain duration). It has been shown that increasing of the signal transmission through the acousto- optic Bragg cell exercises influence on the AOSA information efficiency by the complicated way. The bigger this time, the bigger amount of the spectrum resolved intervals (which means that the information capacity becomes bigger), the less the signal useful duration, and the less the AOSA information transmission capability for the devices processing the signal with periodically variable spectrum. Along with that part of the time is spent for mixed distorted signal. In order to optimize AOSA from the point of view of useful information transmission, it has been proposed to assign different weight factors to each of kinds of information, and, correspondingly, to each of the device parameters. These weight factors define valuability of certain kind of information. Their using for the quantitative estimation of the useful information amount, allows to create the basis of AOSA information metrology.

Organically modified silicates (ormosils) derived from acid catalyzed sol-gel processing of a mixture of phenyl triethoxysilane (PhTES), methyl triethoxysilane (MTES) and tetraethyl orthosilicate (TEOS) are being assessed for photonics applications. PhTES and MTES introduce phenyl (C₆H₅-) and methyl (CH₃-) groups onto the silica backbone, respectively increasing and decreasing the refractive index, so that the refractive index can be tuned from 1.40 to 1.55 (at 633 nm) by varying the composition. Films are deposited onto silicon or glass substrates and dried under nitrogen at or below 200 degree(s)C to remove residual water and ethanol; we present refractive index and absorption data before and after drying for several compositions. Although the triethoxysilane (i.e. MTES and PhTES) content should be maximized to inhibit cracking caused by drying-induced stress, some TEOS appears to be beneficial for mechanical stability. Crack-free films dried at 200 degree(s)C have been produced with thickness up to 15 micrometers .