Self-organizing cellulosic polymers are used to explore implications of intrinsic structural anisotropy on light propagation and on Bragg grating replication in thin film waveguides. Polarized waveguide Raman spectroscopy indicates that cellulose acetate and regenerated cellulose polymers show 2D isotropy in the plane of the film. These measurements require that polarization artifacts be carefully separated to recover faithful spectral representations of massive structural order. Parasitic contributions to polarization dependent Raman data are enumerated. Holographic surface relief gratings can be replicated by partially ordered cellulose acetate. Base hydrolysis of the pyranose ester substituents liberates hydroxycellulose (native cellulose) that is largely amorphous, but retains the bulk structural anisotropy of the esterified parent polymer. The latent image of the grating device is passed from the cellulose acetate to the next generation hydroxycellulose film. This process is called `autoembossing', and self-replicates a functional grating device whose period can be effectively doubled. Anisotropy can also be induced with polarized light in hybrid organic/inorganic glass (organosilicate) waveguides prepared by sol-gel polycondensation. We describe novel photopoling experiments that `write' refractive index variations in thin organosilicate films. These written features can be read by a form of autoscopic polarized Raman scattering, and in some cases `erased' by a guided, polarized laser beam. To our knowledge this is the first example of photo-induced anisotropy in hybrid sol-gel glass waveguides that is unrelated to bond isomerization commonly associated with photo-poling in dye-doped polymers or glasses.

Planar silica waveguide devices offer the possibility for cheap, mass produceable components for optical networks and sensors. So far, such devices have been passive in nature. It is now possible to greatly increase the device functionality by making use of the property of photosensitivity and the effect of rare earth doping in such devices. This paper discusses the results of photosensitivity, and rare-earth doping in silica waveguide devices fabricated using Flame Hydrolysis Deposition. As regards photosensitivity, the paper will consider the basic material effects, grating writing and direct writing of waveguides. Rare earth doping is also possible in such waveguides, and the results of such work are described. Rare earth doping involves solution doping of a porous soot, followed by consolidation to incorporate the rare earth. Issues such as clustering of the rare earth and ion-ion interaction leading to gain quenching are discussed and techniques to reduce deleterious presented. Possibilities for combining photosensitivity and rare earth doping are described which offer the potential for waveguide devices containing passive, photosensitive and active sections on different parts of the same wafer.

Low pressure plasma can effectively be used for the fabrication of films for optical waveguides and for the patterning of photonic devices. The present paper describes the basic physical and chemical processes during the plasma deposition of passive waveguides, particularly of silicon compound layers such as silicon oxide, nitride and oxynitrides. We give an overview of the effects of discharge parameters (reactor design, gas composition, energy of bombarding ions, substrate temperature) on the optical properties of the waveguide materials, and their relation to the microstructural and mechanical characteristics. Advances in plasma- fabricated photonic devices on silicon substrates are discussed.

We describe a new simplified process for inexpensive fabrication of low-loss (0.1 dB/cm) glass waveguides on silicon by ultraviolet light imprinting in photosensitive, organically modified sol-gel silica glass films prepared by one-step dip-coating process. The fabrication process is appealing because the buffer layer between waveguide and substrate is eliminated, and waveguides can be made in a few steps using low-cost equipment.

Single mode buried optical waveguides have been fabricated in fused silica by irradiation with a focussed beam of MeV hydrogen ions (protons). The technique has the potential to direct write waveguide devices and produce multi-layered structures, without the need for intermediate steps such as mask fabrication or the subsequent deposition of layers of material. Two different `near-field' optical techniques have been used to measure the near-field mode- field pattern produced by these waveguides at 670 nm and 633 nm. Methods are described for determining the refractive index distribution within single mode buried waveguides from their output intensity distributions via an inversion of the scalar wave equation. In addition, confocal Raman spectrometry has been used to map out the damage profile within the waveguiding region. Propagation losses of approximately 3 dB.cm^-1 have been measured in unannealed samples, which decrease to less than 0.5 dB/cm^-1 after thermal annealing at 500 degree(s)C for sixty minutes.

We present simple, low temperature methods for inexpensive fabrication of gratings in a photosensitive, organically modified silicate (ORMOSIL) system for integrated optical applications. The material is prepared by the sol-gel method. Gratings are made by UV imprinting through a mask and by an embossing technique. In the first case, UV exposure induces a refractive index change of (Delta) n equals 0.005 in the film and results in an index modulation type grating. Relief type gratings are made by mechanical embossing. Gratings are compared and characterized in terms of diffraction efficiency and grating period.

Small size ring resonators with ring diameter of 2 mm are fabricated using silicon nitride waveguides on silicon. The small diameter of the ring allows a large free spectral range of 26 GHz. Doped polysilicon is used as thermo-optic heating element to temperature tune and ring resonator. A poly-Si resistor is used for the first time as a thermistor to measure the waveguide temperature. The temperature coefficient of the poly-Si thermistor is measured to be 9.5 X 10^-4/ degree(s)C. The finesse of the ring resonator is 68 and the contrast 46%. The propagation loss of the silicon nitride rib waveguide is 0.1 dB/cm at 1312 nm. The temperature coefficient of the optical path length of the waveguide is 1.5 X 10^-5/ degree(s)C.

Different issues in design of passive integrated optics wavelength division multiplexing devices based on glass waveguide technologies are reviewed. The two established fabrication technologies for such devices are ion exchange into substrate glasses, and deposited doped- silica waveguides on silicon wafers. Design aspects for two most important categories of wavelength division demultiplexers/multiplexers, broadband dual wavelength devices and densely spaced multichannel devices, are considered. Particularly, design of phase array devices is discussed in detail.

We describe fabrication and characterization of UV-light imprinted sol-gel silica glass waveguide 1 X 8 beam splitter on silicon. Waveguide fabrication parameters carried out for channel waveguide realization were adapted at this new design. The splitter exhibited a relatively uniform output and a configuration loss of 0.83 dB at 1.55 micrometers wavelength.

A three-layer silica structure was grown on a 4-inch silicon wafer using plasma enhanced chemical vapor deposition. The 2.5 micrometers thick core layer is surrounded by 12 micrometers thick buffer and cladding layers. An aluminum layer, deposited on the cladding glass and patterned with the desired waveguide structures, serves as a mask for the UV exposure. An excimer laser operating on ArF giving an energy of 60 mJ/pulse was used to expose the sample to the total fluence of 4800 J/cm² of 193 nm light. The rise in refractive index is estimated to be around 3 - 10^-3 without hydrogen loading or any other kind of sensitization. The Y-splitters were evaluated on an automatic alignment setup using a semiconductor laser operating at 1542 nm. The splitting ratio was measured to be 1:1 at 1542 nm and 1:0.95 at 1310 nm. We measured the loss in the splitter to be 5 dB (fiber to fiberneglecting the splitting). The minimum coupling loss from fiber to waveguide was theoretically calculated to be 1.1 dB, leaving the propagation loss to be smaller than 2.8 dB/cm. The same value was measured for straight waveguides next to the couplers, indicating no measurable excess loss induced by the Y-splitters.

Germanosilicate film waveguides have been fabricated by plasma enhanced chemical vapor deposition. In the film waveguides straight waveguides, directional couplers and a Y-splitter were written directly point to point with UV-light by focussing a 244 nm beam by a single lens. No kind of mask was used to define the structure. The propagation loss of a multi-mode UV-written waveguide has been measured to 0.3 dB/cm, which is excellent for directly written waveguides. The UV-induced change of refractive index in the written components is estimated to be between 4 (DOT) 10^-3 and 6 (DOT) 10^-3. This provides a highly flexible and fast method for fabrication of new waveguide components.

Dense all-fiber WDM's designed for telecommunication network applications around 1550 nm have been made from the all-fiber Mach-Zehnder interferometers' technology. They demonstrate isolation greater than 20 dB and loss smaller than 0.1 dB. Channel spacing of 0.7 nm has been achieved experimentally supporting a 20.5 dB isolation. A cascaded structure made of two interferometers has also been constructed highlighting the ease with which one can arrange several of them in series and thus increase the quantity of channels supported while maintaining high isolation.

During the last two years investments have been made in order to develop new measurement techniques for the characterization of fiber networks. An important characteristic is the neutrality of polarization dependence losses (PDL). Fiber networks contain beside optical sources and detectors a series of basic components like singlemode fibers, integrated optical components (IOC) for the subdistribution, wavelength selective components (WDM) and amplifying elements. The quality of the optical data between transmitters and receivers and the achieved maximum range are determined essentially by the PDL value. In this report the PDL characteristics of passive splitters made by IOT Integrierte Optik GmbH will be described, especially those of N X M splitters. N stands for the entrance port of the splitter and can be 1 or 2. M stands for the exit port of the splitter and can be 2, 4, 8, or 16. Different measuring processes will be described and the achieved measurement results for the PDL will be discussed, In addition to this the different sources of error during the process are described. The achieved results of IOT's N X M splitters have very low PDL values. They are typically smaller than 0.1 dB what makes them excellently suitable for the construction of long-distance optical communication networks. In the meantime such splitters are valued worldwide by different systems suppliers and installed in first optical networks.

Linear fiber lasers can have single-mode operations especially if their cavities are short. The smallest length achieved is 100 micrometers . Such lasers have low thresholds, slope efficiencies and output powers. Ring lasers have much higher slope efficiencies and output powers, and narrow linewidths (a few kHz), but suffer from instabilities such as mode-hoppings. If double- ring resonators are used, the mode-hoppings can be eliminated without associated frequency shifts by dithering the two ring cavities together with a feedback mechanism. Double-clad fibers can be effectively used to increase the coupling of pump light into the core, while the absorption of the pump light can be greatly increased by codoping an Er³⁺-doped fiber with ytterbium.

RF-sputtering techniques were employed to produce Er-doped phosphate glass films on thermally oxidized silicon wafers. Film compositions were characterized by X-ray photoelectron spectroscopy. As-deposited films showed very low Er luminescence lifetimes. By postannealing of deposited films in pure oxygen, Er photoluminescence emission lifetime of the ⁴I_13/2 - ⁴I_15/2 transition could be increased from 1 - 2 ms to 8 - 9 ms. The long Er lifetime of the deposited films is very promising for achieving an optical gain. A dependence of measured lifetimes on pump power was observed which are related to a up-conversion quenching process. After postannealing, the sputtered waveguides showed relatively low attenuation loss at the potential pumping and signaling wavelengths. The loss spectrum from 700 nm to 1600 nm was measured by two-prism coupling. The films were easy to be patterned by lithography and ridge channel waveguides were developed by argon plasma etching.

This paper reports the results of an experimental study and numerical modelling of the gain characteristics of Erbium doped fiber amplifiers in the presence of pump excited state absorption losses and upconversion losses. The results reveal the differences in the gain characteristics for co and contradirectional pumping when these losses occur simultaneously in the amplifier.

It is aim of this paper to present the results of the simulation of DBR fiber lasers throughout a model based on the rate equations for pump and signal power and for the population of the upper laser level. The DBR laser cavity has been considered with two equal fiber gratings; the model considers the effect of the transversal overlap between the pump mode profile, the signal mode profile and the population inversion, the mode competition among longitudinal modes and the up-conversion process due to the formation of clusters of Er ions because of the high dopant concentration. The mode competition has been considered through the saturation effect on the population inversion due to the standing wave of the lasing cavity mode. The overlap integral along the cavity between the saturated population inversion and the nonlasing longitudinal modes with different standing wave pattern allows to determine their threshold condition. Simulations have been performed in order to determine the monomodality region for different value of the peak reflectivity of the Bragg reflector and different cavity length. The threshold of the fundamental and of the adjacent longitudinal mode in presence of the lasing mode, have been determined for two different values of the Er maximum concentration.

Potential application of polymers containing ferrocene as their backbone compound in fiber optic gas sensors are discussed. The refractive indices of these polymers are comparable to silica glass and vary substantially upon exposure to certain gases. The variation in the refractive index of thin films of a ferrocene-based polymer known as methyl-phenyl-silane ferrocenylene polymer upon exposure to ammonia, nitrous oxide, nitric oxide, nitrogen, and oxygen is examined. The structure and operation of tapered optical fiber gas sensors fabricated with the aforementioned polymer are explained. Also covered are the sensitivity and reaction times of two different sensors to ammonia and nitrogen.

A multilayer capillary fiber was designed for optical sensor applications and its optical properties were evaluated by using a fluorescent layer immobilized on its inner surface. This fiber structure combines a large interaction surface (the inner wall of the capillary fiber) for binding of fluorescent indicators with evanescent wave fluorescence measurement, which may facilitate the design of pseudohomogeneous assays without separation of the bound from nonbound fluorescent indicator. The inner surface of the capillary was derivatized by aminosilanization, followed by biotinylation and addition of streptavidin. This biotin- streptavidin coating facilities subsequent immobilization of any biotinylated species (e.g. antibodies, antigens, etc.) participating in specific molecular recognition. We have evaluated some properties of this capillary fiber design by using fluorescent proteins immobilized on the inner wall of capillary by biotin-avidin-interaction. Fluorescence was excited by a HeNe-laser (fluorescent indicator APC; (lambda) _em equals 660 nm) and by a Ar-laser (fluorescent indicator RPE, (lambda) _em equals 578 nm), and measured with a spectrum analyzer.

We have studied theoretically the performance of symmetric and nonsymmetric Mach-Zehnder interferometer sensors with ridge and buried index profiles. The effect of device parameters on sensor performance is investigated, in particular of the window opening in symmetric and of the path length difference in nonsymmetric interferometers. Sensors with low losses are designed.

Atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) were used to study optical fiber structures. The refractive index profile of fiber was disclosed by surface topography of etched fiber endface using a AFM. The difference of refractive index was resolved to 1 X 10^-6. Near-field optical intensity distribution at fiber endface has been successfully measured by a tapping-mode force regulated SNOM. Combination of tapping-mode AFM and SNOM allowed us to image both refractive index and near-field intensity structures of fibers simultaneously. The correlation between waveguide structures and near-field propagating modes was directly provided by this novel method. Results of single mode fibers and fibers with anisotropic structures illustrated the usefulness of this technique.

A new method for characterizing step index optical waveguides from experimental values of effective indices of guided modes is presented. We find the refractive index of the film by means of a linear fitting between the square of effective index and the square of the sum of mode index plus one, avoiding the use of the highest mode; further, statistical procedure has been used to evaluate the waveguide depth through the dispersion equation (without solving the transcendental equation) avoiding the use of zeroth mode. We have checked the method by using the Monte Carlo method, analyzing all possible guides with step index profile by means of normalized parameters. Furthermore, we compare the method with those presented by other authors and we find good agreement. The proposed method is easier than others and the error analysis shows its accuracy to be good.

The optical limiting behavior has been first observed for C₆₀ solution in toluene and in polymethyl methacrylate by Lee W. Tutt et al and A. Kost et al respectively. In order to make the possible use of the optical limiting in practice, we have studied the optical limiting of Q- switched Nd:YAG radiation at 532 nm using the C₆₀ in KBr as a solid host and the C₆₀ thin film on optical glass. The experimental results for the C₆₀ in KBr show that the threshold power of the optical depends on the concentrations of the C₆₀ in KBr, and the solid KBr-C₆₀ is induced optical damaged as the input fluence reach to 0.7 J/cm². The experiment results for the C₆₀ thin film on optical glass show that the optical limiting behavior is not obvious, and the C₆₀ film is be induced optical damaged when the input fluence is greater than 0.55 J/cm².

Optical links and photonic integrated circuits require integration of photonic and electronic devices at chip, module, or board level. The complexity of such systems is motivating a need for system level CAD tools which can simulate electronic and photonic devices and circuits simultaneously and at multiple levels of abstraction. Furthermore integrating photonic devices into conventional electronic computer and communication systems needs to be justified in terms of cost, performance, and portability of existing computer software and hardware. Thus system level analysis of optoelectronic interconnect system is clearly necessary to ensure that an overall functional and performance requirements are met. The proposed approach for system level modeling is to integrate photonic device simulations into the established electronic design automation environment, particularly VHDL-based one. VHDL description of photonic devices will provide benefits such as portability of individual design, system level performance analysis before building a real system, and synthesis capability for a rapid- prototyping. This paper demonstrates the use of basic VHDL entities of various passive optical waveguide components and a special VHDL package (`Optical_Package') defining physical photonic parameters to verify the feasibility of this approach. It includes modeling and simulation of global signal distribution network on MCMs using optical interconnect and wavelength division (de)multiplexing-based optical link.

Optics has the fundamental capability of dramatically improving computer performance via the reduction of capacitance for intrinsic high bandwidth communications and low power usage. Yet optical devices have not displaced silicon VLSI in any measure to date. The reason is clear. When placed into systems, the optical devices have not had significantly greater performance in equally complex information processing circuits and similarly low manufacturing cost. An approach demonstrated here uses the same system integration techniques that have been successful for silicon electronics, only applied to optics. Essential for creation of Very Large Scale Integrated Optics, with over 50,000 high speed logic gates per square centimeter, is a new class of Ultra High Confinement (UHC) waveguides. These waveguides are created with high index difference (as high as 4.0 to 1.0) between guide and cladding. The waveguides have been demonstrated with infrared cross sections less than 5% of a square free space wavelength. These waveguides can be manufactured today only in the mid- infrared, but the concepts should scale to the near-infrared as lithography improves. Waveguide corners have been designed and demonstrated with a bend radius of less than one free space wavelength. Resonators have been designed which have over 100 times smaller volume than VCSELs, yet efficiently interconnected laterally in high densities. A connector to the UHC waveguides has been developed and demonstrated using diffractive optical element arrays on the back side of the substrate. The coupler arrays can allow up to 10,000 Gaussian beam connections per square centimeter. This connectivity also has advantages for low-cost 3D packaging for reduced cost and thermal dissipation. Experimental results on the above concepts and components will be presented.

Transmission system experiments using surface emitting lasers (SEL) and integrated photoreceivers have been carried out. The surface emitting laser utilizes proton implantation for current confinement and has a small signal bandwidth of 10 GHz. The p-i-n/MODFET photoreceiver has a bandwidth of 11 GHz. Bit error rates of less than 10^-9 was demonstrated using the SEL source and the photoreceiver. The receiver sensitivity is -16.5 dBm at 10 Gb/s.

An algorithm for quickly training the BP neural network system identifier (BPNNSI) of the chaotic optical systems is presented in this paper. The ability of this algorithm, termed as the chaos speedup BP algorithm (CSBPA), has been demonstrated with the computer simulation of identifying the Bragg diffraction acousto-optic system (BDAOS) in which a 1:4:1 BP network was employed in identification. Taking the normalized output time series of the BDAOS as the training series, the BPNNSI was trained with the CSBPA as follows: (1) trained the BPNNSI to learn a chaotic state of the BDAOS with the BP algorithm where the initial weight distribution was set randomly; (2) took the final weight distribution obtained in (1) as the initial weight distribution for the other states of the BDAOS to be identified; (3) trained the BPNNSI to learn the other states still with the BP algorithm but with the initial weight distribution obtained in (2).

We present results on optical switching of a novel monolithic waveguide-based smart pixel. In this smart pixel two surface-normal optical input beams control an optical output beam propagating in-plane through a waveguide modulator. For the operation only DC biases are required. The optical front end of our waveguide-based smart pixel consists of a specially designed n-i-p photoconductive detector in series with a reference n-i-p photodiode. Together, both devices are forming a digital opto-electronic switch, which is directly controlling the waveguide modulator. All components are based on the Franz-Keldysh effect. For a first demonstration of our monolithic waveguide-based smart pixel all components have been processed from the same GaAs/AlGaAs double hetero n-i-p structure grown by MBE on a semi-insulating GaAs substrate. With a non-optimized sample design we obtain an output contrast ratio of 17 dB and an optical gain in excess of 320. The optical input energy is estimated to be 2.6 pJ (detector area 20 X 20 micrometers ²). In this case the wavelength of the input beams was 783 nm, while the waveguide modulator was operated at 910 nm. An evaluation of the switching dynamics indicates that high-speed operation in excess of 400 Mbit/s can be achieved. This waveguide-based smart pixel could for example be used in optical routing networks.

One of the most desirable features for a modern systems architecture is reconfigurability. It facilitates the sharing of various processing and memory resources among many different subsystems, thereby reducing the need for each subsystem to duplicate these resources. Reducing duplication also reduces size, weight, power consumption, and cost; all important considerations, especially in modern military systems. Sensor data requires very-wide- bandwidth, point-to-point connections, which are easily provided by fiber optics with good noise immunity, but the switching of such wide-bandwidth signals is problematic because electrical switches have both limited bandwidth and limited switching times. A wide- bandwidth, reconfigurable optical switch is required that overcomes coupling and splitting losses experienced by the optical signal passing through the switch so that sufficient signal- fidelity is maintained. In this paper, we investigate an integrated, active (i.e. amplifying) photonic crossbar switch to determine the signal degradation incurred for intensity modulation and direct detection using an NRZ data format and an ideal, matched-filter receiver. Various device configurations are analyzed in order to determine which produces the smallest degradation of the signal-to-noise ratio.

The Fourier Transform Infrared (FTIR) absorption spectrum for the range of 500 to 4000 cm^-1 wavenumbers was measured for several Ge films deposited on GaAs using ultra high vacuum E-beam deposition at various substrate temperatures ranging from room temperature (RT) to 500 degree(s)C. Using transmission electron microscopy, we show that Ge films deposited at room temperature and 100 degree(s)C on a (100) GaAs surface that did not have the oxides removed are amorphous while those deposited at 100 degree(s)C with the oxide removed are crystalline, but are highly defective. Secondary ion mass spectroscopy (SIMS) measurements show that the amorphous films at RT contain more than two orders of magnitude more oxygen than the films deposited at 100 degree(s)C or a single crystal film deposited at 400 degree(s)C. The oxygen-18 diffusion studies definitively show that the excess oxygen in the amorphous films percolates in from the atmosphere. SIMS studies further reveal that thermally removing the GaAs substrate surface oxide or depositing a Au film on top of the Ge film has little effect on the incorporation of oxygen.

Static and dynamic characteristics of three different laser structures, by using the same active structure, have been investigated: (1) conventional BRS (Buried Ridge Structure), (2) p-n multi-junctions (MJ) blocking layers and (3) Fe-doped semi-insulating (SI) InP blocking layer. Good blocking properties in MJ and SI laser structures have been showed by measuring the DC leakage current and the linearity of the power versus current (P-I) curve, also at high operating temperature; SI laser, respect to BRS and MJ structures, has shown a large reduction in parasitic capacitance and a considerable improvement in modulation bandwidth, limited only by dynamic characteristic of active region.

A high speed modulator at low voltage is created in the mid-infrared at 10 micrometers wavelengths by using field-induced absorption on otherwise forbidden intersubband transitions. The physical effects could scale to 1.5 micrometers wavelength light. This modulator is packaged into a unique 350 micrometers long ultra high confinement (UHC) waveguide for low capacitance and high speed. The modulator quantum wells are at the interface of a 2.1 micrometers thick by 3.75 micrometers wide UHC Ge waveguide and the GaAs substrate. The quantum wells have a 17% power coupling to the evanescent fields of the Ge waveguide. A connector to the UHC waveguides, with dimensions much smaller than a free space wavelength, has been developed and demonstrated using diffractive optical element arrays on the back side of the substrate and non-uniform grating couplers. Fields are applied across the modulator quantum wells via an ohmic contact to the side of the Ge waveguide on the top of the QWs. The ground is on the other side of the waveguide and lower towards the substrate. The 7 micrometers wide mesa supporting the quantum wells on the bottom of the Ge waveguide is slightly wider to accommodate a gold electrode.

In this work we present the results of a systematic study of H:LiNbO₃, H:LiTaO₃ and Cs:KTP waveguides obtained by combining measurements of propagation constants, optical profiles, and Raman scattering of the exchanged layers. Also, we present direct measurements of the r₃₃ coefficients in proton exchanged and annealed proton exchanged waveguides in LiNbO₃ and LiTaO₃ obtained by means of phase modulation technique and quantitative relations between the waveguide characteristics and the doping level in the Cs:KTP layers.

The results of a theoretical study on collinear acousto-optic (AO) interactions in proton- exchanged lithium niobate (PE:LiNbO₃) planar waveguides are presented. The guided-to- leaky mode-conversion for an input optical beam at the wavelength of 623.8 nm by the induced diffraction grating from a collinear surface acoustic wave is analyzed using the coupled-mode theory. Conversion efficiency and AO bandwidth have been calculated as functions of acoustic frequency, interaction length, and acoustic drive power density for different waveguide structures.

In this work the modeling of non collinear acoustooptic multifrequency interaction in wave- guiding structures is presented. The new model, which is based on the generalized coupled mode theory, allows us to evaluate the diffraction efficiency in Bragg regime when a multifrequency signal is applied to the interdigitated transducer deposited on the optical waveguide surface. The dependence of diffraction efficiency of the output orders on the intermodulation factors and on the transducer driving radiofrequencies has been investigated. The influence of fabrication parameters of Ti:LiNbO₃ waveguides on the linear dynamic range of acoustooptic multifrequency modulators has been extensively studied under monomodal propagation condition. Our results assert that the best performance in terms of linear dynamic range (approximately equals 43 dB) can be obtained on Ti:LiNbO₃ waveguides having weak refractive index change ((Delta) n < 0.001), small initial titanium thickness (< 100 angstroms) and medium enter radiofrequency (approximately equals 500 MHz).

Magneto-optic waveguides show specific properties in comparison with waveguides of other dielectric materials. Depending on the choice of configuration, there is either a coupling between guided TE and TM modes, or a phase shift of TM modes. Both effects are nonreciprocal and depend on the external magnetic field or permanent magnetization. This paper briefly overviews methods for modeling of magneto-optic waveguides. Special attention is paid to the application of perturbation theory for finding modes and to beam propagation.

Radiative coupling offers an alternative to the well-known principle of coupling by evanescent mode fields. Although the entire coupler structure will not suffer from radiation losses, the modes of individual waveguides can be leaky. In this case the mode fields oscillate in the coupling region thus allowing for remote coupling. Combining radiative coupling with the nonreciprocal properties of magneto-optic waveguides seems to be a promising line of investigation towards the realization of integrated optical isolators and circulators. New design for such devices is proposed and critically discussed.

The increasing demand for more advanced photonic integrated circuits has created the need to combine semiconductor materials with different lattice constants, i.e., GaAs on Si. During the past few years, much has been reported concerning the epitaxial lift-off technique. The most widely reported bonding method of epitaxial lift-off films is van der Waals bonding. However, there are problems with van der Waals-bonded devices. For instance, it has a long bonding time, which hinders an industrial use. Recently, we have investigated refinements of the epitaxial lift-off and grafting technique through using a single, transparent polymer membrane to support the material during the etch of a sacrificial layer, then depositing Au and Sn multilayers onto the lifted off devices and new host substrate. The devices are bonded by applying heat and pressure in a reducing atmosphere. The multilayer structures investigated in this work produce a resulting AuSn alloy with approximately 84 wt.% gold, but can be bonded with a peak temperature of 235 degree(s)C. In this paper we report our results in the optimization of the bonding parameters, with different diffusion barriers, new multilayer structures, as well as new applications of our bonding technique. We achieved important improvements in reliability and yield. The main advantages of our technology are thin bonding layers achieved with a minimum use of gold and an outstanding bonding quality reached in the large temperature range between 235 degree(s)C and 286 degree(s)C without flux. A thin, void free bonding layer means low thermal resistivity, which is especially important for laser diodes and high power devices. Further advantages of our new technique are the attainable precise control of the bonding layer thickness and the possible alignment of the devices through the transparent support and bonding membrane. We applied our new bonding technique to different optoelectronic devices such as MQWs and commercial laser bars and have simultaneously bonded a large number of devices. The bonded samples were investigated with several standard surface analysis techniques like optical microscopy, scanning electron microscopy and energy dispersive X-ray analysis as well as mechanical tests.

In this paper, we show how the recently plotted phase diagrams of the HLi1NbO3 and HLi1TaO3 waveguiding layers on top of a crystal of a given orientation allows to understand, and thus to control, the reverse proton exchange (RPE) process in lithium niobate and lithium tantalate crystals to make buried waveguides for extraordinary polarization modes and surface waveguides, supporting ordinary polarization modes. The relationships between ordinary and extraordinary refractive index changes for different crystalline phases in HLi1.NbO3 and HLi1TaO3 systems have been obtained. Keywords: lithium niobate, lithium tantalate, reverse proton exchange, optical waveguides

There are analyzed potential parameters of the planar AO modulators for space-and- wavelength photonic switching. We consider different schemes of superfast AO switching with capability up to 10¹⁵ switch/sec within one multichannel guided wave device. On the basis of the experimentally achieved parameters of the planar Ti:LiNbO₃ AO modulators we discuss a few prospective applications in high speed digital multipliers, commutators for optoelectronic super computers and associative memory systems.

We discuss the fabrication of a monolithically integrated optical displacement sensors using III-V semiconductor technology. The device is configured as a Michelson interferometer and consists of a distributed Bragg reflector laser, a photodetector and waveguides forming a directional coupler. Using this interferometer, displacements in the 100 nm range could be measured at distances of up to 45 cm. We present fabrication, device results and characterization of the completed interferometer, problems, limitations and future applications will also be discussed.

Integrated optics waveguides with reflective and diffractive gratings are analyzed. Accurate models are employed to design waveguides with Bragg gratings having 95% reflectivity for Er-doped glass waveguides laser application. Also, waveguides with grating to diffract a symmetric beam at 1.55 micrometers wavelength normal to the surface of the waveguide are studied.

A three-branch integrated-optic Mach-Zehnder interferometer is proposed for the simultaneous measurement of pressures and temperature. A broadband source coupled with a spectrometer is used to perform phase measurements independently from transmission loss fluctuations. Fast Fourier transform techniques applied to the transmitted spectrum allow demultiplexing of the signal from each pair of branches. Various correlation criteria are applied to establish pressure and temperature values from fractional phase measurements.

Highly sensitive surface plasmon waveguide devices capable of detecting changes in the refractive index of the surrounding environment on the order of 10^-5 have been designed. Inclusion of a high refractive index dielectric layer in the structure allows the spectral response of the plasmon resonance to be tuned over a wide range of wavelengths. A preliminary experimental characterization of these devices has been carried out using air, water, and Nafion fluoropolymer as superstrate materials. Results indicate that surface roughness in the metal layer degrades the extinction ratio, but does not alter the resonance wavelength. In addition, a design for a more durable surface plasmon waveguide sensor, in which the metal layer is protected, is proposed.