In the past few years proton-exchange has developed into a very promising method for fabrication of optical waveguides on LiNbO₃. In this paper we shall review the applications of proton-exchange waveguides, to date, and discuss the relatively new method of proton-exchange using dilute melts.

Channel waveguides fabricated by proton exchange in x-cut plates of LiNbO₃ have been examined using mode effective indices, secondary-ion mass spectroscopy (SIMS), and transmission electron microscopy (TEM). Effective indices measured over a wavelength range from 480 to 1320nm, and inverted with a step index approximation, reveals the dispersion of the proton exchanged layer. The index step,4Lne, depends also on the (Cr) diffusion aperture width used to define the channel; the surface One for 3-5/Am wide channels are 5-10% less than for those lOpm and wider for wavelengths above 632nm. Common 5 minute exchange times at 249C in pure benzoic acid were used throughout. Corroborative evidence, using SIMS, shows reduced Li depletion in narrower guides. Finally, TEM analysis of thinned waveguide samples strongly suggest instabilities observed in proton exchanged waveguides is primarily due to dehydration.

Two methods for measuring the photorefractive susceptibility of LiNb0₃ waveguides are reviewed. Data for waveguides formed by means of Ti indiffusion and also by proton exchange techniques are discussed. The photorefractive effect in channel-waveguide devices is analyzed by means of a model which accurately predicts the time evolution of photorefrac-tive effects. The response of guided-wave Mach-Zehnder interferometers is experimentally evaluated, and the magnitudes of the photovoltaic and photoconductive components which com-prise the photorefractive effect are quantitatively determined. While these initial results were obtained for channel-waveguide devices, the model is believed to be extendable to planar-waveguide devices as well.

Lithiun niobate crystals have been grown from a range of selected melt compositions. Index of refraction measurements on the congruent composition at 6328 Å and 20° C are reported. Variation in index with composition is examined with respect to the congruent composition, used as the standard I0 substrate, to assess its compositional uniformity. Index measurements for congruent lithium tantalate are also reported. Material and composition related properties which can effect I0 substrate behavior are discussed.

The nonlinear optical properties of thin (-1 mm) lithium niobate integrated optical substrates can be obtained from the interference between the free and bound second harmonic waves (Maker fringes). The harmonic power is affected by the homogeneity of the plate, and this provides us with a method of quality control. We use a Q switched YAG laser to generate the harmonic power and the equipment is computer controlled. Fringe patterns that deviate appreciably from those expected for homogeneous plates indicate substrates that may not function properly in devices. In addition, the method can be used to analyze lithium niobate boules to ascertain if they are potentially useful for substrates.

The measurement of the refractive index of lithium niobate integrated optical substrates of various stoichiometries is difficult because of their thinness (≈l mm). We use a prism coupling method and calculate the refractive index from the angle at which the intensity of the light from the total internal reflection in the prism base drops. The equipment is computer controlled. In addition, the method can be used to analyze lithium niobate boules to ascertain if they are potentially useful for substrates.

This paper reviews the variety of ways in which optical signals have been used to control microwave devices in such applications as optical-injection locking, phase shifters, modulators, and switches. Techniques for the generation and detection of microwave radiation by optical means are also described. The feasibility of optical microwave monolithic integrated circuits is considered.

An experimental concept is presented for specifically characterizing GaAs monolithic integrated optic (I0) structures exposed to the space parameters of temperature and radiation. The experiment will measure space radiation and temperature effects during a polar orbit mission. Of particular interest are two monolithic structures, a four port active GaAs optical switch and GaAs channel waveguides. The experiment utilizes apparatus designed for AFWL Experiment #701 ^1-3 currently in space orbit. Prediction of the space effects on IO devices are presented under varying irradiation levels, temperature extremes and other adverse space effects.

Metal-silicon-metal cladding layers on dielectric waveguides exhibit coupling and absorption characteristics which make them useful as high-efficiency thin-film photodetectors for integrated optical applications. Periodic coupling between the guided mode of the lossless waveguide and the lossy modes supported by the semiconductor cladding produces an oscillatory behavior as the semiconductor thickness is increased. A high level of energy transfer from the waveguide to the semiconductor can be obtained, thereby maximizing detector absorption.

A concept is presented for a monolithic, integrated, C³ laser amplifier exhibiting bistable output characteristics, which is composed of three distinct regions: laser, amplifier and optically bistable etalon. Operational characteristics are discussed for single frequency amplification of a low power, digital, optical signal. Theoretical models are viewed with respect to known experimental results. The concept indicates a possible application for improving optical repeater operation.

The important characteristics of three-terminal coupled-cavity lasers are reviewed. Tradeoffs in the design and fabrication of both monolithic and recleaved devices are discussed. New results for the continuous tuning of several coupled-cavity structures are presented. More than 8 Å of tuning in a single longitudinal mode is reported for a monolithically integrated two-section GaInAsP laser.

Proton-exchanged ring resonators with a finesse of 6 at 0.79μm have been fabricated on Z-cut lithium niobate. Measurement of finesse and resonator throughput at resonance and antiresonance are used to calculate propogation loss in the ring. Measurements at 1.3μm indicate that ring losses are lower at this wavelength and a finesse of 22 may be feasible.

Many types of electro-optic modulators have been considered for IOC applications. The mode extinction modulator is particularly interesting in that its operation is based on the composition of several physical mechanisms. These include coupling between guided modes, radiation to substrate modes, and voltage dependent propagation losses. Therefore, in addition to possessing the desired properties of high frequency response, low operating voltage, high efficiency, large packing density, and simplicity in fabrication, the modulator's transfer curve can be altered to optimize a particular curve shape. This is accomplished by adjusting certain physical parameters in the waveguide structure or modulator electrodes. For example, a large linear dynamic range can be achieved by the proper choice of physical parameters. Optimization for high efficiency, linearity, and modulation depth will be reported along with design parameters and trade-offs. In addition, a technique for creating an optical bias will be discussed which allows operating point selection.

In contrast to other III-V materials such as gallium arsenide, it is difficult to dry-etch indium phosphide at temperatures below which most photoresists will deform. Argon ion beams usually sputter phosphorus preferentially, and the common reactive dry etchants which contain fluorine and chlorine produce indium halides which are not volatile unless heated to over 150°. This paper presents some dry-etching techniques for unheated samples which may be used to overcome the above problems. Ion-beam etching at large incident angles and ion-beam assisted etching using iodine vapour are discussed in detail. These processes are investigated by various analytical techniques with respect to aspects which are important for integrated optoelectronics, namely surface composition, crystal damage, smoothness and anisotropy.

We report the fabrication of novel V-groove structures by etching silicon twice in an anisotropic etch solution. This technique is capable of yielding micron size patterns from large patterns. For example, we have been able to reduce a 7 μm pattern down to 1 μm. This technique finds useful application in novel diffracting grating structures.

A plasma activated chemical vapour deposition (CVD) technique is described for fabricating doped silica optical waveguides on silica substrates. Planar, germania doped, silica waveguides have been fabricated with less than 0.3 dB/cm attenuation at λ = 0.633 μm. There is considerable scope for reducing the attenuation much further. Waveguide depositions are normally carried out at 1100°C but guiding films have also been deposited at room temperature.

Low loss planar optical waveguides have been fabricated by thermal nitridation of thick silicon dioxide films. The waveguides were formed by oxidizing silicon wafers at 1100°C in steam and then exposing them to an atmosphere of electronic grade ammonia for periods between one and ten days. Measurements of waveguide loss, effective refractive index and refractive index were performed as functions of nitridation time. Losses for these waveguides ranged between 0.06 and 0.31 dB/cm. Auger electron spectroscopy and ellipsometry were used to characterize the nitrided films. The waveguide loss data were compared with calculations of optical waveguide properties.

The optical properties of proton irradiated n-type GaAs, implanted at room temperature and subsequently furnace annealed, are examined using infrared reflectance spectroscopy. Substantial changes in the reflectance spectra are observed with post-implantation annealing. Computer simulations , based on a Drude model free carrier contribution to the dielectric constant, are used to obtain best fit parameters to the measured spectra. The resulting free carrier profiles display a two layer characteristic. The top layer encompasses the implanted region and remains stable with thermal treatment up to 500 C. A lower layer appears with annealing at 200 C and diffuses deeply into the substrate material. Further annealing eliminates the lower layer but the top layer is present even after a 600 C anneal. An activation energy of 1.2 eV and a diffusion preexponential factor of 4.3 E-1 cm2/s are found for this process.

We report the experimental observation of partial switching of light between two coupled multiple quantum well waveguides caused by an increase in the optical intensity of the input beam. About lmW of power launched into the waveguide was required to switch the coupler from a crossed-over state to one of equal power division at the output. The measured value of the nonlinear refractive index coefficient (n,) in one of the guiding layers was 10 cm²/W when the intensity attenuation was 13.5cm^-1. The possibility of the refractive index change being caused by thermal effects has been ruled out experimentally. We have also obtained a theoretical description of this nonlinear directional coupler action by solving the coupled mode equations in the presence of a nonlinear refractive index and a standing attenuation constant. Very good agreement between our model and the experimental device has been obtained.

We report the first measurements of linear and nonlinear absorption and perpendicular field electro-absorption (Quantum Confined Stark Effect) in GaAs/AlGaAs quantum wells for light propagating parallel to the plane of the layers. This geometry is well-suited for integrated optics. With increasing intensity the absorption is found to saturate at the very low intensity of 300 W/cm². With increasing electric field the absorption edge shifts to longer wavelengths by as much as 40 meV, giving a modulation depth >10 db in a 150 μm long device. The strong dichroism present in this geometry is retained even at high fields, making polarization sensitive electro-optical devices possible. We also demonstrate in the waveguide geometry optical bistability due to the self-electro-optic effect with 20:1 on/off ratio.

This paper describes our recent progress in the realization of all-optical logic devices using integrated waveguides in a III-V semiconductor. The potential for high speed all-optical signal processing is discussed. The physical mechanisms for the optical nonlinearity, including the important role of waveguide heating, are considered for their influence on device design. The measurement of the nonlinearity in several III-V's making use of a wave-guide Fabry-Perot interferometer is presented. A preliminary device based on a Mach-Zehnder waveguide interferometer has been fabricated in GaAs.

A number of organic materials have been observed to possess very large intrinsic nonlinear optical susceptibilities. Second and third order susceptibilities have been measured to be larger than any inorganic materials. These large susceptibilities as well as potentially very fast switching times arise from certain charge correlated features of the electronic states of the constituent molecular or polymeric units. We will review the research in this area, including basic studies into the origin of the susceptibilities on a molecular level. We will also discuss the requirements and properties of bulk materials including molecular and polymeric crystals, as well as thin films. Finally, we will discuss recent efforts to optimize microscopic and bulk properties aimed at making organic nonlinear optical materials a viable technology.

Our recent measurement of the third order nonlinear optical susceptibility of PTS polydiacetylene with six picoseconds temporal resolution has confirmed the previous speculation that this class of fully ordered polymeric crystals is a very promising candidate for nonlinear optical guided wave devices. These measurements were made possible by a new method of crystal growth that uses a shear in order to orient the monomers on the substrate. The low surface and bulk optical scattering that is characteristic of the materials grown with this new method are a necessity in any eventual integrated optical device. Additional fabrication proceedures have been demonstrated using ion implantation to modify the optical and electrical properties of the materials.

The nonlinear mixing of optical beams has led to a rich spectrum of phenomena since the inception of the field in the early 1960's. This includes the generation of new frequencies, a host of nonlinear spectroscopies, and a variety of signal processing operations such as phase conjugation, optical bistability, and optical switching. In general, nonlinear optical interactions occur whenever the optical fields associated with one or more laser beams propagating in a material are large enough to produce polarization fields proportional to the product of two or more of the incident fields.' These nonlinear polarization fields radiate fields at the nonlinear frequency, which grows linearly with propagation distance under optimum conditions of phase matching. Hence the key to obtaining efficient nonlinear optical interactions is to maintain high optical intensities over the longest distance possible.

Waveguides and waveguide resonators are very useful devices for nonlinear interactions. Indeed, they permit having a very high density of energy and quite long interaction lengths, and lead to devices with high conversion efficiency for low pumping power [1, 2] . In the visible and the near infrared, the most convenient material for nonlinear effects is Lithium Niobate in which we are able to realize good waveguides by Titanium Indiffusion (TI). In this paper we shall discuss the new waveguide fabrication process that we developped in Nice : Titanium Indiffusion Proton Exchange (TIPE), and we show by the example of Second Harmonic Generation (SHG) the new possibilities of these waveguides which enables us to design very interesting parametric devices.

Spontaneous optical parametric fluorescence has been observed for the first time in a guided wave structure (Ti:LiNbO₃ channel waveguides). The results allow to study the phase matching (tuning) properties of optical parametric processes. Parametric amplification (together with difference frequency generation) has been investigated in detail to optimize the optical gain. Experimental and theoretical investigations of optical parametric oscillation in Ti:LiNbO₃ waveguide resonators are reported. The oscillator build-up time has been studied as function of the pump power level. With pulses of 150 ns duration a threshold pump power of only 250 mW has been achieved. A tuning range 0.9 μm <X < 1.6μm could already be demonstrated.

A large (n₂ ~ 10^-13 - 10^-14 m²/W) and fast (less than 16 ps) third-order optical susceptibilities has recently been identified in semiconductor doped glasses. Low-loss channel waveguides have been made in these glasses and have been used in the fabrication of integrated nonlinear optical devices such as the nonlinear coherent coupler which may be able to operate as an all-optical logic gate.

The potential applicability of organic materials to integrated optics is substantial owing to both microscopic and bulk properties of organic and polymeric materials. Fabrication flexibility and the tailoring of optical properties via material engineering are but two of the advantages of using organic materials. Both passive (waveguiding/interconnection) and active structures/devices can be built. We will review the structures fabricated from organic materials that can be applied to integrated optics; and the properties of these structures will be discussed. Recent efforts in the application of organics to integrated optics will be presented, including fabrication of polymer waveguides and measurement of waveguide and loss properties.

A discussion of the various TE-TE and TM-TM coupling coefficients derived for both normal and oblique incidence to the rulings of a corrugated waveguide diffraction grating is presented. It is shown that the substantial disparity between the TM-TM coupling coefficients can result in vastly different predictions of peak grating reflectivity. We conclude that experimental examination of the coupling coefficients is necessary before the accurate design and analysis of waveguide gratings can be achieved.

The diffraction of aberration corrected Fresnel lenses in planar GaAs integrated optical waveguides are modeled on a desktop microcomputer. The simulated lenses are shown to be corrected for both spherical aberration and coma.

A number of different methods of calculating the coupling efficiency between a semiconductor waveguide and an optical fibre have been studied. The limitations to the simplest methods have been identified. Practical designs of waveguide have been analysed, and a structure with a coupling efficiency of 0.6 dB has been discussed.

Cross-talk characteristics of optical waveguide directional coupler switches using two-sections of alternating Δβ phase mismatches are studied. In particular, it is found that the cross-talk characteristics can be influenced by the presence of passive coupling between the waveguides outside the electrode-interaction region, by the use of unequal voltages applied to each section and by the use of unequal sectional electrode lengths. The switching diagrams showing the contour maps of the regions corresponding to differing crosstalk levels for each case are presented.

Successful implementation of ultra-high-speed fiber optics local area networks depends not only on the invention of efficient new protocols and architectures but also on the development of new interface devices. These interface devices may take the form of inte-grated optical circuits (I0Cs). This presentation will focus on the various functions of the interface devices which may be performed by different IOCs.

A test bed employing a Ti:LiNbO, 4x4 nonblocking interconnection network has been implemented. As test bed data sourced, four video cameras each generate a 90 Mbs bit-stream. Input data streams feed into the 4x4 switch where any input channel can be switched to any output channel. The output signals are converted back into analog form and drive four video monitors. The Ti:LiNb0₃ switch is composed of 16 single-polarization directional couplers that are arranged in a crossbar configuration. The end-to-end insertion losses, including fiber pigtails, range from 6-25 dB, and the channel-to-channel switching efficiency varies from -6 dB to -16 dB. The paper will focus on the development of the test bed and the associated problems, which include: variation in electrode drive voltages, polarization effects, and coupler drift.

Three classes of integrated optical devices suitable for implementing general combinatorial logic are discussed. The categories considered are electric-electric-optic (EEO), electric-optic-optic (E00), and optic-optic-optic (000). Existing gate geometries based on electro-optic Bragg gratings are modified to permit the realization of the NOT, NAND, OR, NOR, and inhibition functions. A full-adder based entirely on electro-optic Bragg gratings is developed, and the device is compared to current VLSI technology in terms of size and speed. The use of programmable logic arrays (PLA's)for implementing general combinatorial logic is discussed. The paper concludes with a proposal for using electro-optic Bragg gratings to construct an integrated optical PLA.

Lithium niobate electro-optic waveguide frequency translators suitable for use in coherent optical fibre systems are reviewed. The design of double sideband Mach-Zehnder interferometric Y junction frequency translators is discussed and the fabrication and operational tolerances of these devices considered. The continuous generation of frequency translated optical signals with frequency translations upto 6.5 GHz at a wavelength of 1.52 μm are reported and the experimental results compared with theoretical predictions.

Acousto-optic signal processors, such as convolvers and correlators, are usually designed to have increased bandwidth and high dynamic range. We will show how, by simply choosing the proper polarization of interacting light, diffraction efficiencies, bandwidth, and dy-namic range can be enhanced. This will be demonstrated bv examining the case of acousto-optic interactions between an unguided, linearly polarized optical beam and a surface acoustic wave. Using the side-entry technique, the optical beam is launched at grazing incidence onto a YZ-LiNb0₃ substrate, propagating laterally beneath the surface. A conventional coupled-mode analysis is performed, assuming plane wave optical beams. We show how the coupling parameter depends on the polarization and thickness of incident beam and on the acoustic power. Experimental results will also be presented, showing that for p-polarized incident light, diffraction efficiency bandwidths can be larger by a factor of two, when compared to the s-polarized case. Plots of diffraction efficiency versus both deviation from Bragg angle and transducer frequency will be shown. The coupled-mode analysis also gives conditions such that s-polarized light can have a larger bandwidth than p-polarized light, a fact which has not yet been demonstrated experimentally.

This paper presents a design for an integrated optical wavefront sensor. Light from an aperture is focussed by a lens onto a detector array. The resulting signals can be used to determine the amount of angular tilt of the wavefront. Parameters affecting angular resolution are analyzed. Tilt angles as small as 10^-5 rad are detectable. The effect of wavefront curvature is also discussed.

Progress in developing integrated-optical components for fiber sensors is reviewed. Two LiNbO₃ channel-waveguide components are described. Splitting loss as low as 0.5 dB has been achieved in a Y-branch and 40 dB sideband suppression has been obtained in a serrodyne frequency translator.