If I were in the audience, listening to this talk, I am sure I would like to hear answers to questions such as: 'here is Integrated Optics going? What should I do to capitalize on this future? How soon will this market grow? What products will be needed?

The various techniques that have been used to fabricate waveguides in GaAs/GaAkAs are reviewed; including p-n junction, carrier-concentration-reduction, heteroepitaxial growth, and strip-loading methods. The results of this survey show that it is possible to produce waveguides in GaAs/GaAkAs with losses less than 2 dB/cm for wavelengths ranging from 1.06 to 10.6μm. In some cases losses as low as 1 dB/cm have been observed.

As integrated electronic circuits based on GaAs are getting faster and more complex and the relatively new fiber optic communication industry is expanding into new markets, such as shipboard communication links, the need for high speed optical signal processing in a GaAs based system has become increasingly evident. The economy and flexibility of fabricating both electronic and optical circuits on the same wafer promises significant increases in computing power and speed of large distributed systems (those involving more than a few medium density chips.) The obvious medium for integration of optics with eletronics is GaAs. High speed ICs utilizing GaAs MESFETS are already in the marketplace as are GaAs/AlGaAs laser diodes and detectors. Thus, the two building blocks exist and wait only to be stacked together in a useful manner. What must hold these together is any combination of passive waveguides, modulators, switches or optical fibers which will provide high speed links between several electronic systems. It does not matter that these systems may be miles apart or on the same wafer, the interconnecting optical circuits are the same except for the possible insertion of an optical fiber.

Ion implantation of semiconductor materials is a fabrication technique that offers a number of distinct advantages for the formation of guided-wave components and microelectronic devices. Implanted damage and dopants produce optical and electronic changes that can be utilized for sensing and signal processing applications. GaAs is a very attractive material for optical fabrication since it is transparent out to the far infrared. It can be used to fabricate optical waveguides, directional couplers, EO modulators, and detectors, as well as other guided wave structures. The presence of free carriers in GaAs lowers the refractive index from that of the pure semiconductor material. This depression of the refractive index is primarily due to the negative contribution of the free carrier plasma to the dielectric constant of the semiconductor. Bombardment of n-type GaAs by protons creates damage sites near the surface of the crystal structure where free carriers are trapped. This "free carrier compensated" region in the GaAs has a higher refractive index than the bulk region. If the compensated region is sufficiently thick and has a refractive index which is sufficiently larger than that of the bulk n-type region, an optical waveguide is formed. In this paper, a description of ion implantation techniques for the fabrication of both planar and channel integrated optical structures in GaAs is presented, and is related to the selection of ion species, implant energy and fluence, and to the physical processes involved. Lithographic technology and masking techniques are discussed for achieving a particular desired implant profile. Finally, the results of a set of ion implantation experiments are presented.

A 3 inch GaAs optoelectronic integrated circuit (OEIC) process has been developed for the fabrication of an integrated optical detector array Initial work has concentrated on a 16 element array plus amplifier operating in the 2-3 GHz frequency range. The detecting elements can be Schottky barrier photodiodes, photoconductive detectors, or optical MESFETs, whilst the amplification network is based on 1 µm gate length MESFETs with a 2 source-to-drain spacing. Direct writing electron beam lithography is employed for both pattern definition and automatic pattern registration, giving linewidth and alignment tolerances of better than 0.2 μ,m. The active regions of the FET are doped n-type using ion implantation of Si²⁹.

A composite-cavity laser diode demonstrated high power, single optical frequency operation under both CW and modulated conditions. This device consisted of an Al GaAs CSP laser coupled to an external cavity constructed from a 1 mm long single mode ion exchange waveguide. With an average optical power of 10 mW, the composite-cavity laser diode demonstrated a sidemode suppression ratio greater than 577:1 under CW conditions and a side mode suppression ratio of greater than 100:1 under modulation with a modulation index of 1.10 at 100 Mbps.

Integrated optical circuits will be used in high performance optical systems in the future. This paper reviews progress towards making such circuits using semiconductor substrates. Discrete GaAs/GaAlAs devices have been made and have shown low propagation loss (<2dB/cm), low operating voltage (9V for a Tr phase shift) and the potential for high speed (<500ps rise time). InP devices are less well developed but show promise. The proposed implementation of a laser/waveguide component is described, and the prospect of other integrated optical circuits, including matrix switches, is discussed.

This paper describes experimental results and theoretical modeling of optically controlled Dielectric Resonator Oscillator (DRO) and Gunn oscillator circuits operated at X-band. A commercially available DRO device was modified to facilitate the optical control of its output characteristics. The device was found to be optically tunable up to 15 MHz and FM rates up to 130 MHz were observed. The Gunn Oscillator circuit was designed in a microstrip configuration. A high resistivity Si wafer was incorporated in the resonant cavity as the optical tuning element. The circuit was tuned in excess of 10 MHz. The operation of these devices were modeled using analytical and computer aided design techniques and showed good agreement with the experimental results.

The time dependence of the photorefractive effect in single mode LiNbO₃ directional couplers at low powers of 3.2 μ.W in the GaAs wavelength spectrum is discussed. The transient response was found to De consistent with bimolecular relaxation processes which caused tae saturation of this effect to occur for times on the order of an hour. Additional effects having much longer decay times were observed consistent with those found in bulk LiNbO₃.

The general framework for this paper is provided by the hybrid integrated optical spectrum analyser using lithium niobate. The paper will consider the important components of this device and factors which limit the performance. Work carried out at Glasgow University on some of the important components and problems will be described.

The guided wave acousto-optic Bragg interaction has been investigated in proton exchanged waveguides on X and Y-cut lithium niobate. 220 MHz Z-propagating surface acoustic waves were used to probe the piezoelectric, electro-optic, and acousto-optic properties of the proton exchanged waveguides. We have found that the electromechanical coupling coefficient is reduced significantly in these structures, as is the overall acousto-optic interaction efficiency. The reduced interaction efficiency is attributed to the lack of an electro-optic contribution resulting primarily from a reduced magnitude of the r33 electro-optic constant. We have also seen a very marked increase and strong temperature dependence in the surface acoustic wave attenuation.

A new hybrid binary/residue arithmetic processor is proposed which significantly reduces the number of components and lines with respect to ordinary residue processors. Programmable optical threshold logic elements are combined with the hybrid structure to produce an optical architecture which offers substantial advantages over all-electronic approaches.

We propose to implement systolic sampled-data lattice processors optically by means of linear integrated optics arrays of coupled-wave devices such as switched directional couplers and TE-TM mode converters, and indicate some potential signal processing applications such as discrete time and analog frequency filtering and optical pulse compression.

Planar and channel optical waveguide structures formed on silicon substrates using the fabrication techniques of sputtering, thermal oxidation, and chemical vapor deposition are discussed. Losses in the various waveguide structures are reported. The use of polycrystalline silicon deposited by chemical vapor deposition onto any waveguide substrate to form integrated photodetector arrays is discussed. Laser recrystallization of the deposited silicon is used to allow fabrication of high quality devices. Measured values of photodiode reverse current of less than 10^-12 amp and breakdown voltages of 40 volts are respectable values for small photodiodes incorporated into a dense array.

The ability of integrated optic systems to compete in signal processing aplications with more traditional analog and digital electronic systems is discussed. The Acousto-Optic Spectrum Analyzer is an example which motivated the particular work discussed herein. Provided real time processing is more critical than absolute accuracy, such integrated optic systems fulfill a design need. Fan-out waveguide arrays allow crosstalk in system detector arrays to be controlled without directly limiting system resolution. A polyurethane pattern definition process was developed in order to demonstrate fan-out arrays. This novel process is discussed, along with further research needs. Integrated optic system market penetration would be enhanced by development of commercial processes of this type.

We describe the fabrication of low loss (= 0.2 dB) Ag+--Na+ exchanged glass optical waveguides using the novel electrolytic release tecnnique. Development of a concentration cell that can be used to measure the Ag+ ionic concentration in situ provides opportuniites for on-line concentration control. Since the siLver ion generation and control as well as the temperature can be adjusted electronically, the process may be computer controlled.

Correlations between optical properties and structural modifications induced by the fabri cation procedures are reported for both Ti indiffused and proton exchanged LiNbO₃ waveguides. Surface roughness and structural defects account for the dependence of the propagation losses on the diffusion time in Ti:LiNbO₃ waveguides. The heavy lattice distortion induced by the high H concentration is related to the high in-plane scattering levels in proton exchang ed waveguides. Post annealing reduces lattice distortions and improves optical performances.

Major national industrial cooperation in the conduct of generic research and development has been used effectively by countries like Japan to move rapidly and decisively into new world markets. Similar national industrial cooperative activities in this country have been rare, due to a combination of the U.S. anti-trust laws, and the competitive heritage of the American business community.

Optical waveguide structures with symmetric branches preceded by abrupt bends were studied. Measured power-splitting ratios range from 0 to 6 dB and oscillate with the bend-brancn separation. The power splitting also depends on the mode ettective index, wnicn is affected by the polarization, wavelength and waveyuide fabrication parameters. Device implications are also discussed.

A technique was developed that uses bulk and effective indices measured at several wavelengths to determine index profiles in slab and channel waveguides. This technique involves the minimization of a functional J used to match the square of measured effective indices with those calculated. Effective indices are calculated from a modal analysis of a Galerkin type. J is minimized with respect to a number of parameters that are used to describe the refractive index appearing in the reduced wave operator and, in this way, the "inverse problem" of determining index profiles from measured effective indices is solved. Results are reported for slab and channel waveguides.

Precision characterization and alignment of fiber optic components and integrated optical circuits demands a new approach to mechanical manipulation. Positioners based on motor/ screw combinations are limited by discrete stens and backlash. Conventional piezoelectric stack designs approach the required resolution but compliance and hysteresis limit the applications. In this paper, a novel linear piezoelectric motor, the Inchworm, is described and its application to high resolution multi-dimensional fiber optic manipulation is discussed.

An Optical Circuitry Cooperative (OCC) has been formed as an NSF cooperative research center in which six or more companies contribute financial support; NSF provides support which declines to zero in five years. Companies benefit from a center by early access to research results, leverage for their research dollars, participation in research selection, and improved relations with faculty and students. The university receives support for a major research program that increases its research capability, provides reasonably stable funding, and opens more opportunities for graduate students. The potential of optical circuitry has been discussed for many years, but the excitement is growing rapidly on the strength of the success of optical fibers for optical transmission, the generation of subpicosecond opitcal pulses, and the development of promising optical logic elements, such as optical bistable devices. And yet, much research remains to be done to discover the best nonlinear optical materials and fabrication techniques. OCC will perform research to provide a data base to allow the development of optical circuitry devices. The areas encompassed by OCC include all-optical logic, picosecond decision-making, guided-wave preprocessors, opti-cal interconnects within computers (both fiber and whole-array imaging), optical storage, and optical computer architecture and devices.

Recent progress concerning electrooptic modulation and switching are discussed here from various points of view. First the drive voltage/insertion loss optimization is considered. Then the speed problem will be discussed and the different solutions to get polarization independent devices are reviewed.

Certain optics-based register-level devices for digital processing applications are considered. These modular devices have electronic binary inputs and outputs and are based on the electro-optic intensity modulation of near-surface light. The modulation technique combines features of a total internal reflection electro-optical spatial light modulator and a Lloyd's mirror interferometer. The devices may be described as threshold logic elements for which the analog weighting and thresholding operations are effectively implemented using integrated (or near-integrated) optical technology. Such an effective implementation, which is difficult at best using current all-electronic technology, is important because digital processing systems using threshold logic elements require no more and often many fewer interconnections and logic levels than do similar systems using conventional logic gates. Fewer interconnections and logic levels may in turn provide the foundation for exceptionally high-speed, low-power-consumption, small-size, and otherwise attractive digital processing systems.

The sensitivity of Ti : LiNbO₃ waveguide Mach-Zehnder modulator is improved by a new electrode configuration. We show that optimum electrode dimensions exist and a drive voltage as low as 0.35 V is sufficient for complete modulation.

Theory and experiment at 1.3 μm are presented to describe and compare the behavior of two kinds of channel waveguide modulators in Ti-indiffused LiNb03: Mach-Zehnder interferometers and directional couplers. Each device can be operated as a linear modulator when biased to an appropriate point, either by passive geometrical means or by application of a DC voltage. However, the device voltage responses differ, being sinusoidal for an interferometer and varying as sin2x/x2 for a directional coupler. There is good agreement between calculated and measured device responses. The linear dynamic range of each kind of modulator is reported. We have measured linearity over 76 dB and voltage sensitivities of ~ 13 μV.

Optical oscillators and hybrid bistable optical devices are built-up with integrated optical modulators as basic nonlinear element. The oscillator properties are analyzed by the describing function method. 1.5 GHz oscillation frequency is achieved. Delay-time dominated bistable electrooptic devices show phenomena such as periodic and chaotic oscillations, and provide bistable and monostable modes of operation. The bistable device is completely analyzed here by the method of iterated maps.

Guided-wave optics in LiNbO3 has entered an interesting period in its development. The basic properties are being evaluated and modified, high performance devices are being built and demonstrations of systems incorporating these devices are being given. In this paper we would like to review recently reported results which we have obtained in each of these areas.

A novel CAD system for use in the manufacture of high resolution chrome masks for wafer scale integrated optic devices is described. The etching of titanium waveguide structures is considered and it is demonstrated that SF6, plasma etching techniques can be used to advantage. The packaging requirements of water scale integrated optic structures are out-lined and a novel fibre attachment technique described.

The integrated-optic frequency shifter utilizes electro-optic polarization conversion by a travelling index grating in LiNbO₃:Ti stripe waveguides. The optical frequency shift is equal to the frequency of two electric phase-quadrature drive voltages. A device operating at a fixed wavelength of 723 nm with an optical bandwidth of ~ 1 nm shows ≥90% conversion efficiency and ≥30 dB suppression of undesired sidebands at frequency shifts up to ± 10 6Hz.

In this paper, several novel concepts are presented that relate to the propagation of light in nonlinear waveguides with a spatially periodic refractive index or boundary perturbation. The particular nonlinearity considered is an intensity-dependent refractive index. Devices based on these periodic nonlinear waveguides include variable grating couplers, optically-tunable optical filters, light controlled spatial scanners, and distributed feedback bistable optical devices. The possibility of pulse compression by nonlinear periodic structures is also considered.

The bistable reflection effects of an incident homogeneous plane wave upon an interface between a linear and nonlinear magnetic media are studied. At a nonlinear interface, a plane wave is incident from a linear medium with permittivity ε1 and magnetic permeability m1 upon the boundary of a negatively nonlinear medium whose permittivity , varies nonlinearly with the input field intensity. The magnetic permeability 2 of the nonlinear medium is constant. It is shown that as the angle of incidence or the intensity of the incident field is varied, hysteresis jumps of the reflection coefficient can be observed as the interface jumps from the transmission or partial reflection regime to the total internal reflection (TIR) regime, and back. No assumption is made about the smallness of the amount of nonlinearity or the incident angle. The derivations of the nonlinear equations associated with such a nonlinear interface are shown in detail. The effects upon the equations when magnetic permeabilities and large nonlinearities are considered can be seen by comparison with previous works. The reflection characteristics are found to be no longer independent of the input wave polarization.

Requirements for all-optical logic devices for waveguide optics are stated. Existing proposals for such devices are briefly reviewed. The Mach-Zehnder waveguide structure is discussed. The device opportunities offered by the Multiple-Quantum-Well structures are discussed.

An optoelectronic switch uses a photodetector as the switching element. The RF signal to be switched is delivered to the switching element as a modulation on an optical carrier. To place the optoelectronic switch in the on-state, an appropriate electrical bias is applied to the photodetector to allow it to function normally as a detector and recover the RF signal as the output. The off-state is established by changing or removing the electrical bias so that the photodetector no longer functions efficiently as a detector. Three types of photodetectors have been studied as optoelectronic switches; the homojunction photodiode (e.g. Si PIN), the heterojunction photodiode (e.g. InGaAs/InP) and the photoconductive detector (e.g. GaAs). Homojunction analogue optoelectronic matrix switches having isolation and crosstalk losses exceeding 80 dB and a baseband response of 100 MHz are available today. Experiments have shown that the heterojunction matrix can more than match this performance and also be switched in 30 ns. Photoconductive optoelectronic switches having switching times of 1 ns and responses to 1.3 GHz have been demonstrated. The high isolation and fast switching speeds possible with optoelectronic switches should open up many applications in the future, such as in satellite switched time division multiple access (SS-TDMA) systems, rapidly tuneable comb filters with envelope bandwidths in excess of 1 GHz as well as in fiber optic broadband integrated services to the home.

A study was made of a new photodetector switching circuit which incorporates a switching transistor in series with a photodiode. A PIN photodiode was switched between reverse and zero bias to switch intensity-modulated optical signals. Isolation of 40 dB was measured from 50 MHz to 1 GHz, and average switch transition times of 30 ns were measured.

I summarize recent measurements of 2 X 2 and 4 X 1 polarization independent electro-optical switches for 1.3μm wavelength. Conclusions about the performance characteristics and limitations of both polarization-independent and single (TM)-polarization switch arrays are drawn from these results.

Design considerations for high speed integrated optics components are rewiewed, with emphasis on bandwidth-drive power performance, prospects for integration and polarization control. Experimental results concerning multigigabit modulation of LiNb0₃ directional coupler switches will be presented, along with work on fiber and microwave coupling and on the associated microwave circuitry.

Acousto-optic interactions are well known and widely used since long. The main applications for bulk optic devices are Bragg-cells for beam deflection and frequency shifting. Acousto-optic interactions using integrated otpical (I0) waveguides and surface acoustic waves (SAW) are very promising because of expected high efficiency. After some fundamentals we concentrate on I0 single-mode strip-waveguides which can be influenced by SAW. Three different types of structures will be discussed in detail: the surface-acoustic wave driven interferometer (SAWDIF), the surface-acoustic wave driven directional coupler (SAWDIC), both for modulation and switching, and the I0 Bragg-cell, which combines a waveguide-switch with an optical frequency shifter. Experimental results as well as applications for these structures will be presented.

A compact 8x8 optical waveguide matrix switch, with liquid crystal claddin°g on a planer waveguide film, was realized by making use of the large switching angle of 12. In the switch, 64 switching elements were arranged in a 4 mm x 40 mm area, based on a liquid crystal orientation analysis and a ray trace analysis. The switch exhibited 6.8 dB insertion loss and -20.2 dB crosstalk on the average, at 1.3 μm wavelength. A broad-band transmission capability of 400 Mb/s was demonstrated in a transmission experiment.

A 4 X 1 mechanical optical switch has been constructed, which is intended to select laser signal sources in the forthcoming SL Submarine Cable. We described the design philosophy to ensure the very high reliability required for this application ( < 2 FITS as a passive component, and < 10-3 probability of not performing the switch-over function when called upon in 25 years). We describe in detail the grooved silicon chips which were especially designed for this application for precise alignment of the optical fibers. We also describe a novel fiber end seal.