Common techniques for the fabrication of low-loss integrated optical components use two different steps for waveguide-burial. To perform a burial in only one step we examined the ion-exchange from solid-phase silverstripes into glass, covered by an eutecticum of NaNO3/KNO3 melt. Vapor deposited silver could well be structured chemically down to lateral dimensions of 2 um, thus allowing the fabrication of multimode and single mode strip-waveguides. Satisfying waveguide characteristics were achieved by a field assisted ion exchange (elec-tric field > 150 V/mm). This technique offers the advantage of only small increase in lateral cross section, even in the case of deep burial (10 4m). Therefore an independent control of both lateral and vertical waveguide-dimensions is possible, if the dissolution rate of silver for the used type of glass is known. Due to this fact buried waveguides with nearly circular cross-section can be fabricated in only one step. In our experiments a circularity of 92 % was achieved.

Integrated optical components in glass are commonly fabricated by a thermal or a field assisted ion exchange. Applying an elctrical field reduces the ion exchange time drastically. Usually the process is performed at fixed voltages and different exchange times1 . We realized that reproducibility is accompanied with great difficulties using this technique. A reproducible fabrication of optical waveguides is achieved by using the exchanged charge as the determining process parameter. The ion current is integrated by a control unit which automatically terminates the exchange process when the preset charge is reached. The charge corresponds to the amount of exchanged ions and a reproducible process is available.

The use of the proton-exchange method (PEM) for optical waveguide formation in LiNbO3 and LiTaO3 is reviewed. Problems associated with waveguides fabricated by concentrated benzoic acid melts are outlined. The use of diluted benzoic acid melts and annealing to reduce or eliminate the problems is discussed. Finally passive and active waveguide devices formed by the PEM are described.

A number of organic polymers have been prepared for use in the fabrication of high performance optical waveguides operating at short optical wavelengths (< 830 nm). Slab optical waveguides have been realized by spin coating the specialized polymers on substrates such as quartz and silicon wafers. Refractive index profiles were measured to be of the step index type, with the refractive index differences ranging from 0.12 to 0.15. Propagation losses and intermodal scattering levels were measured to be about 1.2-4.5 dB/cm and 15-20 dB, respectively. In addition, the electro-optic properties of the specialized polymers have been studied using suitable optical structures. An electro-optic modulator has been built as a demonstration device utilizing a slab polymer waveguide.

We have investigated use of rapid thermal annealing (RTA) to initiate in-diffusion of Ti into LiNb03 to form optical channel waveguides using several different RTA processes. Each process is characterized by a different RTA temperature versus time variation followed by a common furnace heating step. One set of samples has undergone a slow ramp RTA temperature versus time variation, a second set has undergone a two step variation, a third set has undergone a very rapid ramp, and a fourth set has undergone no RTA processing. Samples processed with the fast RTA ramp of temperature versus time to 875C yielded the lowest channel waveguide propagation loss of about 1 dB/cm measured at a wavelength of 632.8 nm.

GaAs planar channel waveguides are fabricated with diffused boundaries using a zinc-doped spin-on-glass source. Low-loss (� 1.9 dB/cm) single-mode waveguides are achieved. Modal properties of the waveguides are experimentally investigated. A simple model is used to analyse the waveguides.

Sputtered thin films of Corning 7059 glass have been widely used as optical planar waveguides. Here we report results of refractive index, stoichiometry and waveguide loss measurements for electron-beam-deposited Corning 7059 glass films.

A new method to fabricate the gratings useful for integrated optical circuits (IOC) is described. The method combines optical projection lithography with spatial filtering.The projection lens uses nearly coherent illumination. Only the two first orders diffracted by the mask grating are allowed to pass through the lens. This produces a grating pattern in the image plane that has a high contrast (near 100%), a large depth of focus (approx. ± 13 gm), and a period half of what would have been obtained in normal imaging. Thus, with a 5X reduction lens a 5 pm period grating on the mask produces a 0.5 p.m period image on the wafer. Gratings of different periods, sizes, locations, orientations, and configurations (chirped, phase shifted, etc.) can all be produced on the same chip with a single exposure. Using a deep UV lens with a line-narrowed 248 nm KrF excimer laser for illumination, we printed 0.5 pm period gratings in an oxide layer on 10 mm X 10 mm silicon chips. Because of the high contrast, the photoresist patterns had very high quality. In addition, the extended depth of focus was observed. This method is primarily useful for patterning periodic structures. Lenses designed for this system could be made with large numerical apertures and/or image fields, and be able to pattern gratings of 0.23 gm period for semiconductor waveguide devices. This technique opens up the possibility of high-volume production of IOC chips with Bragg filters using standard IC fabrication facilities.

This paper describes work that has been done to develop X-ray contact printing of submicron gratings for integrated optical devices in our department. Previously, integrated optical devices, such as waveguide filters, have been made here using holographic exposure directly onto waveguide or semiconductor substrates. X-ray contact printing of holographically generated masks should make the fabrication of such devices simpler. The paper describes the work to date and gives fabrication details for the X-ray masks. X-ray contact printing is comparatively simple to perform, once the mask fabrication process is worked out. The paper describes our first results from the contact printer. In addition some results are presented on the manufacture of an X-ray mask for Quantum Dot structures.

The basic element of a two - mode - interference (TMI) device is the two - moded waveguide, which is coupled adiabatically to two single - mode feeding waveguides at the input and output ports, respectivly. As an alternative to the directional coupler (DC), the TMI - principle offers the potential of realising a new class of guided - wave devices: electrooptic switches like the X - switch, wavelength multiplexers and demultiplexers with a wavelength periodic characteristic, passive polarization splitters, as well as polarization independent switches.

An integrated-optical 2 x 2 switch consisting of an electrooptic interferometric modulator and asymmetric Y-branch mode splitters/combiners has been demonstrated. This device design offers the important advantages of low crosstalk, fast switching speed, low switching voltage, and ease of fabrication. In this initial device we have demonstrated switching at a wavelength of 1.15 pm with crosstalk of less than -15 dB.

We have fabricated ion-exchanged potassium titanyl phosphate (KTP) Mach Zehnder and phase modulators operating at X = 1.3um and 0.633um. These devices were designed for very high frequency operation with a 3-db modulation bandwidth of greater than 12GHz. Device insertion losses were between 1.5db and 5db with switching voltages (D.C. ) of 10V. Thick (- 3μm) electroplated gold was used to produce low-loss 50Q impedance coplanar strip electrodes. High optical power operation at 0.633um ( -100μW) produced no optical damage effects. Further results such as device stability will be presented at the conference.

The growth of sophisticated military satellite communications, electronic warfare, and radar systems places increasing demands on microwave/millimeter-wave (M/MMW) fiber-optics for wide instantaneous bandwidth, immunity of EMI/EMP, deployment speed/simplicity, and cost effectiveness. The directly modulated laser diode (LD), operating at room temper-ature for a bandwidth above 14 GHz, is very difficult to fabricate and package. Therefore, the laser beam modulated by an electro-optic modulator (EOM) provides the essential way of microwave or millimeter-wave wideband fiberoptic systems above 14 GHz. Both LiNb03 and III-V semiconductor E0Ms are feasible to modulate LD beams in M/MMW frequency range. Various intensity structures, including the Mach-Zehnder interferometer, Franz-Keldysh electro-optic absorbing, and multi-quantum well, and their state-of-the-art performance will be described and compared in this paper. Also, the detail analyses and designs of the M/MMW traveling-wave electrode, Ti-indiffused LiNbO EOM fabrication process, and package technique will be presented. Furthermore, the pracical system parameters and system ap-plications of the EOM are also discussed.

The fabrication of LiNbO3 travelling wave electrodes is described. It is shown that devices with plasma etched Al electrodes can perform as well as devices employing the more conventional electro-plated Au technology and that bandwidths in excess of 12 GHz can readily be achieved. The reliability of travelling wave devices with plasma etched Al electrodes is considered and it is shown that metallisation lifetimes in excess of 16 years are currently predicted. The problems of using LiNb03 travelling wave devices in practical optical fibre systems are reviewed and it is shown that the use of a dedicated high speed drive amplifier can result in considerable simplification. The design and fabrication of such an amplifier based on GaAs technology is described and its use in a 1.8 Gbit s-1 optical fibre system reported.

An improved ridge waveguide modulator in z-cut LiNbO3 fabricated by ion-beam milling is presented. A modulation depth of over 95% was achieved with a drive voltage of ±8V. A theoretical model based on the Beam Propagation Method is used for design optimization purposes.

High-sensitivity lumped-element bandpass modulators in lithium niobate have been designed and evaluated. We discuss what ultimately limits the modulator response, then describe a passive resonant drive circuit, and give some experimental results from modulators using it. This circuit improves the response over that of a baseband device, but does so at the expense of reducing the bandwidth. Finally, we give experimental results from an optical link that uses this modulator. The high modulator response (equivalent to Vπ = 250 mV at 50 0) gives the link an input sensitivity only 16 dB above thermal noise while preserving a large dynamic range.

We assess the design and fabrication of an optically wideband four element polarization controller chip in LiNb03 for use in the 1.55 µm wavelength low loss window of silica fibres. The design allows for mixing of the local oscillator (LO) and signal by the integration of a 3 dB coupler which should provide suitable outputs for a balanced detector pair. In addition, we attempt to optimise mode converter performance in the device by using near Z axis propagation. The results inidicate that there are some unforseen problems that arise when couplers and off axis waveguide structures are fabricated on this particular crystal orientation.

Lossless guided-wave switches with more than 30 dB of crosstalk-isolation are proposed and analyzed. The switches are comprised of branched channel waveguides with laser-like cross-sections. Optical gain, sufficient to overcome power-splitting losses, is provided by carrier-injection currents. Due to its low-noise properties, the single-quantum-well structure is found to be optimum for cascading switches into a multi-stage network. A lossless 1 x N network with 1024 switched outputs should be feasible.

Photonic switching in bulk semiconductor material is of great interest in pulsed power'-3 and microwave applications4. Such interest stems from the low jitter, fast rise time, and high power capabilities of the photonic switch. For long pulse applications4, however, it is often necessary for the switch to remain closed long after the laser pulse is terminated. Such switch behavior is desirable in order to achieve higher efficiency, as well as to accommodate the longer pulse. Recently it was found that GaAs switches exhibit "lock-on" behavior, i.e., the switch recovery times to increase provided the applied electric field and light intensity levels exceed threshold values. In this study we have found that gridded bulk GaAs photonic switches exhibit lock-on behavior. With laser light from a 20 ns Q-switched Nd:YAG laser, delivered via a fiber optic bundle, the switch turn-on was sustained for at least 200 ns, which is the pulse width of the Pulse Forming Line (PFL).

Large-signal modulation of laser diodes generates harmonics which can be exploited to distribute millimeter wave reference signals via fiberoptic links. Experimental results of a large-signal modulation of a laser diode with optical feedback are presented, where the external cavity increases the optical intensity modulation depth. Period doubling has also been observed.

The design, optimisation and fabrication of Mach Zehnder type 1.324m and 1.524m wavelength intensity modulators, in Z-cut LiNbO₃, is described. Fabrication conditions for waveguides and travelling wave electrode structures, in relation to device passive and active performance, are highlighted. Typical polarisation maintaining fibre pigtailed devices at 1.324m and 1.524m had 6dB fibre-to-fibre loss, with an intrinsic modulation bandwidth of 4GHz. The voltage required for on to off operation of the devices was 5-10V, depending on wavelength and waveguide/electrode geometry, with first null extinction ratios between 20 and 45dB. Variations in these performance figures in relation to waveguide fabrication conditions, asymmetry and cross-coupling effects are discussed. Environmental performance of the fibre pigtailed packaged modulators is demonstrated via temperature cycling, shock and vibration testing.

Measurements of the refractive index of semiconductor materials, both in wafer and in waveguide form, are presented. The technique used to this purpose is based on radiation coupling into the material by a prism; this method is used for the first time on semiconductors, by means of a silicon prism. Accuracy to the fourth decimal place is demonstrated, in favorable comparison to the best available data.

Simple and environmentally stable single mode connections to integrated optic (I.O. ) waveguides have been fabricated and tested. The attachments have been operated over a wide temperature range and have undergone high shock testing. This paper will discuss how the devices were fabricated and present some test results.

A simple technique for fabricating single mode star couplers using ion-exchanged glass guides is proposed and demonstrated. Calculations indicate the possibility of achieving an excess loss of 2dB and a uniformity of 3dB for a lx32 star coupler. Furthermore the technique can be scaled to increase the number of ports without changing uniformity or excess loss.

Methods of reducing the insertion loss between single-mode fibers and graded-index channel waveguides, namely annealing and back-diffusion, are analyzed theoretically and compared. Mode mismatch and misalignment losses are calculated in order to determine the best method and the optimal conditions for its use. The main result of this paper is that, for the single-mode regime, there is no apparent advantage in using back-diffusion instead of the simpler annealing process, in contrast with the multimode case.

In an effort to study field-assisted photoconductivity, single crysta's of semi-insulating GaAs, having EL2 defect concentration 10 16 cm-3 and resistivity 10 8 -cm, have been investigated with pulsed illumination at 0.904 µ of 40ns duration. The resulting G-V data, taken for various delay times between the onset of the voltage pulse and the onset of the laser pulse, show similar character except for the condition when the laser pulse over-laps in time the displacement current region due to the voltage pulse. It is interpreted that this difference in behavior is due to the effect of changing polarization (P) during the rise of the voltage. Very rapid oppositional voltage pulses which, in the presence of illumination, drive the total current to zero show that the current falls to the ground level far faster than the voltage and suggests avalanched recombination. Hall Effect studies show reversible sign-change in Vu at the temperature zone 130-110K, which identifies the transition to and from the photo-initiated metastable state of EL2. In samples which contain virtually zero EL2 defect, there is no indication of sign change when traversing this low-temperature region.

Photocurrent studies have been performed on single crystal EL2 compensated semi-insulating GaAs as a function of polarity (using several methods of contact and two crystal orientations) and as a function of position of LED illumination (λ=0.905μ ). The total current (photo + dark) vs time traces for these studies are non linear and reflect three zones of behavior. When the crystal is illuminated near one extremity, the change in polarity causes a non-linear depression in the trace corresponding to positive polarity. In addition, the latter trace consistently shows the presence of small somewhat irregular oscillations of frequency (50MHZ). We interpret the observations to be indicative of: (1) non-uniform longitudinal (110) trap distribution; and (2) non-symmetric potential vs. distance profile suggesting a possible recombination front near the mode.

An optical switch has been designed, built, and tested and is based upon an acousto-optical modulator with dual feedback and a short carrier round trip time. It is observed that: (1) the switching transient itself displays oscillatory behavior; (2) the pre-and post-switching stable states seem to display chaos; and (3) slight variation in feedback will convert the switch to an optical oscillator/modulator with a characteristic zigzag output-input curve.

This paper reviews the basic optical techniques for controlling microwave signals. First, the theory of how an optical signal can affect the microwave signal will be covered, followed by a review of applications in the various areas to illustrate what has been accomplished in the use of optical techniques to control microwave signals. Optical techniques for processing microwave signals can be broken into three major categories related to how the light affects the microwave signal. First is the photogeneration of charge carriers, in which the light generates holes and electrons. This effect has been used to produce phase shifting, on/off switching, modulation, injection locking, and also direct conversion of DC to microwaves. The second way that light can affect the microwave signal is in a photodlode, by generating a photocurrent to be used for on/off switching, microwave pulse generation, injection locking, or for modulating an output beam for the transmission of a microwave signal. The third technique involves interference effects, or heterodyning, used to generate CW microwave signals. An additional topic covered is the monolithic integration of optical and microwave devices to produce opto- microwave integrated circuits. Finally, some systems applications and requirements for these devices are discussed.

In this paper the design of a novel guided-wave correlator for air-bone synthetic aperture radar (SAR) data processing is illustrated. Correlation in azimuth direction is carried out through an optical transmission mask which includes the azimuth reference signal, and a two-dimensional CCD array working in time delay integration mode. The guided-wave correlator proposed in this paper performs the correlation in ground range direction operating in time integration mode. The device utilizes an optical waveguide formed in z-cut LiNb03 by proton exchange in dilute benzoic acid. The waveguide supports a collimation lens, a surface acoustic wave Bragg deflector and a grating filter which allows to remove the undiffracted beam. This new filtering technique does not require fabrication of lenses performing spatial Fourier transform. Moreover, usual procedures of planar technology can be followed to fabricate the correlator. When a laser beam at X = 0.84 pm is intensity modulated by the reference chirp signal having a bandwidth of 50 MHz, a correlation signal referred to the reference signal carrier is obtained. In this way the separation of the real and imaginary parts of the output signal can be carried out leading to an easy digital post-processing. Small size, light weight and low power consumption are further advatanges of the new correlator. Finally, a range swath of 1 Km with a resolution cell of 3m x 3m is easily achieved for an air-bone SAR data processor.

We investigated the application of integrated optic modulators (I0Ms) to wideband fiber optic communications systems. These integrated optic modulators differed in their electrode structures and method of optical launching. Signal-to-noise ratio, harmonic distortion, input impedance, and laser noise effects were measured as functions of modulation frequency and modulator bias voltage. We will present possible system design alternatives to improve operation of the IOM and performance of the overall fiber optic link.

The use of proton-exchanged LiNbO₃ waveguides as an alternative to titanium-diffused waveguides in fiber optic gyro (FOG) circuits is investigated. The proton-exchanged FOG circuits offer far superior polarization control and reduced fiber-to-fiber insertion loss without any degradation in the electrooptic properties of the LiNbO3. A pigtailed three-port FOG circuit operating at 1.55-micron wavelength is demonstrated which exhibits <5.5 dB fiber-to-fiber loss, polarization extinction >60 dB in the chip and >40 dB in the output fibers, V, = 10 Volts, 3-dB bandwidth of 1 GHz, and intensity modulation less than 0.1% over ± 2 V?.

During the past three years Ti:LiNbO3 integrated optic (I0) devices have become commercially available. In this survey paper we will describe the range of I0 products and services that are available from companies based in the United States, Europe, and Japan. Detailed specifications will be included whenever possible to aid the audience in understanding the state of the Ti;LiNbO₃ technology.

Electro-Optically active Guided Wave Optical Components are only commercially available in Lithium Niobate substrate material. In this paper some examples of the applications of these components are given, along with a comparison between Lithium Niobate based components and those fabricated in other materials. The advantages of Lithium Niobate components in terms of cost and performance for both electro-optical, passive and non-linear optical waveguide devices are highlighted.

Some of the practical applications that have been envisaged for Lithium Niobate Integrated Optics are discussed in the light of developments in the technology. Much of the basic physics that governs devices is now fairly well understood and with attention coming to focus on practical engineering developments a number of systems demonstrations are being made which illustrate well the capabilities of the technology. From these demonstrations it is clear that major opportunities exist for integrated optics devices, although the successful exploitation of these depends strongly on continued progress in engineering the devices for use in a broad range of non-research laboratory environments.

In this paper we discuss the design and fabrication of integrated optical Mach Zehnder modulators in LiNb03, with particular emphasis placed on the requirement that these devices can be made commercially available. The particular modulators that we have developed are intended for use at 1.3 µm wavelength which makes them ideally suited to high bit rate communications or signal processing. We will concentrate our attention on three travelling wave modulators designed to operate upto frequencies of 2.5 GHz, 8 GHz and 18 GHz. In addition we include the latest development which is the integration of a 1.3 μm laser and an 18 GHz modulator into a single package to form a compact modulated source of over 1 mW optical output power.

Multimode polymer waveguide circuit fabrication techniques were used to produce several low-cost devices applicable to fiber optic sensor instruments. A 2x1 coupler with 3% reference tap was constructed with 250 and 500 #m diameter plastic fiber pigtails. This coupler had a 2 dB excess loss and could be used to replace the bulk-optic, 3 dB beamsplitter in a fiber optic instrumentation package. Further, a miniature fiber-tipped pressure sensor was produced using waveguide circuit-based photofabrication principles. This device could provide a disposable, catheter-tipped sensor for blood pressure monitoring.

While optical fibers were initially used almost exclusively for point-to-point long haul communications, there is an increasing tendency for fiber to be used in short distance, multi-node configurations. Applications include cable television distribution, subscriber telephone services, high speed data buses, local area and multipoint sensor systems. In these cases the system cost becomes highly dependent on the price of passive branching elements and on splice/connector cost. In addition, there is an increasing requirement for special optical circuits for sensors used in industrial, aeronautical and military systems. Integrated optics offers the possibility of integration coupled with mass production batch methods. While many single-mode integrated optic technologies exist', almost all are incapable of producing waveguides sufficiently large and with an appropriate numerical aperture to couple efficiently to multimode fibers. Ion-exchange in glass can address these shortcomings and thereby has the advantage of being compatible with both single-mode and multimode needs.

A wide variety of integrated optical devices was developed based on silica glass waveguide technologies. High performance waveguide with low loss and well-controlled configuration is formed on silicon substrate by a combination of flame hydrolysis deposition, photolithographic and reactive ion etching processes. This waveguide technology also has the great advantage of guiding groove structure for hybridizing optical fibers and chips onto the waveguide. Based on this silica glass waveguide technology, several types of integrated optical devices such as branching, WDM, polarization control, resonance and switching devices have been constructed and tested.