A market research study was conducted, leading to a ten-year forecast of worldwide integrated optoelectronic circuit (IOEC) market and application trends. Four IOEC categories were considered: lightwave, imaging array, digital IC interface optical bus and other devices. It was concluded that worldwide IOEC production will reach $1.71 billion by 1997. It was also concluded that lightwave IOECs will be the leading device category, with commercial communication the leading application.

Some of the strengths and limitations of the photonic technology as applied to switching systems will be presented. This discussion will define relational and logic switching systems and include some practical system design considerations.

Unique propagation characteristics arise from the coupling of light between the lossless modes of a dielectric waveguide and the lossy modes supported by an absorptive cladding layer such as a semiconductor. These effects occur because the propagating lightwave couples into a variety of modes that exist in the semiconductor-clad waveguide. Properties such as cladding thickness, refractive index, and absorption level greatly affect modes of the clad waveguide. Such mode effects are due to periodic coupling between the dielectric layer and the semiconductor cladding. The resulting characteristics suggest use in various device applications. Here, we characterize the periodic coupling effect and how it creates unique modes in the clad waveguide structure. We also describe how the refractive index and absorption of the cladding work together to influence the properties of those modes.

We report a refinement of a previously reported method' for measuring propagation losses in single-mode optical waveguides. The method as previously described applies to isotropic materials (glass); corrections are necessary when anisotropic materials, such as LiNb0₃, are used. This report describes the method and indicates two means for estimating the corrections for anisotropic materials.

A new class of single mode fiber optic sensors with preliminary data indicating possible applications are described. Basically, the sensor consists of a fused tapered biconical directional coupler surrounded by a stress birefringent medium. Light is launched into one of the input fibers and travels to the fused coupler sensor. Some of the input light is coupled into one or more output fibers within a fused region known as the waist. Ordinarily two output fibers carry the original light intensity, any difference being attributed to a constant excess loss. The two output fibers are each terminated at a photodiode. One of the photodiodes is coupled to the inverting input of a differential operational amplifier. The remaining photodiode is coupled to the non-inverting input. Under static conditions the ratio between the output fibers is a constant. Variations in input light intensity may be taken care of by employing difference over sum processing. It is generally known that the coupling ratio can be very dependent on the index of refraction surrounding the waist region. Thus, a medium which exhibits stress birefringence and is used to intimately surround the waist will cause the coupling ratio to change due to applied stress. Stress in the region surrounding the waist may be applied externally by a force which is transmitted directly into the medium. In the case of an accelerometer, the force is supplied by an attached proof mass. A variety of other physical observables may be sensed through mechanical actuators such as diaphragms, levers, electrostrictive, magnetostrictive, and thermostrictive elements. Internal stress producing mechanisms may be designed by mixing various sensitizing elements into the stress birefringent medium. For example, polystryene or nylon might serve as a sensitizer for acoustic sensors. Experimentally, the sensitivity of a number of couplers was studied by immersion in calibrated index of refraction oils. Coupler fabrication methods were shown to influence the sensitivity of otherwise identical couplers. The sensors were shown to have excellent low frequency response all the way to the steady state. Absence of "one-over-frequency" type noise makes these sensors particularly desirable for low or subhertz detection.

Propagation losses of ZnS thin film waveguides have been investigated. The effects of oxygen and water backpressures during the deposition of ZnS thin films on waveguide performance and microstructure have been observed. These effects dominated losses caused by surface finish. A decrease in losses, and a change in preferential crystal orientation from (111) faces parallel to the substrate to (220) was observed for increased H2O partial pressures. Increasing 02 partial pressure resulted in lower waveguide losses possibly from attachment to unbonded Zn and void filling. Because waveguide scattering losses are Rayleigh-like, a quadratic dependence on crystallite grain size is expected. (220) oriented crystallites had smaller grain sizes than the (111) and overall lower losses.

Low-loss TE-pass polarizers are fabricated in x-cut LiNbO3 utilizing Ti-diffusion in conjunction with proton exchange. The polarizers, which are designed to operate at x = 0.8 to 0.85 um, exhibit an excess insertion loss of < 0.5 dB and a measurement limited polarization extinction ratio of > 50 dB.

An integrated optic polarizer/attenuator based on the selective removal of the TM component of guided light by a drop of mercury serving as a metallic cladding is presented. The position of the liquid metal with respect to the guide can be changed by many techniques, such as electro-wetting. Theoretical predictions and experimental results are discussed along with potential applications.

A monolithic integrated optical circuit consisting of an LED (light emitting diode), a modulator and a detector on a GaAs substrate is demonstrated. The voltage tunable effective bandgap of doping superlattices is utilized to integrate several physically identical devices which perform different functions depending on their individual bias voltage. The detector responds linearly to the emitter intensity. Linear amplitude modulation is observed with change of modulator bias over an appreciable range.

The aberrations of Fresnel type grating lenses immersed in uniaxial waveguides are studied. Lens designs which account for birefringence and which are aplantic are presented.

We have fabricated high speed optical detectors on channel waveguides formed by both potassium ion-exchange in glass and titanium diffusion in lithium niobate. These new waveguide detectors show response times of 200 ps full width at half maximum amplitude (FWHM) when illuminated with subpicosecond optical pulses. The detectors consist of back-to-back Schottky photodiodes formed by chromium-gold metal contacts on hydrogenated amorphous silicon (a-Si:H). When interdigitated metal contacts with the contact separation and semiconductor film thickness dimensions close to one micrometer are used, the detectors are both fast and efficient.

A new 8cm-diam ion source has been fabricated for ion-assisted deposition and sputtering. This source empolies a divergent magnetic field discharge chamber, and the field is gene-rated by a permanent magnet located at the upstream end of chamber. This design permits the source being compactly fabricated and conveniently maintained. Also this source emploies a one-grid ion optics to extract low energy ion beam besides a two-grid ion optics, and the ion optics is easy to be replaced. For the two-grid ion optics, current densities of 500eV Ar+ up to 1.0mA/cm2 were acheived with a uniformity of +5* over the center 7cm-diam of the beam at a distance 15cm from the source and a pressure of 1.5X10-4Torr. At the same conditions, an average current density up to 0.6mA/cm2 for 100eV Ar+ was obtained with an 80mesh-/inch one-grid ion optics. This source has been applied to the IAD, and improvements of the firmness and stability of ZnS/MgF2 and TiO2/SiO2 multilayer filters deposited by the IAD's technique has been studied.

A method of fabricating photoresist grating masks with Shipley's 1400 series positive photoresist by monitoring the negative first-order diffraction efficiency during the photoresist development is presented. The relationship between the monitoring curve and the mask profile evolution is examined.

Results of a study of proton implanted gallium arsenide (GaAs) waveguides are presented. The waveguides were made using standard implant equipment available to the microelectronics industry. Protons at energies of 190 Kev were implanted into heavily doped, n-type gallium arsenide. Implant doses were usually at 5E15 per cm2., with water used as the ion source. The implants were performed at room temperature, although some heating of the samples occurred. The main anneals were done at 350°C for 30 minutes. The waveguides were tested at 1.06μm using a YAG II laser. Loss measurements were done as a function of the substrate doping and etch pit density of the samples. Good guides were made using a doping of 3.5E18 cm^-3 and etch pit density of 35000 cm^-2. Low etch pit densities did not yield acceptable guides using the above fabrication procedures.

New devices using ultra thin layers of GaAs/A1GaAs have been grown employing Molecular Beam Epitaxy (MBE) technology. Superlattice Avalanche Photodiodes SL-APD and Variably Spaced Superlattice Energy Filter (VSSEF) devices have been fabricated and the results are discussed.

The photoluminescence spectrum of a GaAs/GaAlAs multiple quantum well p-i-n diode has been measured as a function of pressure. Room temperature measurements were carried out in a diamond anvil cell to about 4 GPa (40 kbars), and at 77 K to about 0.8 GPa in a conventional high pressure apparatus. Shifts in photoluminescence peaks originating from the GaAlAs capping layer and two regions of the multiple quantum well layers of different thicknesses are discussed in terms of a model for the pressure shifts in the r and X-states of these components. A brief discussion of the emission intensities is also given.

This paper reviews research on extended cavity lasers formed as a combination of InGaAsP/InP and Ti :LiNb0₃ waveguide chips.

The frequency dispersion of integrated optic interferometers fabricated on different lithium niobate cuts is characterized. Only the configuration that uses the r₃₃ electrooptic coefficient is well behaved.

The maximum Ti concentration and corresponding An as well as the minimum waveguide size is limited in diffused waveguides by the diffusion coefficient. Ion implantation offers an interesting alternative with a clear advantage at larger wavelengths for smaller waveguide cross-sections. Both planar and channel waveguides have been fabricated by ion implantation of Ti into a LiNb0₃ substrate. A solid phase epitaxial regrowth of the implant induced crystal damage resulted in excellent waveguides with propagation losses of< 1 db/cm. Guide depth of <1 micron and An of 0.04 have been achieved. Fabrication techniques and optical properties of the waveguides are presented.

In this paper we will show theoretically and experimentally that the mode conversion in converging and diverging channels caused by the asymmetry produced in the fabrication processes is limiting the extinction ratio of single mode crossing channel switches. Degradation of the extinction ratio is caused primarily by asymmetry in the transition regions of the switches.

We report on a linear modulator which automatically operates about its 3-dB point. This device is a 1 x 2 modified directional coupler formed from Ti:LiNbO₃ waveguides operating at the 1.3-μm wavelength. The modulator is theoretically capable of a vol-tage sensitivity of a few microvolts and a linear dynamic range exceeding 85 dB for 1 mW light. Preliminary experimental results for both X-cut and Z-cut devices are presented.

In general, electrooptic switches are sensitive to the state of polarization. While this is not always an obstacle to their use in systems, there are many applications where the polarization of the light is not known or not constant. I present a lithium niobate optical 2x2 switch that is polarization independent at a wavelength of 1.3 μm. The switch operates at a relatively low 20 V, requires but a single control voltage, and exhibits up to 20 dB of crosstalk suppression. The theory of operation and experimental results are presented.

The design, fabrication and performance of a traveling-wave Ti-indiffused LiNbO₃ phase modulator for X = 0.83µm is reported. Emphasis was placed on electrooptic efficiency which was analyzed by means of the finite element method. Total insertion loss of the fiber-pigtailed Y-cut modulator is 2.9dB, the half-wave voltage is 3.8V.

We update our work on optical directional-coupler modulators (ODCMs) for single-shot, analog instrumentation systems operating at 800 nm. We can now fabricate directional-coupler devices that have one input and two output pigtails, with insertion losses of 8.9 dB on average. Data for the ODCMs indicate an impulse response of less than 40 ps. We have implemented these devices in an ultrafast, x-ray measurement system. We discuss our data from this implementation and their implications for continued ODCM development.

We present the results of our investigation of the feasibility of using an optical multiplexer-demultiplexer with diffraction gratings for the photonic streak camera. We describe how gratings can be used in a demultiplexer for a crystal streak camera and evaluate the performance of two gratings in a streak camera. The linear dispersion equation, used to determine the number of channels that can be multiplexed and recovered, accounts for focusing and collimating optics but neglects grating anomalies. To study the performance of the grating in the demultiplexer design, we investigated the characteristics of the gratings. The model reveals that interference from individual, adjacent, diffracted orders is a major restriction when one is recovering a large number of individual wavelengths from a beam containing a large spectral range. We include in this paper the experimental results that verify the model used to describe the multiplexer-demultiplexer.

This paper presents quantitative measurements of two nonideal characteristics of lithium niobate integrated optical devices: nonlinear electrooptic phase modulation and the photo-refractive effect. These effects can occur in any lithium niobate channel-waveguide phase modulator or passive channel waveguide, and may affect the performance of any device that uses these basic building blocks. The measurements described in this paper were performed by means of an integrated-optical Mach-Zehnder interferometer which consists of passive channel waveguides and phase modulators. We have measured a quadratic term in the phase shift vs voltage relation for electrooptic phase modulation. We have also measured the photorefractive effect at wavelengths of 0.85, 1.06, and 1.3 μm, using y- and z-propagation. we evaluate both photovoltaic and photoconductive effects, and give estimates for the constants in a simple model that describes the photorefractive effect.

A new electro-optic deflection amplifier using simulated prism structures has been studied. The theory and experiment on electro-optic deflection amplifier are described. Some of the experiment results are shown in the paper.

Metal:dielectric overlay integrated optical waveguide polarizers have been made using ZnO/A1 layers on Ti:LiNb0₃. The effect of process variations on device performance at 1.3μm wavelength has been determined. The first published report of the use of dielectric:metal overlays to fabricate 1.5μm polarizers is also presented

The key factors in device performance for titanium diffused lithium niobate phase modulator are related to their fabrication parameters. Low optical loss, low drive voltage, and large bandwidth are considered the primary factors. The parameters involved in fabrication are the titanium strip width and thickness, diffusion time and temperature, electrode gap and length. Design examples with fabrication parameters tailored to meet performance needs of fiber gyroscope systems and amplitude modulators are highlighted. Results are given for completely fiber pigtailed packages. A new method for fiber pigtailing using precision ceramic ferrules is also reported.

Coupled mode theory is an approximate, but insightful and often accurate mathematical description of power transfer among two or more waveguides in proximity. Its applications relate to the design and understanding of'modulators, switches, dividers, semiconductor lasers, phased arrays, and fiber optic devices. In this paper we review the theory as it has been employed over the past decade and point out contradictions between the formulations. These result from the neglect of interaction terms, which we show should be retained, especially for the cases of coupling among non-identical waveguides and waveguides with either gain or loss. A newer more accurate and physically meaningful formulation is described and we demonstrate that even in the case of very weak coupling significant differences result.

We present results of an analytical study addressing mode coupling in optical waveguides caused by refractive index fluctuations and apply these results to determine the consequent effects on directional coupler switches.

Modulation diagrams of various integrated-optics coupled-waveguide interferometers and directional couplers are presented. The diagrams display contour maps of various normalized optical output power levels of the modulators. The diagrams are used to describe graphically the modulation depth characteristics of modulators and the crosstalk characteristics of integrated-optics switches as functions of the interaction length and the applied voltage. Various modulation diagrams are constructed to analyze the behaviors of both the conventional and the nonideal / non-conventional coupled-waveguide structures.

Our investigation shows that tapered glass optical waveguides provide the best coupling device for introducting and directing radiation from a semiconductor laser source (e.g., GaAs) into a multichannel Ti:LiNb0₃ optical, array-modulator. Several fabrication methods were considered including R. FTSputter depositing Corning 7059 glass on Corning 2947 microscope slides which were used as substrates. The second method studied previously involved reactive sputtering Nb metal in an 02 atmosphere to produce Nb205 waveguides. A third method was also chosen for this investigation which involved indiffusing silver ions into Corning 2947 slides at temperatures between 270°C and 300°C and with the assistance of applied electric fields ranging from 3 to 200 V/mm. Waveguides with excellent taper geometry had been produced by R.F-Sputtering Corning 7059 glass. However, better optical properties were found in the indiffused silver guides and control of the effective waveguide depth in these guides indicated that tapered waveguides could also be formed. WKB analysis of these graded index guides showed that the most likely refractive index profile was Gaussian in shape. At 632.8 nm losses were found to be around 1dB/cm however, at shorter wavelengths losses were found to increase. A luminescent emission consisting of red and near IR wavelengths is produced normal to the waveguide surface when guided wave modes are excited at 488 and 514.5 nm. This red and near IR emission consists of a series of bands that are produced by a series of spectral shifts ranging from 3190 to 6475 cm 1 from the 488 and 514.5 nm laser excitation lines. It is proposed that this absorption of the excitation radiative and subsequent re-emission is due to the presence of silver aggragates in the waveguide layer.

As integrated optical components become increasingly available, the need for an understanding of methods for characterization of these devices becomes necessary. This paper discusses several techniques for characterization of Ti:LiNb0₃ devices including waveguides, polarizers and phase modulators. Measurement aspects common to all devices are discussed such as polarization requirements, wavelength, power restrictions and power measurement. In addition, specific techniques for measurement of optical loss, fiber to chip coupling, optical retardation and polarization extinction are given.

Ti:LiNb03 channel waveguide devices have become available from a number of sources recently. These devices must be terminated with single mode fiber for use in the target system. System requirements quite often dictate the need for use of polarization maintaining fiber. This paper discusses the experimental results of single mode polarization maintaining fiber connections at the .82 um wavelength. Channel waveguides and y-branch waveguides were terminated and tested for changes in throughput over a temperature range of -40 to +800C. Polarization crosstalk over a -20 to +60°C range also tested.

Depolarization of single-mode channel waveguides on lithium niobate has been measured at a wavelength of 1.3 microns. Y-cut waveguides depolarize in a linear manner, as predicted by theory. Z-cut guides exhibit more random depolarization which is independent of surface roughness, while z-propagating guides exhibit exhibit the largest depolarization. Depolarization is found to be independent of waveguide width.

We have designed and fabricated a Ti:LiNb0₃ waveguide high speed Mach-Zehnder interferometric modulator operating at 1.3 um wavelength. Design considerations for optical waveguide and traveling-wave coplanar-waveguide electrode have been listed. The modulator was optimized with respect to optical insertion loss, switching voltage or drive power, and modulation bandwidth. The fiber-pigtailed device had a 5 dB fiber-to-fiber loss and an intrinsic modulation bandwidth of 18 GHz. The voltage required to switch the device from the on- to off-state was measured to be 9.5 V, with an on/off extinction ratio of 33 dB.

In this paper the theory of the prism coupler is reviewed with regard to the variations found when it is used for the measurement of waveguide attenuation. These variations are caused by a change in the coupling efficiency of the prism coupler which is shown to be due to variations in the prism waveguide spacing and the area of the coupling spot through which coupling occurs. Results are presented for the analysis of attenuation data which enables this technique to be used for the reliable measurement of integrated optical waveguide attenuation.

The spectrum of modal cut-off wavelengths is studied for waveguides with step and graded index profile. It is shown that by measuring the cut-off wavelength of supported modes it is possible to obtain values for the refractive index of the guiding layer in the step-index case, and information on the diffusion length and the best profile shape for graded-index guides. This method has been experimentally applied to InGaAsP and InGaAlAs waveguides, whose indices are obtained with accuracy to the third decimal place, in favorable comparison to other techniques, and to Ti:LiNb0₃ guides.

The spectral properties of single-mode optical fibers and optical waveguides are reviewed including loss, dispersion, coupling, and reflection. Measurement techniques for characterizing these waveguides are described and experimental results are presented. These include measurements of the intrinsic and bending losses for single-mode optical fiber, field mode size, transmission, and reflection losses for waveguide structures when single-mode fibers are used to couple power into the waveguides.

In this paper the characteristics of He implanted stripe otpical waveguides are discussed in relation to the various process parameters. The results show that by careful selection of the energy used for the wall implants, stripe waveguides can be produced with propagation losses down to 1.0dB cm-1 at A = 0.633μm. The electrooptic coefficient in these waveguides has been measured using a simple phase modulator and it has yielded values which are 80% of the theoretical value for the r13 electrooptic coefficient of LiNb03. Experiments have also shown the intensity photoractive effects, which are routinely found in Ti indiffused waveguides, are not present here. The results presented are discussed in terms of the structure of the guides and the various process parameters.

An optical and microanalytical investigation of optical waveguides prepared by K+-Na+ ion exchange in glass is presented. Refractive index profiles and ion concentration profiles are compared, for waveguides prepared on soda lime glass at different processing times and temperatures; this comparison allows a reliable separation of the composition and the stress optical contributions to the resulting refractive index change.

Fiber optic gyroscopes are of interest for low-cost, high performance rotation sensors. Integrated optical implementations of the processing optics offer the hope of mass-production, and associated cost reductions. The development of a suitable integrated optical system has been reported by other authors at a wavelength of 850nm [1]. Despite strong technical advantages at 1.3μm wavelength [2], no results have yet appeared. This wavelength is preferred for telecommunications applications applications, thus significantly reduced fiber costs may be realized. Lithium niobate is relatively immune from the photorefractive effect at this wavelength, whereas it is not at at 850nm [3].

A monolithic integration of InGaAs PIN photodiodes and InP junction field-effect transistors has been demonstrated. The photodiodes show a frequency response beyond 22GHz with a quiantum efficiency of 65%. The FETs have a transconductance of 35mS/mm, a leakage current of less than lOnA/mm and a gate capacitance of less than 0.7pF/mm. The cut-off frequency of the FETs is estimated to be 7GHz. The receiver sensitivity is calculated to be -33dBm at 2 GHz.

A new monolithic dual-mode laser/detector diode which functions both as a laser and a photodetector is described. A laser threshold current of 0.52A was obtained under pulsed operation in broad-area laser/detector diodes (120μm x 350μm) with differential quantum efficiencies of about 30.9%. In the detector mode at the operating wavelength of 905nm, responsivity as high as 0.43A/W was obtained with a reverse bias of 8.0V. Using dual-mode diodes instead of separate lasers and detectors would simplify monolithic integration of optoelectronic circuits.

We describe fabrication and characterization techniques for glass waveguides for integrated optical components using ion-exchange technique, with emphasis on silver-sodium exchange in soda-lime silicate glass. A systematic study of the relationship between process parameters and waveguide performance is presented with the objective of optimization of the I-0 components for fiber compatibility.

Laser requirements and limitations for VLSI optical interconnect networks employing CGHs are discussed from a system point of view. For architectures with a collimating lens at the laser and a collector lens at the (on-chip) detector, the restrictions on laser wavelength stability are typically ± 10 A (thus requiring the laser's temperature to be regulated to approximately ± 5 - 10°C). Dif-fraction limitations are shown to restrict the density of interconnects to the 104 /cm2 range for many architectures (in particular, "space variant" architectures), rather than the 107 /cm2 to 108 /cm2 range frequently quoted for "space invariant" architectures. Archi-tectures with a mixture of space variance and invariance can lead to intermediate densities. Some architectures require low threshold, high efficiency lasers, whereas others require very high output power with much less concern for threshold and efficiency. A network with 3000 point-to-point interconnects/cm2, each transmitting at a 500 Mbit rate with a 10-11 Bit-Error-Rate is analyzed and the best system performance is obtained if very high power laser arrays (5 - 10 W) are available. Laser output pattern control is also con-sidered.

The purpose of this paper is two-fold: (a) To review the need for and the requirements of FOLAN interconnects; and (b) To present Tree-Net, a novel, multilevel, interconnected FOLAN architecture. We first review the basic FOLAN architectures and their requirements. Then, we discuss the problem of FOLAN interconnection and review some interconnect alternatives. Finally, we introduce Tree-Net, as an example of interconnect scheme, and evaluate its performance characteristics.

With the considerable work currently underway to apply optical interconnections within electronic systems, 1I it is of interest to examine how the system architecture impacts potential applications. The use of optical interconnections is very application specific, thus far, primarily being used to relieve pin-out constraints within high speed systems.[21 131 These very same high performance systems are sensitive to EMI making optical interconnections even more attractive. Another proposed application is for distribution of system clock signals within synchronous systems. [4]

The limitations of conventional interconnects and switching technology are rapidly becoming critical issues in the throughput of data within high-speed signal processors using VHSIC/VLSI chips or GaAs integrated circuits. Optical interconnect technology promises to significantly enhance signal processing systems and provide relief from pinout, physical proximity, and clocking problems. Furthermore, by releasing the bandwidth constraints imposed by electrical interconnects, the full processing capability of VHSIC chips could be exploited to improve currently fielded systems. Practical interconnection at the intraboard, backplane, and cabinet levels of signal processor systems can now be realized with optical interconnects.

A novel design concept for a generalized optical crossbar switch is presented. The approach relies on a massive fiber optic logic array and entirely eliminates the need for a spatial light modulator. Interconnection limitations and scaling issues are examined.

An integrated-optic analog vector multiplier can be used to achieve RF beam steering and nulling of a phased array antenna. We have characterized such a device, consisting of two sets of electrooptic grating modulators, using simulated antenna signals. Accurate linear four-quadrant multiplication can be obtained.

Tunable Optical Bistability, where a low power control beam is used to adapt the hysteresis response and the switching of optically bistable elements, is shown to occur in various systems with a bichromatic input. Some applications of this are suggested for more complex logic gates and for pattern recognition.

Present photonic systems involve communication and information processing applications in which optical signals are generated, modulated, transmitted, and detected and then transformed to electrical form for final use. All optical signal processing systems for both optical communications and optical computing have tremendous potential for dramatically improving the information handling capacity and data rate in various signal processing systems by keeping the information in optical form during more of the processing path. Major improvements in real-time signal analysis systems can be obtained through the implementation of all optical circuits due to the advantage of low power consumption, high speed, and noise immunity. Additionally, all optical systems lend themselves directly to implementation in highly parallel, high throughput architectures.