The development of a tantalum pentoxide Luneburg lens for collimating the beam entering an integrated optical wavelength demultiplexer involved improvement of the deposition mask profile, reduction of surface scattering by underlaying the lens, reduction of edge scattering by shims under the mask, and prediction and measurement of TE - TM polarization aberration. The polarization aberration significantly affects the demultiplexer system design.

We present here the theoretical design and the experimental fabrication and evaluation of diffraction lenses in LiNbO₃ waveguides.

We have designed and fabricated an integrated optical device which utilizes bulk acousto-optic modulation to introduce GHz modulation on the guided light. This device, which may be used as either a heterodyne receiver or modulator in a high frequency optical data link, is fabricated on a silicon substrate using photolithographic and etching techniques developed for semiconductor manufacture. Modulation is accomplished utilizing segmented thin film acoustic transducers. Fabrication of this device involves nearly twenty separate operations each of which must be successful in order for the device to work. We discuss these fabrication steps and their influence on the overall yield of this integrated optical device.

We report consiaerabe success in using the technique of laser annealing to reduce scattering in a variety of thin-film optical waveguides deposited onto thermally-oxidized silicon substrates. For the materials Si 3N4, Nb90,, and Ta205 values of waveguide loss less than 1 oB/cm were achieved. Values of waveguide loss as1UW as'.01 db/cm nave been measured for laser-annealed Zn0 waveguides and for Corning 7059 glass wave-guides which have been both laser anneal ea and had surface coatings applied.

Integrated optical circuits have been fabricated using laser-written masks. Straight and curved channel waveguides have been made by ion exchange from a KNO₃ melt of dimensions 10 to 30 pm in width and typically 4 to 5 cm in length. A mask made by a multiple exposure technique from a laser-written curved channel mask has been used to delineate a directional coupler in LiNbO₃.

Integrated optical logic devices offer the potential of operating at high speeds and at low powers. This paper discusses some of the basic requirements of an optical logic device, also presented are the characteristics of various existing and proposed optical logic devices.

Experimental and theoretical data are presented describing progress in the areas of fiber-to-channel waveguide coupling, integrated optic circuit losses, optimization of the electrode generated electric field-optical mode overlap and polarization independent device design and demonstration.

The nonlinear mixing of oppositely propagating waves in an integrated optics waveguide is shown to lead to a sum frequency signal which can be used in conjunction with a CCD array to perform the functions of a picosecond transient digitizer.

Non-linear ring-resonators are shown to exhibit optical bistability with nanosecond switch times, when using GaAs as a non-linear material and photon energies below band gap. A computer program developed specifically to model the transient response of these devices is used to extract values for the non-linearity and its response time from the observed characteristics.

Switching between states of an intrinsic bistable device is usually accomplished by changing the input intensity I_I, increasing it above the switch-up value It or below the switch-down value With a constant input intensity satisfying I↓⪅ I_I < I↑, switching can be actuated by external pulses. Switch-on by a 10-ps, 600-nm, 1-nJ pulse in less than the 200-ps detector response time is attributed to screening of the GaAs free excitons by hot carriers. Switch-off in ≤20 ns by a 7-ns, 600-nm, 300-nJ pulse is attributed to heating the etalon and increasing I4, until it exceeds the constant I_I. Under certain con-ditions the competition between excitonic and thermal effects causes the etalon to switch on and off repeatedly in a relaxation oscillation fashion. These regenerative pulsations could be the basis of an all-optical oscillator. The transverse profile has been examined for switching actuated by intensity modulation of the input. Whole-beam switching is observed, i.e., when switch-on occurs, it occurs out to large radii simultaneously. Computer simulations show whole-beam switching for strong diffractive coupling but show radially dependent switching for weak diffraction, neglecting transverse diffusion. The same etalon emits a near-band-gap laser pulse when pumped sufficiently by an above-band-gap pulse, serving as a wavelength converter. All of these modes of operation of the GaAs etalon, i.e., switchable memory, oscillator, and wavelength converter, could be useful in all-optical logic and computing systems.

The major types of AlGaAs high-power cw single-mode diode lasers are reviewed and compared. The basic approaches for achieving high power (20-50 mW/facet) single-mode operation are presented first. Emphasis is placed on the CDH-LOC laser type, which has demonstrated cw single-mode operation to 40 mW/facet, and 50%-duty-cycle fundamental-mode operation to 100 mW/facet. By using CDH-LOC devices signal-to-noise ratios close to 70 dB were achieved, and peak powers of 40 mW (50% duty cycle) were coupled into 0.2 NA fibers. Lifetests of CDH-LOC lasers at 40 mW/facet initial output power and 50% duty cycle, have shown small drops in output even after 10,000 hours of operation. Monolithic ten-unit arrays of CDH-LOC lasers delivering up to 300 mW in cw operation have been demonstrated as well.

Hewlett Packard fiber optic link products use four types of light emitting diodes (LEDs) based on GaAsP and GaAlAs technologies. The reliability of all four emitters has been extensively studied. In this paper, we report the experimental results and discuss possible failure mechanisms.

Deep Zn diffused stripe GaAs/GaAlAs double heterostructure lasers grown by metalorganic chemical vapor deposition for fiber optic transmitter applications are reported. Stripe widths of 2, 4, and 8 pm are examined in terms of laser threshold currents and far-field radiation patterns. For lasers with a 4 pm stripe, threshold currents as low as 40 mA, a characteristic temperature as large as 170°C, and external differential quantum efficiencies as high as 80-90% are obtained. Single mode operation of these lasers is observed. Preliminary results on the device uniformity and high-speed modulation characteristics are includded.

The monolithic integration of GaAs electronics and light emitting sources (or detectors) is a desirable method for producing compact, reliable, potentially low-cost optoelectronic modules for fiber optic communications. The material's and processing required for opto-electronic components (emitters and detectors) and electronics (FETs) are different and often incompatible. This has been primarily responsible for the relatively slow development of integrated structures. Therefore, it is important that a method be developed for combining the two dissimilar technologies using materials and processes which do nct place prohibitive restrictions on the performance or geometry of the optical and electronic devices. In this paper we present the progress and results of an integration scheme termed "emitter/detector-in-a--well" which presents a simple solution to the problems that have plagued other integration schemes. MESFET compatible A1GaAs light emitting diodes and GaAs p-n junction detectors have been successfully fabricated on semiinsulating substrates using this new integrating scheme. Adjacent to each optoelectronic component there is an exposed surface of the semi-insulating substrate (for MESFET fabrication by direct ion implantation) which is coplanar to the top surface of the GaAs optoelectronic component. The merits of this "all planar" integration technique are discussed. In addition, the fabrication and performance of MESFET compatible Transverse Junction Stripe LEDs and Be-implanted detectors are presented.

Tunneling current has been identified in the reverse I-V characteristics of Be-implanted Ga_0.8A1_0.2As_ySb_1-y avalanche photodiodes. The tunneling energy is considerably less than the bandgap energy. This identifies the tunneling mechanism as defect assisted tunneling rather than a band-to-band process. It is also shown with the proper structure that the defect assisted tunneling can virtually be eliminated, resulting in extremely low dark current GaAlAsSb photodiodes.

Electronically stabilized single-mode optical fiber systems operating at 1300 nm wavelength are being developed at the Jet Propulsion Laboratory (JPL). They will be used to distribute frequency and timing reference signals having a stability of up to 10_-17 for 1000 second averaging times and a timing accuracy of 100 ps over distances up to 30 km. They will also distribute 400 MHz bandwidth IF signals over 20 km distances.

Progress in developing a fiber-optic gyro based on active closed loop phase compensation is described. Comparisons are made between a breadboard proof-of-principle unit built in 1978, a 12.7-cm-diameter, 2.5-cm thick unit built in 1979, and a 6.5-cm-diameter, 1.7-cm thick unit built in 1980.

Hybrid circuits containing integrated optical detectors, waveguides, and electro-optic-switches can be used to perform a variety of digital logic operations. In combining the hybrid circuits with the carry-free residue arithmetic algorithm, different modules are designed to perform basic arithmetic operations, encoding, decoding, and scaling. Based on pipelining and parallel concepts, a vector-vector multiplier is designed to yield very high throughput rate for application involving traditionally slow computation such as matrix-vector multiplication and polynomial evaluation.

The integrated optic spectrum analyzer is a device which utilizes the Bragg interaction between a SAW and a guided optical beam to perform spectral analysis. Hughes has developed the first fully integrated IOSA which uses a butt-coupled GaAlAs semiconductor laser, a LiNb0₃ waveguide substrate, a 400 MHz bandwidth SAW transducer and a silicon detector/CCD array chip. The completed device exhibited a 3 dB bandwidth of 380 MHz with 10%/watt deflection efficiency at ), = 0.82 μm. The RF resolution was found to be 8 MHz and the dynamic range was greaterPthan 20 dB. Data is also discussed on a modified chirp transducer which exhibits a 450 MHz acousto-optic bandwidth with a center frequency of 1.0 GHz.*

A 700 MHz bandwidth guided wave acoustooptic Bragg cell was developed for use in an integrated optic spectrum analyzer. Various configurations of multiple tilted SAW transducers were investigated theoretically and experimentally to find the most efficient combination which would provide a 700 MHz sub-octave acoustooptic bandwidth. Investigated were Bragg cells fabricated on Ti diffused LiNbO₃ waveguides as well as Ti diffused LiNbO₃ waveguides with Nb₂O₅ thin film overlays. A Bragg cell consisting of 6 tilted transducers was designed, fabricated, and tested, exhibiting 700 MHz bandwidth and 2.8%/RF watt diffraction efficiency. The Bragg cell operates between 775 MHz and 1475 MHz. Projections are made on the performance of an integrated optic spectrum analyzer utilizing this Bragg cell based on results obtained from an existing 200 MHz bandwidth spectrum analyzer.

Efforts to improve upon the reported dynamic range of newly developed integrated optical RF spectrum analyzers center about two separate components. One of these is an efficiently coupled, high power, single mode, narrow-beam-spread GaAlAs laser diode and the other is the photodiode array with its associated read-out circuitry. Recent attempts to realize improvements in both of these components are described, as are the design changes in the spectrum analyzer necessitated by the characteristics of available laser diodes.