The injected minority carriers in a p-n junction can recombine both radiatively and nonradiatively. The recombination radiation can interact with valence electrons and be absorbed or interact with electrons in the conduction band to stimulate an identical photon. When the injected carrier concentration becomes large enough, the stimulated emission can exceed the absorption so that optical gain occurs. To obtain oscillation, it is necessary to have positive feedback of a portion of the radiation. This feedback is generally provided by a pair of cleaved facets that are perpendicular to the waveguide axis. Oscillation occurs when the single-pass gain between the cleaved mirrors equals the total loss over this same distance. These concepts are applied to the commonly encountered double heterostructure lasers of GaAs-AlxGa1-xAs to illustrate the basic properties of diode lasers.

GaAs/GaAlAs injection lasers are presently used in a variety of applications including fiber optic communications, optical disk data storage, and laser printing as well as many others. Each of these applications may require a somewhat different type of laser. This paper reviews the operating parameters and physical limitations of many of the different types of GaAs/GaAlAs lasers.

It is shown that small and gradual variations in the effective refractive-index or the grating period as little as 10-4 along the laser axis can have significant effects on the lasing characteristics of DFB (distributed feedback) lasers. Through numerical analyses based on the coupled-mode equations, it has been predicted that, in comparison with a DFB laser with uniform axial distribution of the effective refractive-index or the grating period, the axial-mode selectivity and the threshold gain of the lowest mode are much improved in a DFB laser with symmetric cosineor quadratic distribution and are much deteriorated in that with asymmetric linear distribution. Optically pumped GaAs DFB lasers with variable grating period have been fabricated by a new holographic interference technique, and experimental results consistent with the theoretical predictions are obtained.

GaInAsP/InP lasers with wavelengths of 1.0-1.7µ1-7 have been intensively developed because the optical fibers have their minimum transmission losses in this wavelength region8-9. The transverse mode control obtained in index-guiding structures is very important to im-prove lasing properties, such as modulation linearity, and longitudinal mode behavior as justified experimentally and theoretically. 10-15 Recently single transverse and longitudi-nal mode operation of GaInAsP/InP lasers with index-guiding effect have been realized in various structures.18-28 Newly, 1.6pm wavelength GaInAsP/InP buried heterostructure (BH) lasers have been operated at room temperature in CW condition.21, 22 We also presented, thus far, other types of novel mode-controlled GaInAsP/InP lasers.19,28 In this paper, three types of mode controlled GaInAsP/InP lasers are discussed: (1) buried heterostructure lasers with 1.6μm wavelength, (2) mesa substrate buried hetero-structure (MSB) lasers and (3) terraced substrate (TS) lasers with 1.3-μm wavelength. Specially, the lasing characteristics of 1.6-μm wavelength BH lasers are given. In these de-vices threshold currents as low as 28 mA and differential quantum efficiencys of 43% under room temperature CW condition could be obtained.

Heterodyne-type optical communication will provide a wide bandwidth and a high signal-to-noise ratio. However, at present the frequency drift of semiconductor lasers is the greatest difficulty, which must be overcome before the heterodyne-type communication is realized. This paper describes an automatic frequency control system for GaAkAs semiconductor lasers. The frequency drift can be reduced to below 10 MHz. Besides, without sacri ficing the frequency stability, a tunable frequency range of 0.5 THz is obtained. These values are good enough for heterodyne-type optical communication systems.

The current state of the art of photodetectors, both PIN and avalanche, for 1.1-1.6μm operation is reviewed. The devices are compared as components of optical receivers using several different types of amplifiers. GaInAsP/InP PIN and APD detectors are shown to be clearly superior to Ge devices with respect to dark current and other sources of noise. Receivers with performance within a few dB of the quantum limit appear to be possible with current technology.

The system requirements for fiber optic detectors and the relationship between bit error rate and signal to noise ratio are reviewed. With this relationship the device structure can be designed to provide the required S/N ratio, and the requirements for avalanche gain can be determined. The important material properties for low noise, wide bandwidth avalanche photo-diodes are reviewed, and a structure which separates the multiplication and absorption functions of an avalanche photodiode is described.

A review is given of recent progress in the development of integrated optical circuits involving the GaAs/A/GaAs double heterostructure system. Various devices utilizing period-ic corrugations or gratings are described briefly, whereas alternate attempts to fabricate optical circuits by chemical etching are discussed in more detail. The current trend to explore other III-V compounds is considered, with emphasis on the quaternary system InGaAsP. Recent advances in processing techniques suitable for optical integration, such as reactive-ion etching, laser and electron-beam processing, and the formation of ring lasers, are described, as well as the trend towards integration of optical and electronic devices.

It is not generally known that many modes on certain waveguides used for integrated optics applications are leaky rather than purely bound. Such leakage can result in unwanted cross talk, or form the basis for new types of components. After a brief review of waveguides for integrated optics, the physical mechanism for leakage is described, and it is shown wny the published approximate theories miss such leakage altogether. A summary of which modes leak and which do not, and several numerical examples are presented.

An accurate empirical model of the fundamental modal field distribution of straight and curved indiffused channel waveguides is presented and used to theoretically determine the losses associated with directional changes in the axes of indiffused waveguides. Particularly, the theoretical results are compared to experiment for Ti-diffused LiNbO3 waveguides that are single mode at 0.63 µm. Excellent agreement between the measurements and predictions are observed.

An extension of a recently developed hybrid technique for computing beam propagation in multimode dielectric waveguides is used to treat coupling between two identical parallel slab waveguides. Propagation on these slabs can be described by system (or normal) modes, which are symmetric or antisymmetric combinations of single slab modes. These two groups of modes possess slightly different self-imaging properties which can eventually result in virtually complete power transfer from one guide to the other. Whether or not the resulting beam in the second guide is well-focused depends on the relation of the coupling distance to the self-imaging distance, as well as the properties of the beam itself.

The position of the focal plane, the intensity profile of the first diffraction spot and power losses have been measured for geodesic lenses in Ti-indiffused LiNb03 waveguides. It was intended for the focal plane of a geodesic lens to be situated at a waveguide edge; experimental results have shown that this was achieved to a tolerance of better than 12 im with two of the measured focal planes coinciding with the waveguide edge to within the +2 Inn accuracy of the measurement techniaue. Scans of the intensity profiles of focused diffraction spots have been made for one and two lens systems; the spot sizes in both cases were found to be <1.15 times the diffraction limit at F/12. Throughput losses in geodesic lenses ranged from 2.5 to 17 dB - the larger losses occurring in lenses with small edge rounding and large corrected regions. An analytical program was initiated to determine the various mechanisms responsible for power loss. A simplified model indicates that a significant loss is due to mode mismatch in the vicinity of the edge rounding.

A branching filter having a multi-layered-dielectric-slab-waveguide structure is proposed, and its theoretical characteristics are analyzed by using both a coupled wave theory and an electromagnetic wave theory. Coupling coefficients required for perfect periodicity of the field configurations in the propagation direction, positional selectivity, wavelength selectivity, relations between the coupling coefficients and the structural and material constants, and an numerical example obtained by an exact application of an electromagnetic wave theory are described. The branching of this kind will be a useful device when the dimensions and the material constants can be well controled.

A new method has been devised for producing microlenses on the ends of single-mode optical fibers. A lens is formed by dipping the fiber end into negative photoresist while the fiber core carries Z0.1 mW of HeNe laser light. The photoresist lenses require no developing or rinsing. The lenses are shown to transform the near-Gaussian beam emitted by the fiber into another near-Gaussian beam with a reduced waist diameter. The size of the new waist can be selected by varying the number of times the fiber is dipped into the photoresist. The waist reduction is shown to increase coupling into single-mode optical waveguides.

An important area in integrated optics application is optical interferometer which may benefit from the rigidity of guided-wave optical construction and the precision of optical alignment using photolithographic procedures. Both the mirror reflectors, beam splitter/ combiners can be made of periodic structures. The design aspects of periodic gratings in planar optical waveguide and a sagnac interferometer using periodic gratings are described.

Diffraction gratings on planar waveguides have been improved by removing holographic causes of unwanted scattering of guided waves and by increasing the grating depth to obtain greater diffraction efficiency. Viewing the gratings as holograms of the exposure system permitted identifying and removing offending components such as collimating lenses. Reducing the standing wave pattern in the film during exposure permitted greater groove depth in the resulting grating.

Surface electromagnetic waves (SEW) are the normal modes of the EM radiation coupled to the optically active excitations of solids near the surface (also called surface polaritons). Optical guided waves used in integrated optics are one of the classes of SEW modes that appear in a layered geometry. We have investigated the dispersion and attenuation of SEW in the far infrared by means of inelastic scattering of light. All the expected modes in a single interface geometry (surface of a bulk) and a double interface geometry (film on a substrate) have been found, including the guided waves in thin slabs. These SEW modes occur near the infrared active optical phonon frequencies in semiconductors such as GaP and GaAs, and their behavior can be controlled by doping, roughening of the surface and an ex-ternal magnetic field. This review will focus on the character of these waves and suggest possible use in device applications.

The fabrication and performance of the first operating integrated optical RF spectrum analyzer are described. The device is a three-element hybrid structure consisting of a laser, the I0 substrate, and a photodiode array. It operates over a frequency bandwidth of 400 MHz, centered at 600 MHz, with a complete frame time of 2 psec. Although designed for use with a butt-coupled GaAlAs laser source, it has been tested using an end-fire-coupled HeNe laser. At the Here laser wavelength it divides the 400 MHz frequency band-width among 75 detector elements such that each element represents 5.3 MHz. An RF, input signal dynamic range of at least 18 to 22 dB has been demonstrated, as has the ability to detect two simultaneous pulses of 0.3 µsec duration and 20 MHz frequency separa-tion.

A programmable spatial filter which could be used to impose an arbitrary intensity pattern on a guided optical wave would be generally useful in a number of integrated optical devices. As a first step in the development of such a filter, a static filter consisting of a segmented photoresist Bragg grating on a LiNb03:Ti waveguide has been fabricated. The static grating was tested by performing correlations using a modulated SAW. Plans for a 32-channel programmable filter using electrooptically induced Bragg grating are discussed.

The principles and techniques of writing various types of micro gratings directly on chalcogenide (As2S3) film waveguides using the electron beam are reviewed. A computer-controlled apparatus has been developed so that we can fabricate any gratings of uniform/ chirped periods with slant lines which have the area of the order of 1 mm2, the diffraction efficiency of nearly 100 %, and the minimum grating period of 0.2 µm. Combination of those micro gratings results in integrated grating circuits (IGC). An IGC for guided-beam multiple division has been successfully fabricated.

Fundamental waveguiding properties of amorphous As2S3 film and some applications to passive optical grating devices are presented. The propagation losses of amorphous As2S3 film waveguides were measured t be 4.4 dB /cm. at 0.633 µm. and 1.4 dB /cm. at 1.153 µm. Chalcogenide amorphous semiconductors are characterized by the photoinduced refractive index change. Utilizing this phenomenon, the grating with the period of 0.35 µm and the length of 0.7 mm is fabricated in the As2S3 film. waveguide as the grating deflector with. a two-beam interference technique. A guided wave of 1.153 pm, TM.0 mode, has been deflected approximately with the deflection. angle of 90° and with the efficiency of 100 %. With the same technique, the grating coupler with the period of 0.55 pa and the slant angle of 10.5° is fabricated and the coupling efficiency is 1.7- % at 1.153 µm.

An improved optical channel waveguide TIR switch and the resulting switching network fabricated in a Y-cut LiNb0₃ substrate are reported. Fabrication procedures and testing scheme are first described. Some preliminary experimental results are then given. Some of the advantages of the TIR devices are also mentioned.

This paper describes video signal transmission through a light intensity modulator made of a Ti-diffused multimode branching waveguide in Y-cut LiNb03. High quality images have been displayed on a TV monitor.

Ion implantation of semiconductor materials is a very attractive technique for forming the guided wave components needed in integrated optical circuits. However, to produce optical components with sufficiently deep implanted regions for low loss operation at a wavelength of 10.6 microns, this technique normally requires very high accelerating energies, in excess of 1 MeV. Here we report on a series of experiments exploring an alternative solution to this requirement, namely, the migration of optically active carrier compensating centers produced by implantation at both elevated and cryogenic temperatures. While this mechanism has been observed in the formation of p-n junctions in GaAs, no attempt has previously been made to utilize this enhanced penetration for optical waveguidin:E. Silicon-doped n-type GaAs wafers have been implanted with 300 keV protons at fluence levels up to 5x1015 ion/cm2. During implantation, the wafers have been maintained at temperatures ranging from -170°C to +350°C. The thickness of the compensated region has been determined from infrared specular reflectance curves and from capacitance voltage (C-V) measurements. Theoretical reflectance curves are constructed based on the thickness data and are compared to the experimental curves.

We give a brief survey of the types of acoustic waves that propagate in piezoelectric crystals, touching upon some of the most useful crystal cuts, and some of the practical structures currently used. Materials that may substitute for quartz are considered. Equivalent network structures are dealt with for the characterization of devices, and examples of typical responses achieved for bulk, surface, and shallow bulk configurations are given.

This paper describes the different device geometries available for surface acoustic wave (SAW) bandpass and dispersive filters and gives estimates of the limits on the performance parameters available with each type of device. Two specific bandpass filter applications are described in some detail. The discussion given here serves as background for other papers (presented at the same symposium) that give more detailed discussion of additional applications.

Surface Acoustic Wave (SAW) oscillators are practical from 100 MHz to 1500 MHz and can be in the form of a delay line or resonator. High overtone hulk acoustic resonators on non-piezoelectric substrates operate from 1 GHz to 10 GHz with a 0 better than quartz. The two SAW approaches and the high overtone hulk resonator are compared with each other and with a multiplied 5 MHz standard crystal oscillator for UHF and microwave applications. UHF acoustic oscillators give size, weight, cost and power reductions.

In this paper, a quick review of the different frequency synthesizer architectures is given. Most of the emphasis is given to the design of fast settling direct synthesizers. Three examples are then given showing how the use of SAW devices in frequency synthesizers can reduce its overall size and weight. Photographs and measurements of the SAWs are given as they apply to the performance of the synthesizer.

The storage correlator is an acoustic surface wave device which can store an input signal for times as long as a few seconds and correlate it with a signal read into it at a later time. It can also correlate two signals being read into it at the same time. In this paper we describe a monolithic form of the device using zinc oxide sputter deposited on silicon. Applications to correlation of spread spectrum signals and to adaptive filtering for removal of interfering signals or of distortion are described.

SAW technology is impacting the development of frequency sorting receivers for use in the modern electronic warfare (EW) environment. SAW delay lines and filters can address the typical problems of complexity, cost, size and weight of these receivers while maintaining a high performance level in signal processing. In this paper the application of SAW filters to frequency sorting receivers is discussed and two systems currently under development are described. Each receiver uses contiguous SAW filter banks as the basis for its frequency sorting functions. The two receivers have the common purpose of detecting and analyzing short pulses. They differ in their dynamic range and resolution capabilities. The use of SAW components in these receivers has achieved a high performance level and significantly reduced volume and weight. SAW components give promise of a low-cost, rugged and reliable receiver when manufactured in quantity.

The development of large time-bandwidth product surface acoustic wave (SAW) chirp filters is now a mature technology that is finding an ever broadening range of signal processing applications. By taking advantage of the ease with which these devices can be used to implement the chirp transform algorithm a number of SAW-based signal processors have evolved for realizing electronically variable delay lines, programmable matched filters, and spectral analysis subsystems. Recently the overlapping operating characteristics of SAW filters and high speed digital circuits have been utilized to produce efficient, broadband fast Fourier transform networks with diverse applications in radar and sonar signal processing systems. This paper reviews some of the current applications of SAW devices in analog chirp transform correlator and microscan receiver systems, and describes the improved processing speed that can result from using SAW devices in hybrid analog-digital processing systems. The effect of filter errors on the ultimate performance characteristics of different spectral analysis, and Fourier transform based processors is discussed and the projected capabilities of SAW-based processing systems is addressed.

Interest in acoustoelectric SAW devices has grown rapidly in the past few years. One of the reasons for this expansion is the potential capability of these devices to perform sophisticated real-time programmable signal processing. The essential ingredient in these devices is the acoustoelectric interaction of free carriers in a semiconductor with the evanescent RF electric fields accompanying surface acoustic waves (SAWs) propagating on a nearby piezoelectric substrate. Coupling of the electric fields from the piezoelectric to the semiconductor takes place across a narrow (-300 nm) air gap. The complexity of the semiconductor ranges from the simple distributed surface varactor of the convolver, to the high density diode array (few pm periodicity) of the acoustoelectric devices with charge storage, to the fully integrated microcircuit of the complex charged-coupled devices (SAW/CCD). The convolver provides, in a compact structure, matched filtering with a processing gain in excess of 30 dB and bandwidths up to 200-MHz for spread-spectrum waveforms, a function which would otherwise require a large digital machine operating at 10¹¹ arithmetic operations per second. Other devices, newer than the convolver, are being explored which promise increasingly sophisticated signal processing capability. For instance, the memory correlator and the SAW/CCD programmable matched filter can be used in radar receivers in place of fixed matched filters to reduce the time spent in system alignment and to introduce programmability; the integrating correlator and the SAW/CCD accumulating correlator have the potential to be used in spread-spectrum systems for the correlation of very long (â€â€?msec) waveforms and the coherent integrator could provide a programmable burst-waveform processor for pulse-Doppler radar. As examples of the large variety of acoustoelectric SAW signal processors, three specific air-gap devices, the convolver, the memory correlator, and the coherent integrator will be described.

Range resolution in FMCW radar systems has been achieved using multichannel surface acoustive wave (SAW) filter devices. This paper describes the basic system design concepts employed for developing range cells in linear F!ACW radar using the SAW filters. The techniques discussed are currently being used in low power solid-state millimeter wave radar for air-to-ground terminal guidance of anti-armor munitions. The narrow band SAW filters are incorporated in the receiver IF sections where each filter represents a range cell that is dimensionally proportional to range. The small size, light weight, low power consumption and stable per-formance characteristics make the SAW filter an ideal choice for missile seeker applications.

Fiber-Optic Sensors appear suitable for successfully fulfilling a wide spectrum of sensing transducer requirements in industrial and military applications. Before they supercede existing sensors, a large amount of materials, subsystem and system design research must be accomplished to solve the apparent difficulties. This paper summarizes their promise, the technological problems that arise, and the principle approaches that will solve these problems.

Evolving military systems concepts include the application of optical fibers in dynamic deployments, exposure to a severe environment, or storage under stress. Development of optical fiber technology to meet minimum service requirements is founded on improving the strength through flaw reduction and elimination of static fatigue. Improvements in processing has resulted in steady increases in both the short gauge-length median strengths and long length proof stress of CVD fibers. Stress corrosion resistance has been demonstrated by hermetic coatings of metals and dielectrics. Because of the diversity of applications, however, not all fiber systems will require high strength, fatigue resistant fibers. The most demanding applications, however, may be those in which the fiber itself is the load-bearing member of the cable. Requirements for continuous high-strength fibers in lengths in excess of 5 - 10 km may be prohibitively expensive unless segments can be routinely fusion-spliced with consistent low loss and high strength. The DOD High-Strength Fiber Program and its current status will be reviewed.

This paper identifies and discusses specific applications of the optical transmission technology to various Command Control and Communications (C3) systems. Candidate C3 systems will first be identified and discussed briefly. These will include: 407L/485L Tactical Air Defense Systems (USAF) TAOC-85 Tactical Air Operations Central (USMC) SACDIN Strategic Air Command Digital Integrated Network (USAF) MX-C3 Missile "X" Command Control Communications Network The first tr are classified as tactical C3 systems while the latter two are classified as strategic C systems. Potential optical applications will be identified along with the benefits derived. Each application will be discussed with key parameters, cost performance benefits, potential problem areas, time frame for development identified.

A system is proposed for the utilization of high-speed guided wave components to realize multiple-access data rates above 100 Mbits/s. Angular division multiplexing is used to obtain parallel optical signal transmission and processing in routing data packets between host computers. A novel application of an optically pumped half-ring laser to detect and regenerate multiplexed signals is suggested.

The maturing technology in fiber optics has generated renewed interest in the development of integrated optic devices applicable to single mode guided wave optical systems. Integrated Optics (I0) represents the development of optical circuits which perform the functions of generation, modulation, switching, coupling, and detection of optical signals in an integrated, compact and rugged format. This paper will review several JO components and integrated optical circuits.

The use of optical fibers is being considered for a guided missile system. The proposed missile, with a TV or other imaging seeker, would use a single optical fiber and wavelength multiplexing to relay pictures back to an operator and carry his commands forward. A full duplex, fiber optic link for this system operating over a single fiber at 0.85 μm and 1.06 μm will be described. Video data up to 3 MHz along with nine telemetry channels is transmitted in one direction. A lower data rate signal consisting of six command channels to control missile functions is transmitted in the other direction. Such key areas to be discussed are optical signal isolation techniques between video and command signals, optical power budget, modulation formats, and electronic time-interleaved multiplexing to form the composite video and command channels.

This paper serves as an update for the Multiwavelength Monolithic Integrated Fiber Optic Terminal (MMIFOT) being developed by MDAC-St. Louis for NASA's Johnson Space Center. The program objective is to utilize guided wave optical technology to develop a passive optical wavelength multiplexing/demultiplexing subsystem with a single mode optical fiber serving as the transmission medium.