Integrated optical circuits operating at infrared wavelengths and fabricated monolithically on a GaAs substrate will have a tremendous impact on signal processing systems. These circuits will afford the ultimate merger of VLSI electronics and microwave devices with integrated GaAs optoelectronics. Such GaAs components include planar and channel waveguides, parallel-channel directional couplers, electro-optic modulators and switches, laser diodes, acousto-optic modulators, and detectors. The focus of this paper is the design and fabrication by ion implantation of the necessary fundamental build-ing blocks of optical integrated circuit planar waveguides. Design considerations include the compensation mechanism in doped GaAs substrates and the implantation processing parameters utilized in achieving optimum optical and electrical device characteristics.
Implementation of single-mode optical fiber systems depends largely on the availability of integrated optical components for such functions as switching, multiplexing, and modulation. The technology of integrated optics is maturing very rapidly, and its growth justifies the optimism that now exists in the optical community.
This paper reviews recent progress in the development of integrated optical circuits involving the GaAs/AfGaAs double heterostructure system. Devices utilizing periodic corrugations or gratings are considered briefly, whereas alternative attempts to fabricate optical circuits by chemical etching are discussed in detail. The InGaAsP/InP system is also considered. Recent advances in processing techniques for optical integration, including reactive ion etching, are described, along with recent measurements that correlate waveguide loss with epitaxial layer uniformity.
Recent developments in optoelectronic broadband switch matrices based on GaAs photoconductive detectors are described. Integrated arrays of optoelectronic crosspoints have been constructed and tested to show 70 dB of crosstalk rejection for an array density of 100 crosspoints/mm2 at a frequency of 100 MHz. Such devices may have application for large-scale circuit switching in networks carrying such broadband signals as high definition television. A 3 X3 array with isolation greater than 45 dB at frequencies up to 3.8 GHz has also been demonstrated. Optoelectronic switch arrays can be used in analog and digital signal processing. Sharp, tunable filters with overall bandwidth in excess of 1 GHz have been constructed by means of reflex connections to an optoelectronic matrix using optical delay lines. This apparatus can also be used for high rate digital word generation and other digital signal processing. Switch-ing times below 1 ns have been confirmed. A key area for development is the distribution of light in the matrix. The use of integrated optical waveguides appears to be essential to realize the full potential of optoelectronic switching.
Planar and channel optical waveguide structures formed on silicon substrates using the fabrication techniques of sputtering, thermal oxidation, and chemical vapor deposition are discussed. Losses in the various waveguide structures are reported and related to the fabrication procedure used. The use of polycrystalline silicon deposited by chemical vapor deposition onto any waveguide substrate to form integrated photodetector arrays is discussed. Laser recrystallization of the deposited silicon is used to allow fabrication of high quality devices. Measured values of photodiode reverse current of less than 10-9 A and breakdown voltages of 24 V are respectable values for small photodiodes incorporated into a dense array.
We give experimental results concerning analog Fresnel lenses achieved on silicon nitride waveguides deposited on an oxidized silicon substrate. Comparisons between the measured performances and theoretical predictions are presented, and applications of such lenses in the field of optical signal processing are discussed.
This paper summarizes the measurements of 2 X2 and 4 X 1 polarization-independent electro-optical switches for 1 .3 Am wavelength. Conclusions about the performance characteristics and limitations of both polarization-independent and single (TM) polarization switch arrays are drawn from these results.
The process of ion exchange in relation to the fabrication of low loss integrated optical waveguides on glass is reviewed. Issues relating the exchanging species, glass constituency used, and fabrication to the pertinent waveguide parameters such as numerical aperture and loss are discussed, and guidelines for producing high quality waveguides are outlined.
The Battelle Memorial Institute is presently organizing a cooperative research and development program designed to facilitate rapid transition of optoelectronic technology from research to development. Specifically, the program will help U.S. industry develop the basic manufacturing technology it needs to produce active optoelectronic components efficiently and cost effectively for both long- and short-haul fiber optic systems. Manufacturing methods developed in the program are to be tested under pilot conditions so that fully packaged and connectorized prototypes are made available to the sponsoring companies at the earliest possible time. Three critical issues, microassembly and packaging, optical circuitry, and optoelectronic substrates, will be addressed in separate projects.
In assembling this special issue of Optical Engineering we have taken a broad definition of what constitutes infrared optics. This issue includes papers on lens design, optical system design and alignment, optical materials and detectors, and optical instru-ments. Since infrared optical technology is such an integral part of so many application areas, including sensor systems, scientific instrumentation, and various commercial uses, we thought that such a view was warranted.
The basic principles used to design infrared transmitting glasses are briefly explained. The composition and properties of oxide, halide, and nonoxide chalcogenide glasses show the utility and limitations of these materials for infrared applications. In general, glass systems with an infrared absorption edge at longer wavelengths have smaller compositional areas of glass formation, and the glasses have poorer physical and chemical properties.
Lens systems used in thermal imaging systems frequently employ aspheric surfaces in order to obtain aberration correction with a minimum number of lenses. The use of infrared-transmitting gradient-index materials is a theoretical alternative method for achieving this aim. Moreover, gradient-index materials can be used in some cases to correct chromatic aberrations, which aspherics cannot correct. A design study has been conducted in which it is shown how the polychromatic optical performance of particular lens systems could be improved by utilizing ZnSe/ZnS axial gradient lenses, and how the performance over the field of view could be improved by utilizing a germanium/ silicon spherical gradient.
An introduction to metal-barrier-metal (MBM) electron tunneling devices is given. The introduction is oriented toward applications of tunneling devices as detectors of optical and infrared radiation. The theoretical back-ground of tunneling devices is briefly discussed, as is the historical development of MBM devices. Applications in which MBM devices are currently finding use are presented. The present problems with MBM devices are analyzed, and possible directions for further progress in perfecting MBM devices are explored. The process of fabrication of a particular type of MBM detector, the edge MBM device, is outlined. Measured performance of MBM detectors is covered briefly.
High resolution infrared spectroscopy obtains fundamental information about the kinematics, composition, and energetics of astronomical infrared sources because it can sort out typical Doppler velocity components and separate adjacent lines from various species. In important cases the instrument having the maximum possible sensitivity for detection is a cryogenic Fabry-Perot spectrometer because it rejects noise from the bright and often flickering background without injecting any radiation. Such an instrument need only be limited by the performance of the best detectors. Coupled to a two-dimensional array, a cryogenic Fabry-Perot can produce spectroscopic infrared images of high quality. We have developed a prototype cryogenic infrared Fabry-Perot spectrometer and have operated it successfully on-site. The system uses a unique optical servo control for reliable sensing of the interferometric surfaces, and electromagnetic voice coil displacement drivers for the large motions needed for flexible operation. The present etalons and detector are optimized for the 4 to 5 Am band. We present a description of the instrument, recent astro-physical results obtained at a telescope, and a summary of development plans. Such a system can be operated from space out to submillimeter wavelengths.
An all-reflecting three-mirror infrared optical system has been built by Itek Optical Systems to demonstrate the feasibility of manufacturing such eccentric field designs. The device is a reduced field (1°) version of a three-mirror long wide-field design having a 15.24 cm aperture. Methods for fabricating off-axis aspheric mirrors and aligning eccentric component systems are presented. Results of interferometry to derive image performance characteristics are also given.
Using the nonlinear spinor equation in cylindrical coordinates (r, cp, z), we prove that for some particular amplitudes of the spinor field, there exist quasi-plane-wave solutions xif(r, c a , z) = exp(iKzz) 43(r, (p) such that 11(0, c o , z) = const, rim xl(r,(p,z) = 0 with the integral of 14,12 rdr bounded. Such ---.00 solutions intervene to describe the self-trapping of optical beams. Since one may define the electromagnetic field (E, H) in terms of the spinor V' and its transpose TT, we are able to discuss the possible modes of propagation. A comparison with previous works is also given.
It has been suggested that the principles of tomography should be applicable to image data compression. In this work an extremely simple optical device for the tomographic encoding and decoding of an image is proposed. This device is simulated through digital image processing, and various forms of image data compression are applied so that the resulting reconstructed images may be compared. It is found that indeed the method should be useful in practice, resulting in large factors of data compression, with flexible control over the factors affecting image quality.
Design and performance data are presented for the Strato-spheric Aerosol and Gas Experiment II (SAGE II) instrument, which has been developed for the Earth Radiation Budget Satellite (ERBS). SAGE II is designed to monitor globally the vertical distribution of stratospheric aerosols, ozone, water vapor, and nitrogen dioxide by measuring the ex-tinction of solar radiation through the earth's atmosphere during the ERBS observatory solar occultations. Solar radiation is reflected from a flat scanning mirror into a Cassegrain telescope, which forms a solar image on the entrance slit of a grating spectrometer. The SAGE II instan-taneous field of view is scanned along the vertical solar diameter by the elevation scan mirror. The entire optical system is contained within an azimuth gimbal that tracks the solar radiometric centroid during the data event. This spectrometer, with help from three interference filters, iso-lates seven spectral wavelengths ranging from 0.385 um to 1.02 um. All seven channels use silicon photodiode detectors operated in the photo-voltaic mode. Detector outputs are multiplexed into a serial data stream for readout by the ERBS telemetry system. Each output is sampled 64 times per second and digitized to 12 bit resolution. SAGE II is a third generation instrument, following the highly successful Stratospheric Aerosol Measurement II (SAM II) and SAGE programs.
An optical scanner that is relatively free of radiometric errors, with a nominal focal error resulting from a curvature of scan, is described. Except for the imaging lens, all the optical elements are plane mirrors. The scanner, while scanning contiguous lines in the object plane, images each line onto a linear array in the image plane. The scans are essentially linear with scan angle and symmetric about the axial ray.
Analytic solutions for aplanatic four-spherical-mirror systems are obtained, and the optical aberrations of the systems are examined numerically. These systems consist of Cassegrainian front parts and inverse Cassegrainian rear parts. The front part is afocal and has high light-collecting capacity. Aberra-tions of the inverse Cassegrainian system are counterbalanced with those of the front part. A germanium corrector lens may be used in these systems for improved performance in the thermal infrared region.
About a decade ago, a very remarkable optical system was devised by Offner, mainly for 1:1 projection lithography of microcircuits. This system contains only two reflecting surfaces, which are spherical. The aberration properties in this system are very remarkable in that all the primary and several secondary aberrations are eliminated. The system is completely achromatic since no refraction is involved. In this short paper we make some suggestions for the use of this system in several other areas of optics.
A saddle mirror is a toroidal mirror with the principal curvatures of opposite sign. The mirror can form images of objects without reversing them. This means that a right-handed object can be imaged into a right-handed image that is erect. However, the saddle mirror is not easy to construct accurately. It is possible to devise some equivalent mirrors that have either cylindrical or plane surfaces for the special situation when one is interested in an image that is also free from anamorphic magnification difference. A few such optical devices are presented in this paper.
Infrared presensitization photography is explained, explored, and applied to field optical diagnostics on a high energy 10.6 um laser system. This technique involves recording IR radiation on film normally used for its visible sensitivity.
A new technique for presenting satellite Landsat multispectral scanner (MSS) three-dimensional image data has been developed under a collaboration between the Canada Centre for Remote Sensing (CCRS) and the Polaroid Corporation. It consists of the production of white-light viewable holographic stereograms obtained by digital and optical processing of Landsat MSS stereo pairs. The digital processing extracts elevation information from suitable Landsat image pairs and synthesizes a sequence of fictitious perspective views. Laser optical processing is then used to merge these images into a white-light viewable holographic stereogram producing a black-and-white three-dimensional image of the earth's surface. The high quality of the relief image demonstrates the potential of computer/holographic hybrid techniques as tools for further analyses of remotely sensed data.
A brief review is presented of simulation studies and real-data experiments that were conducted to assess the impact of satellite observations on numerical weather prediction. These experiments show that while there has been some redundancy between observing systems, satellite data have made significant contributions toward improving global forecasting.
Fiber optic sensor technology is explained in terms of theory and applications. Various components common to all fiber optic sensors are compared. Two classes of sensing devices are emphasized: amplitude-modu-lated sensors and phase-modulated sensors. Specific examples of amplitude-modulated devices-one a pressure sensor using an optical reflection technique and another an accelerometer using a microbend technique-are described. Four types of fiber optic interferometers used in phase-modulated sensors are discussed. The effect of the optical fiber jacket on the sensitivity of phase-modulated sensors is considered. A miniature pressure sensor and a highly sensitive fiber optic accelerometer, both employing phase modula-tion, are described.
The microscopic spatial distribution of biological compounds can be imaged using a coherent anti-Stokes Raman scattering (CARS) microscope. Spatial resolution of less than one micrometer has been achieved, and excellent molecular discrimination using chemically similar molecular species has been obtained using digital image processing techniques.
The Texas Instruments virtual phase CCD imager has been successfully operated in the frontside electron-bombarded mode. The entire active area of the imager was covered with 130 nm of thermally grown gate oxide while only the clocked half of each pixel was additionally covered with a 500 nm polysilicon electrode. No protective overcoat was grown over the imager. A 20 kV electron beam was focused onto the imager to a total dose in excess of 120,000 primary electrons per pixel. Both the parallel and serial clocks were operated between -15 V and +2 V throughout, and no adjustment in any of the operating parameters was required. However, flat band shifts on the order of 2 V were detected. Single primary electron events were clearly detected with a signal-to-noise ratio exceeding 10. In excess of 90% of the secondary charge generated by a primary event was collected in a single pixel. The standard virtual phase imager with only the protective overcoat deleted can be used with a photocathode in the electron-bombarded mode for observing low to moderate light levels and can act as a true photon counter.
The 1.4 m Coude Auxiliary Telescope (CAT) was designed for spectroscopy and will be used in coude focus. The telescope was designed as an "alt-alt" mounting ( i.e., altitude-altitude, which means that when the telescope is vertical, both axes about which it rotates are horizontal), which gives, mechanically, an attractive and inexpensive structure without any need for big counterweight systems. The optical configuration is of the Nasmyth type, with a flat, movable third mirror mounted in the center of the telescope. The main mirror has an f-ratio of f/3. The exit f-ratio is f/120. The telescope, situated in a tower separate from the operating center, is completely remote controlled. Guiding is performed via a low-light-level TV camera on the slit of the Coude Echelle Spectrograph (CES). The identical drive systems for the two axes in the alt-alt mounting are of the direct-drive type, with a torque motor, tacho generator, and encoder connected directly to the shaft without any reduction gear. The positioning system is based to a great extent on microprocessors.
Abstract. Lead-rare earth-chalcogenide diode lasers have been grown by molecular beam epitaxy. Emission wavelengths shorter than 5 to 6 Am have been obtained from lead-europium-selenide-telluride (Pb1 -xEuxSeyTe1-y) double heterojunction diode lasers grown lattice-matched to PbTe substrates. Mesa diodes with -25 um wide stripes have been fabricated that have a wide range of single longitudinal mode emission at up to -1 mW/facet output power. These diodes have operated at up to 147 K cw, which to our knowledge is the highest cw operating temperature ever achieved with lead-chalcogenide diode lasers. The wavelength coverage of the PbTe system has so far been extended to 4.06 um cw. Longer wavelength coverage is obtained from double heterojunction diode lasers with Ma1-ySnyTe active regions lattice-matched to (Pb1-ySny)1-xYbxTe confinement layers. I n preliminary studies of diodes with x = 0.034, y = 0.14, the cw emission wavelength varied from 10.7 µm (at 10 K) to 7.1 µm (at 128 K).
Over a period of years an editor deals with numerous reviewers-most of them careful and thorough in their task. To these reviewers we owe much gratitude and praise, but it is not of them I now write. I want to comment instead on the reviewer who might be described as a perfectionist.
As I struggled to complete my thesis research, for advanced degrees in electrical engineering at MIT (1927 and 1931), little did I realize that two important developments of considerable engineering application were in their embryonic stages, and I was right on the cutting edge of both. These were (1) the first practical analog computer?"' with the capability to solve nonlinear differential equations and (2) the strobe light,5-7 which gives ample light to record rapidly moving mechanical motions. These two devices were used together as a system to study the transient performance of synchronous machines for my graduate studies. I must say that they did it well for many years.
When several authors collaborate to write a highly
technical book, the resulting work can benefit in
its scope from their differing perspectives. While
the book gains in completeness, there are, however,
often trade-offs in the form of cohesion.
Such appears to be the case with Multiphoton
Spectroscopy of Molecules by S. H. Lin, Y.
Fujimura, H. J. Neusser, and E. W. Schlag four
authors from three different institutions on three
different continents. Accepting this shortcoming,
however, one who wishes to familiarize himself
with either the theoretical or experimental aspects
of this relatively new field will find much material
in this book to make it worthwhile reading.