Unique properties of a phase-conjugate Michelson interferometer are discussed and some applications utilizing this experimental technique are presented. Specifically, the method is used to demonstrate the Doppler-free nature of phase-conjugate reflection.
The physics of the photorefractive effect and the unique nonlinear optical properties of photorefractive crystals are described. A survey of the optical applications of the photorefractive effect follows. We include the use of photorefractive crystals as holographic storage elements, optical image amplifiers, phase conjugate mirrors, correction elements for intracavity laser distortions, phase conjugate windows for field transmission through inhomogeneous media, and coherent image processors.
This paper presents the principle of a new method of laser beamsteering using the photo-refractive effect. This method uses variable, thick diffraction gratings recorded in a photorefractive medium to deflect a laser beam. Two geometrical configurations for writing .he thick gratings, and the relative merits of each are discussed using k-space diagrams. Two methods of controlling the writing beams to vary the recorded grating are also discussed. The results of a proof of concept experiment using bismuth silicon oxide crystals are reported.
A novel wavelength filtering mechanism in a three-layer dielectric stripline structure is described. The waveguide consists of two high-index layers separated by a low-index layer in which the fields are evanescent perpendicular to the layer surfaces. The stripline is defined by a local extremum in the thickness of the middle, low-index layer. The analysis shows that upper or lower wavelength limits for propagation along the stripline can be set by proper choice of the thicknesses of the two high-index layers, if all layer refractive indices are specified. Outside these limits, the modes arc contained in the direction perpendicular to the layer surfaces, but are leaky in the direction parallel to them. The wavelength filtering mechanism is explained in terms of the wavelength dependence of the mode profile within and without the stripline. In this three-layer structure, for a particular mode, there is a critical wavelength for which the dependence of propagation constant on the thickness of the middle layer vanishes. At this wavelength, the mode does not see the stripline at all. On one side of this critical wavelength the effective index is at a local maximum along the stripline axis, while on the other it is at a local minimum. In the former case the structure acts as a dielectric stripline waveguide, containing the mode near the axis, while in the latter case the mode leaks away parallel to the layer surfaces. The structure gives sharp cutoffs in the transmittance vs. wavelength, with none of the oscillations beyond cutoff characteristic of distributed Bragg reflection filters.
Equilibrium dielectric properties are discussed for a multi-component medium consisting of suspended ellipsoidal microparticles in a homogeneous background host medium. An estimate is given of the electric-field induced orientation time for forming optical anisotropy.
A novel technique has been demonstrated for increasing the efficiency of bulk wave Bragg devices. The technique consists of returning the undeflected Io beam through the sound wave a multiplicity of times, allowing a series of acousto/optic interactions which contribute to the overall deflection efficiency of the Bragg cell. This technique has been demonstrated both with experimental benchtop assemblies and in monolithic form with 3-5dB improvements in deflected optical power. Research results, tradeoffs, and conclusions are discussed.
This paper reports a demonstration of channelizing rf signals with optical techniques. RF signals are upconverted to optical frequencies and demultiplexed with an etalon. The etalon is used as a filter transmitting modulated light at discrete incidence angles. The band 100-1000 MHz is channelized into 70 MHz wide channels.
A traveling-wave, electro-optic phase modulator using bulk LiNbO3 was designed and constructed for efficient wideband operation. A second design which uses total internal reflection to couple the RF and optical fields was also constructed. This design is tunable over the efficiency-bandwidth curve and is thus quite versatile in many optical modulation applications.
Vision modules have primarily been developed to relieve those pressures newly brought into existence by Inspection (QUALITY) and Robotic (PRODUCTIVITY) mandates. Industrial Control pressure stems on the other hand from the older first industrial revolution mandate of throughput. Satisfying such pressure calls for speed in both imaging and decision making. Vision companies have, however, put speed on a backburner or ignore it entirely because most modules are computer/software based which limits their speed potential. Increasingly, the keynote being struck at machine vision seminars is that "Visual and Computational Speed Must Be Increased and Dramatically!" There are modular hardwired-logic systems that are fast but, all too often, they are not very bright. Such units: Measure the fill factor of bottles as they spin by, Read labels on cans, Count stacked plastic cups or Monitor the width of parts streaming past the camera. Many are only a bit more complex than a photodetector. Once in place, most of these units are incapable of simple upgrading to a new task and are Vision's analog to the robot industry's pick and place (RIA TYPE E) robot. Vision thus finds itself amidst the same quandries that once beset the Robot Industry of America when it tried to define a robot, excluded dumb ones, and was left with only slow machines whose unit volume potential is shatteringly low. This paper develops an approach to meeting the need of a vision system that cuts a swath into the terra incognita of intelligent, high-speed vision processing. Main attention is directed to vision for industrial control. Some presently untapped vision application areas that will be serviced include: Electronics, Food, Sports, Pharmaceuticals, Machine Tools and Arc Welding.
We have developed a new approach to constructing large aperture optical switches for next generation inertial confinement fusion lasers. A transparent plasma electrode formed in low pressure ionized gas acts as a conductive coating to allow the uniform charging of the optical faces of an electro-optic material. In this manner large electric fields can be applied longitudinally to large aperture, high aspect ratio Pockels cells. We propose a four-electrode geometry to create the necessary high conductivity plasma sheets, and have demonstrated fast (< 10 nsec) switching in a 5x5 cm aperture KD*P Pockels cell with such a design. Detailed modelling of Pockels cell performance with plasma electrodes has been carried out for 15 and 30 cm aperture designs.
Recent advances in thin film fabrication techniques have made metal multilayer mirrors an important new addition in the field of soft x-ray diffraction optics. A metal multilayer is one dimensional periodic structure which consists of an alternating sequence of high/low atomic number elements evaporated or sputtered onto a substrate. Characterization of these devices have been carried out on a variety of x-ray sources, including synchrotron radiation, over a large range of parameters. Extensive modelling of the diffraction characteristics of multilayers has shown that the theory of optics of thin film gives good agreement between measured and calculated diffraction profiles. Application of metal multilayer mirrors as normal incidence x-ray collectors, monochromators and beam splitters is being explored.
Design considerations for three-reflection polarizers that maintain collinearity of the input and out-put beams, and that consist of three mirrors made of the same metallic substrate and coated by the same dielectric film, are discussed. An illustrative example is included of dielectric-coated titanium D- and s- suppressing polarizers at wavelength X=4im.
Examples are shown of the different electrical signal waveforms generated by linear photodetection of the light flux transmitted by an optical train of polarizing elements subjected to periodic azimuth or retardation modulation. A basic train is assumed that consists of parallel or orthogonal input and output linear polarizers sandwitching two linear retarders of variable azimuth or retardance. Provision is made for adding other optical elements to the train.
There are at least two general categories of absorptive-type glass polarizers which involve silver metal in their polarizing mechanism. Glasses of the first category, permanent polarizers, contain elongated, submicroscopic particles of silver metal aligned along a common axis. Their polarizing capacity is due to a resonant absorption of the silver conduction electrons, the spectral location of which depends on the extent of silver particle elongation and the particle orientation with respect to the applied electromagnetic (light) field. These polarizers have been made with dichroic ratios (optical density ratios) in excess of 40. The best performance is obtained in the long wavelength visible and near infrared regions. They are useful in applications similar to those of plastic sheet polari-zers. They have better optical quality and better thermal, mechanical, and chemical durability. Polarizing glasses of the second category are optically alterable. That is, their color and degree of polarization can be changed by intense visible or near infrared irradiation. These glasses owe their polarizing properties to small, nonspherical specks of silver metal in contact with silver halide crystallites within the glass. The change in color and polarization is believed due to the growth and dissolution of differently shaped and oriented specks during irradiation. This second category of glass polarizer shows much lower dichroic ratios than the first, generally less than 5, but has the advantage that the orientation of the polarizing axis can be changed, or made to vary from one region of the glass to another, by suitable high intensity irradiation.
The properties of a newly-developed high efficiency dichroic polarizer, Polaroid HN42HE, are described and compared to those of existing commercial polarizers. The new polarizer has good neutrality, very high extinction and high transmittance, a combination of attributes previously unavailable in dichroic polarizers. The use of high efficiency polarizers in flashblindness goggles and other applications is discussed.
The use of generalized gradient-index layers increases the degrees of freedom in the design and synthesis of spectral filters, which should provide improved or new solutions for a wide range of problems. The theory of the Fourier transform technique and an iterative numerical synthesis method for the synthesis of gradient-index filters are reviewed.
Narrowband birefringent filters have traditionally been used by solar physicists to simultaneously isolate narrow spectral bands over wide spatial regions of the sun. Recent development of optical communication and detection systems, however, has stimulated broader interest in birefringent filters because of their unique filtering abilities. Tenability and large fields of view make these filters attractive for imaging and non-imaging applications. The purpose of this paper is to illustrate the capabilities of birefringent filter concepts by presenting examples of actual working units which have been built at the Lockheed Solar Observatory. An adequate theoretical background is available in the literaturel'2'3 but practical considerations are generally neglected. As a result, there is little appreciation for the capabilities and limitations of current birefringent filter technology. The following discussion will concentrate on the practical aspects of the filters and will also consider the restrictions imposed by material limitations. Although this presentation is mainly concerned with the practical capabilities of the filters, brief discussions of the theoretical foundations are included for convenience. Specifically, short descriptions of the basic polarization interference principle, the wide field element construction and the tuning technique are included.