Abstract: A semiconductor laser array that discriminates in favor of a fundamental array mode of oscillation and provides a far-field radiation pattern that is single lobed and diffraction-limited. The array includes a first set of parallel waveguides, a wide-waveguide section and a second set of parallel waveguides. Oscillation in the fundamental or 0.degree.-phase-shift array mode is easily coupled from the first set of waveguides to the wide-waveguide section, and from the wide-waveguide section to the second set of waveguides. When adjacent waveguides oscillate out of phase, as in the 180.degree.-phase-shift array mode, easy coupling is not obtained because the waveguides of the second set are not colinear with those of the first set. The structure of the invention also avoids the large radiation losses inherent in Y-junction arrays.

Abstract: A multidigit arm contains a plurality of sections, each of which is positionable angularly and spatially to a predetermined degree with respect to an adjacent section. Control means are provided for selectively individually positioning each section within said arm with respect to an adjacent section, such control means including actuator means positioned within and carried by and between the arm sections. The arm may be formed into a variety of curves and position the arm end at a variety of positions.

Abstract: Objects, particularly spacecraft structures, antennas, solar arrays and other spacecraft equipment, are shielded against damage from momentary exposure to high energy electromagnetic radiation in the form of high energy optical (laser) radiation or nuclear radiation by a radiation barrier or shield constructed of fibrous silica refractory composite material like that used for the heat shield tiles on the shuttle spacecraft.

Abstract: Apparatus and a related method for control of the colinearity of multiple laser output beams in a wavelength-multiplexed optical communications system. Multiple lasers of different wavelengths formed into a single composite beam by means of a diffraction grating and other optical components are subject to loss in colinearity due to wavelength drift and mechanical alignment drift. The apparatus of one disclosed embodiment of the invention includes an alignment detector for the output beam and a set of tracer modulation detectors responsive to tracer modulation signals impressed on the individual laser beams. Misalignment detected in any one or more of the laser beams contained in the output beam is corrected by temperature control of the appropriate lasers.

Abstract: Spacecraft components having critical surfaces which must arrive in outer space in a contamination-free, pristine state to assure their effecient operation over the entire spacecraft mission life are protected against contamination by applying to the surfaces a protective coating which sublimes away when exposed to the outer space environment, thereby exposing the surfaces in their pristine state to the environment.

Abstract: A method and related apparatus for selectively line spin scrambling, reversing and inverting certain video lines or video segments to minimize amplitude gaps in a line-spin scrambled video signal and for unscrambling the line-spin scrambled video signal. The method for minimizing the amplitude gaps in the line-spin scrambled video signal involves measuring various amplitude differentials, prior to line spin scrambling, between certain points along the active portion of each video line. The values of the various amplitude differentials are then compared to a preselected value and, depending on which amplitude differential is less than or equal to the preselected value, the video line is line spin scrambled, reversed or left unchanged and one of the video segments is inverted or reversed to reduce the amplitude gap in the scrambled video line to at least the preselected value.

Abstract: A beam deflection system for use in optical radar, communications, or optical display apparatus, having the ability to scan multiple "target" clusters that are widely scattered over a large angular field. In its transmission mode of operation, the system switches a laser beam sequentially across an array of focal elements, moving the beam at high speed, since total beam movement across the array is limited to only a few degrees. The system includes an expansion telescope, which expands the succession of beams from the array of focal elements and directs them onto an array of larger, movable optical elements, such as gimbaled mirrors, which direct the successive beams toward scattered target areas in a large angular field. The system also includes a beam scanning device, for "microscanning" the beam through a number of separately resolvable positions within the field of view of each of the array of focal elements.

Abstract: A semiconductor laser structure having the same advantages as a channeled substrate planar laser, but without the difficulties of fabrication associated with this structure. The structure includes a substrate, a planar first cladding layer, a planar active layer, and a second cladding layer in which a mesa region is formed. A blocking layer is formed over the second cladding layer and electrical contact is made through the blocking layer in the region of the mesa. The blocking layer functions to confine current flow in the mesa region and to provide index-guiding of light in the mesa region. Because of its simple geometry, the structure can be conveniently formed using a desirable fabrication process, such as metalorganic chemical vapor deposition (MOCVD). In one disclosed embodiment of the invention, the mesa is broadened to include at least one intermediate ledge on each side of a central pedestal.

Abstract: A directional coupler having two coupled waveguides that receive a single optical input through a Y-junction power splitter, and two outputs from the coupled waveguides. Electrodes positioned over the coupled waveguides apply opposite electric fields to the waveguides and, through the electrooptical effect, modulate the optical outputs. For a zero applied voltage and zero electric field, the outputs are both equal to approximately half of the maximum possible output intensity, and no bias voltage is needed for operation as a modulator. As the voltage is varied from zero, positively or negatively, the optical intensity from either of the outputs varies linearly over a useful range. Moreover, the voltage required to switch full power from one output to the other is less than that required for conventional electrooptical modulators or switches.

Abstract: An optical communication system in which at least two separate modal groups are launched into a single graded index transmission fiber. The system includes two light sources and a lens to focus the light sources into the transmission fiber. A spatial filter is used to selectively limit the angles of incidence of the light on the fiber, and operates in conjunction with the lens to launch light from one source at appropriate angles and points of excitation to excite higher-order modes in the fiber, and to launch light from the other source at appropriate angles and points of excitation to excite lower-order modes in the fiber.

Abstract: A multilayer printed circuit board in which multiple layers of a composite material, fabricated by the lay-up of an aramid fiber tape, are employed to provide a circuit board with a desired coefficient of thermal expansion. Tape lay-up of aramid fibers provides a composite layer having a lower thermal coefficient of expansion than a composite layer fabricated from woven aramid fibers. Degradation in the tensile modulus of elasticity caused by the over and under characteristics of woven fabrics is also eliminated by tape lay-up, thus providing a circuit board with better mechanical strength. In addition, tape lay-up reduces the amount of resin required to fabricate the circuit board and eliminates the need for twisting the aramid fibers into yarns and then weaving the yarns, thus reducing the cost of the circuit board.

Abstract: A high-speed synchronous comparator circuit, well suited for use in an analog to digital converter. The circuit is switched between acquisition and regeneration modes and includes an amplifier that is operated with positive feedback loop gain in both modes. In the acquisition mode, a relatively low impedance is connected between internal nodes of the amplifier, to improve acquisition speed and keep the positive feedback loop again less than unity. In regeneration mode, the low impedance is disconnected, resulting in a high positive feedback loop again and a desirably amplified output indicative of the polarity of the input differential signal, and the input signal is isolated from the latching nodes. The invention may be implemented in a variety of fabrication technologies, including gallium arsenide field-effect transistors, complementary metal-oxide semiconductor (CMOS) circuitry, and bipolar transistors.

Abstract: An improved switch controller and related method for regulating the supply voltage of a solar cell array. The switch controller includes at least two shift registers, with additional shift registers concatenated as required by the size of the array. Each of the shift registers controls segments of the solar cell array having increasingly larger outputs, with the first shift register providing fine resolution control of the supply voltage and the second and additional shift registers providing increasingly-coarser resolution control of the supply voltage. The improved switch controller provides improved switching characteristics for the regulation of the supply voltage of a solar cell array.

Abstract: A circuit board having multiple layers of a dielectric material, multiple layers of a conductive metal and multiple layers of graphite bonded together to form a composite multilayer printed circuit board having a desired coefficient of expansion and having strip and microstrip transmission lines for electrically connecting very high frequency electronic components mounted on the circuit board. The multiple layers of graphite are positioned in a symmetrical manner with respect to the thickness of the circuit board and selected in number to provide the circuit board with a desired coefficient of expansion. In addition, at least some of the layers of graphite are positioned in close proximity to some of the layers of conductive metal to provide enhanced thermal conduction from the mounted components.

Abstract: A plurality of small segments stowed in a compact stack are assembled, essentially automatically, into a large construction surface, such as a flat or parabolic reflector.

Abstract: A free-electron laser capable of operation at a shorter wavelength than the fundamental lasing wavelength, but without any increase in electron energy requirements. The laser includes a conventional high-energy electron beam source and a wiggler transverse magnetic field through which the beam is passed to produce lasing. Opposed optical mirrors are selected to be reflective at a selected harmonic wavelength as well as at the fundamental wavelength. Lasing is initiated at the fundamental wavelength, but is then supported at the selected harmonic wavelength as well. By appropriate design lasing at the fundamental wavelength may be subsequently terminated without affecting lasing at the harmonic wavelength, which continues at a substantially reduced energy cost than would have been incurred if lasing at the harmonic frequency been initiated in a fundamental mode.

Abstract: Apparatus and a related method for generating a uniphase reference beam from a weak and aberrated input probe beam in an optical system. A portion of the input probe beam is split off and injected into the cavity of a laser, such as a semiconductor diode laser, where four-wave mixing takes place and an amplified input wave or its phase conjugate is output. Because the laser cavity is selected to provide single-mode operation, the laser provides not only amplification but an output that includes a uniphase wave, which may be interfered with the original aberrated input probe beam for purposes of obtaining wavefront information.

Abstract: A technique for compensating for chromatic aberration in particle beams, caused by differing particle energy levels when a beam is deflected for beam steering or beam focusing. A compensating deflection is applied to the beam upstream of its intended point of deflection. When the particles reach the point of deflection, the effect of the compensating deflection is proportional to the energy level of each particle, and compensates for the aberration that would normally occur. The point at which the compensating deflection is applied is selected to be one-fourth of a cycle in longitudinal phase space and an integral number of half-cycles in transverse phase space. With this critical spacing, the compensating deflection at the point of its application is proportional to relative phase in longitudinal phase space, but is proportional to energy level at the intended point of deflection.

Abstract: A technique in which one or more phase conjugation cells, such as stimulated Brillouin scattering cells, are controlled by use of a seed beam injected into the cells. When a laser beam is focused into a phase conjugation cell, a reflected phase conjugated beam is produced. The seed beam is injected at the same frequency and in the same direction as the expected phase conjugated beam, and is adjusted to control the phase and other characteristics of the phase conjugated beam. In multiple cell arrays, seed beams are employed to ensure phase coherency of multiple beams. For lower energy applications, use of the seed beam allows a phase conjugation cell to be operated with incident beams of lower energy than would be needed without the seed beam.

Abstract: Apparatus, and a corresponding method for its use, for producing a phased array of high-energy laser beams from multiple laser amplifiers. A reference beam produced by a master oscillator senses phase and piston errors in a primary mirror array, and is divided into multiple probe beams, each of which makes multiple passes of its own laser amplifier. The multiple probe beams are together focused into a single phase conjugation cell, which not only produces phase-conjugated reflected beams, to effect compensation for various phase aberrations, but also locks all of the reflected beams together in phase. An arrangement of a birefringent wedge and a quaterwave plate for each of the beams prevents the reflected beams from returning to the master oscillator and facilitates combining of the reflected beams for output as a cophasal array.