Abstract: A photochemical method for changing the isotopic composition of an element is disclosed. The method involves passing an electron discharge through a mixture of a buffer gas, which controls the uniformity and electron temperature of the discharge, and a vapor of the element. By means of the phenomenon of resonance radiation trapping, the electron discharge preferentially excites and ionizes one isotope. Removal of the ions by cataphoresis separates the element into two amounts with different isotopic ratios.

Abstract: Distributed feedback devices such as distributed feedback lasers are modified by introduction of a central coupling strength discontinuity or other deviation from uniform nature of the distributed perturbations, in order to promote the transmission of oscillation of a single mode in preference over the nearest redundant modes. The class of deviations from uniform coupling strength may be mathematically termed antisymmetric deviations, because they are deviations about the midpoint of the perturbation pattern which result in a distinction of effect of the two halves of the pattern, taking either half as a reference pattern by itself.

Abstract: The invention relates to a high-power tunable infrared source employing a four-photon mixing process, with three input lasers, in which process the output power is resonantly enhanced by exciton states in the conversion medium.

Abstract: A helium cadmium laser generates an output beam of radiation which is coupled through a spatial filter and beam expander to a beam splitter which in turn provides two enlarged beams of coherent radiation of approximately equal power. Two highly reflective mirrors are used to direct the two beams such that the two beams interfere and create the usual interference pattern in a positive photoresist layer covering an optical substrate. A thin sheet of high index glass is held by two blocks of quartz in a position adjacent to the photoresist layer and oriented such that a part of each beam of coherent radiation is caused to pass through the high index glass before interfering with the other beam on the photoresist layer. As a result, a grating having a quarter wavelength step or discontinuity in the middle of the grating is fabricated in the photoresist. The photoresist pattern is then transferred to the optical waveguide by ion-beam milling.

Abstract: An optical polarization rotator is developed for use with infrared radiation using a nonlinear, two-photon interaction in a solid medium. The mechanism employed is resonance dispersion, where the sum frequency of an infrared beam to be rotated and a visible control beam is close to the frequency of a two-photon transition of exciton states, thereby producing different amounts of dispersion for the two orthogonal components of the linearly polarized infrared beam. The result of a phase difference between the two components is a rotation of the plane of polarization of the infrared beam.

Abstract: An improvement on an optical levitation device is disclosed for damping perturbations of the position of a particle levitated in vacuum. It combines feedback control of the supporting laser beam with adjustment of the beam shape and size in order to damp perturbations in both the vertical and horizontal directions by means of the vertical feedback damping apparatus.

Abstract: A source of tunable vacuum ionizing radiation is disclosed in which the range of resonance enhancement is extended by Stark-shifting the frequencies of autoionizing states in the continuum of the conversion medium.

Abstract: An input video signal is coupled to one input of a summing amplifier, to the input of a low-pass filter, and to one input of a movement detector. The output signal from the apparatus is delayed by one frame interval, and this delayed output signal is coupled to a second input of the summing amplifier and to a second input of the movement detector. The movement detector is of a type which generates a control signal to indicate movement in response to a plurality of frame-to-frame differences for adjacent picture elements. This control signal is utilized to selectively gate either the output from the summing amplifier or the output of the low-pass filter through to an output terminal.

Abstract: A tunable radiation source employing the stimulated Raman-scattering process is disclosed. The source generates several orders of Stokes radiation in an optical-fiber oscillator cavity, which Stokes radiation may be independently tuned by incorporating separate tuning elements for the several Stokes orders. Several different arrangements of fiber and tuning elements are disclosed.

Abstract: A method and apparatus for phase-matching the output of a four-wave nonlinear optical mixing process is disclosed. The method produces phase-matching that is independent of variations in density of the conversion medium and extends over the entire frequency spectrum from the far infrared to the vacuum ultraviolet. The phase-matching is accomplished by adjustment of the frequencies of three input lasers so that the desired frequency is produced, the condition for two-photon resonance enhancement is met, and the phase-matching condition is satisfied.

Abstract: A graded index optical fiber waveguide for use in an optical communication system is disclosed. The waveguide is a circular symmetric fiber having a cladding with an index of refraction n.sub.2 surrounding a core whose index of refraction is graded from an on axis value of n.sub.1 to a value of n.sub.2 at the core-cladding interface. The index of refraction within the core is defined in terms of a profile function F by the following equationn.sup.2 = n.sub.1.sup.2 (1-F)where F is O on the axis and a function of the radial coordinate r and wavelength .lambda. within the core and satisfies the following equation ##EQU1## where D is a function of .lambda. having a value approximately equal to 2 for minimum modal dispersion and ##EQU2## IS THE GROUP INDEX ON AXIS. The modal dispersion achieved with this design is only a function of n.sub.1 - n.sub.

Abstract: The optically pumped submillimeter wave lasers employing molecular gases having dipole moments are improved by employing as a polyatomic buffer gas a molecular gas or vapor of a hydrocarbon having a significantly large vibrational heat capacity in relation to its molecular weight. An example is C.sub.6 H.sub.14 added to such lasers as the methyl fluoride laser at 496 micrometers. Other examples of saturated hydrocarbon buffers are also given; and in each case the vapor molecule is complex enough to absorb many vibrational quanta from the active molecules, yet is small enough to move rapidly to the tube walls.

Abstract: There is disclosed a technique for growing, from a melt, doped single-crystal fibers for use as lasers or other active or passive optical devices of a size that is compatible with proposed optical fiber communications systems. A rod of undoped material has deposited thereon, by mechanical means, a powder or a slurry of a compound of the active ion or other dopant. A melt is formed at the end of the rod with a laser beam and a reduced diameter doped single-crystal fiber is grown or drawn from the melt by pulling with a wire or, when desired crystalline orientation is needed, by pulling with a pointed and oriented seed crystal. The pulling step, at least in the specific case of a neodymium-doped yttrium aluminum garnet (YAG) fiber, is repeated a plurality of times with approximately a 3:1 diameter reduction each time in order to obtain the desired fiber size; but only one deposition of the dopant compound is needed.

Abstract: There is disclosed a time-dispersion tuned Raman oscillator which makes use of the frequency-dependent transit time of Stokes radiation through a long optical fiber. Time-dispersion tuning is effected by synchronizing Stokes radiation of the desired frequency with a pump pulse. This synchronization may be accomplished either by adjusting the delay of the feedback pulse relative to a pump pulse or by adjusting the repetition rate of the pulsed pump laser.

Abstract: Graded-index fibers, which are the most promising for first-generation optical communication links, are improved for multimode transmission by employing two or more glassy dopants in the core mutually graded with respect to the silica host and to each other to provide simultaneously minimized intermode dispersion at a first-selected wavelength and, in addition, a broader wavelength range of minimized intermode dispersion, or minimized intermode dispersion at a second distinct wavelength pertinent to the multimode transmission, or optimization of another dispersion-related property of said fiber.

Abstract: A new method of semiconductor diode processing is described in which the resulting diode chips have an ohmic contact on four side faces of the chip. This is accomplished by cutting notches in the back side of a semiconductor slice before processing and by breaking the slice along the notches after fabricating the diodes on the front side of the slice. The new diode chip has a smaller series resistance than conventional millimeter-wave structures, and it can be readily bonded or soldered to millimeter-wave thin film circuits.

Abstract: A new method of manufacturing semiconductor diodes is described in which the resulting diode chips have ohmic contacts on the four side surfaces of the diode chip. An insulating layer of a material such as silicon-dioxide is first formed on the epitaxial layer of a semiconductor wafer. Notches are then cut in a gridlike pattern into the semiconductor wafer on the side of the chip having the insulating layer. The notches extend approximately halfway into the semiconductor wafer and form a plurality of areas, each one of which has the dimensions of a desired diode chip. An ohmic contact is then established on the walls and bottoms of the notches by depositing a metallic layer and alloying this layer to the semiconductor material. A plurality of diodes are formed in holes in the insulating layer on each one of the areas representing an individual chip.

Abstract: The disclosed optical fiber communication system employs a fiber with a core having an index of refraction graded in an approximately parabolic fashion and a light-emitting diode joined directly to the fiber to serve as the light source for the system. It has been found that the overall electrical efficiency of the system, at least with respect to drive power for the diode, is maximized when the ratio of the diode radius to the radius of the fiber core is about 0.2. More broadly, the ratio of radii is found advantageously to lie in the range between about 0.1 and about 0.8, not only for efficiency reasons but also to maximize the amount of light injected into the fiber.

Abstract: An optical switching network employing a plurality of optical switching crosspoints is implemented by providing the first and second pluralities of strip waveguide channels passing one over the other in parallel planes separated by an intervening medium. The implementation is further characterized by including at each of the proposed switching crosspoints, that is, at the regions of closest approach of the different strip guides, beam-guide couplers such as grating-type couplers to couple the modulated optical energy from one of the first plurality of channels to one of the second plurality of channels through an intervening, supporting medium. There are provided two couplers at each optical crosspoint; and they are controllable between coupling and noncoupling conditions with respect to their respective waveguide channels.

Abstract: An optical switch of the switched directional coupler type is provided with an adjustable cross-over state as well as an adjustable straight-through state, in order to provide reduced crosstalk in the cross-over state, for example, when the switches are used in an optical switching system. The improved switch is based on asynchronous or phase-mismatched coupling between two parallel optical strip guides driven by electrodes to which the voltage is applied. In order to use phase-mismatched coupling instead of phase-matched coupling for the cross-over state, in order thereby to obtain electrical adjustability of that state, the driving electrodes are split into two or more sequential sections, thereby defining two sequential coupling sections of the parallel optical strip guides. The cross-over coupling is then achieved by switching the mismatch conditions so that at the point of partial coupling the "nonoriginating" guide appears to the coupled optical waves to be the "originating" guide.