Abstract: A laser apparatus for inverting a population in an atomic or molecular species is provided. Energy is stored in a first species and a laser induced collisional energy transfer from that first species to a selected dissociative molecular state of a second species causes an inversion of one of the constituents of the second species. This is represented, in one embodiment of the present invention which utilizes a second species comprising a diatomic molecule, by the reactionA*+BC+h.nu..fwdarw.A+(BC)*.fwdarw.A+B*+C,where A and A* are the ground and excited states of the first species respectively, denoted as the storage species, BC and (BC)* are the ground and excited states of the second species respectively, which comprises atoms B and C, and B* is the excited state of atom B, which excited state is inverted.

Abstract: The invention relates to a variable attenuator having two phase gratings (1 and 2) with rectangular grooves. In a first embodiment of the present invention the gratings are slidably mounted (10, 20, 30) so that the gratings have the grooves parallel and the faces in close proximity. As one grating is translated relative to the other the light passing through the device may be varied from total extinction to substantially total transmittance. A single device can be fabricated to provide this attenuation for radiation spanning the visible spectrum. In other embodiments the gratings are fixed relative to one another and the entire device is moved relative to the beam to be attenuated.

Abstract: A 3-terminal totally integrated demultiplexing photodiode is disclosed wherein information present simultaneously at two wavelengths can be developed into two separate currents available at the three terminals. Two quaternary n-type layers (103 and 105) of indium gallium arsenide phosphide having unequal bandgaps and each having a pn junction are separated by a layer (104) of n-type indium phosphide. The device is oriented so as to present the incoming radiation first to the quaternary layer having the larger bandgap and then to the quaternary layer having the lower bandgap. One of the contacts (111) is attached to the top layer (106) of n-type indium phosphide, a second contact (112) is attached to a central p-type region (110) established in the top layer of indium phosphide and penetrating through the top quaternary layer, and the third contact (113 or 302) is connected either to the indium phosphide substrate (101) or to a p-type outer region (301) that surrounds all of the layers.

Abstract: A stripe geometry is fabricated in a laser-diode structure having a plurality of epitaxial layers, including in tandem an undoped active semiconductor layer (3), a p-doped semiconductor layer (4), a moderately n-doped semiconductor layer (5) and a heavily p.sup.+ -doped layer (6) by focusing laser radiation on the n-doped semiconductor layer (5). The laser radiation is chosen to have a wavelength which passes through the p.sup.+ -doped layer (6) without absorption. When the laser radiation is absorbed in the n-doped layer, heat is generated which causes diffusion of p-dopant from the two adjacent layers to convert the exposed region to p-type. As the laser beam is scanned, a stripe having a forward pn junction for laser action is formed.

Abstract: An rf sputter etch or reactive sputter etch apparatus which can be used for etching substrates at oblique angles utilizes a cathode formed from a metal grid and an equipotential enclosure. The substrate is supported in the enclosure either parallel to or at an oblique angle to the surface of the grid.

Abstract: Longitudinal mode control is achieved in a heterojunction semiconductor laser (201-208) by doping the active region (203) of the laser with a deep level electron or hole trap. The trap is chosen to have a carrier capture cross section .sigma..sub.e and an optical cross section .sigma..sub.o such that the ratio of P, the average number of photons per cubic centimeter, to P.sub.s is between 0.1 and 100 where P.sub.s is equal to (N.sigma..sub.e V/.sigma..sub.o C.sub.o), N is the carrier density, V is the carrier thermal velocity, and C.sub.o is the speed of light in the material. In a specific embodiment the active region is bombarded by photons to achieve deep level electron traps in the active region.

Abstract: A three terminal, totally integrated demultiplexing photodiode is disclosed wherein information present simultaneously at two wavelengths can be developed into two separate currents available at the three terminals. Two quaternary layers (203 and 205) of indium, gallium, arsenide phosphide having unequal bandgaps and each having a pn junction are separated by a buffer layer (204) of n type indium phosphide. Operation at longer wavelengths is achieved by causing the bottom quaternary layer to have the higher bandgap energy thereby permitting it to detect the shorter wavelengths in the radiation and causing the topmost quaternary layer (205) to have the lower bandgap energy thereby permitting it to detect the longer wavelengths. The bottom contact (213) on the substrate has an opening thereby providing a window (230) through which incoming radiation (250) can be coupled through the substrate to the two quaternary layers.

Abstract: A semiconductor laser is disclosed wherein the active region has been doped with deep-level electron traps either by proton bombarding the active region or by doping with an impurity, such as oxygen, iron, or chromium. The density of traps is such that an optical absorption parameter of greater than 30 cm.sup.-1 is achieved. This laser, when combined with an ordinary photodiode, exhibits overall optical gain thereby permitting an array of optical logic circuits.

Abstract: A magneto-optic modulator of the bounce-cavity type is disclosed wherein the mirrors that are attached to the garnet crystal to provide the reflections are multilayered dielectric mirrors. By polarizing the input beam such that its E vector is perpendicular to the plane of incidence substantially total reflection is achieved from the mirrors and all of the input beam emerges from the garnet crystal. A metal film deposited on a plane of the crystal that is perpendicular to the mirrors permits the establishment of a magnetic field that is substantially parallel to the reflected beams within the crystal. When the field is established by passing current through the film, much of the light is lost during each of the reflections since substantial amounts of the polarized light having polarizations in the plane of incidence are coupled through the dielectric mirrors. Hence the intensity of the output beam is modulated by the current in the metal film.

Abstract: An optical apparatus which provides a nonlinear characteristic between input and output amplitude levels is disclosed. A single frequency linearly polarized single mode light beam having amplitude variations that are to be acted upon is coupled to a Fabry-Perot interferometer (10) having two mirrored ends (11 and 12) and substantially filled with an electrooptic material (13) having electrodes (14 and 15). A beam splitter (21) is positioned and oriented so as to deflect optical energy that is reflected from the cavity into a photodetector circuit (22 and 23) whose output voltage is applied to the electrodes of the electrooptic material. Adjustment of the cavity length provides a wide range of nonlinear characteristics including some that permit the apparatus to be used as a bistable memory element and others which permit the device to be used as a clipper for all input power levels below a predetermined threshold level.

Abstract: Linear phase aberrations in laser amplifier systems are adaptively corrected by a device which propagates an object beam formed by reflection of a laser beam from a target backwards through a laser amplifier chain in order to sample the linear phase aberrations and produces a conjugate image beam by degenerate four-wave mixing in a medium having a third order nonlinearity in susceptibility. The conjugate image beam which is amplified as it propagates back through the laser amplifier chain has the linear phase aberrations removed. The device also corrects for birefringent aberrations contained in the laser amplifier chain when (1) the medium has an isotropic nonlinearity; (2) the polarization of the pump beams, required for four-wave mixing, lies in the plane formed by the object beam and the pump beams; and (3) the angle between the object beams and the pump beams is substantially 90 degrees. The degenerate four-wave mixing is accomplished in one embodiment by gain saturation in Nd:YAG.

Abstract: A transmitter of information to be communicated in secure form is optically coupled to a composite optical fiber at one end, the fiber being connected to a receiver of the secure information at the other end. The composite optical fiber has cores including a central core for carrying the secure information, one or more guard signal cores, a cladding matrix surrounding all the cores, and a metallic or other nontransmissive film surrounding the central core but not the guard cores. A guard signal optical transmitter section is coupled to the guard cores for jamming any leakage of secure information through the film, and a guard signal receiver section is provided at the other end of the fiber for monitoring purposes. The optical transmitter apparatus employs pulse code modulation (PCM) and sends related security bits in the guard and secure signals.

Abstract: Far-infrared tunable radiation is produced in a four-level laser system by using a pumping means for exciting population from the lowest level of the system to the upper level of a laser transition to create a population inversion between the upper and lower levels of the laser transition and a laser beam which is nearly resonant with the lower level of the laser transition and a fourth level of the system. The laser beam shifts the lower level of the laser transition according to the dynamic Stark effect to provide for tuning of the far-infrared radiation.

Abstract: A 3-terminal totally integrated demultiplexing photodiode is disclosed wherein information present simultaneously at two wavelengths can be developed into two separate currents available at the three terminals. Two quaternary n-type layers (103 and 105) of indium gallium arsenide phoshide having unequal bandgaps and each having a pn junction are separated by a layer of (104) of n-type indium phosphide. The device is oriented so as to present the incoming radiation first to the quaternary layer having the larger bandgap and then to the quaternary layer having the lower bandgap. One of the contacts (111) is attached to the top layer (106) of n-type indium phosphide, a second contact (112) is attached to a central p-type region (110) established in the top layer of indium phosphide and penetrating through to the top quaternary layer, and the third contact (113 or 302) is connected either to the indium phosphide substrate (101) or to a p-type outer region (301) that surrounds all of the layers.

Abstract: An integrated optically-controlled 4-port bistable switch having a waveguide directional coupler as one of its elements is disclosed. A photodetector is positioned so as to be sensitive to the optical energy at one output port of the directional coupler and the voltage developed by this photodetector is coupled to electrode elements of the directional coupler. The resulting bistable device permits such functions as remote optical switching to be performed.

Abstract: A rugged, compact optical switch is disclosed which comprises a quarter-period graded refractive index (GRIN) lens (1); a rotatable reflecting surface (2.1) disposed at a first surface (1.3) of the GRIN lens at an angle to the first surface; an optical source (8) mounted at the second surface (1.2) of the GRIN lens on the lens axis; and a plurality of optical receptors 6, 7, 9, 10, 11 and 12 mounted at the same second surface of the lens, all at the same distance from the lens axis but displaced at a plurality of angular positions about the lens axis. Rotation of the reflecting surface about the lens axis couples light between the optical source selectively to optical receptors at the appropriate angular orientation. The switch is reciprocal in that the common optical source may be an optical receptor and the various optical receptors, optical sources. Typically, the optical sources and receptors are optical fibers.

Abstract: Devices constructed according to the present invention provide low noise avalanche photodetectors. The devices are comprised of a sequence of at least four layers of semiconductor material of alternating opposed conductivity. In a first embodiment the layers form alternating homojunctions and heterojunctions at the interface between adjacent layers, and the bandgap of the layers on either side of the homojunctions decreases in the direction of the propagating signal. In another embodiment the layers form heterojunctions at the interfaces between adjacent layers; the layers are grouped into a sequence of pairs of layers where the bandgap of the two layers in each pair are substantially equal; and the bandgap of the layers in the sequence of pairs of layers decreases in the direction of the propagating signal. The effect of the structure of the multilayer device is to create traps for one sign of carrier and to prevent the trapped carrier from avalanching through amplification regions of the device.

Abstract: The cleavage planes of a lithium niobate crystal (100) are used to provide the parallel surfaces (121 and 122) of a Fabry-Perot resonator established in a titanium diffused waveguide (110). To enable use of the extraordinary wave and therefore to provide a higher efficiency resonator, the waveguide is diffused into the crystal at a predetermined oblique angle (.PSI.) with respect to the cleaved ends. The resonator is utilized in an optically pumped laser and in an electrically controllable Fabry-Perot resonator wherein the reflection provided by the cleaved ends is supplemented by multilayered dielectric mirrors (201 and 202 or 301 and 302) that are bonded to each of the cleaved ends. In the electrically controllable resonator a dielectric layer (330) is deposited over the surface of the crystal before electrodes (310 and 311) are formed on the layer parallel to the waveguide.

Abstract: A wide angular aperture, tunable filter device is achieved by using degenerate four-wave mixing. The apparatus utilizes two counter-propagating pump beams at substantially the same frequency to interact with an object beam, containing a spread of frequency components through a third order nonlinearity in the susceptibility of a medium. This produces a conjugate image beam formed with frequency components close to the frequency of the pump beams. By tuning the frequency of the pump beams the object beam frequency spectrum may be scanned while preserving all of the spatial information in the object beam. Apparatus for generating velocity contours of moving objects is also disclosed.

Abstract: A nonlinear interferometer apparatus is disclosed wherein a Fabry-Perot cavity is substantially filled with an electro-optic material having terminals to which a potential can be applied. A single frequency, single mode, linearly polarized source of optical radiation is coupled into the cavity and a beam splitter at the output of the cavity deflects a portion of the optical energy coming from the cavity. This deflected portion of output optical energy is incident on a photodetector whose output is amplified and connected to the terminals of the electro-optic material. The resulting device exhibits differential gain, and can function as an optical switch, limiter or optical memory element. With sufficient amplification of the detector output, an optical quantizer is provided.