Abstract: A DFB laser with improved loss grating is disclosed. The grating contains periodically patterned first and second semiconductor layers that are embedded in semiconductor material of composition selected to provide relatively low loss for the laser radiation. The composition of the first layer is selected to provide a relatively high refractive index and loss for the laser radiation, and the composition of the second layer is selected to provide relatively low refractive index and loss for the laser radiation. The thicknesses of the first and second layers are selected such that the real part of the coupling constant .vertline..kappa.'.vertline. is less than the imaginary part of the coupling constant .vertline..kappa.".vertline.. In preferred embodiments .vertline..kappa.'.vertline..ltoreq.0.5.vertline..kappa.".vertline., even.ltoreq.0.2.vertline..kappa.".vertline..

Abstract: Articles according to the invention include a semiconductor waveguide having a core and a cladding, with the cladding including doped semiconductor material. The doping level is selected such that both the real part n and the imaginary part k of the complex refractive index of the doped material are relatively low, exemplarily n<0.5 .epsilon..sub..infin..sup.1/2 and k<1, where .epsilon..sub..infin. is the high frequency lattice dielectric constant of the material. Appropriate choice of the doping level can result in improved confinement of the guided radiation without undue increase in the attenuation of the guided radiation. The invention exemplarily is embodied in a long wavelength (.about.8.5 .mu.m) quantum cascade laser. Other embodiments are contemplated.

Abstract: A technique that involves selective removal of material from a surface of a polycrystalline diamond (polyD) film such that a non-planar surface results. Exemplarily the technique is used to form polyD optical elements, e.g., convex or concave lenses, or Fresnel lenses, including arrays of such lenses. The technique involves maintaining on appropriately shaped hot template body in intimate contact with a polyD surface for a time (e.g., in the range 1-1000 hours) sufficient to result in formation of the desired feature in the polyD surface. The template body involves a rare earth metal (La and Ce are preferred), Mn and/or Fe, and the temperature is below the melting temperature of the template body. Removal of "spent" template material by, e.g., chemical etching and finishing of the polyD feature, e.g., by laser ablation and/or polishing, are contemplated.

Abstract: A Novel method of making a semiconductor device (e.g., a HBT) is disclosed. A semiconductor body that comprises bulk semiconductor material and epitaxial semiconductor material on the bulk material is processed by carrying out a first sequence of processing steps on the epitaxial material. The sequence comprises forming at least first and second contact means on the epitaxial material. The resulting intermediate body is mounted, epitaxial material down, on a carrier body (e.g., a Si wafer with integrated circuitry thereon), such that the first and second contact means are electrically connected to, respectively, third and fourth contact means on the carrier body. Mounting is accomplished, exemplarily, by means of anisotropically conductive adhesive means. Subsequent to mounting of the intermediate body on the carrier body, a second sequence of processing steps is carried out on the intermediate body.

Abstract: Optical microcavities are potentially useful as light emitters for, e.g., flat panel displays. Such microcavities comprise a layer structure, including two spaced apart reflectors that define the cavity, with a layer of organic (electroluminescent) material disposed between the reflectors. We have discovered that a microcavity can simultaneously emit radiation of two or more predetermined colors such that the emission has a desired apparent color, exemplarily white. Emission of two or more colors requires that the effective optical length of the cavity is selected such that the cavity is a multimode cavity, with the wavelengths of two or more of the standing wave modes that are supported by the cavity lying within the emission region of the electroluminescence spectrum of the active material.

Abstract: Material comprising an effective amount of a novel intermetallic bulk superconductor compound is disclosed. The compound has the composition LnNi.sub.2 B.sub.2 C, with Ln being Y or a rare earth (atomic number 57-71), preferably Tm, Er, Ho or Ln. A compound of composition XPt.sub.2 B.sub.2 C, with X=Y and/or La, is also a superconductor.

Abstract: The novel bipolar transistor has at least two separated emitter contacts and no base contact, and the emitter/base p-n junction has backward diode characteristics. The transistor can function as a logic device, but can also function as an amplifying device in digital or analog circuits.

Abstract: This application discloses, to the best of our knowledge, the first unipolar laser. An exemplary embodiment of the laser was implemented in the GaInAs/AlInAs system and emits radiation of about 4.2 .mu.m wavelength. Embodiments in other material systems are possible, and the lasers can be readily designed to emit at a predetermined wavelength in a wide spectral region. We have designated the laser the "quantum cascade" (QC) laser. The QC laser comprises a multilayer semiconductor structure that comprises a multiplicity of essentially identical undoper "active" regions, a given active region being separated from an adjoining one by a doped "energy relaxation" region. In a currently preferred embodiment each active region comprises three coupled quantum wells designed to facilitate attainment of population inversion. In the currently preferred embodiment the energy relaxation regions are digitally graded gap regions. However, other energy relaxation regions are possible.

Abstract: We have discovered that at least some optical waveguide lasers such as Er-doped fiber lasers are subject to excessive output amplitude fluctuations, including severe fluctuations when the laser is subjected to mechanical shock. We have determined that these highly undesirable fluctuations are due to a resonance phenomenon, and that the fluctuations can be at least substantially reduced by means of a feedback loop that makes the amplitude of the output of the pump laser responsive to the amplitude of the output of the waveguide laser. We have also discovered that the operation of a pump laser/waveguide laser combination is frequently improved if an appropriate non-reciprocal element (e.g., an isolator or a tilted wavelength filter) is placed between the two lasers. An exemplary embodiment of the invention comprises the feedback loop as well as the non-reciprocal element.

Abstract: The quantum well lasers according to the invention comprise an electron stopper layer that provides a barrier for the flow of electrons from the active region to the p-side waveguide and cladding layers and in preferred embodiments also comprise a hole stopper layer that provides a barrier for the flow of holes from the active region to the n-side waveguide and cladding layers. An exemplary InP-based laser according to the invention comprises AlInGaAs quantum well layers and barrier layers, and an AlInAs electron stopper layer and an InP hole stopper layer. Lasers according to the invention can have relatively low temperature dependence of, e.g., threshold current and/or external quantum efficiency, and may be advantageously incorporated in, e.g., optical fiber communication systems.

Abstract: Disclosed is optical fiber that can advantageously be used to compensate chromatic dispersion in an optical fiber communication system, typically a system that is upgraded from 1.3 .mu.m to 1.55 .mu.m operating wavelength (.lambda..sub.op). The fiber typically has a power law core refractive index profile, a refractive index "trench" surrounding the core, and a refractive index "ridge" surrounding the trench. The refractive index profile of the fiber preferably is designed such that the fiber supports the fundamental mode (LP.sub.01), does not support the LP.sub.11 mode but does support the LP.sub.02 mode, all at .lambda..sub.op. At .lambda..sub.op, LP.sub.01 has dispersion more negative than -150 ps/nm.multidot.km and, in a preferred embodiment, LP.sub.01 also has negative dispersion slope at .lambda..sub.op. In a further embodiment of the invention the refractive index profile is designed such that the cut-off wavelength of the LP.sub.11 mode is less than that of the higher order mode, typically LP.sub.

Abstract: Disclosed are high reliability semiconductor lasers that need not be maintained inside a hermetic enclosure. Such lasers can advantageously be used in a variety of applications, e.g., in optical fiber telecommunications, and in compact disc players. Such "non-hermetic" lasers comprise facet coatings that comprise a dielectric layer that has very low water saturation value. In preferred embodiments this dielectric layer is SiO.sub.x (1.ltoreq.x<2), deposited by a molecular beam method. Deposition conditions are selected to result in a dense material that is largely free of particulates and blisters, and is substantially impermeable to moisture. Among the deposition conditions is substantially normal beam incidence, and a relatively low deposition rate. Deposition is advantageously carried out under relatively high vacuum conditions. A quantitative method of determining the water level in a SiO.sub.x film is disclosed.

Abstract: We have discovered that at least some optical waveguide lasers such as Er-doped fiber lasers are subject to excessive output amplitude fluctuations, including severe fluctuations when the laser is subjected to mechanical shock. We have determined that these highly undesirable fluctuations are due to a resonance phenomenon, and that the fluctuations can be at least substantially reduced by means of a feedback loop that makes the amplitude of the output of the pump laser responsive to the amplitude of the output of the waveguide laser. We have also discovered that the operation of a pump laser/waveguide laser combination is frequently improved if an appropriate non-reciprocal element (e.g., an isolator or a tilted wavelength filter) is placed between the two lasers. An exemplary embodiment of the invention comprises the feedback loop as well as the non-reciprocal element.

Abstract: Disclosed is a laser, to be referred to as a "Z-laser", which comprises means that can ensure excitation of a laser mode that has a far field pattern that comes substantially to a focus at a point external to the laser. Typically, a Z-laser is a vertical cavity surface emitting laser (VCSEL) that comprises an appropriately patterned top surface. Exemplarily, appropriately spaced circular concentric features ("trenches") are formed in the surface. Lasers according to the invention can be advantageously used in variety of applications, e.g., as pump lasers in an optically amplified optical fiber communication system.

Abstract: The presence of (typically unintended) birefringence in single mode optical fiber can severely limit the usefulness of the fiber for, e.g., high bit rate or analog optical fiber communication systems, due to the resulting polarization mode dispersion (PMD). It has now been discovered that PMD can be substantially reduced if, during drawing of the fiber, a torque is applied to the fiber such that a "spin" is impressed on the fiber. Desirably the torque is applied such that the spin impressed on the fiber does not have constant spatial frequency, e.g., has alternately clockwise and counterclockwise helicity. At least a portion of optical fiber according to the invention has spin alternately clockwise and counterclockwise.

Abstract: Disclosed is a method for forming a superconductive oxide layer on a substrate. The method comprises applying a precursor solution to a major surface of the substrate such that a metal-containing layer is formed on the surface, and heat treating the substrate/layer combination such that at least a substantial portion of the layer material is transformed into superconductive oxide. Exemplarily, the precursor solution is formed by dissolving Ba--, Y--, and Cu-containing compounds in acetic acid and water, spinning the solution on a MgO substrate, driving of unwanted constituents of the resulting layer at 400.degree. C., heating the combination to about 830.degree. C. in O.sub.2 such that the (perovskite) phase that is associated with superconductivity in YBa.sub.2 Cu.sub.3 O.sub.7 is formed, and oxygenating the layer at about 400.degree. C. in O.sub.2.

Abstract: A novel intermetallic superconductor with surprisingly high transition temperature is disclosed. Exemplary of the novel superconductor is material of overall composition Y.sub.1.5 Pd.sub.4.5 B.sub.4. A bulk sample of that composition has T.sub.c (onset) of 22.6K, with about 0.5 volume % of the sample being superconducting.

Abstract: A novel vapor phase Si cleaning process comprises simultaneous exposure of the Si surface to a flux of neutral atomic hydrogen and to a flux of ionized particles. The former flux is substantially derived from a plasma, typically a microwave plasma, that is spaced apart from a second plasma, typically a RF plasma, from which the ionized particles are derived. The novel method can be implemented at relatively low cost and facilitates adjustment of the ratio between the two fluxes to result in optimal removal of, e.g., native oxide from the surface.

Abstract: We have discovered that the addition of a relatively small amount of Sr and/or Ba to La-Ca-Mn-O can yield material of improved magnetoresistive properties at room temperature and in a small applied field, as compared to the analogous Sr and/or Ba-free material. An exemplary composition is La.sub.0.55 Ca.sub.0.25 Sr.sub.0.08 MnO.sub.x. Material according to the invention has a substantially larger value of .vertline.d.rho./dH.vertline. than the analogous comparison material at 25.degree. C. and H.ltoreq.0.05 Tesla. Preferred compositions also can exhibit a substantially linear dependence of resistivity on applied magnetic field under these conditions, as well as have a relatively large value of zero field resistivity. The novel materials can advantageously be used in applications that involve sensing of a magnetic field, or of changes in such a field.

Abstract: Apparatus according to the invention comprises at least two optical microcavity light emitters. Each one of the at least two light emitters comprises spaced apart reflectors that define a microcavity, and further comprises organic material that is capable of electro-luminescence (e.g., tris (8-hydroxyquinolinol) aluminum, commonly referred to as "Alq"), and means for applying an electric field across the organic material. One of the at least two microcavities has effective optical length L.sub.1, and the other microcavity has effective optical length L.sub.2 .noteq.L.sub.1, with the optical lengths selected such that one of the microcavities emits radiation of a first color (e.g., red), and the other microcavity emits radiation of a second color (e.g., green). In many cases there will be present also a third microcavity that emits radiation of a third color (e.g., blue).