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 a spin whose spatial frequency exceeds 4 spins/meter.

Abstract: The disclosed article comprises a semiconductor laser (typically a multi-segment DBR laser) and feedback means for controlling the laser wavelength. The wavelength reference element in the feedback means advantageously is an optical fiber comprising an in-line refractive index grating. Such gratings frequently have a transmission spectrum that exhibits subsidiary lobes, in addition to the desired main lobe, potentially compromising the "cold-start" ability of prior art systems. This and other drawbacks of prior art systems exemplarily are overcome by apparatus that comprises a feedback loop that comprises means for causing a current I.sub.B to flow to the "Bragg" section of a multi-segment DBR laser such that wavelength of the laser output is a function of I.sub.B, and that further comprises means for changing the temperature of the laser in response to a change in the wavelength of the laser. Use of a wavelength reference element that has a relatively wide primary minimum facilitates cold starting.

Abstract: An article according to the invention comprises two bodies that are joined together by means of a compression bond, such as to form an enclosure. One of the bodies comprises a (exemplarily Au-covered) textured surface region, and the other body comprises a (exemplarily Au) "O-ring" positioned such as to mate with the textured region, substantially surrounding the enclosure. The textured region comprises at least one (typically two or more) "ridge" that substantially surrounds the enclosure and that, after joining of the two bodies by compression bonding, provides a leakage barrier. Optional ridges between said two or more enclosure-surrounding ridges can further reduce the probability of leakage. The bodies exemplarily are Si bodies, with the enclosure serving to provide a controlled environment for a semiconductor laser. In another exemplary embodiment, the article is a flat panel field emission display.

Abstract: Unexpectedly large normalized refractive index changes (.DELTA.>10.sup.-5, but possibly even larger than 10.sup.-3) can be obtained in oxide glass, e.g., high-silica glass, by a treatment that comprises exposing at least a portion of the glass at a temperature of at most 250.degree. C. to H.sub.2 or D.sub.2 (partial H.sub.2 or D.sub.2 pressure greater than 1 atmosphere), and irradiating at least a part of the exposed portion with actinic (typically UV) radiation. The method can be used to make optical components that comprise a region (or regions) of raised refractive index, e.g., an in-line refractive index grating in an optical waveguide, a planar optical waveguide, or a phase grating.

Abstract: We have discovered that the yield of DFB lasers suitable, e.g., for use in AM CATV systems can be substantially increased if the lasers have a back facet with a higher reflectivity (>80%, preferably >90%) HR coating thereon than is conventional (e.g., .about.65%). Exemplary currently preferred embodiments of the invention comprise a three-pair stack of .lambda./4 yttrium-stablized zirconia/Si having about 95% reflectivity.

Abstract: The disclosed flat panel field emitter display (FPFED) comprises a first impedance that carries all of the current to all of the micropoint emitters of one or more (preferably one, typically fewer than about five, always fewer than all the pixels of a given row or column of the display) pixels. Provision of the first impedance can provide self-compensation to the involved pixel, making it possible to substantially reduce the required number of micropoint emitters/pixel and color. This in turn can lead to increased speed of the display, and/or to lower power consumption. The first impedance advantageously is a capacitor rather than a resistor, and embodiments that comprise a capacitive first impedance are disclosed. Other advantageous optional features are also disclosed. These include provision of gate impedances, of photoconductive elements, of an auxiliary gate electrode, or of gettering means.

Abstract: We have discovered that silica-based optical fibers that are doped with Ge, Al and a rare earth (e.g., Er) can be very susceptible to hydrogen-induced attenuation change. For instance, such fiber can exhibit loss increase rates that are, at 20.degree. C., 10.sup.6 times larger than those of a standard single mode fiber. We also believe that transition metal-doped silica-based fibers can exhibit large hydrogen-induced attenuation change. In many circumstances (e.g., amplifier fiber, attenuator fiber) significant attenuation change of optical fiber is undesirable. We disclose that such change can be substantially eliminated by provision of hydrogen gettering material and/or a "hermetic" fiber coating. It is currently preferred to provide silica cladding material that is a hydrogen getter, and also provide a "hermetic" fiber coating. Containment of the fiber, together with a quantity of a gettering material (e.g., ErFe.sub.2) in an essentially hermetic enclosure is also disclosed.

Abstract: Filamentary and sheet-like oxide superconductive bodies can be produced by ceramic fabrication techniques such as extrusion, screen printing, tape casting and slip casting, provided the firing conditions are chosen such that the correct amount of oxygen deficiency is attained in the ceramic, and such that contact with chemically non-compatible material is avoided. Thus produced superconductive bodies are advantageously incorporated into apparatus such as magnets, power cables, interconnects, electrical components, and sensors.

Abstract: This invention is an apparatus which comprises a low reflection optical fiber termination. The apparatus comprises an optical fiber having a core, a cladding and a designated end. The core of the fiber has an effective refractive index N (exemplarily 1.484.+-.0.026). A terminator having a refractive index approximately equal to N (e.g. to within .+-.3.5%) is attached in such a manner that the terminator and the designated fiber end are in intimate contact. The closer the refractive index of the terminator is to the refractive index of the core of the fiber, the less back reflection occurs. A curable polymer having a high refractive index can be used to coat the terminator and a portion of the fiber. There is no need to polish, bend, cleave, twist or taper the end of the optical fiber prior to attaching the substrate to the optical fiber. Thus, the apparatus can be readily and inexpensively practiced not only in the factory but also in the field.

Abstract: An optical fiber communication system according to the invention comprises, in addition to conventional single mode (SM) optical fiber, dispersion compensating (DC) optical fiber. The DC fiber is selected such that its chromatic dispersion (D.sub.DC (.lambda.)) and first derivative of the chromatic dispersion with respect to wavelength (D'.sub.DC (.lambda.)) at a wavelength .lambda.=.lambda..sub.op have opposite sign from those of the SM fiber. Advantageously, the DC fiber is selected such that L.sub.DC .multidot.D.sub.DC (.lambda.)+L.multidot.D(.lambda.) is approximately zero at .lambda.=.lambda..sub.op, and such that D'.sub.DC (.lambda.) is approximately equal to --(L/L.sub.DC).multidot.D'(.lambda.) at .lambda.=.lambda..sub.op, where L.sub.DC and L are appropriate lengths of DC and SM fiber, respectively. Typically, L is much greater than L.sub.DC, and .lambda..sub.op typically is about 1.5 .mu.m, e.g., about 1.56 .mu.m.

Abstract: Optical waveguide amplifiers and lasers having a novel fluorescent dopant distribution are disclosed. Exemplarily, in a Si-based optical fiber the fluorescent dopant (e.g., Er) has an annular distribution, with the concentration maximum not at the center of the core but typically between the center and the core/cladding interface. The novel waveguides can be relatively insensitive to variations in cut-off wavelength and/or modal distribution of pump power.

Abstract: Relatively large bodies of low-alkali silicate and other glass can be prepared conveniently by a particulate sol-gel process. The glass comprises at least 85 mole % SiO.sub.2, 1-12 mole % oxide of one or more of Li, Na, K, Rb, Cs, Ti and Zr, 0-6 mole % of oxide of Al, and optionally at most 2.5 mole % of oxide of elements other than Si, Li, Na, K, Rb, Cs, Ti, Zr and Al. The process comprises forming particles from a first sol that comprises Si and one or more of Li, Na, K, Rb, Cs, Ti and Zr, and optionally additionally comprises Al. The process further comprises forming a second sol by dispersing the particles in an aqueous liquid, gelling the second sol, and heat treating the resulting gel body such that the glass results.

Abstract: The disclosed method can produce high T.sub.c superconductor material e.g., YBa.sub.2 Cu.sub.3 O.sub.7) of substantially increased intra-grain critical current density (J'.sub.c), as compared to conventionally produced bulk material of analogous composition. Exemplarily, YBa.sub.2 Cu.sub.3 O.sub.7 pellets produced according to the invention had J'.sub.c of about 10.sup.5 A/cm.sup.2 at 77 K. in an applied magnetic field of 0.9 Telsa. The inventive method comprises providing a precursor material whose composition differs from that of the desired superconductor with respect to at least one of the metal constituents of the desired superconductor. It further comprises heating the precursor material above the decomposition temperature (T.sub.d) of the precursor material such that a multiphase material results. The multiphase material comprises, in addition to a majority first phase, a dispersed precipitate phase. The method further comprises cooling the multiphase material to a temperature below T.sub.

Abstract: We have found a way to, e.g., substantially increase the number of layers in a pseudomorphic strained layer semiconductor mirror over the number obtainable in an analogous conventional mirror, making it possible to obtain pseudomorphic strained layer mirrors of increased reflectance. Such a pseudomorphic mirror consists of alternating layers of a first and a second semiconductor material (e.g., Ge.sub.x Si.sub.1-x /Si), of thickness t.sub.1 and t.sub.2, and refractive index n.sub.1 and n.sub.2, respectively, with the number of layer pairs chosen such that the mirror thickness is less than or equal to the "critical thickness" L.sub.c. For thicknesses >L.sub.c the mirror will contain dislocations.An article according to the invention comprises a mirror whose layer thicknesses are chosen such that n.sub.1 t.sub.1 .noteq.n.sub.2 t.sub.2, with n.sub.1 t.sub.1 +n.sub.2 t.sub.2 =p.lambda./2, (p being an odd integer, typically 1). In other words, the optical thickness of the layers is not the conventional p.

Abstract: Fusion splicing of optical fiber generally requires removal of a polymer coating from the end portions of two lengths of fiber. A conventional removal method involves immersion of the fiber ends in an appropriate polymer stripping liquid, e.g., in hot, concentrated sulfuric acid. It is known that the strength of fusion splices generally is statistically distributed, such that there exists a probability that a given splice will pass at a given proof test level. We have found that the splice strength distribution can be shifted towards higher strength if the polymer stripping liquid comprises means for insuring that the liquid is essentially free of strength-reducing particles. Preferred means are concentrated nitric acid. Exemplarily, the liquid is at a temperature in the range 170.degree.-200.degree. C. and comprises concentrated (about 95%) sulfuric acid and about 5% b.v. concentrated (about 70%) nitric acid.

Abstract: A method for manufacturing a semiconductor device which includes a step of evaluating the dopant profile, in at least the depth dimension, in a processed or partially processed wafer. The evaluation is performed nondestructively, by measuring a differential reflectivity spectrum of the doped portion of the wafer. The resulting spectrum can be related to the Fourier transform of the dopant profile in the depth dimension.

Abstract: A novel light emitting semiconductor device is disclosed. The device utilizes real space transfer (RST) of carriers, and comprises regions of opposite conductivity type separated by a barrier layer. The first region (termed the "emitter") comprises at least two contacts. Application of appropriate bias between the two contacts and between the emitter and the second region results in injection of hot carriers into the second region, resulting in luminescence in the second region. The invention can be embodied in coherent as well as incoherent light sources. A preferred embodiment is a vertical cavity surface emitting laser. The device can serve as a novel logic element that has electrical inputs and an optical output, and provides a non-trivial logic function.

Abstract: The inventive method is advantageously used in the manufacture of an article that comprises an opto-electronic device (e.g., LED or photodetector diode) that has a substantially planar radiation-emitting or receiving (first) surface region. The method comprises preliminarily positioning the end of a length of optical fiber relative to the first surface region, and causing radiation from a radiation source to be emitted from the fiber end so as to be incident substantially normally on the first surface region. A part of the radiation is reflected, collected by the fiber end, and transmitted to a power meter. The output of the power meter (or a quantity derived therefrom) is compared to a pre-determined measurement value and, if indicated by the comparison, the position of the fiber end is adjusted. A significant aspect of the invention is the existence of an easily measured relationship between the reflected power received by the power meter and the distance .DELTA.

Abstract: Broadband in-line gratings in optical waveguides are disclosed. The gratings have a bandwidth of at least 2 nm (preferably at least 4 nm) and a peak reflectivity of at least 70% (preferably at least 90%). Exemplarily, such gratings can be formed in H.sub.2 -treated Si-based fibers that support a normalized index change of at least 10.sup.-3. Gratings according to the invention can be used, for instance, to form pump radiation reflectors in an optical fiber communication system with Er-doped fiber amplifiers.

Abstract: An optical fiber which is enclosed within a polymeric jacket. At least a portion of the jacket material comprises a particulate material which is at least partially soluble in water, such that a solution can be formed which has reduced reactivity toward the optical fiber, relative to pure water. An amount of such material is incorporated in the jacket, sufficient to delay the expected onset of accelerated fiber fatigue in a standard fatigue test by at least a factor of 2 relative to an otherwise similar fiber enclosed within a jacket which is free of the particulate material.