Abstract: A self-tuning optical waveguide filter for attenuating a lower power light signal at .lambda..sub.1 more than a higher power signal at .lambda..sub.2 comprises a length of single core waveguide and a light injector for applying .lambda..sub.1, .lambda..sub.2 into the waveguide in two propagating modes subject to mode beating. The mode beating produces high intensity regions of .lambda..sub.1 physically displaced from high intensity regions of .lambda..sub.2. A portion of the waveguide is doped with a saturable absorber for disproportionately attenuating wavelengths at lower power levels. Advantageously the waveguide is a single-core fiber having its central core doped with rare-earth saturable absorber. In a preferred embodiment, the fiber is dimensioned to propagate .lambda..sub.1, .lambda..sub.2 in the LP.sub.01 and LP.sub.02 modes, and the saturable absorber is Erbium.

Abstract: The present invention relates to a single-mode optical fiber having a configuration which enables lowering of dispersion slope while securing a sufficient MFD. This single-mode optical fiber has a refractive index profile in which an indent with a sufficient width is provided at the center of its core region. In particular, this indent satisfies the following relationship:a.multidot.(.DELTA.n.sub.2 -.DELTA.n.sub.1)/(b.multidot..DELTA.n.sub.2).gtoreq.0.04when the first core portion in the single-mode optical fiber has a mean relative refractive index difference of .DELTA.n.sub.1 with respect to the cladding portion and an outer diameter of a while the second core portion has a mean relative refractive index difference of .DELTA.n.sub.2 with respect to the cladding portion and an outer diameter of b.

Abstract: An optical integrated circuit wherein the waveguide network is constructed of a passive waveguide and a functional material is used on the functional portions, an optical circuit device which uses transparent electrodes, an optical switch which uses transparent electrodes and a functional portion made of a non-linear optical material, a matrix optical switch which converts inputted and outputted light at an electrical/optical converter element, and an optical integrated circuit or optical circuit device prepared by selective vapor growth of a functional material on desired regions, as well as an organic film growth process by which an organic film is selectively grown on recess walls and an organic film formation process whereby organic CVD or MLD is performed using a chamber divided into multiple regions.

Abstract: A new light-transmitting device using a SCIN glass core and a novel calcium sodium cladding has been developed. The very high index of refraction, radiation hardness, similar solubility for rare earths and similar melt and viscosity characteristics of core and cladding materials makes them attractive for several applications such as high-numerical-aperture optical fibers and specialty lenses. Optical fibers up to 60 m in length have been drawn, and several simple lenses have been designed, ground, and polished. Preliminary results on the ability to directly cast optical components of lead-indium phosphate glass are also discussed as well as the suitability of these glasses as a host medium for rare-earth ion lasers and amplifiers.

Abstract: Known dispersion-compensating (DC) optical fibers typically are sensitive to small changes in fiber parameter (e.g., fiber diameter and/or core refractive index), and thus are difficult to manufacture. The disclosed DC fibers are relatively insensitive to small departures from the nominal fiber parameters, and are therefore more manufacturable. Exemplarily, the nominal refractive index profile of a DC fiber is selected such that the fiber supports LP.sub.01 and LP.sub.02 (and typically one or more further higher order modes), and the dispersion is substantially all in LP.sub.02. The total dispersion is more negative than -200 ps/nm.km over a relatively wide wavelength range. The nominal refractive index profile typically comprises a refractive index "ring" that is spaced from the fiber core.

Abstract: A dispersion compensating fiber is provided which is capable of reducing the birefringence of the core caused in spinning to suppress an increase in polarization mode dispersion due to the birefringence of the core even though the surface of the core rod is ground to shape the profile of the core during manufacturing. A silica glass cladding 2 doped with fluorine is disposed to surround a silica glass core 1 doped with germanium. The variation in circumferential concentration of germanium at the periphery of the core 1 is set at 0.05% or smaller in relative refractive index difference value.

Abstract: A rare earth doped optical fiber consisting of a first core doped with a rare earth element and having a relative index difference ranging from about 0.76% to about 1.5%, a second core surrounding the first core and having a relative index difference of about 1.8% or more, and a clad surrounding the second core. The refractive index of the first core is set smaller than the refractive index of the second core, and only the first core is doped with a rare earth element, thereby suppressing the influence of concentration quenching.

Abstract: An improved optical glass fiber for transmitting mid infrared wavelength laser light in surgical instruments, includes a heavy-metal oxide component, preferably GeO.sub.2 doped with heavier cations and anions, and which is capable of delivering at least three watts of laser power continuously for more than ten minutes, without failure. This glass fiber has an .alpha.(dB/m) at 2.94 .mu.m of 10, preferably less, and can transmit at least 27% of the IR through a thickness of one foot.

Abstract: This invention provides an optical waveguide having diffraction gratings with sufficiently high reflectivity, a waveguide member for obtaining the optical waveguide, and a production process thereof. An optical waveguide in which desired diffraction gratings are formed in a core and in a cladding at a predetermined portion by using a waveguide member in which germanium dioxide is added in the core and in the cladding and irradiating the predetermined portion of the waveguide member with interference fringes of ultraviolet light. By this, the optical waveguide according to the present invention reflects guided light throughout the entire mode field region, thus having a high reflectivity.

Abstract: A halide glass composition contains iodide and/or bromide. In addition the halide content preferably includes chloride. The preferred metal composition includes no aluminium and 1-10 mole % of (In+Y). These compositions are used as hosts for rare earth lasing dopants, e.g, Pr.sup.3+.

Abstract: This invention relates to fluoride glass with a specific composition having wide infrared transmission. A fluoride optical fiber using this fluoride glass can give high efficiency with a low loss. The fluoride optical fiber having a second cladding on the outer periphery of a first cladding can adjust the refractive index of the first cladding suitably.

Abstract: The present invention provides an optical signal shaping device, such as a long period grating, for use with an optical fiber having a core of a first prescribed refractive index n.sub.1 and a cladding of a second prescribed refractive index n.sub.2 and configured to transmit an optical signal therethrough. The optical signal shaping device comprises a long period grating of predetermined length formed within the optical fiber. The long period grating has a nonuniform refractive index profile extending over at least a portion of the predetermined length and is configured to alter the optical signal to produce an asymmetrical optical signal.

Abstract: Disclosed are laser glasses composed of a Ga--Na--S glasses doped with one or more kinds of activating ions, laser glass fibers comprising a core and a clad wherein the core is composed of the above-mentioned laser glasses of the present invention and optical fiber amplifiers comprising a pumping source, a laser glass fiber and a means for introducing pumping light and signal light into the laser glass fiber wherein the laser glass fiber is the above-mentioned laser glass fiber of the present invention. The laser glasses of the present invention show high radiative quantum efficiency and host glass stability and can be produced easily.

Abstract: A glass body for optical fiber containing GeO.sub.2 --SiO.sub.2 glass in a core portion thereof, in which the GeO.sub.2 --SiO.sub.2 glass has an absorbance at 5.16 eV of at least 1/mm but not higher than 2.5/mm or in which concentration of Ge.sup.2+ contained in the GeO.sub.2 --SiO.sub.2 glass substantially lies within the range of 1.1.times.10.sup.-9 to 2.8.times.10.sup.-9 mol/mm.sup.3 as calculated by the following general equation:A=.epsilon..sub.5.16ev .multidot.C.sub.(Ge2+) .multidot.1wherein A is absorbance which is expressed by A=-log T (T being transmittance) and normalized per 1 mm of optical path length, C.sub.(Ge2+) is Ge.sup.2+ concentration, .epsilon..sub.5.16ev is absorption coefficient (1/mol/cm), and 1 is optical path length.

Abstract: A method of fabricating a dispersion shifted optical fiber with a smooth annular ring refractive index profile has the steps of heating a quartz tube with an external oxygen or hydrogen burner and supplying the quartz tube with raw materials including SiCl.sub.4, GeCl.sub.4, POCl.sub.3 and CF.sub.4. O.sub.2 is later supplied. Then, the quartz tube is heated in nine passes of decreasing temperature from 1920.degree. C. to 1890.degree. C., so as to deposit a core section. In the nine passes, the quantity of SiCl.sub.4 feed flow decreases from 380 milligrams per minute to 260 milligrams per minute, the quantity of GeCl.sub.4 feed flow increases from 20 milligrams per minute to 195 milligrams per minute, and the quantity of O.sub.2 feed flow is kept constant at 1500 cubic centimeters per minute.

Abstract: This invention relates to a dispersion-compensating fiber which can be drawn at a lower temperature and can further reduce optical transmission loss. This dispersion-compensating fiber comprises a core portion containing a high concentration of GeO.sub.2 and a cladding portion formed around the outer periphery of the core portion. The cladding portion comprises a first cladding containing fluorine or the like as an index reducer, a second cladding having a higher refractive index than that of the first cladding, and a third cladding which becomes a glass region substantially noncontributory to propagation of signal light. In particular, the third cladding contains a desired impurity such that the glass viscosity thereof becomes lower than that of the second cladding or pure silica cladding at a predetermined temperature.

Abstract: Dehydroxylated, silica-containing, glass surfaces are known to be at least partially terminated by strained siloxane rings. According to the invention, a surface of this kind is exposed to a selected silane compound or mixture of silane compounds under reaction-promoting conditions. The ensuing reaction results in opening of the strained siloxane rings, and termination of surface atoms by chemical species, such as organic or organosilicon species, having desirable properties. These species can be chosen to provide qualities such as hydrophobicity, or improved coupling to a polymeric coating.

Abstract: The present invention relates to a multicore plastic optical fiber for light signal transmission comprising 7 or more cores having a diameter of 50 to 200 .mu.m which are covered with a cladding resin having a refractive index lower than that of the core resin by 0.005 to 0.04. The multicore plastic optical fiber of the present invention has low transmission loss in a broad transmission bandwidth and exhibits excellent bending characteristics. Therefore, it is suitable for transmission at a high speed in short and medium distances.

Abstract: This invention relates to a dispersion-shifted fiber containing silica glass as the major component and in which the zero-dispersion wavelength is set to fall within a range of 1,560 nm to 1,580 nm and the mode field diameter with respect to light having a predetermined wavelength is set to 8 .mu.or more. This dispersion-shifted fiber is a single-mode optical fiber capable of decreasing the influence of nonlinear optical effect and having a structure for suppressing an increase in bending loss of the optical fiber, and includes a core region constituted by the first core portion and the second core portion, and a cladding portion. In particular, an outer diameter a of the first core portion and an outer diameter b of the second core portion satisfy at least a relationship 0.10.ltoreq.a/b .ltoreq.0.29.

Abstract: The present invention relates to a dispersion-shifted fiber having a structure for effectively lowering polarization-mode dispersion. This dispersion-shifted fiber is a single-mode optical fiber mainly composed of silica glass and has a zero-dispersion wavelength set within the range of at least 1.4 .mu.m but not longer than 1.7 .mu.m. In particular, at least the whole core region of the dispersion-shifted fiber contains fluorine.

Abstract: An optical waveguide for fiber-optic amplifiers is disclosed where the Progression of the fluorescence band of optical waveguides that are doped with erbium and aluminum can be additionally flattened if the core contains fluorine, e.g., in the form of ErF.sub.3 and AIF.sub.3, as an additional doping agent.

Abstract: A high power laser transmitting fluoride glass fiber of an enhanced 2.94- .mu.m laser damage threshold value is disclosed, in which either of the core with a high refractive index and the cladding with a low refractive index is formed of fluoride glass which contains fluorine (F) as a component but has it substituted with 0 to 4.1 mol % of bromine (Br), chlorine (Cl), or bromine and chlorine. The optical fiber of the present invention may have its core formed of fluoride glass and its cladding formed of fluorine-contained resin, and the core glass has a composition that 70 to 80% of fluorine (F) is substituted with 0 to 4.1 mol % of bromine (Br), or chlorine (Cl), or bromine and chlorine.

Abstract: A cladding pumped optical fiber laser comprises a length of optical fiber having a rare earth-doped region of diameter d.sub.RE >d.sub.01 where d.sub.01 is the mode diameter of the LP.sub.01 mode of the fiber at the laser radiation at wavelength .lambda.. In one embodiment the fiber has a core diameter d.sub.c selected such that the LP.sub.01 mode is the only guided spatial mode of the fiber, and d.sub.RE is greater than d.sub.c. In another embodiment the fiber supports at least one higher order guided spatial mode, typically LP.sub.11 or LP.sub.02, and d.sub.RE is approximately equal to or larger than d.sub.c. Currently preferred embodiments comprise a grating-defined laser cavity that comprises a mode-coupling refractive index grating. Cladding pumped lasers according to the invention will typically have efficient conversion of pump radiation to laser radiation, and consequently can typically be shorter than analogous prior art cladding pumped lasers.

Abstract: A compact monolithic interferometric switch such as a Mach-Zehnder switch is formed such that one of the waveguide paths between the input and output couplers contains a material having exhibits a resonant nonlinearity, whereby its refractive index changes when pump power propagates through it. Each of the waveguide paths has a different propagation constant whereby signal light is subjected to a different delay in each path when no pump power is propagating through the rare nonlinear path. An input signal applied to the input of the switch appears at a first output terminal when the pump power does not propagate through the nonlinear path, and it appears at a second output terminal when the pump power is applied to the nonlinear path. Switching occurs at relatively low levels of pump power.

Abstract: Lead-containing fluoride glass comprises 50-70 mol % of ZrF.sub.4, 3-5 mol % of LaF.sub.3, 0.1-3 mol % of YF.sub.3, and 2-15 mol % of NaF and/or LiF and/or CsF, where LaF.sub.3 +YF.sub.3 =4.5-6 mol %, and further comprises lead. An optical fiber comprises a core made of the lead-containing fluoride glass and a cladding surrounding the core. A process for producing an optical fiber comprises forming a base material for a core of the lead-containing fluoride glass, forming a base material for a cladding of fluoride glass containing 30-60 mol % of HfF.sub.4, and drawing the base materials into an optical fiber at a drawing temperature of 315-340 .degree. C.

Abstract: Dysprosium-doped metal chloride materials offer laser properties advantageous for use as optical amplifiers in the 1.3 .mu.m telecommunications fiber optic network. The upper laser level is characterized by a millisecond lifetime, the host material possesses a moderately low refractive index, and the gain peak occurs near 1.31 .mu.m. Related halide materials, including bromides and iodides, are also useful. The Dy.sup.3+ -doped metal chlorides can be pumped with laser diodes and yield 1.3 .mu.m signal gain levels significantly beyond those currently available.

Abstract: The polarization-maintaining optical fiber 10 of the present invention is designed so that a plurality of core portions 12a,12b which have a high refractive index is provided in parallel along a single diameter direction in the cross section of the optical fiber, these core portions 12a,12b cooperating to propagate a single fundamental mode. In the production method for the polarization-maintaining optical fiber of the present invention, a plurality of holes 22 are formed longitudinally in parallel along a single diameter direction of a glass rod 21 having a low refractive index which forms the cladding, glass rods 23 for core use having a high refractive index which form the core portions are inserted into these holes 22, heating to form a unitary body is carried out, creating a preform which is then drawn.

Abstract: A liquid light guide system for ultraviolet light is disclosed that has a light shaping arrangement for the emitted light, a stable liquid core and sheath and reliable and effective end closures.

Abstract: Illuminating equipment with a light source and a liquid light guide, which is coupled optically to the light source and the liquid core of which contains a mixture of heavy and light water in a ratio by volume of 50:50 to 98:2, depending on the length of the light guide. The light guide transfers the visible range of the spectrum in a color-neutral manner. At the same time, the long-wave radiation, which causes unwanted heating effects, is suppressed.

Abstract: An optical attenuator uses a segment of attenuating fiber interposed in the optical path. The attenuating fiber is produced by using a solution doping technique to introduce transition or rare earth elements into the fiber's core. The dopant reduces the transmission of the fiber. The degree of attenuation depends upon the material used as the dopant, the dopant level, and the length of the attenuation segment. In a specific embodiment, an optical attenuator is provided having a first and second signal carrying optical fibers and an attenuating fiber segment, each of which has a core, a cladding substantially coaxial with the core, and a substantially planar endface. The attenuating fiber segment is fusion spliced between the first and second signal carrying optical fibers. In a second embodiment a portion of the cladding of the attenuating fiber is chemically etched.

Abstract: The present invention provides an optical switching system for use with an optical fiber that has a core of a prescribed refractive index and a cladding and that is configured to carry an optical signal of a prescribed bandwidth. Preferably, the optical fiber's core includes a photosensitive dopant. In a preferred embodiment, the optical switching system comprises an optical switch coupled to the optical fiber and includes a grating within the core. The optical switch has selectable non-diverting and forward-diverting modes of operation wherein the optical switch alters the prescribed refractive index: to render the grating substantially transparent to the optical signal as the optical switch operates in the non-diverting mode or, alternatively, to allow the grating to divert at least a portion of the optical signal forward and into the cladding as the optical switch operates in the forward-diverting mode.

Abstract: An optical coupler 10 has two fibers 20, 30 that are adjacent each other in a coupling region 12. One of the fibers has a clad doped with a photosensitive glass, such as germania. The photosensitive glass is exposed to suitable radiation to alter the index of refraction of fiber and tune the coupler 10 to the selected coupling frequency.

Abstract: Optoelectric article includes a substrate made of an optoelectric single crystal and a film of a single crystal of lithium niobate formed on the substrate by a liquid phase epitaxial process, wherein a ratio of lithium/niobium of a composition of the film of the lithium niobate single crystal falls in a range of 48.6/51.4 to 49.5 to 50.5 or 50.5/49.5 to 52.3/47.7.

Abstract: An optical attenuator uses a segment of attenuating fiber interposed in the optical path. The attenuating fiber is produced by using a solution doping technique to introduce transition or rare earth elements into the fiber's core. The dopant reduces the transmission of the fiber. The degree of attenuation depends upon the material used as the dopant, the dopant level, and the length of the attenuation segment. In a specific embodiment, an optical attenuator is provided having a first and second signal carrying optical fibers and an attenuating fiber segment, each of which has a core, a cladding substantially coaxial with the core, and a substantially planar endface. The attenuating fiber segment is fusion spliced between the first and second signal carrying optical fibers. In a second embodiment a portion of the cladding of the attenuating fiber is chemically etched.

Abstract: An optical circuit device has a carbon optical waveguide structure which has a substrate. A first carbon layer is atop the substrate and has a first refractive index. A carbon optical waveguide core is positioned atop the first layer and has a second refractive index different than the first refractive index. A cladding layer of carbon is positioned atop the first layer and the waveguide core and has a third refractive index different than the refractive index of the waveguide core.

Abstract: This invention provides an optical waveguide having diffraction gratings with sufficiently high reflectivity, a waveguide member for obtaining the optical waveguide, and a production process thereof. An optical waveguide in which desired diffraction gratings are formed in a core and in a cladding at a predetermined portion by using a waveguide member in which germanium dioxide is added in the core and in the cladding and irradiating the predetermined portion of the waveguide member with interference fringes of ultraviolet light. By this, the optical waveguide according to the present invention reflects guided light throughout the entire mode field region, thus having a high reflectivity.

Abstract: A single mode optical waveguide fiber designed for high data rate, or WDM systems or systems incorporating optical amplifiers. The optical waveguide has a compound core having a central region and at least one annular region surrounding the central region. A distinguishing feature of the waveguide core is that the minimum refractive index of the central core region is less than the minimum index of the adjacent annular region. A relatively simple profile design has the characteristics of ease in manufacturing together with, flexibility in tailoring D.sub.w to yield a preselected zero dispersion wavelength, dispersion magnitude over a target wavelength range, and dispersion slope. The simplicity of profile gives reduced polarization mode dispersion.

Abstract: The optical fiber amplifier includes a rare earth doped optical fiber and a pumping light source for outputting pumping light for pumping the rare earth doped optical fiber, the optical fiber amplifier optically amplifying signal light received at an input end and outputting the amplified signal light from an output end, wherein the optical fiber amplifier further includes an optical fiber resonator for laser-oscillating a portion of light of spontaneous emission generated in the rare earth doped optical fiber, which has a wavelength shorter than the wavelength of the signal light, thereby to keep a gain substantially fixed independent of a variation in the wavelength of the signal light.

Abstract: A process for radiation hardening a pure-silica-core fiber, the process comprising the steps of:(a) providing a pure-silica-core fiber having a core index of refraction and having an outer surface;(b) exposing the fiber to a dose of ionizing radiation sufficient to permanently reduce transmission losses of the fiber to no more than about 30 dB/km within a wavelength range of about 400 nm to about 700 nm. In addition, white light may simultaneously be transmitted through the fiber during the exposure of the fiber to ionizing radiation. The presently claimed invention is directed to the above process and the radiation hardened fiber formed according to the above processing steps.

Abstract: An active optical device comprises a glass, waveguiding structure disposed on a substantially planar principal surface of a substrate. The structure includes a silica-based, erbium-doped active core. The active core has an absolute erbium concentration of at least about 0.5.times.10.sup.20 atoms per cubic centimeter, and a radiative lifetime of the erbium lasing level of at least about 5 milliseconds. The active core does not contain significant amounts of alkali metals or alkaline earth metals but does contain at least two modifier metals. Also disclosed is a method for forming an active optical device, including the step of depositing an erbium-doped active core by sputtering.

Abstract: Halide glasses having particular utility as hosts for praseodynmium in order to provide optical amplification by laser activity have a halide content provided as a small proportion, e.g., 1-10 percent, of choride with the remainder as fluoride. The metal content is similar to conventional ZBLAN glasses. The replacement of A1 by Y and In and/or the partial replacement of Na by Cs has synergistic benefits. PR.sup.3+ constitutes a good lasing species for amplifying telecommunication signals at 1300 nm using pumped radiation at 1020 nm.

Abstract: A method of controlling the polarization properties of a photo-induced device in an optical waveguide and a method of investigating the structure of a light guiding body such as an optical waveguide are disclosed. A device, such as gratings, is written by exposing one side of the optical waveguide to light. The unexposed side is then exposed to an amount of light sufficient to impart the desired birefringence to the written device. The birefringence can be minimized in the written device by exposing the opposite side to light in an amount sufficient to minimize the amount of birefringence. The light guiding body is investigated by cleaving the elongated light guiding body, such as an optical waveguide, to expose its cross-section. The cleaved section is then treated to expose difference between the core and cladding. Treatment may include etching in an acid or base.

Abstract: A planar waveguide and a process for making a planar waveguide is disclosed. The waveguide has a layer of doped host material formed on a substrate. The host material is a trivalent material such as a metal fluoride, wherein the metal is selected from the Group III B metals and the lanthanide series rare earth metals of the Mendeleevian Periodic Table. The dopant is a rare earth metal such as erbium. The waveguide has an emission spectrum with a bandwidth of about 60 nm for amplification of an optical signal at a wavelength of about 1.51 .mu.m to about 1.57 .mu.m. The waveguide is made by forming the layer of doped host material on a substrate. The film is formed by evaporating materials from two separate sources, one source for the dopant material and a separate source for the host material and forming a film of the evaporated materials on a substrate.

Abstract: The present invention is directed to the preparation of two groups of transparent glass-ceramics exhibiting high optical clarity and containing essentially only one crystal phase. The first group consists essentially, in cation percent, of______________________________________ SiO.sub.2 20-35 PbF.sub.2 19-23 AlO.sub.1.5 10-20 YF.sub.3 3-7, CdF.sub.2 19-34 ______________________________________and the second group consists essentially, in cation percent, of ______________________________________ SiO.sub.2 20-35 PbF.sub.2 15-25 AlO.sub.1.5 10-20 YF.sub.3 3-7 CdF.sub.2 21-31 ZnF.sub.2 3-7. ______________________________________These glass-ceramics may be used to fabricate optical waveguide fibers. Also when doped with certain rare earth elements, notably Pr, Er, and Dy, the glass-ceramic materials may be used to fabricate optical amplifiers and lasers.

Abstract: A manufacturing method for erbium doped silica, having a soot formation process, in which a silica glass soot is deposited on a seed rod for forming a soot preform in a porous state on the seed rod, a dopant impregnation process, wherein the soot preform is impregnated with at least an erbium compound, and a preform formation process, wherein this soot preform impregnated with a dopant is heated and rendered transparent. The dopant impregnation process is provided with an operation in which the soot preform obtained in the soot formation process is dipped in a solution containing an erbium compound, an aluminum compound, and a phosphorus compound; this is then desiccated, and soot preform which is impregnated with the erbium compound, the aluminum compound, and the phosphorus compound is obtained.

Abstract: Plural planar optical devices are simultaneously pumped by a single pumping source. Various arrangements for accomplishing such pumping are disclosed. By utilizing these arrangements, the topology and routing of integrated arrays including optical devices are simplified.

Abstract: The object of the invention is to provide a method which makes it possible to determine the correlation between two optical signals, which makes it possible to correlate two optical signals, without using a crystal element which is associated with a plurality of drawbacks, because the components are quite expensive. It has been found possible to replace a frequency doubling crystal by an active, optical wave guide, e.g. in the form of an active, optical fiber, said wave guide transmitting fluorescence which is intensity-related to the arrived signal. When this fluorescence is detected in spectral bands, e.g. in the blue region of the visible light, an image of the strength of the arriving signal may be formed. Current distance delaying of the two correlated signals makes it possible to produce an image of the correlation between the signals.

Abstract: A radiation resistant optical waveguide fiber doped with fluorine or drawn with low tension in the fiber. The fluorine doping is substantially constant across the core and a portion of the clad adjacent the core. The concentration of the fluorine is in the range of about 0.3 to 3.0 weight percent. The draw tension is less than or equal to about 5 grams (40 dynes/cm.sup.2) to achieve optimum radiation resistance. A synergy is found when fluorine and low draw tension are applied to a fiber. Improvement in radiation resistance is largely independent of fiber type and geometry.Further improvement in radiation resistance is found when germanium is doped in a portion of the clad adjacent the core.

Abstract: A new method for preparing low loss multimode and monomode glass optical fibers which avoids casting or pouring the core and clad melts is disclosed. The new technique is based on a reactive-gas-transport approach which avoids contamination from absorbing impurities and scattering centers by reacting the glass melt with reactive gases which remove impurities and increase the refractive index of the fiber.

Abstract: An optical fibre for use in fibre lasers has the lasing additive eg Er.sup.3+, concentrated in center of the core. Preferably the core has an inner region which contains the additive and an outer region which is dopant free. The concentration of the dopant reduces the pump threshold for a laser and improves the gain performance for a given pump power. The fibre is conveniently made in MCVD. The use of Al.sub.2 O.sub.3 in the inner zone appears to reduce loss of dopant during tube collapse.