Abstract: A self-contained unit and method for splicing together the ends of jacketed optical fibers. The unit comprises a guide to align fibers, such as a capillary tube, having opposite ends into which the ends of optical fibers to be spliced pass until they are in contact in a central portion of the guide. A heater high temperature proximal to the central portion of the guide, when activated, generates sufficient heat to fuse and splice together the contacting fiber ends. A securing means, such as spaced ferrules with a tube of ceramic material joining the ferrules, is mechanically associated with the guide to mechanically hold in position the optical fibers when spliced together. By bringing the ends of jacketed optical fibers into contact within the guide, in the vicinity of heater, and subjecting the ends to high temperature heating, the fibers are fused and spliced at their ends.

Abstract: A fiber optic coupler is formed by providing a glass tube having a longitudinal bore and first and second funnels connecting the bore to the ends of the tube. The protective coating is stripped from the central portion of two optical fibers. The first and second fibers are threaded into the tube bore until the uncoated portions thereof are located within the bore. The protective coating of only one of the fibers extends into the first end of the bore, and the protective coating or only one of the fibers extends into the second end of the bore. The fibers extend beyond the tube ends. The bore diameter is just slightly larger than the sum of the diameter of the first fiber and the diameter of the coating of the second fiber. The resultant tight fit of the fibers in the tube promotes the retention the fibers in parallel alignment during the subsequent tube collapse step. The midregion of the tube is heated, collapsed about the fibers, and drawn to form a coupling region.

Abstract: A fiber optic polarization maintaining apparatus for use in fabrication of fused optical couplers, where the fused optical couplers include first and second optical fibers. The apparatus includes apparatus for holding the first and second optical fibers in a first predetermined alignment where the first and second fibers each include a stripped portion and where the stripped portions are held in contact along their length. Apparatus for heating the first and second optical fibers are located adjacent the holding apparatus wherein the heating apparatus is brushed across the length of the first and second fibers so as to oscillate across the fibers in an amplitude varied in an ever decreasing stepped manner until fusion of the fibers is complete.

Abstract: A glass vacuum flask coating method comprising a step to put a metal material in the gap between an inner flask and an outer flask before said inner and outer flasks being formed into a blank for a glass vacuum flask, after the process of exhausting and tipping-off said metal material being heated by a magnetic field generated from an inductance coil into a metal vapor inside said gap, permitting said metal vapor to be adhered to the glass surface inside said gap, forming into a metal reflecting film thereon.

Abstract: Fiber composites, particularly for imaging, easy to manufacture even with great cross-sectional area, in which fibers are in a peak-to-valley relation with abutting pairs of fibers throughout.

Abstract: A micro-welder for optical fibers includes a stand having a central support surrounded by two lateral supports or beams. The beams are suitable for moving under drive from a bending movement about respective X-axes. The stand also supports a device for securing optical fibers on the beams and a device for accurately guiding the fibers on the central support. A low accuracy first displacement device is adapted to displace the beams to bring the fibers into end-to-end contact with each other by relative translation movement along their longitudinal Z-axis which is orthogonal to the X-axes. A high accuracy second displacement device is adapted for moving the beams to drive the fibers with accurate relative translation movements along the Z-axis. Two welding electrodes are provided and an optical device which includes a microscope for observing the ends of said optical fibers.

Abstract: An optical interconnect structure, formed on a substrate, optically interconnects optoelectronic transmitting and receiving devices. The optical interconnect structure includes optical interconnects each of which includes a core member constructed of a material having a first predetermined index of refraction. The ends of the core members are chemically bonded either to an optoelectronic device or a core member of another optical interconnect. A cladding layer surrounds each core member. Each end of a cladding layer proximate to an optoelectronic device is chemically bonded to that device. The cladding layer is formed of a material having a second predetermined index of refraction, the magnitude of which is less than the magnitude of the first predetermined index of refraction.

Abstract: A CRT bulb that has been preloaded to counter the atmospheric load placed on the seal area of an evacuated and sealed CRT is disclosed along with methods of constructing the bulb. The front panel is simply supported on the funnel and deflected inwardly during affixation of the panel to the funnel to form the bulb. When the deflection load is removed from the affixed panel, the resultant strain energy imparted to the bulb seal area offsets at least some of the atmosphericly induced strain on the sealed CRT. The bulb has a more evenly balanced stress distribution between the front panel and the funnel seal area than previous flat panel CRTs, enabling the use of thinner front panels and seal land.

Abstract: The invention relates to a method of making multi-ferrules. It provides a method of making multi-ferrules from a vitreous material, the multi-ferrules having a series of cylindrical channels with parallel axes.

Abstract: An optical two-way transmission-received communications system utilizing a coaxial coupler in place of a standard coupler, the optical system being capable of operation either in a single or multiple wavelength mode by designing the coupling region to have the proper length (i.e., either in 3dB or WDM operation), and further comprising a transmitter and a detector adjacent a coaxial coupler. The detector of the system is provided with a hole in its center in order to allow the transmitter access to the core waveguide of the coaxial coupler. The coaxial coupler may be formed from a rod in tube structure with a core waveguide extension adjacent the Tx/Rx and an integral pigtail on the opposite side of the coupler.

Abstract: The invention provides a method for producing an optical-fiber coupler with a preset branching ratio. The present invention relates to a method in which part of a plurality of optical fibers are made to closely contact with each other so as to form a coupler. The coupler is heated to thereby obtain a predetermined branching ratio; the flow rate of a gas to be supplied to a heat source is increased/decreased by a quantity proportional to a difference between the drawing speed and a preset drawing speed while predetermined tension is applied to the optical fibers.

Abstract: A process for manufacturing various series of plug-in light bulbs wherein a glass tube used in making a Wedge lamp having an increasing diameter toward one end, inserting two conductive wires and a button rod within this tube integrated with its bottom end by heating, pinching and attaching three filaments to the top portion of the button rod by heating and connecting to the conductive wires with a plurality of tungsten filaments to form a glow portion, inserting a bulb portion over the top end of the tube, then shaping a integral body by heating a lower portion of the tube rod slightly below the bottom end of the button rod, which is fused off by heating, the lower portion of the conductive wires being folded and stuck to the respective outside walls of the bottom end of the tube.

Abstract: A need often arises for micro-optical components, such as optical fibres and couplers, and micromechanical components with complex cross-sections which are different at opposite ends or, for directional couplers, at points along the length of the couplers. In the present invention, a soluble material 38 is added to at least one primary preform 35 to make a secondary preform 37 of circular cross-section. The secondary preform is then drawn to reduce the cross-section of the primary preform as required but the cross-sectional shape of the secondary preform is preserved. The soluble material is then removed and then part of the resulting product is heated and plastically deformed to give the required different ends 39 and 40 or other different cross-sections. In another aspect of the invention two soluble materials are used with different solubilities.

Abstract: A method for manufacturing a fiber type coupler of the present invention by fusing and elongating a plurality of optical fibers is characterized in that a multi-wire optical fiber wire is used as the plurality of optical fibers.

Abstract: A catheter for delivering radiant energy, such as a laser beam, is used in a technique to controllably apply the radiant energy in a patient's body, such as in a blood vessel. The radiant energy is applied in a manner which erodes biological material and may be used to drill through vascular obstructions. The catheter emtis the radiant energy from its distal end in a pattern which defines a relatively small working region in which the energy density level is sufficiently high to remove the biological material. The energy disribution is substantially uniform across the beam. Distally beyond the working region, the energy density of the beam decays sharply so that biological material beyond the working region is not removed. Biological material is removed in very limited layer-like regions and in a manner in which a distally propagated segment of the beam will not have sufficient energy density to puncture the blood bessel wall.

Abstract: Disclosed is a fiber organizing tool having a frame with a channel with narrow raised sidewalls for piercing an adhesive tape to be laid on fibers laid straight in the channel. The optical fibers are arranged in a narrow slot in a member hingedly mounted to the frame.

Abstract: An apparatus for fushion splicing optical fiber with three pairs at clamps; the outermost pair of clamps has one rotatable clamp mechanism that is manually operated and a second rotatable clamp mechanism that is operated by a motor. A rapid fine adjustment of the alignment of the polarization maintaining optical fibers can be made.

Abstract: Disclosed is a method of making a polarization retaining single-mode optical fiber. Longitudinal grooves are formed on opposite sides of a cylindrically-shaped core perform having a glass core surrounded by cladding glass. The core preform is inserted into a glass tube, the tube is shrunk onto the core preform, and the interface between the core preform and the tube is fused to form a solid preform having longitudinal apertures on opposite sides of the core. An etchant gas is flowed through the apertures to enlarge the apertures into holes having a substantially round cross-section. Inserted into each aperture is a stress rod formed of glass having a coefficient of expansion different from that of the cladding glass. The resultant draw blank is drawn to form a single-mode optical fiber having a core that is subjected to a stress-induced birefringence.

Abstract: An apparatus for fusion splicing optical fibers has one rotatable clamp mechanism that is manually operated, a second rotatable clamp mechanism that is operated by a motor and a twist preventing means removably coupled to the apparatus with an arm member. A rapid fine adjustment of the alignment of the polarization maintaining optical fibers can be made.

Abstract: A method for manufacturing a metallic, luminescent screen for a CRT includes the steps of: depositing at least one phosphor layer on an inner surface of a faceplate of a panel, to form the luminescent screen; preheating the panel containing the screen to a temperature in excess of a minimum film-forming temperature; and depositing an aqueous emulsion of at least one acrylic film-forming resin onto a screen and drying said emulsion to form the film. Then, a metallic coating is deposited onto the film and the panel bearing the metallized screen is sealed to a funnel by heating the panel and funnel through a sealing cycle. The sealing cycle has predetermined rates of temperature increase and includes a temperature range within which the film is volatilized. The rate of temperature increase within the volatilization range is less than the rate of temperature increase in other portions of the sealing cycle.

Abstract: A glass-to-glass hermetic sealing technique is disclosed which can be used to splice lengths of glass fibers together. A solid glass preform is inserted into the cavity of a metal component which is then heated to melt the glass. An end of an optical fiber is then advanced into the molten glass and the entire structure cooled to solidify the glass in sealing engagement with the optical fiber end and the metal cavity. The surface of the re-solidified glass may be machined for mating engagement with another component to make a spliced fiber optic connection. The resultant structure has a helium leak rate of less than 1.times.10.sup.-8 cm.sup.3 /sec.

Abstract: When effecting a fusion splice between two optical fibres, end parts of the two fibres are introduced transversely into opposite ends of an open-ended channel in a surface of a rigid elongate support member having at a position intermediate of its ends and in the surface a transversely extending open-ended slot for temporarily accommodating the electrodes by which fusion splicing is to be effected. After fusion splicing of the fibres and withdrawal of the electrodes, any space in the channel not occupied by the fushion spliced fibres and the transversely extending slot are filled with a curable material which is permitted or caused to set. A preformed elongate lid is secured to the surface of the support member 1 and the support member and lid provide permanent protection for the fusion splice.

Abstract: A fused coupler is formed from two twisted optic fibers (2, 3) of fluoride glass by heating them in the slot (18) of a temperature-controlled heater (15) in a shroud (14) containing an oxygen-free atmosphere. The glass of the fibers may be ZBLAN glass in which case the temperature is 323.degree. C..+-.10.degree. C. In an alternative embodiment the shroud is dispensed with and inert gas (nitrogen) is injected into a hole in the slot (18).

Abstract: A method is provided for making a hermetically sealed package for a power semiconductor wafer having substantially entirely silicon materials selected to have coefficients of thermal expansion closely matching that of the power semiconductor wafer. A semiconductor wafer such as a power diode includes a layer of silicon material having first and second device regions on respective sides. An electrically conductive cap and base of silicon are disposed in electrical contact with the first and second regions of the semiconductor device, respectively. An electrically insulative sidewall of silicon glass material surrounds the semiconductor wafer, is spaced from an edge thereof, and is bonded to the cap and base for hermetically sealing the package.

Abstract: Optical interconnectors and methods for optically interconnecting structures, such as printed circuit boards. The optical interconnectors comprise at least two optical fibers having one end embedded in a structure such as a printed circuit board and at least one sleeve for housing termination portions of two optical fibers. The termination portions of the fibers are positioned and secured within the sleeve so that end surfaces of the optical fibers are abutted together. The resulting optical interconnectors have low loss and occupy a small amount of space while maintaining a flat profile.

Abstract: A metehod of manufacturing planar optical waveguides in which a planar optical preform which is stretched to form a planar optical cane with substantially smaller cross-sectional dimensions than the original preform, and in which the optical circuitry pattern is achieved by lithographic techniques. Optical fiber preforms may be inserted in slots in a substrate to form the planar optical preform.

Abstract: The optical waveguide coupler device is formed on two laterally adjacent optical fibers for splitting with wavelength-flattened ratios an incident light intensity into the two fibers. Adjacent sections of the two fibers are fused together and first and second concatenated tapered portions are formed. These two tapered portions are separated by a central optical waveguide portion including two parallel branches of slightly different lengths, each capable of propagating a light signal from either tapered portion to the other. The first and second tapered portions define optical waveguide couplers presenting coupling ratios varying with optical wavelength in accordance with different curves. The different lengths of the two parallel branches of the central portion cause a shift .phi. between the phases of the optical signals propagating through these two branches. The coupling ratios of the tapered portions and the phase shift .phi. are selected to wavelength-flatten the coupling ratios of the coupler device.

Abstract: In the production of an optical waveguide preform, particularly for the production of mono-mode optical waveguides, a tube, or several tubes, of quartz glass are fused onto a crude preform rod of quartz glass. In a known device, the crude preform rod and the quartz glass tube slid over this are clamped at the same end into jaw chucks in the headstock of the glass lathe. Since it happens that optical waveguides that have been drawn from an optical waveguide preform produced with the known device show an inadmissibly high core eccentricity, it is proposed that another jaw chuck be provided in the tailstock for the other end of the tube preform.

Abstract: A fiber optic coupler is formed by providing a glass tube having a longitudinal aperture extending therethrough. Protective coating is removed from a region of a first optical fiber intermediate the ends thereof. Protective coating is removed from an end region of at least one other optical fiber. The coated portion of the first fiber is threaded through the tube until the uncoated region thereof is near the tube end. The size of the aperture is insufficient for simultaneously receiving the coated portions of the first and second fibers in side-by-side relationship at the coated portion of both. The uncoated region of the second fiber is placed adjacent that of the first fiber, and both uncoated regions are simultaneously fed into the tube aperture.

Abstract: A method of producing an optical multi-fibre cable element provided with a secondary sheathing by extruding (1) a loose secondary sheathing (10) around a fibre bundle (9) and providing the fibres with a desired extra length with respect to the secondary sheathing. To avoid variation in fibre length in the production of cable elements the secondary sheathing (10) together with the fibre bundle (9) is twisted (12) around its axis after the extrusion step (1) at least to such an extent that the longitudinal sliding of the fibres with respect to each other is prevented in the twisted fibre bundle and that the stretching of the fibres in the fibre bundle at the step of providing the extra length (3; 18) is kept within the elastic range of the fibres.

Abstract: Signal strength in an optical fiber transmission path is attenuated in one direction to a desired lower level by incorporating a selected length of coreless, undoped fiber of the same diameter into the signal-carrying fiber. On encountering the insert, the beam diameter expands to a pre-selected value at the far end of the insert. The ratio of the beam diameter at this point to the diameter of the adjacent fiber end establishes the attenuation factor. Steps are taught for achieving high consistency in both structural strength of the attenuator as well as the attenuation factor.

Abstract: A flying-type composite magnetic head includes (a) a magnetic core constituted by a pair of core pieces bonded together by a first glass portion, at least one of opposing surfaces of the core pieces being formed with a thin magnetic metal layer; (b) a non-magnetic slider having a slit for receiving the magnetic core; and (c) a second glass portion for fixing the magnetic core in the slit; the first glass portion having a softening point lower than a first bonding temperature by 70.degree. C. or more and a yielding temperature higher than a second bonding temperature, and the second glass portion having a softening point lower than a second bonding temperature by 70.degree. C. or more. The first bonding temperature T.sub.1 (.degree.C.) for forming the first glass portion satisfies the following relation:T.sub.1 .ltoreq.aW+b,wherein W is a thickness (.mu.m) of the thin magnetic metal layer, a is between -25 and -15 and b is between 720 and 770, and a second bonding temperature T.sub.

Abstract: A method disclosure for making an economical fiber coupler including providing a glass tube having first and second end portions and a midregion, and a longitudinal aperture extending through it. Two suitably prepared glass optical fibers, each having a core and cladding, are disposed within the longitudinal aperture, the fibers extending beyond each end of the tube. The fibers are glued to each end portion. The midregion of the tube is evacuated, heated, collapsed about the fibers, and drawn to reduce the diameter of the resulting composite.

Abstract: An optical fiber star amplifier coupler and a fabricating method thereof are disclosed, wherein at least two signal fibers and at least one pump fiber are twisted together and by means of flame fusion method, the twisted portion are fused to form a biconical tapered portion which is then split at the midpoint thereof, a section Er-doped amplifier fiber being then spliced between the two fused tapered ends and the pump fibers being grouped together and put into an N.times.M array connector to mate with a pump light source, the signal fibers being respectively connected to input ports and output ports, the pump light source emitting pump light with specific wavelength and coupling the pump light into the amplifier fiber through the pump fiber, the amplifier fiber then converting the pump light into a radiation with the same wavelength and phase as the signal light which is guided in through the signal fibers so as to amplify the signal light.

Abstract: A ferrule having an optical fiber connected thereto and a spherical lens are fixed in a cylindrical lens holder to form a fiber collimator. The thickness of a cylindrical wall of the lens holder is made smaller at a spherical lens receiving portion than the other portion and the cylindrical lens holder is fixed to a substrate by welding. A pair of such fiber collimators are provided in an opposing relationship to each other on the substrate, and an optical function element is disposed between the opposing fiber collimators to form an optical device. By provision of a light path changing over mechanism as such optical function element, an optical switch of a small size having a high performance can be provided.

Abstract: Fiber composites, particularly for imaging, easy to manufacture even with great cross-sectional area, in which fibers are in a peak-to-valley relation with abutting pairs of fibers throughout.

Abstract: An arrangement for effectively fusing together two optical fibers. Many fibers currently have a carbon-based coating applied to the bare fiber, with the coating being surrounded by a plastic jacket. It has been difficult to fuse the two fibers together due to the coating. The present invention provides an effective method for removing the coating using a rapid and high temperature electric discharge. The removal of the coating allows a better connection of the two fibers with the connection having a low transmission loss.

Abstract: A method is provided for making a hermetically sealed package for a power semiconductor wafer with silicon materials selected to have coefficients of thermal expansion closely matching that of the power semiconductor water. A semiconductor wafer such as a power diode has a layer of silicon material having first and second device regions on respective sides thereof. An electrically conductive cap and base of silicon are disposed in electrical contact with the first and second regions of the semiconductor device, respectively. An electrically insulative sidewall of silicon glass material surrounds the semiconductor wafer, is spaced from the edge, and is bonded to the cap and base for hermetically sealing the package. The glass sidewall is directly bonded to the base by bringing the base and sidewall into intimate contact under a slight pressure and heating to a temperature at which the glass wets the silicon base, holding this temperature for a time and then cooling the composite to complete the bond.

Abstract: A optical fiber coupler manufacturing device is disclosed for the manufacture of fused-elongated type optical fiber couplers. The disclosed invention provides an optical fiber coupler manufacturing device having a chassis, a pair of movable stands provided within the chassis forming a space therebetween, optical fiber mounting units for mounting and fixing two or more component optical fibers on the above mentioned pair of movable stands, and a drive mechanism whereby the pair of movable stands can be driven back and forth in a direction parallel to the longitudinal axes of the component optical fibers.

Abstract: A process for fusion-splicing hermetically coated optical fibers each of which comprises an inorganic coating, an optical fiber glass and optionally an organic coating, which process comprises removing the inorganic coating, fusion-splicing the fibers and then coating a portion where the inorganic coating is removed with an inorganic material.

Abstract: A fiber optic coupler is formed by assembling a coupler preform having two concentric glass tubes having a gap between them. The shape and/or size of the inner tube relative to the shape and/or size of the outer tube is such that a plurality of output optical fibers can be equally spaced in the gap. An input optical fiber is disposed in an aperture in the inner tube. The input and output fibers extend through the midregion of the resultant coupler preform. The midregion is heated to collapse it about the fibers, and the central portion of the midregion is stretched to reduce the diameter over a predetermined length.

Abstract: An asymmetric multi-mode fibre optic coupler is assembled from two or more multi-mode optical fibres of different core and cladding diameters but substantially equal cladding refractive indices. The fibres are selected so as to have substantially equal effective refractive indices for their respective highest-order cladding modes, at least in the fabricated coupler.

Abstract: Fusion-splicing polarization maintaining optical fibers includes the steps of: observing a polarization maintaining optical fiber containing stress applying members in a predetermined direction, using a core direct monitoring method to obtain a reference image; aligning the pair of polarization maintaining optical fibers to be fusion-spliced; automatically rotating the fibers while observing them with the core direct monitoring method until the images of the pair coincide with the reference image; and fusion splicing the pair together.

Abstract: A thermal device, such as a glow discharge starter, includes an hermetically sealed envelope containing an ionizable medium, a bimetallic electrode having a bimetallic element associated therewith, and a counter electrode. A mount sealed in the envelope includes a glass stem having a disk-shaped portion extending substantially across the envelope and a longitudinally-extending planar portion. The transverse portion of the mount assists in centering the electrodes within the envelope and preventing the bimetallic element from oxidizing during the manufacturing process when the mount is sealed to the envelope. Preferably, the transverse portion is disk-shaped having a radius within the range of from about 89 to 93 percent of the internal radius of the envelope. The defined thickness of the planar portion of the glass stem allows rapid transfer of heat during sealing so that the planar portion can effectively be sealed to the envelope without developing seal cracks.

Abstract: In a method of making an optical fiber coupler through heat elongation of optical fibers, the performance of the coupled optical fibers is measured after the optical fibers are heat elongated at least once, and based on the measured elongation length and the performance of the coupled optical fibers, a functional equation representing their relationship is determined by approximate calculation. The functional equation is used to calculate an elongation length which provides the intended performance of the coupled optical fibers, and then the optical fibers are heat elongated to the calculated length.

Abstract: A fiber optic coupler has at least two optical fibers each having a core with a cladding material disposed thereabout. The fibers, in a limited length coupling region, have the cladding material removed and the core exposed, the thickness of the cladding material increasing is smooth transition from immediately adjacent the exposed core in the limited length coupling region. The fibers in the limited length coupling region are joined by coalescing. In preferred embodiments, in the limited length coupling region, a portion of the core is removed, the core diameter in the coupling region being less than the core diameter in regions adjacent thereto, the outer diameter of the core decreasing in smooth transition from immediately adjacent the cladding material. A method and product of forming these couplers or others with the fibers in crossed relationship are also described.

Abstract: An electronic device package is made by first making in a stencil member (11) an opening (12) in the shape of a closed loop that surrounds an inner portion (13) of the stencil member. The closed loop is a continuous opening except for a plurality of web members (15), each of which extends across the opening to secure the inner stencil portion to the remainder of the stencil member. A glass slurry (7) is forced through the opening of the stencil member onto a first substrate (18) so as to form on the substrate a substantially closed loop of glass slurry, which is thereafter glazed to form a glass loop (32) bonded to the first substrate. The first substrate is used as cover plate and placed over a second substrate (24) containing an electronic device (23) such that the glass loop surrounds the electronic device and contacts the second substrate along its entire length. The glass is heated sufficiently to soften it and cause it to bond to the second substrate as well as the first substrate.

Abstract: A method for making an airtight and highly precise fitting for a spherical lens in a cylindrical opening within a metallic body. The spherical lens is axially pressed into the opening where the diameter of the opening is smaller than the diameter of the spherical lens. The diameter of the cylindrical opening is designed so that the spherical lens plastically deforms the metallic body when it is inserted into the opening.

Abstract: In a method for the production of cylindrically symmetric bodies with given radial gradient of the material properties, for example of the refractive index, at least two rod-shaped molded bodies consisting of materials with different properties are joined in parallel and, following lowering of the viscosity of both materials, the bodies are twisted many times in a spiral around a longitudinal axis, such that a desired radial gradient of the material properties arises, where metallic, semiconducting, or insulating materials may be used, and the viscosity is varied through changing the temperature or adding or removing a solvent.

Abstract: An overclad fiber optic coupler is formed from a coupler preform including a glass tube having a longitudinal aperture. The aperture is formed of a plurality of similarly shaped side walls, each of which includes a longitudinally extending, inwardly projecting protrusions. The region between each two adjacent protrusions constitutes a corner region. Disposed within the aperture are at least a portion of each of a plurality of glass optical fibers, one fiber being situated in each corner region. The midregion of the tube is collapsed onto the fibers, the protrusions maintaining the fibers in their relative positions. At least a portion of the midregion is stretched to reduce the tube midregion diameter.