JP4801886B2 - Devices and methods for reducing glass flow during the manufacture of microchannel plates - Google Patents

Description

(Field of Invention)
The present invention relates to a microchannel plate for use with an image amplifier, and more particularly to an arrangement for reducing glass flow during the manufacture of the plate.

(Background of the Invention)
The microchannel plate is used as an electron multiplier in an optical amplifier. They are thin glass plates that have an array of channels extending through them and are positioned between a photocathode and a phosphor screen. Incoming electrons from the photocathode enter the input side of the microchannel plate and strike the channel wall. When a voltage is applied across the microchannel plate, these incoming potentials, or primary electrons, are amplified and produce secondary electrons. These secondary electrons then exit the channel at the back end of the microchannel plate and are used to create an image on the phosphor screen.

  In general, the fabrication of the microchannel plate begins with a fiber drawing process. An etchable core rod is drawn in a non-etchable silicate tube to form a round fiber composed of the core rod and the cladding layer. These fibers are then bundled and drawn into an equilateral hexagonal shaped preform known as a bundle of multiple fibers. Each multi-fiber bundle may include more than 10,000 core rod sites. These hexagonal multi-fiber bundles are packed in a glass packing tube, and a non-etchable hexagonal support rod is packed between this bundle and the cylindrical wall and fused together in a heating process To form a solid boule of rim glass and optical fiber. The next process step requires a glass boule splicing step, a chamfering step, and a polishing step. The plate is then etched to remove the core rod in the plate, thus forming a channel, each of which is defined by a cladding layer. These channels are then activated and metallized.

  Because of the geometry involved in the process described above, the distance between the cylindrical inner wall of the glass packing tube 22 and the support rod 24 varies when the fibers are fused together. See Figure 1 of the drawings. In other words, the space (or open space) of the gap between the outermost fiber and the inner surface of the glass packing tube is not constant. This variation means that the inner wall of the glass tube 22 contacts several rods 24 rather than others during the fusion operation. This time-dependent fiber contact shifts the fiber bundle 16 and their individual fibers in the packing scheme during the time that occurs during the fusion operation. This fiber shift moves the core rods in these bundles from the position established by each prior to the start of the fusion operation. The movement of fibers that are closer together can lead to the loss of channel walls after the etching process. This is because there is not enough cladding glass to form walls between the channels. These lost channel walls can lead to any number of defects such as ion barrier or film emission points, reduced structural integrity and rupture.

(Summary of the Invention)
The present invention includes a hollow packing tube formed from generally non-etchable glass for use in making microchannel plates. The packing tube has a plurality of flat inner surfaces. Each surface is substantially flat and extends substantially parallel to the long axis of the tube.

  In another aspect, the invention comprises a plurality of optical fibers, each of which is formed from a core formed from an etchable material and a cladding layer formed from a non-etchable material, and a non-etchable material. A boule having a plurality of support rods. The fibers and rods are placed in a glass packing tube, and the rods are placed between the fibers and the flat inner surface of the packing tube.

  In yet another aspect, the present invention includes a method of forming a microchannel plate. The method includes providing a bundle of fibers having an etchable core surrounded by a non-etchable cladding, packing the fibers into a glass packing tube having a plurality of flat inner surfaces, the fibers and the fibers Positioning a plurality of support rods between the flat inner surface of the packing tube to form a packed boule and fusing the packed boule to a solid boule.

  In particular, the present invention relates to a boule for use in making a microchannel plate, the boule being a hollow glass tube formed from non-etchable glass having a plurality of flat inner surfaces, Each surface may comprise a tube that is substantially planar and extends substantially parallel to the long axis of the tube.

  The boule may further comprise a plurality of optical fibers, each of the optical fibers comprising a cladding layer formed from a non-etchable material and a core formed from an etchable material, and the flat inner surface and the optical fiber There may be a plurality of support rods formed from non-etchable material located between the two.

  The glass tube may have at least 8 flat inner surfaces.

  The glass tube may have 12 flat inner surfaces.

  The width of the flat surface can vary.

  The width of each of the first plurality of flat surfaces has a first dimension, and the width of each of the second plurality of flat surfaces has a second dimension that is different from the first width. Can do.

  In one embodiment, the first dimension is smaller than the second dimension.

  The fiber, rod and glass tube can be fused together.

  The support rod may have a cross-sectional shape including a flat surface for engaging the flat inner surface of the tube.

  In one aspect, the present invention also relates to a microchannel plate formed from the boule described above.

  The invention also relates to a method of forming a microchannel plate, the method providing a bundle of fibers, each fiber having an etchable core surrounded by a non-etchable cladding; Packing a plurality of the bundles into a hollow glass tube formed of a non-etchable material and having a plurality of flat inner surfaces; positioning a plurality of support rods between the fibers and the flat inner surfaces Forming a packed boule; and fusing the fiber, glass tube and support rod.

  The glass tube may have at least 8 flat inner surfaces.

  The glass tube may have 12 flat inner surfaces.

  The width of the flat surface can vary.

  The width of each of the first plurality of flat surfaces has a first dimension, and the width of each of the second plurality of flat surfaces has a second dimension that is different from the first width. Can do.

  The first dimension may be smaller than the second dimension.

  The support rod has a cross-sectional shape that includes a flat surface, and wherein at least some of the flat surfaces of the support rod can engage the flat inner surface of the tube.

  The present invention also relates to a microchannel plate formed by the above method.

  The invention may be better understood by reference to the following detailed description in conjunction with the accompanying drawings.

  A comparison between the prior art boule open space 300 shown in FIG. 1 and the open space seen in FIG. 5 shows a large reduction in open area. This reduction is easily over 50% when compared to the prior art boule. Such a reduction in open space is important. This is because it reduces the glass flow during the fusion process. Any level of glass flow moves the core rod within each bundle of fibers in the boule. This movement of the core rod has the ability to reduce the cladding dimension between each core site, as discussed above. If the reduction in cladding glass thickness between the two sites is too great, then this cladding glass may be completely eliminated during the etching process. The absence of any cladding glass between the two core sites will cause the channel walls in the plate to disappear, which damages the performance of the plate. Thus, a reduction in glass flow associated with a reduction in open space increases the uniformity of the core within each hexagonal fiber bundle in the boule. This increase in uniformity produces a superior plate when compared to prior art packing tubes formed with rounded inner walls.

(Detailed description of the invention)
The present invention relates to a glass packing tube 550 used to form a boule, and the tube is configured to reduce the amount of glass flow when fusing the boule during the manufacture of a microchannel plate. . More particularly, this packing tube 550 according to the present invention is made of non-etchable glass and has a plurality of flat inner surfaces 501 through 512. These flat surfaces are planar surfaces and allow the packing of fiber bundles 16 and support rods 24 within this glass packing tube 550, while the outermost support rods and packing tube's Maintain a minimum open space between the inner surface (when compared to the round inner surface). This minimization of open space is advantageous because it reduces the glass flow during the fusing process to form a fused boule.

  FIG. 3 shows a starting fiber 10 that is used to manufacture a microchannel plate for use as an electron multiplier. The fiber 10 includes a glass core 12 and a glass cladding 14 surrounding the core. The core 12 is made from a material that can be etched in a suitable etching solution so that the core can then be removed. The glass cladding 14 is made of glass having a softening point substantially the same as that of the glass core 2. The glass material of the cladding 14 differs from that of the core 12 in that it has a higher lead content that renders it unetchable under the conditions used to etch the core material. Thus, this cladding 14 remains after etching the glass core 12 and becomes the boundary of the remaining channel 32.

  The optical fiber 10 can be formed in the following manner. An etchable glass rod and a cladding tube that coaxially surround the rod are suspended vertically in a draw machine incorporating a zone furnace. The furnace temperature is increased to the glass softening point. The rod and tube are fused together and pulled into a single fiber 10. This fiber 10 is fed into a ductile mechanism where the speed is adjusted until the desired fiber diameter is achieved. The fiber 10 is then cut to a shorter length.

  Next, thousands of cut-length single fibers 10 are stacked in a graphite mold and heated to form a multi-fiber bundle 16 as shown in FIG. The cutting length is fused in a hexagonal form. This hexagonal form provides a better stacking arrangement.

  The multiple fiber or bundle 16 includes thousands of single fibers 10, each having a core 12 and a cladding 14 as discussed above. This bundle 16 is then suspended vertically in the draw-through and pulled to reduce the fiber diameter again while still maintaining the hexagonal form of the individual fibers. This bundle 16 can then be cut into shorter lengths.

  Next, a number of cut multi-fiber bundles 16 are packed into an accurate bore glass packing tube 550 as shown in FIG. The packing tube 550 is made of a glass material similar to the glass cladding 14 and it is also non-etchable when the glass core 12 is etched away. The glass packing tube 550 has an expansion coefficient that is approximately the same as that of the fiber 10. The lead glass packing tube 550 eventually becomes the edge of the solid rim of the microchannel plate as shown in FIG.

  In order to protect the fibers 10 of each bundle 16 during processing to form the microchannel plate, a plurality of support structures are provided through the tube 512 to provide a glass packing tube between the bundle 16 and the flat inner surface 501. 550 is positioned. This support structure is not etched under the etching conditions later used to etch the core 12, and can take the form of a hexagonal rod of any material having the strength and ability necessary to fuse with the glass fiber. . Such a support structure is shown as a support rod 24. The support rod can be a single optical fiber or preferably a bundle of any number of fibers up to several hundred. The final geometric shape and outer diameter of one support rod is substantially the same as that of bundle 16. Thus, the assembly formed by fiber 10, support rod 24 and packing tube 550 is a packed boule 500 as shown in FIG.

  This boule 500 is then suspended in the furnace and connected to a vacuum system. The furnace temperature is increased to the softening point of the bundle 16 and support rod 24 materials. The bundles 16 fuse together and the support rod 24 fuses to its adjacent bundle 16 and to the inner surface of the packing tube 550.

  During this heating step, the support rod 24 acts as a cushion between the inner surface of the glass packing tube 550 and the bundle 16. This cushioning provides structural support so that the individual fibers 10 do not deform during heat treatment. Furthermore, this cushioning effect of the support fiber 24 allows higher heat to be used during fusion without causing deformation of the fiber 10.

  The fused boule is then sliced into thin cross-section plates. This flat end surface is sharpened and polished. To form the channel 32, the core 12 of the fiber 10 is removed by etching with dilute hydrochloric acid. After etching, this high lead content glass cladding 14 remains and forms a channel 32. The support rod 24 also remains solid and therefore provides a good transition from the solid rim of the glass packing tube 550 to the microchannel 32.

  After etching, the plates are placed in an atmosphere of hydrogen gas, thereby reducing the lead oxide in the unetched lead glass and making the cladding electrons radioactive. In this way, a semiconductor layer is formed in each of the glass claddings 14 and this layer extends inwardly from the surface connected to each microchannel 32.

  A thin metal layer is applied as an electrical contact to each of the flat end surfaces of the microchannel plate, which is an entrance for electrons when an electric field is established across the microchannel plate by the metallized contacts. Provides a route and exit route.

  FIG. 5 shows a cross-sectional view of a packed boule 500 having a packing tube 550 formed with a plurality of flat or planar inner surfaces 501-512 (in the case of FIG. The number is twelve). By being flat, it is that each surface forms a plane and each plane, ie, each surface, extends in the longitudinal direction and parallel to the central axis 600 of the tube 550 and the radius of the outer wall of the tube It is almost perpendicular to. These inner surfaces can be provided either by machining or mandrel shrinking (on the forming mandrel) of the inner surface of the glass packing tube. Such techniques for forming such glass tubes are known to those skilled in the art. The number of sides can vary and depends on the size and shape of the fused boule. In the embodiments disclosed herein in which the boule has a generally annular cross-section, the tube 550 preferably has at least 8 flat surfaces, and preferably 12 such surfaces.

  Because of the inner surfaces 501-512, the support rod 24 can be pushed into the tube 550 either withstanding contact with the inner surface or in close proximity to it. In a preferred embodiment where the rod 24 has a hexagonal cross section, the flat surface of at least some of the rods rests on some of the flat inner surfaces 501-512 of the packing tube 550 and some highest of the other rods. The point is applied to a flat surface. In this way, the open space between the rod 24 and the tube 550 is mainly in the vicinity of the highest point between the flat inner surfaces 501-512. Furthermore, it is often preferred for certain bundle dimensions that the end faces or surfaces of the multi-sided glass packing tube have different widths (dimensions across the long axis of the tube 550) to maximize the reduction in open space. FIG. 5 illustrates this feature. Variation in the width of the flat surface depends on the size and shape of the boule that is formed. In the embodiments disclosed herein, two different widths are disclosed. The width surfaces 501, 503, 505, 507, 509 and 511 are the same dimensions and are smaller than the widths of the surfaces 502, 504, 506, 508, 510 and 512, and all of this latter group are the same dimensions. . Different modifications may be used for other desired boule shapes.

  A comparison between the prior art boule open space 300 shown in FIG. 1 and the open space seen in FIG. 5 shows a large reduction in open area. This reduction is easily over 50% when compared to the prior art boule. Such a reduction in open space is important. This is because it reduces the glass flow during the fusion process. Any level of glass flow moves the core rod within each bundle of fibers in the boule. This movement of the core rod has the ability to reduce the cladding dimension between each core site, as discussed above. If the reduction in cladding glass thickness between the two sites is too great, then this cladding glass may be completely eliminated during the etching process. The absence of any cladding glass between the two core sites will cause the channel walls in the plate to disappear, which damages the performance of the plate. Thus, a reduction in glass flow associated with a reduction in open space increases the uniformity of the core within each hexagonal fiber bundle in the boule. This increase in uniformity produces a superior plate when compared to prior art packing tubes formed with rounded inner walls.

  Although the invention is described and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims without departing from the invention. Furthermore, the use of a packing tube shaped with an inner surface at the end face can be used for any other application that requires a bundle of fibers in the outer tube where movement of the inner fibers is not desired.

  A microchannel plate for use as an electron multiplier in an optical amplifier and a method for manufacturing the same are provided. This manufacturing method may be used for any other application that uses a packing tube shaped with an inner surface at the end face and requires a bundle of fibers in the outer tube where movement of the inner fibers is not desired.

FIG. 1 is a cross-sectional view of a packed boule according to the prior art. FIG. 2 is a partially cutaway view of a microchannel plate. FIG. 3 is a partial view of a fiber used by fabricating a microchannel plate. FIG. 4 is a partial view of the bundle shown in FIG. 1 for use in fabricating a microchannel plate. FIG. 5 is a cross-sectional view of a packed boule according to the present invention.

Explanation of symbols

10 Fiber 12 Glass core 14
14 Glass cladding 16 Fiber bundle 24 Support rod 500 Boule 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512 Inner surface 550 Packing tube

Claims (19)

A boule for use in making microchannel plates:
A hollow glass tube formed of non-etchable glass having a plurality of flat inner surfaces, each surface being substantially planar and extending substantially parallel to the long axis of the tube ;
A plurality of optical fibers, each of which is located between a cladding layer formed from a non-etchable material and a core formed from an etchable material, and between the planar inner surface and the optical fiber Comprising a plurality of support rods formed from a non-etchable material ;
It said plurality of support rods completely surrounds the optical fiber, and the cross-sectional dimensions of the support rod to be the same as the optical fiber is substantially a Boolean. The boule of claim 1, wherein the glass tube has at least eight flat inner surfaces. The boule of claim 1, wherein the glass tube has twelve flat inner surfaces. The boule of claim 1, wherein the width of the flat surface varies. The width of each of the first plurality of flat surfaces has a first dimension, and the width of each of the second plurality of flat surfaces has a second dimension different from the first width; The boule of claim 1. The boule of claim 5 , wherein the first dimension is less than the second dimension. The boule of claim 1 , wherein the fiber, rod and glass tube are fused together. The boule of claim 1 , wherein the support rod has a cross-sectional shape including a flat surface for engaging a flat inner surface of the tube. A microchannel plate formed from the boule of claim 7 . A method of forming a microchannel plate comprising:
Providing a bundle of fibers, each fiber having an etchable core surrounded by a non-etchable cladding;
Packing the plurality of bundles into a hollow glass tube formed of a non-etchable material and having a plurality of flat inner surfaces;
Positioning a plurality of support rods formed from etched non material between said fiber and said plurality of flat inner surfaces, comprising: forming a packed boule, the supporting rod and bundle are substantially And having the same dimensions ; and fusing the fiber, glass tube and support rod. The method of claim 10 , wherein the glass tube has at least eight flat inner surfaces. The method of claim 10 , wherein the glass tube has 12 flat inner surfaces. The method of claim 10 , wherein a width of the flat surface varies. The width of each of the first plurality of flat surfaces has a first dimension, and the width of each of the second plurality of flat surfaces has a second dimension different from the first width; The method of claim 10 . The method of claim 14 , wherein the first dimension is less than the second dimension. Wherein the support rod has a cross-sectional shape including a flat surface, and wherein at least some of the flat surface of the support rod, engages a flat inner surface of the tube, according to claim 10 the method of. A microchannel plate formed by the method according to claim 10 . The boule of claim 1, wherein the cross-sectional geometry of the support rod and the optical fiber is hexagonal. The boule of claim 18, wherein a hexagonal cross section of the support rod includes an apex that supports the flat surface.

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