Optical waveguides – Optical fiber bundle – Fiber bundle plate
Reexamination Certificate
1999-10-06
2001-10-30
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical fiber bundle
Fiber bundle plate
Reexamination Certificate
active
06311001
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microchannel plates for use in image intensifier tubes, and in particular, to a microchannel plate having microchannels with funneled openings produced by partially removing interface layers defined by cores and clad layers of fibers which form the microchannel plate.
BACKGROUND OF THE INVENTION
Image intensifier tubes are used in night/low light vision applications to amplify ambient light into a useful image. A typical image intensifier tube is a vacuum device, roughly cylindrical in shape, that generally includes a body, photocathode and faceplate, microchannel plate (MCP), and output optic and phosphor screen. Incoming photons are focused on the glass faceplate by external optics, and strike the photocathode which is bonded to the inside surface of the faceplate. The photocathode or cathode converts the photons to electrons, which are accelerated toward the input side or electron-receiving face of the MCP by an electric field. The MCP has many microchannels, each of which functions as an independent electron amplifier, and roughly corresponds to a pixel of a CRT. The amplified electron stream emanating from the output side or electron-discharge face of the MCP excites the phosphor screen and the resulting visible image is passed through the output optics to any additional external optics. The body holds these components in precise alignment, provides electrical connections, and also forms the vacuum envelope.
Conventional MCPs are formed from the fusion of a large number of glass fibers, each having an acid etchable glass core and one or more acid-resistant glass cladding layers, into a solid rod or boule. Individual plates are sliced transversely from the boule, polished, and chemically etched. The MCPs are then subjected first to a hydrochloric acid bath that removes the acid etchable core rod (decore), followed by a hot sodium hydroxide bath that removes mobile alkali metal ions from the glass cladding.
The microchannels of a MCP are typically cylindrical in shape and inclined 1-10° from normal to the MCP surface, The ratio of the combined channel area to the overall active area of the MCP is known as open-area-ratio (OAR). The ratio of the core rod area to overall area prior to acid etch is approximately 45%.
Acid etching (decore) of the MCP increases OAR to 55%, and the alkaline (e.g. sodium hydroxide) leach step further increases the OAR to approximately 60% by alkali removal of acid-resistant cladding.
Unfortunately, the output image of conventional MCPs is degraded, i.e., the output image is not a perfect replica of the input image. Degradation of the output image is caused by a number of factors. For example, a photoelectron released from the photocathode may not fall into one of the microchannels of a conventional MCP but, will impact the flat face of the MCP in a region between the openings of the microchannels. Electrons that hit the flat face are likely to be deflected or bounce back toward the photocathode before being directed back to the MCP by the electrostatic field. These bounced photoelectrons produce a number of secondary electrons from a part of the MCP that is not aligned with the proper location of photocathode generation. Such an alignment problem results in both decreased signal-to-noise ratio, and distortion of the image produced by the image intensifier, i.e., halos in the output image. At other times the errant electron is simply absorbed by the face of the plate and is not further amplified, thus reducing the signal-to-noise ratio.
One solution to this problem is to increase the open-area ratio by using fibers with thinner acid resistant cladding layers relative to the acid soluble cores. However, a MCP having parallel walls is limited to an open area ratio of approximately 65% so that 1) sufficient glass remains for structural integrity, and 2) no deleterious electric field effects appear. These latter electric field effects arc induced by spike structures resulting from close packed, thin clad fibers after acid etching.
Accordingly, there remains a need for an improved MCP which overcomes the disadvantages of conventional MCPs.
SUMMARY OF THE INVENTION
A method of making a microchannel plate having a plurality of microchannels with funnel-shaped openings, the microchannel plate used as an electron multiplier in an image intensifier tube. The method comprises providing a plurality of glass fibers each having an acid etchable core, an acid resistant cladding, and an interface therebetween, and forming the glass fibers into a thin plate of glass. The plate is first treated with an alkaline material having an affinity for the acid resistant cladding to etch the cladding at the interface to a pre-determined depth. The plate is then treated in an acid solution for a predetermined time and temperature to form a plurality of microchannels in the plate, the microchannels having funnel-shaped openings.
Further, a microchannel plate having a plurality of microchannels with funnel-shaped openings made according to the above method.
REFERENCES:
patent: 4737013 (1988-04-01), Wilcox
patent: 5493169 (1996-02-01), Pierle et al.
patent: 5776538 (1998-07-01), Pierle et al.
J.R. Horton, et al., Characteristics and Applications of Advanced Technology Microchannel Plates, Sociedty of Photo-Optical Instrumentation Engineers, vol. 1306, 1990, pp. 169-178.
Martin J. Needham, Microchannel Plates Advance Night-Viewing Technology, Electronics—The International Magazine of Electronics Technology, vol. 46, No. 20, Sep. 27, 1973, pp. 117-124.
Connelly-Cushwa Michelle R.
Duane Morris LLP
LTT Manufacturing Enterprises
Plevy Arthur L.
Ullah Akm E.
LandOfFree
Microchannel plate having microchannels with funneled... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Microchannel plate having microchannels with funneled..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Microchannel plate having microchannels with funneled... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2617720