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High Contrast Optical Bandpass Filter

IP.com Disclosure Number: IPCOM000079609D
Original Publication Date: 1973-Aug-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Murphy, HM: AUTHOR

Abstract

The light filter 10, Fig. 1, provides high contrast for viewing a cathode-ray tube (CRT) image display in high and low ambients, such as in cockpit of an aircraft. For certain phosphors, light filter 10 also provides high contrast for night viewing by placing an aviation red filter, not shown, in front of the device 10.

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High Contrast Optical Bandpass Filter

The light filter 10, Fig. 1, provides high contrast for viewing a cathode-ray tube (CRT) image display in high and low ambients, such as in cockpit of an aircraft. For certain phosphors, light filter 10 also provides high contrast for night viewing by placing an aviation red filter, not shown, in front of the device 10.

The first layer 1 has an antireflectance coating la on its outer surface to reduce spectral reflections. Layer 1 is a neutral density glass.

The second layer 2 is an epoxy type material used as a narrow bandpass absorption filter. For example, the bandpass is 50 nanometers wide at the midpoint of its spectral content waveform characteristic, and the peak is matched closely to the peak of the phosphor spectral-energy distribution of the CRT.

The third layer 3 has an electromagnetic interference (EMI) coating 3a on the side which faces the CRT. Coating 3a is a transparent dielectric,

Layer 3 is also a neutral density filter or glass. Preferably, it is a neutral density circular polarizer. The neutral density circular polarizer provides more enhancement than a neutral density filter.

A uniform density distribution is provided on the three layers 1, 2, 3. For example, in one such filter, the spectral content characteristics A, B, C for layers 1, 2, 3, respectively, are shown in Fig. 2 and have, respectively, peak transmission levels of 40%, 60%, and 30% which result in a product or peak transmission level for the...