Darrell F Hatch

US Patent:

56026560, Feb 11, 1997

Filed:

Dec 9, 1994

Appl. No.:

8/353576

Inventors:

John E. Wreede - Azusa CA
Richard B. Upper - Sherman Oaks CA
Darrell F. Hatch - Sedro Woolley WA
Lane W. Cosner - Cave Junction OR
Stephen T. Babbitt - Redondo Beach CA

Assignee:

Hughes Electronics - Los Angeles CA

International Classification:

G03H 102

US Classification:

359 3

Abstract:

Method and apparatus for monitoring wavelength shift in a holographic light protection filter to determine if the hologram has been damaged by moisture. The hologram is provided with first, second and third areas. The first area is an extra moisture protected area covered by a moisture resistant material. The second area is adjacent to the first area and is recorded at a different wavelength than the bulk of the hologram. The third area is the remainder of the hologram. The user compares light reflections at these specific areas of the hologram and observes color variations to determine if the hologram has been damaged by moisture. In another embodiment, scribe lines are drawn in the hologram through the three areas. The user detects moisture damage by observing the apparent displacement of these scribe lines in the three areas when viewed through a diffraction grating.