Abstract: A method of producing a diffraction grating master which comprises exposing a plurality of reduced first grating patterns on a light sensitive layer in conformance with a predetermined code; processing the light sensitive layer to produce first gratings therein; exposing a plurality of reduced second grating patterns on the light sensitive layer (superimposed on the first gratings) and repeating the processing step to produce the second gratings; vacuum depositing a layer of silver on the superimposed first and second gratings; electroplating a layer of nickel on the silver layer on the superimposed gratings; separating the resulting nickel-silver layer from the light sensitive layer; and reinforcing the nickel-silver layer (formed in the pattern of the first and second gratings) for use as an embossing master. A special electroplating fixture used in the electroplating step insures that the nickel layer being deposited lies flat without "peeling".

Abstract: A method of producing a diffraction grating master which comprises exposing a plurality of reduced first grating patterns on a light sensitive layer in conformance with a predetermined code; processing the light sensitive layer to produce first gratings therein; exposing a plurality of reduced second grating patterns on the light sensitive layer (superimposed on the first gratings) and repeating the processing step to produce the second gratings; vacuum depositing a layer of silver on the superimposed first and second gratings; electroplating a layer of nickel on the silver layer on the superimposed gratings; separating the resulting nickel-silver layer from the light sensitive layer; and reinforcing the nickel-silver layer (formed in the pattern of the first and second gratings) for use as an embossing master. A special electroplating fixture used in the electroplating step insures that the nickel layer being deposited lies flat without "peeling".

Abstract: An optical identification system including a reader for reading superimposed optical gratings on a record medium in which the reader has a grating plane and a radiant energy source for directing energy therefrom along an optical axis to the grating plane. Detectors are positioned in the reader to receive diffracted beams from the optical gratings on a record medium positioned at the grating plane. The reader also includes an optical imaging system having a concave lens for directing a zero order reflected beam which is displaced from the optical axis back to the grating plane to enable the resulting beams diffracted from the optical gratings to be received at the detectors whenever a record medium is displaced slightly from the grating plane.