Abstract: Prior to the production of microlenses (29) by the reactive ion etch technique, a pattern of notches (25) is formed in a second surface of a substrate (11) opposite a first surface on which the microlenses (29) are to be formed. Reactive ion etching of the first surface to produce the microlenses is sufficiently deep to reach the pattern of notches, thereby to separate the substrate. The array of notches may define, for example, an array of first areas (26) on the second surface, each area being surrounded by a notch. Photoresist elements (28) are then each located on an area of the first surface corresponding to a first area of the second surface, so that the separation separates the substrate into a plurality of segments (26) each containing only one of the microlenses (29). The notches can be made such that each of the segments (26) is cylindrical so that each of the microlenses formed from the substrate has a circular outer periphery.

Abstract: During a reactive ion etching process (FIG. 5) for making lens elements (15, FIG. 4) in a silica substrate (12), the gas constituency in the reactive ion etch chamber is changed to adjust the curvature of lens elements formed in the silica substrate and to reduce the aberrations of such lens elements. For example, two gases, CHF.sub.3 and oxygen may be supplied to the reactive ion etch chamber and, during the reactive ion etch process, the proportion of oxygen is significantly reduced, which reduces the aberrations of the lens elements formed by the process.

Abstract: Invention provides optical correlation apparatus comprised of optical means producing a light image of the mailpiece including the address information, holographic filter means receiving the optical means light image and producing a filtered light image correlated to an address information reference pattern, detector means receiving the holographic filter means filtered light image and producing an output electronic signal which contains the degree of correlation of the mailpiece address information to the address information reference pattern, and signal processor means receiving the detector means output electronic signal and producing an address location signal based on a high degree of correlation of the mailpiece address information to the address information reference pattern.