Abstract: A position encoder including a holographically recorded, single-frequency, phase grating. When this phase grating is illuminated by a spatially coherent light source, it acts as a basic common path interferometer and constitutes a highly efficient source of high contrast, stable, interference fringe patterns. In the position encoder, a carrier moves the grating in a plane that is orthogonal to an axis from the light source. Motion of the carrier is detected as the fringe pattern moves past detecting means thereby to sense motion and provide position information in the form of electrical signals.

Abstract: Optical measuring and testing apparatus incorporates a holographically recorded, single-frequency, optically thin phase grating. When this phase grating is illuminated by a quasi-monochromatic, spatially coherent light source, it acts as a basic common path interferometer and constitutes a highly efficient source for a high contrast, stable, interference fringe pattern. Various apparatus embodiments incorporating the phase grating are described which permit (1) measurement of central and peripheral retinal acuity, (2) variable contrast testing to measure the ability of the eye to detect low contrast stimuli, (3) measurement of visually evoked responses to help diagnose retinal-neurological dysfunction, and (4) the testing of optical lenses.

Abstract: Optical measuring and testing apparatus incorporating a holographically recorded, single-frequency, optically thin phase grating. When this phase grating is illuminated by a quasi-monochromatic spatially coherent light source, it acts as a basic common path interferometer and constitutes a highly efficient source for a high contrast, stable, interference fringe pattern. In one embodiment, elements are repositioned to move the light source with respect to the grating thereby to alter the number of fringes in a given area. In another embodiment, elements are rotated about the optical axis of the apparatus to control the orientation of the fringe pattern. Provision is also made for allowing the examiner to view the patient's eye pupil during testing.

Abstract: A position encoder including a holographically recorded, single-frequency, phase grating. When this phase grating is illuminated by a quasi-monochromatic spatially coherent light source, it acts as a basic common path interferometer and constitutes a highly efficient source of high contrast, stable, interference fringe patterns. In a position encoder application, a carrier moves the grating in a plane that is orthogonal to an axis from the light source. Motion of the carrier is detected as the fringe pattern moves past detecting means thereby to sense motion and provide position information in the form of electrical signals.