Design of an integrated measurement meter using circular Dammann gratings

Abstract

An integrated distance and area measurement meter based on first-order circular Dammann grating (CDG) is proposed. With a limited aperture of the grating, doubled-humped radial rings are observed in the spectrum. By adjusting the position of the lens, the separation of doubled rings projected onto the distant object reaches its minimum. The distance between object and the lens can hence be identified using the thin lens formula. Four designs of CDG with different number of periods and transition points are employed in both simulation and experiment. They are fabricated using dry etch lithography process in clean room environment. This proposed meter has 0.5% to 4% error. The result shows that its accuracy is associated with the measured distance and the grating design. The longer the measured distance, the higher the percentage of error resulted. For the area measurement, it is developed according to the linear relationship between the spectrum diameter and the distance travelled by the CDG. Similar to the distance measurement, its percentage of error is investigated and analysed. Throughout the project, the relationship between the size of spectrum, the focal length of lens, the design of CDG and the degree of accuracy in both simulation and practical cases are studied. Finally, a portable device for this integrated measurement meter is proposed.