Abstract

An embossed diffractive optical element (DOE) is used as an efficient planar inexpensive collimator for a point source light-emitting diode. The DOE, with a 1-mm diameter and 2.1-mm focal length, is installed in a 2.5-mm square read/write head on-axis with an 890-nm LED. This collimated beam emits through a magnetic-coated floppy disk, which includes a transmission diffraction grating, the grating pitch corresponding to the magnetic track width. A similar head on the opposite side contains a photodetector etched with lines of the same grating pitch. The detector output signal obtained provides a position error signal. This paper discusses the design, fabrication, testing, measurement, and operation of the diffractive optical element in this device. Throughput efficiency of >25%, full angle divergence of <1 mrad, and cross-sectional analysis featuring <3-μm linewidths are presented. Signal data obtained using the DOE are compared with that from a molded plastic collimating lens. In addition, results using the DOE with other light sources, such as red LEDs and laser diodes, are discussed.

© 1988 Optical Society of America