Optical Doppler shifts may be detected directly by filtering and dispersing the return light. The direct detection method is far more relaxed optically, requiring only "photon bucket" collection optics. A narrowband interference filter and two etalons are enough to distribute the frequency shifted light into the radial pattern ofonly one free spectral range ofthe last etalon. This paper describes a novel system using three hoes to perform transmission, collection, filtering and redistribution of the imaged zonal signal light onto a linear string of detectors. The light collection optic is a large area scanning and focusing hoe made in DCG. This optic may also serves as the laser transmitting optic. Holographically recorded etalons of medium finesse are made to do final filtering of the return signal down to picometer bandwidths. Finally a 24-channel circle to point converter has been fabricated in DCG and also transferred to resist and subsequently etched into a fused silica substrate. Reactive ion etching (RIE) was attempted using a Faraday cage to form tilted fringes in the silica. An Ion mill was rebuilt to perform a similar task. All components worked well when made in DCG but problems with dry etching were not all resolved. Circle-to-point conversion has been used for collecting the output of an etalon where a suitable detector of equal area circular zones was not readily available. The output is converted to a line of points so that it may be read with a simple and readily available linear photon counting detector.

Date Published: 16 April 2001
PDF: 10 pages
Proc. SPIE 4291, Diffractive and Holographic Technologies for Integrated Photonic Systems, (16 April 2001); doi: 10.1117/12.424853

Published in SPIE Proceedings Vol. 4291:
Diffractive and Holographic Technologies for Integrated Photonic Systems
Richard L. Sutherland; Dennis W. Prather; Ivan Cindrich, Editor(s)