COHERENT OPTICAL PROCESSING OF TEMPORAL FUNCTIONS.
Abstract
Radarlike pulses were detected in the laboratory when the signal-to-noise ratio was as low as -40 dB, using optical matched filters. A matched filter timebandwidth product of 90,000 has been realized and this product can be easily increased by a factor of 10. Coherent-light optical filters usually use holographic techniques that require the positioning of filter transparencies with accuracies of several microns when the input aperture diameter is 35 mm. An optical matched filter using a new principle has been developed. A standard 35 mm film transport will position the transparencies with sufficient accuracy. A signal and noise intensity modulates a TV-type raster, and a transparency made from this raster is positioned below the optical axis of a collimated laser beam and in front of a 'transforming' lens. A second transparency made from a raster modulated with the matched-filter impulse response is placed in the plane of the first transparency but above the optical axis. The resulting image on the back focal plane of the transforming lens is photographed and the film is developed to have a transmittance that is proportional to the magnitude squared of the light amplitude. If this third transparency is placed in front of the transforming lens, the filter output or the convolution of the signal and noise with the matched-filter impulse response will be imaged on the back focal plane where the signal is detected. This technique may be used to realize a large bank of matched filters to detect radar signals and to estimate various radar parameters when the signal-to-noise ratio is much less than unity. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1968
- Accession Number
- AD0681832
Entities
People
- S. David Ramsey Jr
Organizations
- Stanford University