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Optical Engineering

Intensity-modulated diode laser radar using frequency-modulation/continuous-wave ranging techniques
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Paper Abstract

This paper treats a practical adaptation of frequency modulation (FM) radar ranging principles to an incoherent laser radar (ladar). In the simplest sense, the ladar’s laser transmitter output is amplitudemodulated with a radio-frequency subcarrier, which itself is linearly frequency-modulated. The subcarrier signal may have a start frequency in the tens to low hundreds of megahertz and a stop frequency in the hundreds of megahertz to low gigahertz. The difference between the start and stop frequency, ?F, is chosen to establish the desired range resolution ?R according to the usual equation from FM radar theory, ?R= c/2 ?F, where c is the velocity of light. The target-reflected light is incoherently detected with a photodiode and converted into a voltage waveform. This waveform is then mixed with an undelayed sample of the original modulation waveform. The output of the mixer is processed to remove ‘‘self-clutter’’ that is commonly generated in FM ranging systems and obscures the true target signals. The clutter-free waveform is then processed coherently using the discrete Fourier transform to recover target amplitude and range. A breadboard of the ladar architecture was developed around a 100-mW GaAlAs diode laser operating at 817 nm. Imagery and range responses obtained show that the theoretical range resolution of 0.25 m was attained for a ?F of 600 MHz. Embodiments of this ladar are likely to be practical and economical for both military and commercial applications because low-cost continuous wave (cw) laser diodes are used, coherent optical mixing is not required, and the postmixing processor bandwidth is low.

Paper Details

Date Published: 1 November 1996
PDF: 9 pages
Opt. Eng. 35(11) doi: 10.1117/1.601067
Published in: Optical Engineering Volume 35, Issue 11
Show Author Affiliations
Barry L. Stann, Army Research Lab. (United States)
William C. Ruff, Army Research Lab. (United States)
Zoltan G. Sztankay, Army Research Lab. (United States)


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