Optical time-domain reflectometer using heterodyne reception

Details Optical time-domain reflectometer using heterodyne reception Optical time-domain reflectometer using heterodyne reception

1986-02-21

1987-11-24

McGraw, Vincent P.

Inductor devices

With closed coil or conductor member

G01N 2184, G01N 2188

Patent

active

047084715

ABSTRACT:
The invention relates to an optical time-domain reflectometer (OTDR) using heterodyne reception for determining the attenuation of an optical fiber guide by measuring the backscattered portion of light pulses launched into the fiber. The reflectometer comprises a light source whose light is split into a local-oscillator beam and a measuring beam. The measuring beam is pulsed by an acousto-optical modulator (AOM) and is then launched into the optical fiber to be tested. The measuring beam thus has a frequency which is offset from the optical frequency by an acoustic frequency. The local-oscillator beam and the back-scattered portion of the measuring beam are both directed to an optical receiver producing an electric output signal. A component of the output signal has a frequency corresponding to the acoustic frequency. The time-dependent amplitude of this component is a measure of the length-dependent attenuation of the optical fiber. In order to reduce the losses in the path between the light source and the optical receiver via the fiber to be tested, the acousto-optical modulator (AOM) also functions as an optical deflection element.

REFERENCES:
Abbas, G. L. et al., "Local-Oscillator Excess-Noise Suppression for Homodyne and Heterodyne Detection", Opt. Lett., vol. 8, No. 8, pp. 419-421 (Aug., 1983).
Healey, P., "Fading in Heterodyne OTDR." Elec. Lett., vol. 20, No. 1, pp. 30-32 (Jan. 5, 1984).
Wright, S., et al., "High Dynamic Range Coherent Reflectometer for Fault Location In Monomode and Multimode Fibres." 9th ECOC, pp. 177-180 (1983).

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