Optics: measuring and testing – For optical fiber or waveguide inspection
Patent
1988-12-12
1990-09-18
McGraw, Vincent P.
Optics: measuring and testing
For optical fiber or waveguide inspection
356 5, G01N 2188, G01C 308
Patent
active
049573659
ABSTRACT:
An optical backscattering meter includes an optical transmitter whose transmission power is modulated (wobbled) with a variable frequency via an oscillator and whose transmission beam is coupled into a light wave cable (LWL) via a beam splitter. It further includes an optical receiver including an avalanche photodiode, to which receiver are applied, via the beam splitter, portions of the transmission beam that are scattered back from the light wave cable (LWL). A mixing signal is formed from a signal proportional to the optical backscattering power and a modulation voltage having the oscillator frequency and is evaluated for determining the location of the backscattering and the intensity thereof. The cost of the optical receiver is reduced by the use of the avalanche photodiode (4), whose bias voltage is a d.c. voltage (U.sub.G) modulated by the modulation voltage (U.sub.M), and because the mixing signal (U.sub.P) can be tapped at a parallel circuit comprising an ohmic resistor R.sub.P) and a capacitor (C.sub.P) inserted in the energizing circuit of the photodiode.
REFERENCES:
patent: 4320968 (1982-03-01), Wakabayashi
McGraw Vincent P.
U.S. Philips Corp.
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