The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 27, 1988
Filed:
Mar. 17, 1987
Friedrich-Karl Beckmann, Pinneberg, DE;
Wolfgang Hoppe, Norderstedt, DE;
Reinhard Knochel, Elmshorn, DE;
Jurgen Kordts, Wedel, DE;
U.S. Philips Corporation, New York, NY (US);
Abstract
The invention relates to an optical time domain reflectometer (OTDR) with heterodyne reception for determining the attentuation of an optical waveguide (measuring waveguide) by measuring the back-scattered portion of light pulses sent into the measuring waveguide. This structure is comprised of a modulated laser light source sending a send beam into the measuring waveguide and a laser light source which constitutes a local oscillator and transmits continuous light, on whose light of a wavelength differing by an intermediate-frequency from the back-scattered light from the transmission light source is superposed and is applied to a photodetector having an intermediate-frequency electric output signal which is filtered and evaluated. To improve the signal-to-noise ratio it is provided that the transmission light source is a transmission laser 1 whose light is influenced in consecutive time intervals (t.sub.1 to t.sub.2) such that the light frequency varies between two cut-off frequencies f.sub.L1 and f.sub.L2 and that the light source forming the local oscillator is a laser transmitting light at a frequency f.sub.LO, which is located outside the range between the cut-off frequencies f.sub.L1 and f.sub.L2 and differs from a frequency value (f.sub.LM), located between the frequencies f.sub.L1 and f.sub.L2, by the intermediate frequency (F.sub.ZF).