Optics: measuring and testing – For optical fiber or waveguide inspection
Patent
1996-11-13
1998-08-11
Font, Frank G.
Optics: measuring and testing
For optical fiber or waveguide inspection
356432, 356128, G01N 2100
Patent
active
057934819
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a system for monitoring a fiber optic cable.
Specifically, the invention concerns a system for monitoring a fiber optic cable connected between a transmitting equipment and a receiving equipment of optical signals, which system is connected to a central control unit through a bus and comprises compact electro-optical devices for measuring optical power which are permanently connected to the opposite ends of the fiber optic cable.
The invention further relates to a method of monitoring a fiber optics link which includes the above monitoring system.
The invention further relates to a compact electro-optical device for measuring optical power which is adapted to be permanently connected to a network of fiber optic cables, which devices have an optic input and an optic output as well as an electric input and an electric output, and are of a type which comprises an optical power measuring circuit having an input connected to the optic input and an output to the electric output, the electric output providing the value of the operating optical power being flowed through the fiber optic cable.
2. Background Art
As is well known, fiber optic cables are widely used in telecommunications networks. Information exchanged on such optical carriers can improve the overall quality of telecommunications systems and their operational speed.
In the specific field of this invention, a need exists for a quick troubleshooting procedure.
Of special interest is an ability to prevent the occurrence of failures by spotting variations in the attenuation through each fiber optic cable, regarded as a sure indication of a deteriorating cable link.
For the purpose, arrangements for monitoring fiber optic cable systems have been available which can provide useful information to the evaluation of the cable characteristics.
A first prior art solution provides a measurement of the attenuation through a fiber optic cable "out-of-service", that is: a cable which has been disconnected from the equipment to which it is normally connected.
This prior solution consists of using a measuring system which simulates a transmitter/receiver system and inputs a test signal to the fiber optic cable. The cable performance can be checked upon measuring the transmitted and received signals.
However, this first solution does not allow the performance of fiber optic cables "in-service", that is during their normal operation, to be checked. In addition, the monitoring of each cable and the network as a whole is time consuming.
A second prior art solution provides a measurement of the attenuation through a fiber optic cable using a reflectometer or OTDR (Optical Time Domain Reflectometer).
The reflectometer is connected to a first end of a fiber optic cable and caused to send an optical test signal therethrough.
From this first end, the strength and time of arrival of the optical wave reflected back through the cable are measured; from these values, one can work back to the attenuation value of the fiber optic cable and/or the location of a possible fault.
Measurements with an OTDR test set are easily made on "out-of-service" cables, and are feasible on cables in operation.
In the latter case, the optical test signal is added to the operating optical signal by means of a suitable optical coupler. It is on this account that the wavelength of the optical test signal and that of the operating optical signal must lie far apart, so as to minimize interference on said signal.
Although achieving its objective, not even this second prior solution is entirely devoid of drawbacks, a major one being the bulk and high cost of an OTDR test set.
Due to these limitations, one OTDR test set is usually shared by a plurality of cables which, therefore, can only be monitored on a cyclic basis. This involves, the use of a large number of optical switches.
In addition, the presence of two optical signals with discrete wavelengths may cause noise to appear at the receiving end which cannot be completely suppresse
REFERENCES:
patent: 4183666 (1980-01-01), Tahara et al.
patent: 4600310 (1986-07-01), Cramp et al.
patent: 5535139 (1996-07-01), Barringer et al.
Font Frank G.
Oh Seong-Kun
PLLB Elettronica S.p.A.
Ratliff Reginald A.
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