Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1993-09-20
1995-10-24
Pascal, Leslie
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359179, H04B 1017, H04B 1016
Patent
active
054614970
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
I. Field of the Invention
This invention relates to photonic amplifiers and especially to photonic amplifiers which are intended for use in a long series of amplifiers.
II. Related Art and Other Considerations
Photonic amplifiers are used in telecommunications, e.g. in optical submarine cable systems, and it is desirable that such systems should include provision to indicate the probable location of certain faults. Specifically it is desirable to provide for the approximate location of a broken link which, of course, completely terminates any communication across the break. Clearly, a break implies that signal levels fall to zero. In addition to the breakage of a link, a similar condition occurs due to the deterioration of components. Thus, the failure of an amplifier would be equivalent to a break, and the deterioration of an amplifier would result in loss of gain whereby signal levels might fall to an unacceptably low level. Conditions such as the total loss of signal would probably be noticed in any system. However the location of the fault may not be apparent in a larger system and it is the object of this invention to provide information which helps to locate a fault.
A photonic amplifier amplifies optical signals using laser action, that is, signal photons stimulate the emission of similar photons whereby the signal is amplified. It is convenient to distinguish between two types of photonic amplifier by reference to the nature of the lasing medium. In the first type, the lasing medium is a semiconductor and the amplifier has a complicated structure involving several functional regions and interfaces. In the case of a semi-conductor amplifier, the power to drive the amplification is provided by an electric current from a suitable electronic circuit. In the second type of amplifier, the lasing medium is an optical fibre which is doped with a lasing species such as Nd or Er. In the case of a fibre amplifier, the power for the amplification is provided in the form of pump radiation which may have a shorter wavelength than the signal radiation. The pump radiation produces a population inversion in the lasing species in accordance with the well known theory for the operation of lasers.
SUMMARY
In accordance with this invention a photonic amplifier which includes a detector means and a distress transmitter, the said detector means capable of detecting valid signals which include a control tone modulated onto a traffic signal, in normal operation, on receipt of valid signals the detector means is adapted to disable the distress transmitter, and the distress transmitter when enabled to provide to an output of the amplifier an optical distress signal which is recognisable as a valid signal and which is modulated with information which includes the identity of the amplifier. More specifically, the default condition occurs when the signal level falls to an unacceptably low level. As mentioned above, the case where the signal falls not merely to a low level, but to zero is of particular interest. In accordance with the invention, a photonic amplifier, for use with signals modulated with a control tone, wherein the detector means is configured to disable the distress transmitter when control tone above a predetermined level is detected, and to enable the distress transmitter when control tone below the predetermined level is detected, and wherein the distress transmitter produces a distress signal modulated with control tone such that said distress signal disables the distress transmitters of similar amplifiers, to which the amplifier may be connected. The distress signal adopts the same signal format as the normal signal so that subsequent amplifiers remain in the normal configuration. It should be understood that normal traffic signals are digitally modulated, and therefore the distress signal can also be digitally modulated. According to another aspect of this invention the distress signal is digitally modulated with the identity of the originating amplifier in order that the location of the faul
REFERENCES:
patent: 4995100 (1991-02-01), Stallard
patent: 5023863 (1991-06-01), Masuda
patent: 5117196 (1992-05-01), Epworth
British Telecommunications Public Limited Company
Pascal Leslie
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