Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-06-30
2001-08-14
Tarcza, Thomas H. (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S341430
Reexamination Certificate
active
06275331
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical amplifiers for optically amplified transmission systems, and in particular to optical amplifiers that employ erbium doped fibre amplification.
BACKGROUND TO THE INVENTION
In a transmission system employing erbium doped fibre amplifiers (EDFAs), the optical data signal may be conveyed along with an optical service signal used for servicing the transmission system, this service signal being used at least in part for monitoring and controlling the operation of the optical amplifiers of the system. The channel used for conveying the optical service signal, the optical service channel, does not need to lie within the amplification band of the optical amplifiers. This is because the service signal needs to be available for use at those amplifiers, and hence can readily be regenerated (reconstituted) at those amplifiers. Indeed it is generally advantageous to choose, for the optical service channel, a waveband lying outside the amplification waveband so as not to take up bandwidth that would otherwise be available for the transmission of data. Thus a simple unidirectional wavelength division multiplexed (WDM) transmission system incorporating EDFAs in its transmission path typically has its WDM data signals lying within the conventional amplification band (C-band) of an EDFA that extends from approximately 1525 nm to approximately 1565 nm, this WDM data being itself wavelength multiplexed with an optical service signal lying in an optical service channel typically nominally at 1480 nm, 1510 nm or 1610 nm.
At each amplifier, the service channel is picked off before the data is amplified, and then, after the data has been amplified, a fresh service channel signal is re-multiplexed with the amplified data. The picking off of the old service channel signal, and reinsertion of the new, is typically effected by means of obliquely oriented dielectric filters designed to reflect everything except for the optical service channel, which they transmit. (In principle, it is possible to use the inverse configuration in which the filters transmit everything except for the optical service channel, which they reflect. This however is not generally the preferred option because reflection loss can generally be made smaller than transmission loss, and it will generally be preferred to minimise the attenuation of the data, rather than that of the service channel signals.)
For a given route, the anticipated traffic demand may initially be too small to warrant the extra expense involved in the installation of a higher capacity system. Later however, an upgrade of the system may become desirable in order to meet increased traffic demand. Such an upgrade may involve conversion from a unidirectional transmission system to one carrying bi-directional traffic. Alternatively, or additionally, a traffic handling capacity increase may be accomplished by incorporating one or more additional amplification wavebands into the system, for instance the EDFA extended amplification band (E-band) that lies between approximately 1565 nm and approximately 1610 nm.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a form of optical amplifier that can be upgraded without breakage of the existing data transmission path through the amplifier.
According to a first aspect of the present invention there is provided an optical amplifier having a gain block between a spectrally matched pair of filters consisting of a wavelength demultiplexing channel dropping filter and a wavelength multiplexing channel insertion filter, wherein the gain block includes a length of optically amplifying optical waveguide and an optical pump therefor, wherein the channel dropping filter is provided with an input port, and output port and a channel drop port, wherein the channel insertion filter is provided with an input port, an output port and a channel insertion port, and wherein the channel drop port of the channel dropping filter is optically coupled with the channel insertion port of the channel insertion filter via the gain block.
The invention also resides in optical transmission systems incorporating amplifiers of the type defined in the preceding paragraph.
According to a second aspect of the present invention there is provided a method of providing an optical amplifier that amplifies data within a first spectral band with a facility to amplify data in a non-overlapping second spectral band, which amplifier has a gain block and supervisory circuitry connected in parallel between a wavelength demultiplexing first spectral band channel dropping filter and a wavelength multiplexing first spectral band channel insertion filter, wherein the gain block includes a length of optically amplifying optical waveguide and an optical pump therefor, wherein the channel dropping filter is provided with an input port, and output port and a channel drop port, wherein the channel insertion filter is provided with an input port, an output port and a channel insertion port, wherein the gain block is provided with an input and an output connected respectively to the channel drop port of the channel dropping filter and the channel insertion port of the channel insertion filter, and wherein the supervisory circuitry is provided with an input and an output connected respectively to the output port of the channel dropping filter and the input port of the channel insertion filter,
which method includes the step of modifying the supervisory circuitry to provide additional facility for supervising the second spectral band amplification,
the step of breaking the connections between the input and output of the supervisory circuitry and the output and input ports respectively of the channel dropping and channel insertion filters,
the step of restoring the broken connections respectively via second spectral band channel dropping and channel insertion filters, wherein the second spectral band channel dropping filter is provided with an input port, and output port and a channel drop port, and wherein the second spectral band channel insertion filter is provided with an input port, an output port and a channel insertion port,
and the step of connecting a further gain block between the channel drop and channel insertion ports of the second spectral band channel dropping and channel insertion filters.
Alternatively, the places of the second spectral band channel dropping and channel insertion filters may be interchanged.
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Baker Robert A
Bray Mark E
Flintham Barrie
Gibb Roger M
Hinds Mark R
Hughes Deandra M.
Lee Mann Smith McWilliams Sweeney & Ohlson
Nortel Networks Limited
Tarcza Thomas H.
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