Nortel Networks Corporation

Kevan Jones

Robert William Keys

Maurice M O'Sullivan

Ian Peter McClean

Nigel Edward Jolley

Mark E Bray

Ross T Elliott

Fiona Davies

To support interleaving of optical channels and to provide sufficient isolation between such interleaved channels, a circulator ( ) receives, on an optical fiber ( ), a broadband signal containing a plurality of adjacent channels. The circulator selectively routes the broadband signal through a filter ( ) to isolate, on an individual basis, at least one desired channel. A filtered signal, corresponding to the at least one desired channel, is then output from the filter ( ) and reflected back into the filter by a mirror ( ) such that the at least one desired channel is subjected to a second filtering process that further improves isolation of the at least one desired channel. Following this second filtering process, the at least one desired channel is applied to the circulator ( ) for re-inserting into the optical fiber ( ), as illustrated in FIG. To mitigate the effects of four-wave mixing in each bidirectional optical fiber, a channel assignment plan ensures that pairs of adjacent channels are assigned on a mutually exclusive basis to at least one of an up-link and a down-link direction.

Circuit and channel assignment plan for optical transmissions

An optical amplifier for amplifying the channel signals of a WDM signal comprises an amplifier arrangement for amplifying a band of the channels. The amplifier arrangement comprises an amplifier ( ) and a filter ( ). The filter comprises a controllable optical filter having an attenuation characteristic which comprises a region of positive gradient and a region of negative gradient with respect to input frequency. The magnitude and alignment along the frequency axis of the attenuation characteristic is variable, such that the filter can be tuned to provide gain flattening for the amplified band of channels. The filter can be tuned to the requirements of a particular sub-band, whilst identical filters can be used for each sub-band. This invention enables identical filters to be used, and gives good pump power efficiency, as the attenuation of each filter can be controlled to the desired level, thereby avoiding the need for large increases in pump power.

Optical amplifier

An inexpensive broadband source such as an ASE source, used for erbium amplifier measurements, compares well with the use of a prior art ITU grid. Deltas are less than 0.4 and 0.3 dB for gain and noise figure respectively. The spectral loading used to test erbium amplifiers needs to closely resemble conditions seen in the field. Use of an ITU grid is a good way of achieving this, however it is a costly solution and may restrict the spectral resolution. Use of a high power amplified spontaneous emission source gives a cost-effective alternative, which compares well with ITU grid measurements. In addition the spectral resolution of the measurement is then only limited by the spectral resolution of the optical spectrum analyzer.

Method and apparatus for the measurement of erbium optical amplifiers

The intrinsic optical loss exhibited by a circulator-based optical fiber chirped Bragg reflection grating optical fibre dispersion compensator is compensated by including a length of amplifying fibre in the path between the circulator and the Bragg grating, this amplifier fibre being optically pumped by pump power launched into the amplifier fibre from the far side of the Bragg grating.

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Totnes, United Kingdom

Kevan Jones