Nortel Networks Corporation

Jowan Masum-Thomas

Andrew V Maroney

Richard Thomas

Christopher R Fludger

Rodolfo Di-Muro

Daria Crippa

An optical amplification system has an active fibre section having an optical fibre and containment means containing light of a specific wavelength within the active fibre section. The specific wavelength of light is the result of the spontaneous transition of photons. The contained photons stimulate further photons emissions, which depopulates energy levels involved in the amplification process.

Optical fibre amplifiers

In a first aspect, a Raman amplifier is pumped using pumps just above and below the fiber water peak. This enables lower power pumps to be used, as the high attenuation is avoided. In a second aspect, a first pump provides a signal having a first wavelength and a first power, and a second pump source provides a plurality of signals, each having a power lower than the first power and a wavelength in a range approximately one Stokes shift higher than the first wavelength. In this way, the second pump source signals are amplified by the Raman effect by the first pump source signal, and the amplified second pump source signals cause signal amplification. The amplified second pump source signals can then include wavelengths above and below the water peak.

Raman amplification

An optical amplifier has at least first stage in the form of a distributed Raman amplifier and a second stage in the form of a discrete Raman amplifier. The discrete amplifier has an output for unused pump power, and the distributed Raman amplifier is pumped using the unused pump power from the second stage. This arrangement enables unused pump power to be used in a distributed Raman amplifier, in particular using the transmission fiber at the input to the second stage amplifier.

Raman amplifier

A Raman amplifier comprises first and second stages, in which a single pump source is used for both stages. The pump source output is coupled to one end of the second stage and unused pump power is tapped from the other end of the second stage. The unused pump power is then introduced into the first stage. The attenuation of the pump source signal in the second stage results in a lower power pump signal being applied to the first stage. The specific design of the amplifier stages enables the two pump power levels to be suitable for different fiber types so that the advantages of a multi-stage amplifier are maintained (with each stage being designed taking into account the signal powers in the different stages) whilst simplifying the pump source requirements.

An optical amplifier comprises a pumped Thulium doped fiber amplifier and a Raman amplifier provided in series. The Thulium doped fiber amplifier provides gain over a first wavelength range, and is range is extended by the Raman amplifier by suitable pumping. The Thulium amplifier operates in the S band, but the wavelength range is extended to the C band by the Raman amplifier. The amplifier thus has increased bandwidth, thereby allowing it to be used in higher capacity optical communications systems.

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Halstead, United Kingdom

Jowan Masum-Thomas