non-linear effect
When an optical signal enters an optical fibre, the amplitude of the incident optical signal power varies the refractive index, which means the light speeds of it and other wavelengths are modulated. Especially in the case of long-distance transmission of up to 10,000 kilometers or 100 or more multiplexed wavelength signals, the accumulation of this effect becomes serious. Accordingly, crosstalk occurs among the WDM signals during the transmission and the waveforms are gradually distorted. The degree of distortion caused by the occurrence of non-linear effects is closely related to the chromatic dispersion in the fibre, so highly accurate dispersion management in the transmission line is required. With the pump light, the signal light is amplified by scattering due to the molecule vibration in the substance of which the fibre is composed. This is a non-linear effect called the stimulated Raman scattering.
 erbium-doped fibre amplifiers
An amplifier that amplifies an optical signal in the 1.5mm band, employing pump light at 0.98mm or 1.48mm in an optical fibre doped with the element erbium. It has found wide practical application in WDM transmission systems.
 Raman amplifier
An amplifier that employs pump light in the 1.4mm band and amplifies an optical signal in the 1.5mm band, applying the stimulated Raman scattering effect. It has already been applied for repeater-less transmission systems. Adjusting the pump wavelengths and optical power allows engineers to freely design advantageous gain wavelength characteristics.
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Date: 24 October, 2001
Company: Fujitsu Limited
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