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A new source for optical multi-wavelength signals

A German research institute has developed an innovative compact arrangement for the production of optical multi-wavelength signals. Its application in the production of Wavelength Division Multiplexing (WDM) sources will substantially reduce their complexity and production costs.
A new source for optical multi-wavelength signals
Telecommunication networks are constantly demanding more capacity in order to serve the dramatic growth of data traffic due to Internet services. Optical fibre networks have recently attracted significant research since they provide more bandwidth. In other words they are capable of carrying greater amounts of data than traditional electronic networks.

Wave Division Multiplexing (WDM) is one of the most critical technologies enabling the capacity expansion of fibre optic systems. A WDM system enables the transmission of several different independent wavelengths down a fibre simultaneously. These optical multi-wavelength signals can carry different data at high speeds, thus multiplying the capacity of the network.

The research of a German institute has led to the development of a new method for the generation of multi-wavelength signals, using a diode pump for the generation of pump pulses and a multi-core photonic crystal fibre. Photonic crystal fibres are characterized by a micro-scale structure with a regular array of microscopic air holes running along their length. These air holes constitute a cladding of a smaller refractive index than that of the cores. Furthermore, the cores can demonstrate different refractive indices, by being doped by a second material with a varying doping rate.

The propagation of the pump pulses in the multi-core photonic crystal fibre, gives rise to the Four-Wave Mixing phenomenon, which occurs when light of three different wavelengths is launched into a fibre. This leads to the generation of a new wave - an idler wave- the wavelength of which does not coincide with any of the others. Given the different doping rates and refractive indices from core to core, the idler frequencies in the fibre make a frequency comb, which can be applied as a light source in a WDM system.
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