Community Research and Development Information Service - CORDIS

Optical communications made faster

Sending a message down an optical fibre can in principle be thought of as one flash for yes, two flashes for no. This project describes a way of making these flashes extremely short in order to achieve higher speeds of communication.
Optical communications made faster
Optical fibres are glass pipes surrounded by another glassy material called cladding with total diameter less than that of the human hair. Light pulses propagate in the core by being reflected at the interface of the cladding. A new technique for generating ultra-fast pulses has been developed. The pulses are generated from a semiconductor laser that was designed by a Danish laboratory.

The laser is based on a triple-section diode that was already proposed and studied at the Lebedev Physics Institute in Russia. A system to register the pulses has also been developed. The experimental study showed that the flashes from the triple-section diode laser have wavelengths of 450μm and the duration of each flash is as small as 470fs. Given that a femtosecond (fs) is 10-15 of a second we are dealing with very short pulses.

The laser is able to produce one such pulse approximately every 10-10 of a second, i.e. at a repetition rate of exactly 9.5GHz. It is the limited speed of conventional electronic devices, due to fundamental physical limitations, that is shifting the interest towards photonic devices. Work in the field is progressing towards an all-optical transparent network that currently remains the problem with switching. Switching light from one fibre to another means converting it to an electrical signal and then back to an optical one. This detour slows traffic considerably in today's fibre-optic networks.

This project has also experimented and analyzed four-wave mixing in order to achieve optical switching and avoid the electrical conversion. The experiments made use of a continuous wave pump and probe with a pump-probe frequency detuning up to 8.6 THz. The analysis allowed the investigation of the semiconductor optical non-linearity with a time resolution of 20fs. The theoretical and experimental study conducted, has resulted in a better understanding of ultra fast optical communications and lead to the opportunity of designing an all-optical information network with identical non-linear laser elements.
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