Plasmonic all-optical tunable wavelength shifter

At present, wavelength-division-multiplexed fibre lines routinely operate at 10 Gbit s(-1) per channel. The transition from static-path networks to true all-optical networks encompassing many nodes, in which channels are added/dropped and efficiently reassigned, will require improved tools for all-optical wavelength shifting. Specifically, one must be able to shift the carrier wavelength ( frequency) of an optical data signal over tens of nanometres ( a THz range) without the bottleneck of electrical conversion. Popular approaches to this problem make use of the nonlinear interaction between two wavelengths within a semiconductor optical amplifier(1) whereas more novel methods invoke terahertz-frequency electro-optic modulation(2) and polaritons(3). Here we outline the principles and demonstrate the use of optically excited plasmons as a tunable frequency source that can be mixed with a laser frequency through Raman scattering. The scheme is all-optical and enables dynamical control of the output carrier wavelength simply by varying the power of a control laser.