The nonlinear coefficient γ is a key parameter for studying nonlinear pulse propagation, as it relates the power in a waveguide mode to the nonlinear phase shift per unit length. It is well understood in dielectric waveguides, but less so in lossy plasmonic waveguides. A number of methods for calculating γ have been proposed, each producing different expressions. Here, we comprehensively compare these methods for a surface plasmon polariton propagating at a gold-air interface, obtaining new insights into the nonlinear response of lossy waveguides.
Stimulated Brillouin scattering (SBS) is a strong nonlinear interaction between optical and mechanical modes of nanophotonic waveguides, whereby the optical field can generate and maintain extremely strong acoustic waves. Until recently, it was believed that the high losses associated with metals would render SBS unmeasureable in plasmonic systems. However recent work has shown that the confinement of acoustic modes in metallic structures, together with strong field gradients that occur on metal-dielectric surfaces, can result in SBS gain orders-of-magnitude greater than that in dielectric waveguides. This gain scales such that it is able to overcome the intrinsic loss of some surface plasmon polariton (SPP) configurations, depending on the waveguide geometry.
Here we examine the interaction of light and sound in plasmonic systems, including the forces and scattering processes in the presence of highly-lossy optical and acoustic modes. We examine the thermal effects arising from the optical loss and show how the measured gain is determined by the CW power-handling capabilities of the plasmonic mode. We examine a range of possible waveguide geometries and establish relevant Figures of Merit for evaluating a range of realistic plasmonic waveguides, and examine how geometrical scaling affects the SBS gain in both forward (co-propagating) and backward (counter-propagating) SBS configurations. We find that SPP-driven SBS will be measureable within a broad range of waveguides, and present general design rules for measuring SBS in different material systems. Finally, we discuss the challenges and opportunities for harnessing this effect in the first experiments.
Polymer optical fibres (POF) have historically focused on applications in data transmission over short distances, using
highly multimode step-index or graded-index fibre designs. This paper will focus on a qualitatively different type of
polymer fibres - microstructured polymer optical fibres (mPOF) - which allow a wider variety of fibre designs and
optical properties to be achieved. Fibres with similar properties to conventional step- and graded-index POF can be made
for data transmission applications, as well as single-mode fibres which can be used for grating inscription and gratingbased
sensing. The use of microstructures can also be extended to longer wavelengths for the transmission of THz
radiation, and both solid-core and hollow-core mPOF-based THz waveguides have been demonstrated. Finally, the
development and extension of mPOF to form metal-dielectric structures for the manufacture of metamaterials using
fibre-drawing methods will be discussed. Such drawn-metamaterials with electric and magnetic responses at THz
frequencies have been demonstrated.