We demonstrate record giant birefringence, nearly twice as large as has previously been achieved (Delta n(group) = 1.5 over more than 60 nm of bandwidth near lambda= 1550 nm) using a multi-slotted silicon nanophotonic waveguide. The birefringence is optimized by the use of materials with high refractive index contrast to create a compact single-mode waveguide, and the etching of deeply sub-wavelength channels within the waveguide, which are strongly coupled in the near field and separated by narrow air channels of optimum lateral width. When used as a polarization-selective delay element, the delay-bandwidth product per unit length is 46.6/mm over a bandwidth of 8.74 T Hz. We also design and demonstrate mode shaping of both the TE and TM polarizations to achieve near-identical coupling to a macroscopic external object, such as a lensed fiber or detector.
The possibility of light manipulation at the nanoscale relies on the efficient coupling of the electromagnetic waves to surface excitations such as surface plasmon polaritons ͑SPPs͒. We expand on the work by Pendry, who put forward the idea of spoof surface plasmons in conducting films as a way to engineer SPP dispersion curves. We find that the surface texture and geometry can play an important role in determining the dispersion. We then compare the specific cases of circular versus rectangular textured surfaces and observe that the plasmon modes are less tightly bound in the former case. This dependence on geometry can also be used as a means for defect engineering or fine-tuning the regular plasmon dispersion.
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