Negative refraction in a Si-polymer photonic crystal membrane

We have observed negative refraction in a photonic crystal (PC) membrane structure at near-infrared wavelengths. The device is fabricated on a silicon-on-insulator substrate and consists of a silicon rod matrix suspended in a polymer where optical energy is delivered by ridge waveguides with various incident angles. The propagation direction inside the PC shows extraordinary refraction with an angle consistent with our two-dimensional numerical simulations. To our knowledge, this is the first experimental observation of isotropic negative refraction in a Si-based planar PC structure at optical frequencies. The realization of negative refraction in a planar Si-based system enables applications in negative index imaging to be integrated into compact optical circuits.