Polarization-transparent microphotonic devices in the strong confinement limit

Microphotonic structures that strongly confine light, such as photonic crystals and micron-sized resonators, have unique characteristics that could radically advance technology. However, such devices cannot be used in most applications because of their inherent polarization sensitivity; they respond differently to light polarized along different axes. To take advantage of the distinctive properties of these structures, a general, integrated, broadband solution to their polarization sensitivity is needed. Here, we show the first demonstration of such a solution. It enables arbitrary, polarization-sensitive, strong-confinement (SC) microphotonic devices to be rendered insensitive (transparent) to the input polarization at all wavelengths of operation. To test our approach, we create the first polarization-transparent add-drop filter from polarization-sensitive microring resonators. It shows almost complete elimination of polarization sensitivity over the 60-nm bandwidth measured, while maintaining outstanding filter performance. This development is a milestone for SC microphotonics, allowing the applications of photonic-crystal and microring devices to several areas, including communications, spectroscopy and remote sensing.