Spectroscopy of a tapered-fiber photonic crystal waveguide coupler

A spectroscopic technique based on a full four port modeling and measurement is developed and utilized to study a tapered- fiber photonic crystal waveguide coupler. The coupler is made by directly situating the tapered fiber on the defect region of a silicon membrane photonic crystal waveguide. The waveguide is lithographically terminated resulting a Fabry- Perot cavity. It turns out that the line-shape of the resonances is not merely a Lorentzian but can be constructed from that of the unloaded waveguide resonator. By knowing how the resonances broaden the experimental data is then fit and the coupling efficiency is extracted for the entire spectrum.