Probing the dispersive and spatial properties of photonic crystal waveguides via highly efficient coupling from fiber tapers

The demonstration of an optical fiber based probe for efficiently exciting the waveguide modes of high-index contrast planar photonic crystal (PC) slabs is presented. Fiber taper waveguides formed from standard silica single-mode optical fibers are used to evanescently couple light into the guided modes of a patterned silicon membrane. A coupling efficiency of ∼95% is obtained between the fiber taper and a PC waveguide mode suitably designed for integration with a previously studied ultrasmall mode volume high-QPC resonant cavity [Srinivasan et al., Appl. Phys. Lett. 83, 1915 (2003)]. The micron-scale lateral extent and dispersion of the fiber taper is used as a near-field spatial and spectral probe to study the profile and dispersion of PC waveguide modes.