Momentum-resolved reflectivity of 2D photonic crystals in the near-infrared

Two-dimensional (2D) photonic crystals offer strong control over the propagation of light through their photonic bands. Theoretical methods for computing the band structure in 2D are well-established and fast because 2D photonic crystals are homogeneous in the third dimension. Experimental verification is scarce, however, especially in the near-infrared (NIR) range including telecom ranges, because real photonic crystals and experimental methods inherently cannot be homogeneous in the third dimension. In this work, we report momentum-resolved reflectivity measurements on photonic crystals that are periodic in two dimensions and homogeneous over a thickness of 5 µm. Using Fourier spectroscopy, we carefully select wave vectors in the 2D plane of periodicity of the photonic crystal to experimentally map band structures. Our experimental results agree excellently with 2D band structure calculations and with 2D finite-difference time-domain simulations, confirming that our experimental methods truly pertain to nanophotonics in 2D. Our results provide a robust bridge between theory and experiment, and our techniques can be readily extended to other 2D structures, including those with functional defects.