Our paper in ACS Photonics shows how cathodoluminescence microscopy can image optical modes in Si photonic crystals.

Near-infrared spectroscopic cathodoluminescence imaging polarimetry of silicon photonic crystal waveguides
B.J.M. Brenny, D.M. Beggs, R.E.C. van der Wel, L. Kuipers, and A. Polman, ACS Photon. doi: 10.1021/acsphotonics.6b00557 (2016)