Characterisation of waveguide microcavities using high-resolution transmission spectroscopy and near-field scanning optical microscopy

A wide variety of optoelectronic devices with novel gratings are being created for which knowledge of the internal optical fields and derails of loss mechanisms are highly desirable. To this end, the authors have built apparatus and developed techniques for simultaneous measurement of the scattered and evanescent fields in the near-field of the active region of grating-type waveguide devices combined with high-resolution transmission measurements. Here they report characterisation and analysis of a waveguide microcavity. The transmission scans improve greatly on previous measurements, showing detailed structure which the authors explain using transfer matrix simulations including the structure of the input and output waveguides of the device. They also present nearfield scanning optical microscopy data of the active region of the waveguide. Internal mode patterns and height dependent data, when compared with simulations of the electric field magnitude, show that the device may suffer from significant scattering at the grating interfaces.