End-fire mode spectroscopy technique of examination of planar waveguides

A new technique of mode spectrum measurement in planar waveguides is presented. Unlike conventional m-line spectroscopy which does not provide reliable measurements of the whole mode spectra in waveguides with non-monotonic index profiles (in particular, step-index waveguides with thick cover layers or deep-buried graded-index waveguide structures) the proposed technique allows such measurements in any planar waveguides. The developed technique exploits the difference of refraction angles of different modes skew-incident to the output face of the waveguide. The viability of the technique is verified by the comparative study of mode spectra measured by the m-line spectroscopy and the proposed technique.