Local complex reflectivity in optical waveguides

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Abstract
With the aim of probing the photonic band structure of waveguiding micro- and nanooptical devices, we re-introduce the modal local complex reflectivity (LCR) and review the impact of scanning near-field optical microscopy (SNOM) methods on the determination of LCR in such devices. These methods include intensity and complex field mapping of standing waves, as a function of the wavelength. A unified treatment of the LCR probing is given for both standard SNOM and phase sensitive SNOM. Experimental demonstration of these two methods on several microstructured devices (Bragg grating structures) is done using a scattering-type SNOM whose specific advantages in terms of resolution and accuracy are addressed. The phase sensitive version of the scattering-type SNOM is shown to be very well suited for LCR measurement as well as general modal and dispersion analysis. The possibility to obtain the scattering matrix of micro- and nanodevices as a function of the wavelength is foreseen by using the described microscope.