Photonic Crystal Band-Structure Mapping
Photonic crystals (PhCs) are built up by a strong, periodic modification of the refractive index, that
affects light propagation in very much the same way as a solid state crystal effects the transport properties
of electrons. The strong light-matter interaction leads to peculiar effects like slow-light propagation, photonic
band gaps or even negative refractive indices. Just like in semiconductors, PhCs have a band structure which
characterizes their photonic properties and therefore presents the basis for all further applications.
By fabricating a quantum well infrared photodetector (QWIP) as a PhC, incident light gets resonantly
coupled into the device whenever a photonic state is present. Each PhC-mode therefore appears as peak
in the spectral photocurrent. In this way we created new and direct characterization procedure for photonic
crystals. Broad-band light is polarization filtered and shined at different angles onto the device in order
to map the photonic band structure including its polarization and symmetry properties as well as the coupling
efficiency of different PhC modes.
Mapping of responsivity peaks to photonic crystal modes