Characterization of planar photonic crystals using a quantum well infrared photodetector

A GaAs/AlGaAs quantum well infrared photodetector was combined with a deeply etched three-fold PhC structure. This makes the detector sensitive to mid-infrared radiation incident via the sample surface. The geometrically tunable peak responsivity is polarization independent when operated at normal incidence. Changing the angle of incidence a structure of several peaks is observed. In contrast to normal incidence illumination where the single peak can be identified as one particular PhC mode at the Γ-point near the second order Bragg condition, the multiple peaks apparent under an arbitrary angle refer to all PhC modes which lie within the spectral responsivity of the detector. The measurement therefore represents a direct characterization procedure for band structure mapping of photonic crystals. A study of the polarization dependence shows that TM polarized waves excite even modes while TE waves couple to modes with odd symmetry. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)