Photonic crystals are semiconductors for light. Their periodic variation in refractive index in one, two, or three dimensions results in a photonic bandgap, that is, a frequency range for which light is not allowed to travel through the material. By locally disturbing this periodicity, light can be confined to small volumes within the photonic crystal or guided along a path through the photonic crystal. Photonic crystal components are ideal building blocks for photonic integrated circuits. The first goal of this project is to install and explore the possibilities of a unique multi-functional setup for investigating photonic crystals. An important operation mode of this setup is Scanning Near-field Optical Microscopy (SNOM) combined with transmission spectroscopy and photoluminescence experiments. At the same time, the sample can be viewed with visible-light and infrared cameras through a microscope. All functionalities have been demonstrated using InGaAsP photonic crystals. Subsequently, this setup is used to study a new type of hybrid photonic integrated circuits consisting of InGaAsP membranes connected to InP-InGaAsP waveguides. SNOM as well as transmission spectroscopy are used to study the effect that the local conversion of photonic crystals into membranes has on the bandgap. The bandgap appears much sharper after this conversion. The light distribution in a planar waveguide, a photonic crystal, a photonic crystal cavity, and a photonic crystal waveguide are investigated with SNOM. Periodic variations in the light intensity is observed which can be attributed to standing waves in most cases. The effect of the photonic bandgap is also seen in these SNOM measurements. An increased transmission is measured near the frequency at which the cavity mode is expected from simulations. Finally, the interface between a membrane waveguide and a conventional waveguide is observed by infrared microscopy.
Scanning near-field optical microscopy and transmission spectroscopy of InGaAsP photonic crystal membranes
Kersten, S. P. (Auteur). 28 feb. 2009