Pillar-Array Based Two-Dimensional Photonic Crystal Cavities

Alan Tao Xu

The Edward S. Rogers Sr. Department of Electrical and Computer Engineering (Photonics)

Abstract:

Pillar-array based optical cavities have unique properties, e.g., having a large and connected low dielectric index space (normally air space), exhibiting a large band gap for transverse magnetic modes and standing on a substrate. These properties make them well suitable for applications such as optical sensing and terahertz quantum cascade lasers. However there has been rare research in it due to the common belief that pillar arrays have excessive leakage to the substrate.  With careful design, we provided several methods to reduce such leakage and experimentally proved a high quality factor (Q) pillar-array based cavity is practical. We also explored the usage of such a cavity for sensing.

Numerical methods such as finite-difference time-domain and plane-wave expansion were used in the design of the cavity. Then in microwave spectrum, cavities consisting of dielectric rods were used to test the validity of the theory. Additionally, the dependence of the Q on the materials losses was nvestigated. We observed that a high-Q cavity for modes above light line is feasible and it is very suitable to measure the optical absorption of materials introduce inside the mode volume.  Finally in the optical domain, pillar arrays were fabricated in Si/SiO2 material system and measured. Q as high as 27,600 was shown and when applying accurate refractive indices, for every delta n = 0.01, the peak wavelength shifts as large as 3.5 nm, testifying the ultra sensitivity of the cavity to the environmental dielectric change.

Biography:

Tao Xu obtained a bachelor of engineering degree from the Electronics Engineering Department of Tsinghua University in 2002. After graduation, he entered the optical communication lab in Tsinghua University as a research assistant, where he studied the performance of a Raman Amplifier for long-haul optical communication. In 2003, he joined the advanced nanotechnology center at the University of Toronto to pursue a master degree and continued for his PhD study in the same group, supervised by Dr. Harry Ruda. His research interests are photonic crystals, optical biosensing and semiconductor nanomaterials.