University PhD Dissertation Defense for Sora Kim

Photonic crystal mirrors:

Fundamental components for integrated photonic crystal MEMS

 

Sora Kim

Research Advisor: Olav Solgaard

 

Time: 1:15pm, March 14th, 2008 (Refreshment: 1:00pm)

Place: CISX-Auditorium

 

Abstract:

The 2D photonic crystal (PC) slab is an interesting optical component due to its ability to confine photons 3-dimensionally and couple to external radiation as well as its simplicity of fabrication. Many novel optical devices have been proposed based on the 2D PC slabs such as PC-based light-emitting diodes, lasers, directional output couplers, and sensors. Specifically, we are interested in integrating 2D PC slabs in optical MEMS devices such as tunable filters, position sensors, and scanners in order to achieve compactness and better sensitivity.

 

In the first part of the talk, a broadband PC mirror based on a 2D PC slab, which is a basic component of the optical PC MEMS devices, is discussed. Dielectric mirrors are preferred to metal mirrors in optical communication wavelengths because of their low loss. For example, Distributed Bragg Reflector (DBR) mirrors are commonly used for very high reflectivity (~99.5%). However, these mirrors consist of several pairs of dielectric layers, complicating their fabrication and resulting in bulky mirrors. 2D PC mirrors can be excellent alternatives to DBR mirrors because they have comparable reflectivity with a single dielectric layer. In the talk, I will review the basic principles of how to achieve a broadband spectrum by 2D PC slabs and present a broadband mirror with high reflectivity around 1550nm and small polarization and angular dependences.

 

In the second part of the talk, I will focus on ways to improve the optical spectrum of 2D PC mirrors by controlling the surface quality. Hydrogen annealing is a traditional way of reducing the roughness of etched silicon surfaces. We showed that the silicon migration of hydrogen annealing could be used to improve the optical spectrum of 2D PC mirrors by smoothing the rough interfaces and increasing the uniformity of PC holes. In particular, we applied hydrogen annealing on a 2D PC mirror that was processed on a silicon substrate by isotropic silicon etching (GOPHER). The reflectivity of the 2D PC mirror increased and the polarization dependence decreased.

 

In the last part, I will briefly introduce a 2D PC MEMS scanner and a 2D PC displacement sensor as applications of 2D PC mirrors that are integrated into optical MEMS are introduced.