Ashley J. Maker

Optical toroid resonators are doughnut-shaped silica devices made on a silicon pillar. Due to their smooth surface and isolation from the silicon substrate, toroids make excellent optical resonators with quality factors on the order of 100 million. As a result, optical toroids can be used in many key applications, including integrated optics, lasers, and even as biosensors capable of detecting single molecules.

The goal of my current research project is to make toroid biosensors, and use these sensors to study biological systems. This research is currently in progress. Please check back soon for more updates.

To develop effective waveguide sensors, we must first fabricate waveguides which trap light very effectively and thus have low optical loss. My first research project in the Armani Lab focused on developing a low loss waveguide usable for biosensing and integrated optics applications.

Optical waveguides are devices which trap and transfer light. They effectively confine light by total internal reflection. Total internal reflection is an optical phenomenon which causes light to be trapped between a core of refractive index n1 surrounded by another medium with lower refractive index n2 (cladding).

Some light escapes through the waveguide’s cladding and forms an exponentially decaying electromagnetic wave, known as the evanescent field. For waveguide sensors, the evanescent field can be used to probe the area surrounding the waveguide for changes in refractive index.

In a biosensor, the waveguide’s surface may be covered with antibodies or other materials to which specific biomolecules can bind. When an analyte molecule binds to the waveguide’s surface, the refractive index of the surface changes. This refractive index change alters the waveguide’s evanescent field, causing either a power change or a phase shift in the light traveling through the core.

A detector at the end of the waveguide measures these changes, from which the concentration of the analyte can be determined. In this way, the waveguide can be used as a label-free sensing device to detect the presence of specific analytes.