Design of Integrated Optoelectronic Sensors with Novel III-V Laser

Abstract

Optical sensing techniques are under continuous development and can offer clinicians reliable and efficient tools for monitoring, diagnosis, prognosis and therapeutic purposes. For example, many diseases, such as diabetes and cardiovascular disease, require continuous monitoring of glucose levels and other intermittent signs from time to time. Existing methods required for monitoring have limitations to the volume of analytes extracted plus, system bulkiness and immobility makes it expensive for both patient and healthcare practitioners to cope with the treatment requirements. In this work we address those challenges by designing an integrated optical sensor that consists of a quantum well laser as the light source and an optical sensing head occupying a small chip area of about 2cmx2cm. First the laser is designed to emit light of longer wavelengths in the infrared region of the electromagnetic spectrum. This is achieved by using III-V alloys such as, InP, InxGa(1-x)As, InxAl(1-x)As and InxAlyGa(1-x-y)As which constrain the laser to emit at wavelengths between 1300nm and 2100nm by varying their mole-fractions, x and y. Secondly, the laser is made widely tunable by introducing racetrack array resonators with high quality factor as opposed to straight cavity lengths used in traditional laser systems. The electronic behavior of the quantum well laser was simulated using TCAD Sentaurus, device simulator, and the optical behavior modeled using MIT-MEEP FDTD simulator. Next we design the sensor head using coupled mode theory (CMT) and effective index approximation method. The proposed sensor is built on a SiO2 substrate with refractive index (RI) 1.5 and consists of 7 waveguides made of Silicon oxynitride with RI of 1.45. The principle of detection rests on observing power changes in the sensor due to small RI change in the cladding. The detection range of the sensor is from 1.33 to 1.448 and the sensitivity is about 10ppm.

Date of Award	Jun 2013
Original language	American English
Supervisor	JAIME Viegas (Supervisor)