Graduate Exam Abstract

Abstract: B iosensors are powerful analytical devices that integrate biological sensing elements with physicochemical transducers to detect and quantify specific analytes, offering wide-ranging applications in fields such as medical diagnostics, environmental monitoring, food safety, and drug discovery. Bimodal waveguide (BiMW) biosensors, a type of interferometric optical biosensor, proven to be one of the best optical biosensors based on their high sensitivity, real-time detection and compact design. During its early development stages in the early 2010’s, the height of the bimodal waveguide was increased to induce interference between the fundamental and first-order modes. Later, in late 2010’s, changes in the width of the bimodal waveguide were used instead to induce this interference. Our novel design builds upon these advancements, focusing on optimizing the sensitivity and fringe visibility. Our device consists of three main parts: A single-mode input waveguide, a bimodal waveguide interferometer, and two output waveguide arms. The analyses and simulations were conducted using varFDTD, a 2.5 variational finite-difference time-domain (FDTD) method, and Finite-Difference Eigenmode (FDE) methods in Ansys Lumerical. To explore the fringe visibility of the interferometer, we monitor the simulated transmission in the output waveguide arms. To maximize the fringe visibility and sensitivity, we varied multiple parameters. In particular, we varied the input waveguide width from 250 nm to 450 nm, and the input waveguide offset, which is the lateral displacement between the input single-mode waveguide and the bimodal waveguide, from 0 to 150 nm. In addition, we varied the bimodal waveguide width from 600 nm to 850 nm, and the gap between the output waveguide arms from 50 nm to 150 nm. We found that increasing the input offset and the gap can lead to a decrease in the fringe visibility. On the other hand, decreasing the input width and the bimodal waveguide width can lead to an increase in the fringe visibility. We concluded that the best design is the one with 102 rad/RIU cm, which is the change in phase (measured in radians) per unit change in refractive index (RIU) per unit length (cm) of the sensing region.

Adviser: Mahdi Nikdast
Co-Adviser: Kevin Lear
Non-ECE Member: Matt Kipper
Member 3: N/A
Addional Members: N/A

Publications:
N/A

Program of Study:
ECE544
ECE556
ECE527B/F
ECE516
ECE580C6
ECE561
GRAD510
GRAD530