On Chip Optical Sensing Platforms

Abstract

Sensing has become an important field of research because of its wide variety of applications, such as; chemical sensing, biomedical diagnostics, environmental gas monitoring and oil quality monitoring. This has spurred researcher across various fields for innovative development of new sensing techniques. These new techniques need to be both sensitive and selective to give direct evidence of the presence of the target analyte/molecule. Compared to the traditional electronic and mechanical based sensing techniques, optical sensing offers superior sensitivity and selectivity. However, to sense low concentrations, meter-long interaction path between the target molecules and light is required, thus making it bulky and unsuitable for portable applications. On-chip photonic sensor based on waveguide could address the challenges in the conventional optical sensing system by taking advantages of reduction in the system footprint by orders of magnitude. Additionally, the compatibility with micro- and nano-fabrication technology reducing the cost. For small-scale production, electron beam lithography (EBL) based fixed-beam-moving-stage (FBMS) technique is widely used for writing stich-error-free structures. However, the writing is limited to primitive patterns such as circles, squares and rectangles. A combination of FBMS and area mode is used to write a smoothly varying polygon, which often results in a misalignment between the two-writing process. To mitigate this, we propose and demonstrate a method that offers smooth and alignment-error-free tapering. Using the proposed method, we experimentally demonstrated a stitch-error and misalignment free patterning of different photonic circuit components such as power splitter, interferometer and resonator. In waveguide-based sensing, sensitivity is a combination of the strength of interaction and the underlying waveguide/resonator s sensitivity to the change in refractive index or absorbance...