Abstract
Optical waveguide-based sensors are gaining popularity due to their cost-effectiveness, compact size, and high sensitivity. There are two primary techniques for designing these sensors: changes in effective refractive index or changes in the evanescent field ratio. The absorption property, specifically the evanescent field-based photonic sensing approach, is preferred over effective index-based sensing. This preference arises from the fact that the change in effective index is relatively smaller when the sensing material is present, compared to the change in the evanescent field. The absorption of light depends on the dimension and material of the sensor device, the operating wavelength, and the material being sensed. The percentage of evanescent field/light in the upper cladding/slot region of the photonic waveguide changes during its interaction with the molecules of the sensing material. Therefore, it is crucial to design photonic sensors with waveguides that have a relatively larger evanescent field in the upper cladding region. In slot waveguides, light is predominantly confined to the slot region, resulting in a higher evanescent field value. As the sensitivity of the photonic sensor depends on the percentage of evanescent field/light in the upper cladding region, the slot waveguide offers significantly higher sensitivity compared to other photonic waveguide structures.