Highly Sensitive and Cost-effective Liquid Refractive Index Sensor Based on Polymer Two-mode Waveguide Interferometer

We propose and demonstrate a highly sensitive and cost-effective liquid refractive index (RI) sensor based on polymer two-mode interferometer (TMI). The proposed sensor uses a rectangular two-mode waveguide as the sensing probe. The structural parameters of the sensor are designed and simulated meticulously, and a transverse offset between the single-mode waveguide and the two-mode waveguide is introduced to increase the extinction ratio so as to improves the accuracy of the sensing. The experimental results show that the RI sensitivity of the sensor can reach 5274nm/RIU, while the limit of detection (LOD) is about 5.68×10
⁻⁶
RIU. Our proposed polymer TMI sensor can realize high RI sensitivity and has a simple structure and low cost, which is suitable for large-scale fabrication.