Highly sensitive liquid refractive index sensor based on a polymer two-mode ridge waveguide interferometer

In this paper, we propose and experimentally demonstrate a highly sensitive liquid refractive index (RI) sensor based on a two-mode interferometer (TMI) formed with a polymer ridge waveguide. Compared with the rectangular waveguide TMI sensor, our proposed ridge waveguide TMI sensor enables a higher waveguide sensitivity and hence device sensitivity. Our experimental results show that the fabricated ridge waveguide TMI sensor achieves a sensitivity of 6980.62 nm/RIU, indicating a significant improvement over the fabricated rectangular waveguide TMI sensor with almost identical dimensions; the latter exhibits a sensitivity of 3753.81 nm/RIU. Our proposed sensor is simple in structure but has high sensitivity and low cost.