The slot structure has great advantages in improving the sensitivity of integrated waveguide optical sensors and reducing the detection limit. We propose a polymer Mach-Zehnder interferometer (MZI) optical sensor based on the slot structure and adopted the suspended structure to improve optical field interaction with the analyte, hence boosting the sensor's sensing accuracy. In this paper, the effects of the single waveguide width, slot width, and coupling structure of the slot waveguide on the performance of the sensor operating at a 1550 nm wavelength were analyzed. Under the premise of satisfying single-mode transmission, we designed an MZI with a branch spacing of 10 µm, arm length of 2045 µm, branch span of 700 µm, and slot region of 500 µm. The sensor's average sensitivity was 972.1 dB/RIU, and its average detection resolution was 1.6 × 10-6 RIU, which is approximately 1.5 times higher than that of the suspended strip waveguide, 1.6 times higher than that of the non-suspended slot structure, and 2.1 times higher than that of the non-suspended strip waveguide.
Keywords: integrated optics; optical sensing; polymeric Mach–Zehnder interferometer; slot waveguide.