Femtosecond Laser Direct-Writing On-Chip MZI Temperature Sensor Based on Polymer Waveguides

A Mach–Zehnder interferometer (MZI) based on-chip integrated photonic made of polymer waveguides (PWs) sensor with a pair of interference arms of different sizes was directly written using a two-photon polymerization (TPP) technique. The sensor exhibits good temperature response characteristics due to the effective refractive index of two asymmetric interference arms to temperature changes varies, and the temperature sensitivity can reach −348.5 pm/°C in the temperature range of 20 °C–60 °C without any treatment. Moreover, after packaging with temperature-sensitive material polydimethylsiloxane (PDMS), the sensitivity of the sensor increased by about six times, exhibiting similar heating and cooling sensitivity within the range of 30 °C–70 °C, approximately −2.01 nm/°C. As a compact on-chip photonic device, the proposed sensor has excellent temperature sensitivity, biocompatibility, and stability. It is expected to be integrated into a variety of small and complex environments to achieve temperature monitoring.