Noval chiral azobenzene-containing polyurethanes: synthesis, optical properties and simulation comparison of two kind of polymeric thermo-optic switches

In this work, three different structures of chiral side-chain azo polyurethane (CAPU-1), chiral graft azo polyurethane (CAPU-2) and chiral disazo polyurethane (CAPU-3) were synthesized by diazo coupling reaction. The structures of the synthesized compounds of CAPU-1 ~ 3 were measured by FT-IR and UV-Vis spectroscopy. The thermal and mechanical properties of CAPU-1 ~ 3 were investigated. The refractive index (n) and transmission loss of CAPU-1 ~ 3 was measured by ATR technique and CCD digital imaging devices. The Y-branch and Mach–Zehnder polymeric thermo-optic switches were simulated based on the synthesized three chiral azo polyurethanes as waveguide materials. The results demonstrate that the thermo-optic coefficients (dn/dT) of CAPU-1 are −7.21 × 10 °C (532 nm), −8.01 × 10 °C (650 nm) and −8.34 × 10 °C (850 nm); CAPU-2 are −6.39 × 10 °C (532 nm), −7.83 × 10 °C (650 nm) and −8.71 × 10 °C (850 nm); CAPU-3 are −8.22 × 10 °C (532 nm), −8.74 × 10 °C (650 nm) and −9.78 × 10 °C (850 nm), respectively. The transmission losses of CAPU-1 ~ 3 are 0.1816 dB/cm, 0.1908 dB/cm and 0.1705 dB/cm, respectively. The response times of the Y-branch thermo-optic switch of CAPU-1 ~ 3 are 4 ms, 18 ms and 18 ms, respectively; and the response times of the Mach–Zehnder polymeric thermo-optic switch of CAPU-1 ~ 3 are 0.8 ms, 4 ms and 4 ms, respectively. The significant differences in performance are owing to the different substituents and structure of the azo compound. The conclusion had potential significance to improve and develop the new digital optical and thermo-optic switch with short response time and low driving power.