Wavelength tunable thermo-optic filter using buckling effect of etalon composed poly-Si/SiO2 multi-layers

Wavelength tunable thermo-optic filter has been designed and fabricated for 1550 nm transmission. Its basic structure has a Fabry–Perot resonator with a poly-Si cavity layer at the center and two sets of distributed Bragg reflector (DBR) mirrors consisting of four poly-Si/SiO ₂ multi-layers. The device uses free-standing membrane surrounded by thick silicon frame and thus its surface is buckled due to the residual stress. Its transmitted wavelength can be tuned from 1554.4 nm at 25.3 °C to 1565.7 nm at 100 °C, and thus tuning efficiency of 0.15 nm/K for the temperature range of 74.7 °C is obtained. It is believed that the buckling effect of the filter results in wider tuning range and higher tuning efficiency than that of plane filters without buckling effect. It is also found that the buckled membrane increases the tolerance limit of tilting errors of the filter.