Low-Power Broadband Thermo-Optic Switch With Weak Polarization Dependence Using a Segmented Graphene Heater

We propose and demonstrate experimentally a 2 × 2 polymer optical waveguide thermo-optic switch, featuring wide bandwidth, low power, and weak polarization dependence. Our proposed switch is based on Mach-Zehnder interferometer (MZI) configuration and driven by a segmented graphene electrode heater formed with four identical small heaters in parallel. The use of the parallel graphene electrode heater can improve the heating efficiency by placing the heater in direct contact with the waveguide core and achieve a low driving voltage. Unlike the works reported previously, the graphene electrode heater used here achieves negligible light absorption for both the transverse electric (TE) and the transverse magnetic (TM) polarizations and, hence, weak polarization-dependent operation because a large cross-sectional square waveguide structure without upper cladding is employed. Meanwhile, two asymmetric directional couplers are employed to achieve broadband operation. Our fabricated device, which has a length of 9.5 mm, exhibits extinction ratios higher than ~13.5 dB over a wavelength range of 1530 - 1605 nm and higher than ~26 dB at 1561 nm for all channels. The switching powers are ~3.30 and 3.12 mW for the TE and TM polarizations, respectively. The insertion losses are lower than 10.5 dB for all channels. The rise and fall time of switching are 0.98 and 0.52 ms, respectively.