Tunable Grating Couplers for Broadband Operation Using Thermo-Optic Effect in Silicon

We demonstrate a tunable grating coupler for broadband operation using an impurity-doped thermo-optic heater fabricated by complementary metal-oxide-semiconductor-compatible processes. As a thermo-optic heater, a p-n diode is employed to have a p-type region inside of an in-coupling grating connected with outside p+/n+ contacts and is heated directly by a current flow through the grating. Applying a forward-bias voltage of 7 V, we shift the central wavelength of the grating coupler from 1525 to 1574 nm with a coupling efficiency of close to -4 dB. Considering a 1-dB bandwidth at each central wavelength, we extend the operational bandwidth to nearly 90 nm. A thermal tuning efficiency of 0.23 nm/mW and transient responses of 32/22 μs for heating/cooling times are obtained.