title: Tunable spiral Bragg gratings in 60-nm-thick silicon-on-insulator strip waveguides.
abstract: We demonstrate spiral integrated Bragg gratings (IBGs) in 60-nm-thick strip waveguides on the silicon-on-insulator (SOI) platform. The length of the spiral IBG is 2 mm, occupying an area of 147 × 141 μm2with a minimum bending radius of 20 μm. Experiments show that the spiral IBGs exhibit a single narrow transparent peak with a Q-factor of 1 × 105in a broad stopband, induced by the phase shift of the S-junction at the spiral center. This phenomenon is analogous to the electromagnetically induced transparency (EIT) effect. The transparent peak can periodically shift in the stopband upon heating of the S-junction using a TiN-based heater on top. The peak transmittance and Q-factor are dependent on the reflectivity of the spiral IBG. The transparent peak can be completely eliminated under a certain tuning power, and the spiral IBG hence behaves as a bandstop optical filter. The bandwidth is 0.94 nm and the extinction ratio is as high as 43 dB. The stopband can also be shifted by heating the Bragg gratings using a separate TiN heater. The experimental results agree well with the modeling results based on the transfer matrix method.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Zou
authors.forename: Linjie
authors.initials: L
authors.lastname: Zhou
authors.forename: Minjuan
authors.initials: M
authors.lastname: Wang
authors.forename: Kan
authors.initials: K
authors.lastname: Wu
authors.forename: Jianping
authors.initials: J
authors.lastname: Chen