Polarization-insensitivity and rapid-calibration optical delay line on 3-μm-thick SOI photonics platform

We design, fabricate, and characterize a polarization-insensitivity 8-bit optical tunable delay line (OTDL) on the 3-μm-thick silicon-on-insulator (SOI) platform, employing low-loss waveguide spirals and rapid-calibrated integrated optical switches. The spirals integrate mode converters and Euler bends, have high fabrication tolerance, low wavelength sensitivity, and propagation loss as low as 0.32 dB/cm within 140 nm bandwidth. The 4-cm-length waveguide spiral has polarization dependent loss (PDL) less than 0.3 dB within 140nm bandwidth. OTTDL utilizes optical switches with extinction ratio (ER) of up to 50 dB for path switching. The switch integrated multimode interferences (MMIs), thermo-optic phase shifter and variable optical attenuators (VOAs). VOAs not only enhance the delay signal-to-noise ratio, but also facilitate rapid calibration in OTDLs. With maximum delay time of 3570 ps and resolution of 14 ps, our OTDL holds significant promise for future applications, particularly in the integration of delay line arrays for microwave photon radar systems.