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.
An optical coupling interface is a crucial component in Silicon Photonics (SiPh) technology for optical signal transmission. It is widely utilized to achieve on-chip light sources and optical input/output for SiPh chips. In this work, we report a coupling interface with a focusing structure based on the 3μm SOI waveguide platform to minimize mode profile mismatch, resulting in a high coupling efficiency and relatively large -1dB alignment tolerances across a wide bandwidth. Simulation results show that our design achieved a high transmission of greater than -0.85dB across the 1500-1600nm range, with a maximum of -0.847dB. When the laser is positioned 1.5μm away from the waveguide facet, the -1dB tolerances are ±0.62μm and ±0.45μm in the horizontal and vertical directions, respectively. Additionally, the interface is safe for lasers as it has a return loss (caused by reflection) of less than -30dB.
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