Integrated Discretely Tunable Optical Delay Line Based on Step-Chirped Subwavelength Grating Waveguide Bragg Gratings

We demonstrate experimentally a discretely tunable optical delay line (ODL) using a step-chirped subwavelength grating (SWG) waveguide Bragg grating (BG) in silicon-on-insulator (SOI). The step-chirped structure is implemented using a serial array of 10 SWG waveguide BGs. It is designed using 3D finite-difference time-domain (FDTD) and the transfer matrix method (TMM), and is fabricated using electron beam lithography with a single etch. The grating structure has a total time delay of ~60 ps in steps of ~6.6 ps over an operating bandwidth of 41.7 nm; the measured results are in good agreement with simulations. We demonstrate the application of the ODL for antenna beamforming in simulations; in particular, we calculate the array factors for different phased array antennas using the measured time delays.