PROJECT TITLE :

Photonic Generation of Linearly Chirped Microwave Waveforms Using a Silicon-Based On-Chip Spectral Shaper Incorporating Two Linearly Chirped Waveguide Bragg Gratings

ABSTRACT:

Photonic generation of linearly chirped microwave waveforms employing a silicon-based mostly on-chip spectral shaper is proposed and demonstrated. The on-chip optical spectral shaper includes a Mach–Zehnder interferometer (MZI) structure, in which 2 identical linearly chirped waveguide gratings (LC-WBGs) with opposite chirp rates are incorporated into the two arms. The LC-WBGs are fabricated on 2 rib waveguides by linearly varying the rib widths along the gratings to produce linear chirps. By adding an offset waveguide to 1 arm of the MZI and controlling the length of the offset waveguide, the spectral response of the shaper will be controlled to possess a symmetrical, linearly increasing, or linearly decreasing free spectral range, that is needed for the generation of a linearly chirped microwave waveform primarily based on spectral-shaping and wavelength-to-time mapping. The proposed device is fabricated employing a CMOS-compatible process with 193-nm deep ultraviolet lithography. A theoretical analysis on the chirped microwave waveform generation is performed, that is verified by an experiment. 2 linearly chirped microwave waveforms with symmetrical and uniform chirp profiles are experimentally generated using 2 fabricated spectral shapers with completely different lengths of the offset waveguides.