Digitally tunable dispersion controller using chirped multimode waveguide gratings

Abstract

We propose a digitally tunable dispersion controller (DTDC) for dispersion management that shows potential for realizing phase correction, waveform generation, beamforming, and pulse sculpting in many photonic systems. The controller consists of N stages of cascaded chirped multimode waveguide gratings (MWGs) as well as ( N +1) Mach–Zehnder switches (MZSs) on silicon. We introduce MWG technology so that the reflected light can be separated from the input signal even without a circulator, which makes it convenient for various system applications. All the chirped MWGs are identical so that the photonic circuit design is convenient, while the number, m , of the chirped MWGs in cascade for the n th stage is given by m =2 ( n −1) . The total dispersion from the DTDC is accumulated by all the stages, depending on the states of all the 2×2 optical switches. Since there are 2 N −1 chirped MWGs in total, the total dispersion can be freely tuned from 0 to (2 N −1) D 0 by a step of D 0 , where D 0 is the dispersion provided by a single chirped MWG. As an example, we designed a DTDC consisting of four stages of chirped MWGs ( N =4) and five MZSs and demonstrated its low loss as well as its high-quality group delay response. A chirped MWG with a 2-mm-long grating section has a dispersion of D 0 =2.82ps/nm in a 20-nm-wide bandwidth, and accordingly the maximum dispersion is given as 42.8 ps/nm by switching the MZSs appropriately. Our on-chip DTDC provides a brand-promising option for broadband flexible dispersion management in optical systems of microwave photonics and optical communications.