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 nth 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)D0 by a step of D0, where D0 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 D0=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.