A silicon-based digitally tunable positive/negative dispersion controller (DC) is proposed and realized for the first time using the cascaded bidirectional chirped multimode waveguide gratings (CMWGs), achieving positive and negative dispersion by switching the light propagation direction. A 1 × 2 Mach–Zehnder switch (MZS) and a 2 × 1 MZS are placed before and after to route the light path for realizing positive/negative switching. The device has Q stages of identical bidirectional CMWGs with a binary sequence. Thus the digital tuning is convenient and scalable, and the total dispersion accumulated by all the stages can be tuned digitally from − ( 2Q − 1 ) D0 to ( 2Q − 1 ) D0 with a step of D0 by controlling the switching states of all 2 × 2 MZSs, where D0 is the dispersion provided by a single bidirectional CMWG unit. Finally, a digitally tunable positive/negative DC with Q = 4 is designed and fabricated. These CMWGs are designed with a 4-mm-long grating section, enabling the dispersion D0 of about 4.16 ps / nm in a 20-nm-wide bandwidth. The dispersion is tuned from −61.53 to 63.77 ps / nm by switching all MZSs appropriately, and the corresponding group delay is varied from −1021 to 1037 ps.
Dispersion management is highly desired in various applications such as microwave photonics and optical communication, helping reduce the delay disorder and modulate the pulse profiles. In this paper, we propose a new concept of digitally-tunable dispersion management. and a digitally-tunable dispersion controller (DTDC) on silicon composed of optical switches and chirped multimode waveguide gratings (CMWGs) is demonstrated for the first time. All the CMWGs are identical and have the same dispersion value of D0 and dispersion ranging from 0 to (2N-1)D0 can be tuned with a step of D0 by switching the propagation path of light. More importantly, the DTDC is circulator-free. finally, a DTDC is realized with four stages of 2-mm-long CMWGs, enabling the dispersion tuning from 0 to 42.8 ps/nm with a step of 2.82 ps/nm.
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