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Authors: A. Pandey, S. Dwivedi, Z. Tang, Shilong Pan, D. Van Thourhout
Title: Nonreciprocal Light Propagation in a Cascaded All-Silicon Microring Modulator
Format: International Journal
Publication date: 6/2021
Journal/Conference/Book: ACS Photonics
Editor/Publisher: American Chemical Society, 
Volume(Issue): 8(7) p.1997-2006
DOI: /10.1021/acsphotonics.1c00040
Citations: Look up on Google Scholar
Download: Download this Publication (7MB) (7MB)


Optical isolators and circulators are critical building blocks for large-scale photonic integrated circuits. Among the several methods proposed to realize such nonreciprocal devices, including heterogeneous integration with garnet-based materials or using nonlinearities, dynamic modulation of the waveguide properties is a potentially practical and easily accessible method. However, most proposals relying on this method rely on modulators with a very large footprint, limiting their practical applicability. This paper overcomes this issue by presenting a method to achieve nonreciprocal optical transmission taking advantage of compact ring modulators. We use a cascaded system of microring modulators with a footprint as small as 15 μm × 220 μm and propose that, by tuning the relative time delay between the RF driving signals and the optical delay between the modulators, nonreciprocal transmission can be achieved. We present a detailed theoretical analysis of our design and investigate the origin of the asymmetric transmission. The modulators were designed and fabricated on IMEC’s Silicon-on-Insulator platform iSiPP50G. We achieve a 16 dB difference between forward and backward optical signals at a driving voltage (Vpp) of 8 V at 6 GHz. Moreover, we analyze the impact of fabrication imperfections on the device performance. Our work leads to a significant reduction in device footprint compared to formerly explored solutions using dynamic modulation and is well suited for monolithic integration with photonic integrated circuits.

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