Nonreciprocal Light Propagation in a Cascaded All-Silicon Microring Modulator

Abstract

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 (V pp ) 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.

On-chip wavelength division multiplexing filters using extremely efficient gate-driven silicon microring resonator array

“…To meet the grand challenge of bandwidth density, on-chip wavelength division multiplexing (WDM) optical interconnects are proposed and demonstrated for highly parallel optical interconnect systems 2 – 4 . For on-chip WDM optical interconnects, silicon microring resonators (Si-MRRs) can function both as wavelength filters and as electro-optic modulators with great advantages in ultra-compact footprint and high energy efficiency 2 , 5 , 6 . A typical on-chip WDM module can be formed by coupling an array of Si-MRRs with different resonant wavelengths (λ res ) to a single bus waveguide, and each Si-MRR can be independently tuned and modulated 3 .…”

Design Guidelines for a Tunable SOI Based Optical Isolator in a Partially Time-Modulated Ring Resonator

“…An optical isolator based on the indirect interband transition in a silicon nitride ring resonator was demonstrated, with better performance and smaller footprint, however in this structure spatio-temporal modulation is realized using acousto-optic modulation with aluminum nitride piezoelectric actuators, which requires additional step compared to the conventional CMOS fabrication process [28]. Recently an experimental proposal, based on two cascaded silicon microring modulators was presented [29], in which non-reciprocity was obtained by tuning the relative time delay between the RF driving signals and the optical delay between the modulators. Although in this method traveling wave modulation is not required and it provides even better isolation, using two ring resonators requires more space and may add more complexity to the design.…”

Sub-Volt High-Speed Silicon MOSCAP Microring Modulator Driven by High Mobility Conductive Oxide

“…Existing Si-MRMs available in the foundry process are based on reversed PN junctions, which can achieve ultra-high modulation bandwidth but usually require more than 2 V of driving voltage (V pp ) [13][14][15][16] . Such high V pp is induced by the relatively weak plasma dispersion effect of silicon and the small capacitance per unit length of the reversed PN-junction, which is usually less than 2 fF/μm 17,18 .…”