Guilherme F. M. Rezende

Embedded coupled microrings with high-finesse and close-spaced resonances for optical signal processing

Single microring resonators have been used in applications such as wavelength multicasting and microwave photonics, but the dependence of the free spectral range with ring radius imposes a trade-off between the required GHz optical channel spacing, footprint and power consumption. We demonstrate four-channel all-optical wavelength multicasting using only 1 mW of control power, with converted channel spacing of 40-60 GHz. Our device is based on a compact embedded microring design fabricated on a scalable SOI platform. The coexistence of close resonance spacing and high finesse (205) in a compact footprint is possible due to enhanced quality factors (30,000) resulting from the embedded configuration and the coupling-strength dependence of resonance spacing, instead of ring size. In addition, we discuss the possibility of achieving continuously mode splitting from a single-notch resonance up to 40 GHz.

Spectral Engineering With CMOS Compatible SOI Photonic Molecules

Photonic systems based on microring resonators have a fundamental constraint given by the strict relationship among free spectral range, total quality factor QT , and resonator size, intrinsically making filter spacing, photonic lifetime, and footprint interdependent. Here, we break this paradigm employing CMOS-compatible silicon-on-insulator photonic molecules based on coupled multiple inner ring resonators. The resonance wavelengths and their respective linewidths are controlled by the hybridization of the quasi-orthogonal photonic states. We demonstrate photonic molecules with doublet and triplet resonances with spectral splitting only achievable with single-ring orders of magnitude larger in footprint. In addition, this splitting is potentially controllable based on the coupling (bonds) between resonators. Finally, the spatial distribution of the hybrid states allows up to sevenfold QT enhancement.

Modeling quasi-dark states with temporal coupled-mode theory.

Coupled resonators are commonly used to achieve tailored spectral responses and allow novel functionalities in a broad range of applications. The Temporal Coupled-Mode Theory (TCMT) provides a simple and general tool that is widely used to model these devices. Relying on TCMT to model coupled resonators might however be misleading in some circumstances due to the lumped-element nature of the model. In this article, we report an important limitation of TCMT related to the prediction of dark states. Studying a coupled system composed of three microring resonators, we demonstrate that TCMT predicts the existence of a dark state that is in disagreement with experimental observations and with the more general results obtained with the Transfer Matrix Method (TMM) and the Finite-Difference Time-Domain (FDTD) simulations. We identify the limitation in the TCMT model to be related to the mechanism of excitation/decay of the supermodes and we propose a correction that effectively reconciles the model with expected results. Our discussion based on coupled microring resonators can be useful for other electromagnetic resonant systems due to the generality and far-reach of the TCMT formalism.

Low-power four-channel wavelength multicasting in embedded microring resonators

We demonstrate four-channel all-optical wavelength multicasting using only 1 mW of pump power and channel spacing of 40-60 GHz. Our device is based on a compact embedded microring design fabricated on a scalable SOI platform.