Fabrication-friendly subwavelength-structure-assisted waveguide for dispersion engineering

Phased-locked two-color single soliton microcombs in dispersion-engineered Si3N4 resonators

We propose and theoretically investigate a dispersion-engineered Si3N4 microring resonator, based on a cross section containing a partially-etched trench, that supports phase-locked, two-color soliton microcomb states. These soliton states consist of a single circulating intracavity pulse with a modulated envelope that sits on a continuous wave background. Such temporal waveforms produce a frequency comb whose spectrum is spread over two widely-spaced spectral windows, each exhibiting a squared hyperbolic secant envelope, with the two windows phase-locked to each other via Cherenkov radiation. The first spectral window is centered near the 1550 nm pump, while the second spectral window is tailored based on straightforward geometric control, and can be centered as short as 750 nm and as long as 3000 nm. We numerically analyze the robustness of the design to parameter variation, and consider its implications to self-referencing and visible wavelength comb generation.

Compact fabrication-tolerant subwavelength-grating-based two-mode division (de)multiplexer

Regarding the importance of bandwidth and capacity expansion in communication systems, a novel mode division (de)multiplexer based on subwavelength grating (SWG) is proposed. SWG-based devices could have smaller sizes, be much more fabrication-tolerant, and have much wider bandwidths due to the reduced confinement of the field and dispersion. It is also feasible to reduce the loss of a SWG-based device by tuning the duty cycle of the grating. Owing to these properties of SWGs, we have designed a compact fabrication-tolerant two-mode division (de)multiplexer. A flat-top transmission of >0.89 (loss <0.5  dB) is obtained over 65 nm from 1500 to 1565 nm, completely covering the entire C-band used for dense wavelength division multiplexing. Moreover, the cross-talk is <-10  dB for a broad bandwidth of ∼120  nm over which the loss of the complete device including both multiplexer and demultiplexer is <1  dB. Therefore, the proposed device is promising for high-capacity optical communications in both conventional and entirely SWG-based silicon photonic circuits.

Dispersion control of silicon nanophotonic waveguides using sub-wavelength grating metamaterials in near- and mid-IR wavelengths

Controlling the group velocity dispersion of silicon nanophotonic waveguides has been recognized as a key ingredient to enhance the development of various on-chip optical applications. However, the strong wavelength dependence of the dispersion in waveguides implemented on the high index contrast silicon-on-insulator (SOI) platform substantially hinders their wideband operation, which in turn, limits their deployment. In this work, we exploit the potential of non-resonant sub-wavelength grating (SWG) nanostructures to perform a flexible and wideband control of dispersion in SOI waveguides. In particular, we demonstrated that the overall dispersion of the SWG-engineered metamaterial waveguides can be tailored across the transparency window of the SOI platform, keeping easy-to-handle single-etch step manufacturing. The SWG silicon waveguides overcladded by silicon nitride exhibit significant reduction of wavelength dependence of dispersion, yet providing intriguing and customizable synthesis of various attractive dispersion profiles. These include large normal up to low anomalous operation regimes, both of which could make a great promise for plethora of emerging applications in silicon photonics.