Nano-focusing structures based on hybrid plasmonic waveguides are likely to play a key role in strong nonlinear optical devices. Although the insertion loss is considerable, a significant nonlinear phase shift may be achieved by decreasing the nano-focusing device footprint and careful parameter optimization. Here, we study the Kerr effect in hybrid plasmonic waveguides by analyzing the mode effective area, energy velocity, and insertion loss. Particularly, by utilizing plasmonics to manipulate the effective index and mode similarity, the TM mode is reflected and absorbed, while the TE mode passes through with relatively low propagation loss. By providing a deep understanding of hybrid plasmonic waveguides for nonlinear applications, we indicate pathways for their future optimization.

Optical microring resonators are extensively employed in a wide range of physical studies and applications due to the resonance enhancement property. Incorporating coupling control of a microring resonator is necessary in many scenarios, but modifications are essentially added to the resonator and impair the capability of optical enhancement. Here, we propose a flexible coupling structure based on adiabatic elimination that allows low-loss active coupling control without any modifications to the resonators. The self-coupling coefficient can be monotonically or non-monotonically controllable by the proposed coupler, potentially at a high speed. The characteristic of the coupler when implemented in silicon microring resonators is investigated in detail using substantiated analytical theory and experiments. This work provides a general method in coupling control while ensuring the resonance enhancement property, making active coupling control in a resonator-waveguide system feasible.

The optical saturation characteristics in the germanium-on-silicon (Ge-on-Si) photodetector are studied for the first time, to the best of our knowledge. The relationship between the optical saturation characteristics and the optical field distribution in the Ge layer is illustrated by the simulation. This theory is verified by comparative experiments with single-injection and dual-injection structures. The dual-injection photodetector with a more balanced and uniform optical field distribution has a 13% higher responsivity at low optical power and 74.4% higher saturation current at 1550 nm. At higher optical power, the bandwidth of the dual-injection photodetector is five times larger than that of the single-injection photodetector.