Taiki Hatakeyama

Adiabatic elimination-based coupling control in densely packed subwavelength waveguides

The ability to control light propagation in photonic integrated circuits is at the foundation of modern light-based communication. However, the inherent crosstalk in densely packed waveguides and the lack of robust control of the coupling are a major roadblock toward ultra-high density photonic integrated circuits. As a result, the diffraction limit is often considered as the lower bound for ultra-dense silicon photonics circuits. Here we experimentally demonstrate an active control of the coupling between two closely packed waveguides via the interaction with a decoupled waveguide. This control scheme is analogous to the adiabatic elimination, a well-known procedure in atomic physics. This approach offers an attractive solution for ultra-dense integrated nanophotonics for light-based communications and integrated quantum computing.

Sensitive method for measuring third order nonlinearities in compact dielectric and hybrid plasmonic waveguides.

We demonstrate a sensitive method for the nonlinear optical characterization of micrometer long waveguides, and apply it to typical silicon-on-insulator nanowires and to hybrid plasmonic waveguides. We demonstrate that our method can detect extremely small nonlinear phase shifts, as low as 7.5·10<(-4) rad. The high sensitivity achieved imparts an advantage when investigating the nonlinear behavior of metallic structures as their short propagation distances complicates the task for conventional methods. Our results constitute the first experimental observation of χ((3)) nonlinearities in the hybrid plasmonic platform and is important to test claims of hybrid plasmonic structures as candidates for efficient nonlinear optical devices.

Experimental Realization of Two Decoupled Directional Couplers in a Subwavelength Packing by Adiabatic Elimination.

On-chip optical data processing and photonic quantum integrated circuits require the integration of densely packed directional couplers at the nanoscale. However, the inherent evanescent coupling at this length scale severely limits the compactness of such on-chip photonic circuits. Here, inspired by the adiabatic elimination in a N-level atomic system, we report an experimental realization of a pair of directional couplers that are effectively isolated from each other despite their subwavelength packing. This approach opens the way to ultradense arrays of waveguide couplers for integrated optical and quantum logic gates.

Sub-wavelength critical coupling for densely integrated nano-photonics

We experimentally demonstrate a novel approach for densely packed coupled waveguides, based on adiabatic elimination scheme, allowing control of the inherent coupling between waveguides. At the nano-scale, zero coupling between the waveguides can be achieved.