The University of Tokyo · Physics and Astronomy
Professor Hironobu Yoshimi's research lab specializes in photonic integrated circuits with a focus on topological photonics and slow light phenomena in valley photonic crystals. The lab develops novel waveguide platforms that enable robust, low-loss light transmission even around sharp bends, leveraging topological protection and high group index modes for enhanced light-matter interaction. They also design and demonstrate efficient couplers between topological waveguides and conventional waveguides, as well as compact, low-noise fiber lasers for applications in optical communications and sensing. Their work bridges theoretical design, numerical simulation, and experimental validation in nanophotonic devices using silicon-based platforms.
Figures are computed from collected data and may differ slightly.
Valley photonic crystals (VPhCs) are an attractive platform for the implementation of topologically protected optical waveguides in photonic integrated circuits (PICs). The realization of slow light modes in the topological waveguides may lead to further miniaturization and functionalization of the PICs. In this Letter, we report an approach to realize topological slow light waveguides in semiconductor-slab-based VPhCs. We show that a bearded interface of two topologically distinct VPhCs can sup
We experimentally demonstrate topological slow light waveguides in valley photonic crystals (VPhCs). We employed a bearded interface formed between two topologically-distinct VPhCs patterned in an air-bridged silicon slab. The interface supports both topological and non-topological slow light modes below the light line. By means of optical microscopy, we observed light propagation in the topological mode in the slow light regime with a group index <i>n</i><sub><i>g</i></sub> over 30. Furthermore
We demonstrate a polarization-maintaining Er fiber laser incorporating a nonlinear amplifying loop mirror (NALM) and a chirped fiber Bragg grating (CFBG) to generate a train of 9.0-ps pulses at a repetition rate of 40 MHz with an average power of ∼8 mW. Its intensity noise at 8 MHz is measured to be almost shot-noise-limited, and the corresponding relative intensity noise is as low as −165 dB/Hz.
We numerically and experimentally demonstrate efficient light couplers between topological slow light waveguides in valley photonic crystals (VPhCs) and wire waveguides. By numerical simulations, we obtained a high coupling efficiency of -0.84 dB/coupler on average in the slow light regime of a group index n<sub>g</sub> = 10 - 30. Experimentally, we fabricated the couplers in a Si slab and measured the transmitted power of the devices. We realized a high coupling efficiency of approximately -1.2
We demonstrate a polarization-maintaining fiber laser generating 8.4-ps pulses at 40 MHz with an average power of ~5 mW. Its intensity noise is measured to be only 2.4-dB higher than the shot noise limit.
We numerically and experimentally demonstrate efficient light couplers between topological slow light waveguides in valley photonic crystals (VPhCs) and wire waveguides. By numerical simulations, we obtained a high coupling efficiency of -0.84 dB/coupler on average in the slow light regime of a group index ng = 10 - 30. Experimentally, we fabricated the couplers in a Si slab and measured the transmitted power of the devices. We realized a high coupling efficiency of approximately -1.2 dB/coupler
We report a topologically-protected single photon source in a slow light waveguide based on valley photonic crystals. Purcell-enhanced single photon generation from a quantum dot and its robust propagation in the topological waveguide are demonstrated.
We demonstrate slow light waveguides using topological valley kink states. We found in-gap high-group-index inodes at bearded interfaces of silicon-based valley photonic crystals, clearing the path to build topologically-protected slow light waveguides only using semiconductors.
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