Masaaki Ono

Photonic-crystal nano-photodetector with ultrasmall capacitance for on-chip light-to-voltage conversion without an amplifier

The power consumption of a conventional photoreceiver is dominated by that of the electric amplifier connected to the photodetector (PD). An ultralow-capacitance PD can overcome this limitation, because it can generate sufficiently large voltage without an amplifier when combined with a high-impedance load. In this work, we demonstrate an ultracompact InGaAs PD based on a photonic crystal waveguide with a length of only 1.7xa0μm and a capacitance of less than 1xa0fF. Despite the small size of the device, a high responsivity of 1xa0A/W and a clear 40xa0Gbit/s eye diagram are observed, overcoming the conventional trade-off between size and responsivity. A resistor-loaded PD was actually fabricated for light-to-voltage conversion, and a kilo-volt/watt efficiency with a gigahertz bandwidth even without amplifiers was measured with an electro-optic probe. Combined experimental and theoretical results reveal that a bandwidth in excess of 10xa0GHz can be expected, leading to an ultralow energy consumption of less than 1xa0fJ/bit for the photoreceiver. Amplifier-less PDs with attractive performance levels are therefore feasible and a step toward a densely integrated photonic network/processor on a chip.

Deep-subwavelength plasmonic mode converter with large size reduction for Si-wire waveguide

If we are to utilize deep-subwavelength plasmonic waveguides in photonic integrated circuit applications, highly efficient three-dimensional (3D) mode conversion must be achieved between deep-subwavelength plasmonic waveguides and conventional dielectric waveguides such as Si-wire waveguides. Here, we describe 3D mode conversion from a Si-wire waveguide (the core size is 400u2009u2009nm×200u2009u2009nm) to a plasmonic slot waveguide (the air core size is 50u2009u2009nm×20u2009u2009nm) with a coupling loss of 1.7 dB. Our mode converter has only a two-dimensional laterally tapered structure even with the presence of a large discontinuity in the thickness, and can still produce efficient full 3D mode conversion with a very short taper length (600 nm). Calculation results obtained with the finite element method agreed well with the experimental results. We believe our mode converter will provide a new deep-subwavelength photonic platform.

Coherent control of high efficiency metasurface beam deflectors with a back partial reflector

Recently, coherent control of absorption in metallic metasurfaces has been demonstrated, and this phenomenon was applied to intriguing light-by-light switching operation. Here we experimentally demonstrate coherent control of beam deflection by high-efficiency metasurfaces for the first time. Although the beam deflection efficiency by a metasurface is generally small, high-efficiency metasurfaces, which consist of a single layer metasurface with a back reflector, are known to exhibit significantly high deflection efficiency. A key point of our study is to replace the back reflector with a partial reflector instead, which enables light-by-light control of a high-efficiency metasurface with a pair of counter-propagating coherent beam inputs. By adjusting the partial reflector thickness appropriately, the proposed device outperforms ones without a reflector, especially for the deflection efficiency. We finally experimentally demonstrate the expected operation of the fabricated device at a visible wavelength,...

Nanowire-nanoantenna coupled system fabricated by nanomanipulation

Here we demonstrate the combination of a semiconductor nanowire and a plasmonic bowtie nanoantenna. A subwavelength InP nanowire was placed precisely in the middle of the nanogap of a gold bowtie nanoantenna with a nanomanipulator installed in a focused ion beam system. We observed a significantly large enhancement (by a factor of 110) of the photoluminescence intensity from this coupled system when the excitation wavelength was at the plasmonic resonance with its polarization parallel to the nanoantenna. Moreover, simulation results revealed that this large enhancement was caused by an interesting interplay between the plasmonic resonance of the nanoantenna and the breakdown of the field suppression effect in the subwavelength nanowire. Our results show that the combination of a nanowire and a nanoantenna gives us a new degree of freedom to design light-matter interactions on a nanoscale.

Position controlled nanocavity using a single nanowire in photonic crystals

We propose a position controlled nanocavity from a single semiconductor nanowire inside a slot of photonic crystals. A cavity is created by modifying the refractive index in the line defect using a nanowire. Preliminary experiments are shown.

Deep-subwavelength Si core plasmonic waveguide monolithically integrated with Si photonic waveguide

A plasmonic waveguide with a deep-subwavelength Si core is integrated with a Si photonic waveguide. By utilizing horizontal Al-Si-Al structure, we obtained a 4-dB/μm propagation loss with a 60 × 60 nm2 surface-oxidized Si core.

Connecting deep sub-wavelength plasmonic waveguide to Si photonics waveguides

We achieved three-dimensional mode conversion between a Si-wire waveguide and a deep sub-λ plasmonic slot waveguide (60 × 50 nm²) for the first time. The coupling loss was only about 2 dB.