Masato Takiguchi

Movable high-Q nanoresonators realized by semiconductor nanowires on a Si photonic crystal platform.

Subwavelength semiconductor nanowires have recently attracted interest for photonic applications because they possess various unique optical properties and offer great potential for miniaturizing devices. However, realizing tight light confinement or efficient coupling with photonic circuits is not straightforward and remains a challenge. Here we show that a high-Q nanocavity can be created by placing a single III–V semiconductor nanowire with a diameter of under 100 nm in a grooved waveguide in a Si photonic crystal, by means of nanoprobe manipulation. We observe very fast spontaneous emission (91 ps) from nanowires accelerated by the strong Purcell enhancement in nanocavities, which proves that very strong light confinement can be achieved. Furthermore, this system enables us to move the nanocavity anywhere along the waveguide. This configuration provides a significant degree of flexibility in integrated photonics and permits the addition and displacement of various functionalities of III–V nanocavity devices in Si photonic circuits.

Design for ultrahigh-Q position-controlled nanocavities of single semiconductor nanowires in two-dimensional photonic crystals

Using finite-difference time-domain simulation, we show that ultrahigh-Q nanocavities can be obtained through the manipulation of a single semiconductor nanowire (NW) inside a slot in a line defect of a two-dimensional photonic crystal. By controlling the design and its lattice parameters of the photonic crystal, we have achieved a quality factor Q larger than 106 and a mode volume Vc smaller than 0.11u2009μm3 (1.25 of a cubic wavelength in the NW) for a cavity peak in the telecommunication band. This design is useful for realizing a position-controlled cavity in a photonic crystal. Here, we also discuss the small dependence of the Q-factor, the Vc, and the cavity peak in relation to the position of the NW inside the slot and the potential application to the cavity quantum electrodynamics using the embedded-emitter NW.

Bridging the Gap between the Nanometer-Scale Bottom-Up and Micrometer-Scale Top-Down Approaches for Site-Defined InP/InAs Nanowires

This work presents a method that bridges the gap between the nanometer-scale bottom-up and micrometer-scale top-down approaches for site-defined nanostructures, which has long been a significant challenge for applications that require low-cost and high-throughput manufacturing processes. We realized the bridging by controlling the seed indium nanoparticle position through a self-assembly process. Site-defined InP nanowires were then grown from the indium-nanoparticle array in the vapor-liquid-solid mode through a seed and grow process. The nanometer-scale indium particles do not always occupy the same locations within the micrometer-scale open window of an InP exposed substrate due to the scale difference. We developed a technique for aligning the nanometer-scale indium particles on the same side of the micrometer-scale window by structuring the surface of a misoriented InP (111)B substrate. Finally, we demonstrated that the developed method can be used to grow a uniform InP/InAs axial-heterostructure nanowire array. The ability to form a heterostructure nanowire array with this method makes it possible to tune the emission wavelength over a wide range by employing the quantum confinement effect and thus expand the application of this technology to optoelectronic devices. Successfully pairing a controllable bottom-up growth technique with a top-down substrate preparation technique greatly improves the potential for the mass-production and widespread adoption of this technology.

Enhanced and suppressed spontaneous emission from a buried heterostructure photonic crystal cavity

Buried-heterostructure photonic-crystal cavities strongly confine photons and carriers. Here, we demonstrate that we can greatly enhance and suppress the spontaneous emission rate in them by the cavity quantum-electrodynamics effect.

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.

10-Gb/s operation of a telecom-band InAsP/InP subwavelength nanowire laser on silicon photonic crystal

We demonstrated directly modulated telecom-band sub-wavelength (diameter ~114 nm) nanowire lasers on silicon photonic crystal for the first time. The dynamic properties were estimated using a photon counting system. A 10Gb/s opened eye-diagram was obtained.

Smooth lasing transition in high β buried multiple-quantum-well 2D photonic crystal lasers

By adopting high β buried-multiple-quantum-well photonic crystal nanocavities, we have demonstrated smooth lasing operation, which indicates thresholdless-like lasing theoretically predicted, by mean of light-in versus light-out curve analysis, linewidth analysis, and photon correlation measurements.

Controlling inhibited spontaneous emission of InAs/InP nanowires in different environment

We experimentally investigate the inhibited spontaneous emission of telecom-band InAs quantum disks in InP nanowires near gold, SiO2, and silicon interfaces. We have evaluated how the inhibition is affected by different interfaces and disk thickness.