Kazuya Ohira

On-chip quantum interference between silicon photon-pair sources

A silicon-on-insulator device combining two four-wave-mixing photon-pair sources in an interferometer with a reconfigurable phase shifter is used to create and manipulate non-degenerate or degenerate, path-entangled or path-unentangled photon pairs. A quantum interference visibility of nearly 100% is observed on-chip. This device is a first step towards fully integrated quantum technologies.

Photon pair generation in a silicon micro-ring resonator with reverse bias enhancement

Photon sources are fundamental components for any quantum photonic technology. The ability to generate high count-rate and low-noise correlated photon pairs via spontaneous parametric down-conversion using bulk crystals has been the cornerstone of modern quantum optics. However, future practical quantum technologies will require a scalable integration approach, and waveguide-based photon sources with high-count rate and low-noise characteristics will be an essential part of chip-based quantum technologies. Here, we demonstrate photon pair generation through spontaneous four-wave mixing in a silicon micro-ring resonator, reporting separately a maximum coincidence-to-accidental (CAR) ratio of 602 ± 37 (for a generation rate of 827kHz), and a maximum photon pair generation rate of 123 MHz ± 11 kHz (with a CAR value of 37). To overcome free-carrier related performance degradations we have investigated reverse biased p-i-n structures, demonstrating an improvement in the pair generation rate by a factor of up to 2 with negligible impact on CAR.

Quantum interference and manipulation of entanglement in silicon wire waveguide quantum circuits

Integrated quantum photonic waveguide circuits are a promising approach to realizing future photonic quantum technologies. Here, we present an integrated photonic quantum technology platform utilizing the silicon-on- insulator material system, where quantum interference and the manipulation of quantum states of light are demonstrated in components orders of magnitude smaller than previous implementations. Two-photon quantum interference is presented in a multi-mode interference coupler, and the manipulation of entanglement is demonstrated in a Mach-Zehnder interferometer, opening the way to an all-silicon photonic quantum technology platform.

On-chip optical interconnection by using integrated III-V laser diode and photodetector with silicon waveguide

On-chip integration of III-V laser diodes and photodetectors with silicon nanowire waveguides is demonstrated. Through flip-chip bonding of GaInNAs/GaAs laser diodes directly onto the silicon substrate, efficient heat dissipation was realized and characteristic temperatures as high as 132K were achieved. Spot-size converters for the laser-to-waveguide coupling were used, with efficiencies greater than 60%. The photodetectors were fabricated by bonding of InGaAs/InP wafers directly to silicon waveguides and formation of metal-semiconductor-metal structures, giving responsivities as high as 0.74 A/W. Both laser diode and the photodetector were integrated with a single silicon waveguide to demonstrate a complete on-chip optical transmission link.

A novel thin-overcladding spot-size converter for efficient silicon-wire optical interconnections and waveguide circuits

We present a novel inverse-taper spot-size converter with submicron-thick overcladding for silicon-based optical interconnections and waveguide circuits. Utilizing this structure, a flying-junction underpass silicon-wire cross-connect on a silicon-on-insulator (SOI) wafer is demonstrated.

High responsivity and low dark current operation of ultra-small InGaAs MSM photodetector integrated on Si waveguide

We demonstrated a small footprint of 2 × 10 µm2 InGaAs MSM photodetector integrated on Si waveguide with high-efficiency and low dark current property. The detectors have responsivities of 0.94 A/W and the dark current of less than 20 nA, and are capable of 10 Gbps data rate.

Quantum interference in silicon waveguide circuits

Quantum interference and manipulation of quantum states of light using silicon-on-insulator waveguide circuits is presented, demonstrating the potential for a silicon quantum photonics technology platform.

Silicon quantum photonic sources and circuits

Elementary components required for photonic quantum information processing are realised in a silicon-on-insulator platform. On-chip quantum interference, manipulation of entangled states and photon-pair generation in a ring resonator with record high coincidental-to-accidental rates are demonstrated.