Research

Research

Quantum Optics and Quantum Communication

Telecom-band entangled photons (Fig. 1,2).
Quantum frequency conversion (Fig. 3).
Differential phase shift quantum key distribution (Fig. 4, 5).
Silicon photonics quantum information (Fig. 6).

Fig.1: Configuration for generating polarization entanglement using spontaneous four-wave mixing (SFWM) in dispersion shifted fiber (DSF). H. Takesue and K. Inoue, Phys. Rev. A 70, 031802(R) (2004).

Fig.2: Configuration for generating time-bin entanglement using SFWM in cooled DSF. The DSF was cooled to suppress noise photons caused by spontaneous Raman scattering. H. Takesue and K. Inoue, Phys. Rev. A 72, 041804(R) (2005): H. Takesue and K. Inoue, Opt. Express, 13, 7832 (2005).

Fig.3: Frequency up-conversion single photon counter. C. Langrock et al., Opt. Lett., 30, 1725 (2005).

Fig.4: Configuration of differential phase shift quantum key distribution (DPS-QKD).

Fig.5: Experimental result of DPS-QKD: secure key generation rate as function of transmission fiber length. Secure keys with a bit rate of 12 bit/s was successfully generated over 200 km of fiber. H. Takesue et al., Nature Photonics 1, 343 (2007).

Fig.6: The setup of the first experimental entanglement generation using a silicon waveguide. Inset: the silicon wire waveguide used for the experiment fabricated by NTT Microsystem Integration Laboratories. H. Takesue et al., Appl. Phys. Lett. 91, 201108 (2007).

Wavelength-Division Multiplexing (WDM) Access Networks

WDM access ring using light source centralization.
Data rewriting of wavelength channels using saturated semiconductor optical amplifier.

Lightwave Frequency Synthesis and Its Applications

Broadband lightwave frequency sweeper using synchronous filtering.
Stabilization of lightwave frequency sweeper using Fabry-Perot cavity composed of Faraday rotator mirrors.
Chromatic dispersion measurement using lightwave frequency sweeper.

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