Enhanced Optical Nonlinearity in a Silicon Photonic Crystal Slow-Light Waveguide
Nobuyuki Matsuda, Ken-ichi Harada, Hiroki Takesue,
Eiichi Kuramochi, Hideaki Taniyama, and Masaya Notomi
Optical Science Laboratory
Slow light (SL) in an optical chip provides an enhanced light-matter interaction, thanks to the longitudinally compressed optical field and the prolonged interaction time between the medium and the slowly-propagating light within. We have already fabricated high-bandwidth SL waveguides using a 1-D chain of silicon photonic-crystal ultrahigh-Q (〜1 million) nanocavities and demonstrated vg less than c/100 in the telecom band . This time we demonstrated SL enhancement of all-optical wavelength-conversion efficiency in our device via the four-wave-mixing (FWM) experiment .
Schematic of our SL waveguide (γ = c/36, 0.42-mm long) is shown in Fig. 1. We input telecom-band pump and signal beam into the device and observed a new idler field that was created by the stimulated FWM, which arises from the third-order optical nonlinearity in the core material (Si). We plotted measured signal-to-idler wavelength conversion efficiency as a function of input pump power as shown in Fig. 2. The conversion efficiency was proportional to the the square of the pump power because the FWM is a two-photon absorption process. From the result, we obtained the value of nonlinear constant γ , which is the degree of waveguide nonlinearity, as 18,600 /W/m. The value is 107 times larger than that of standard single-mode fibers and even larger than 300 /W/m of a silicon wire waveguide (vg = c/4.2)  and 2,930 /W/m of a photonic crystal SL waveguide that employed a line defect mode (vg = c/30) . The extremely high nonlinearity of our device is originating from SL enhancement ((1/vg)2 dependence of γ ) and a strong spatial confinement of the SL mode due to wavelengthsized photonic crystal cavities. This value is the highest yet reported for silicon-core nonlinear waveguides with an integrated structure, indicating a potential to provide a new stage for integrated waveguide photonic devices with ultralow power consumption.
This work was supported by KAKENHI.
 M. Notomi, E. Kuramochi, and T. Tanabe, Nature Photon. 2 (2008) 741.
 N. Matsuda et al., Opt. Express 19 (2011) 19861.
 K. Harada et al., IEEE J. Sel. Top. Quantum Electron. 16 (2010) 325.
 C. Monat et al., IEEE. J. Sel. Top. Quantum Electron. 16 (2010) 344.
Fig. 1. Silicon photonic-crystal coupled-resonator optical
Fig. 2. Signal-to-idler wavelength conversion
efficiency via the FWM.
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