Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX A pulsed mid-infrared pump at λ = 2173 nm is used to demonstrate wideband optical parametric gain in a low-loss 2-cm long silicon photonic wire. Using dispersion engineering to obtain negative second-order (β 2 ) and positive fourth-order (β 4 ) dispersion, we generate broadband modulation instability and parametric fluorescence extending from 1911 nm -2486 nm. Using a cw probe signal to interrogate the modulation instability spectrum, we demonstrate parametric amplification > 40 dB with an on-chip gain bandwidth wider than 580 nm, as well as narrowband Raman-assisted peak gain > 50 dB. © 2011 Optical Society of America OCIS Codes: 130.4310, 190.4380, 190.4970 Two-photon absorption (TPA) in Si vanishes at wavelengths approaching λ = 2200 nm, while its nonlinear Kerr refractive index n2 stays comparatively constant [1,2]. Hence, the nonlinear figure of merit (FOM) (n2/βλ) increases dramatically near silicon's TPA threshold. The large intrinsic nonlinearity of Si, when patterned into high-index-contrast dispersion-engineered silicon photonic wires, produces an ideal platform for the exploration of highly efficient, broadband, coherent nonlinear optical processes [3,4]. This platform can serve as an ideal host for chip-scale mid-IR applications [5-8] including molecular spectroscopy, free-space communication, and environmental monitoring.Previously we reported a mid-IR optical parametric amplifier (OPA) with on-chip gain over a bandwidth of 220 nm in a 4-mm long silicon wire [5]. Using an improved Si wire design, we demonstrate here broadband mid-IR modulation instability (MI), having a bandwidth greater than 580 nm centered at a 2173 nm pump wavelength. The intense MI spectrum correlates with unprecedented values of on-chip parametric gain, exceeding 40 dB. Moreover, we demonstrate that on-chip gain can exceed 50 dB in narrow Raman-scatteringassisted bands.Our silicon wire is fabricated on a 200 mm silicon-oninsulator (SOI) wafer in a CMOS pilot line and is 2 cm long, with cross-sectional dimensions of 900 nm x 220 nm (inset Fig. 1(a)). The top and bottom cladding consist of air and a 2 µm buried oxide (BOX), respectively. The waveguide operates in the fundamental quasi-TE mode, and has propagation losses of < 2.8 dB/cm for λ = 2000 -2500 nm. These engineered waveguide dimensions produce a waveguide effective nonlinear parameter γ ~ 130 W -1 m -1 and anomalous dispersion conditions (β2 < 0) at wavelengths from 1800 -2400 nm, as plotted in Fig. 1(a). Furthermore, 4 th -order dispersion is small and positive (β4 > 0) within the same wavelength range, which is needed for achieving broadband phase matching.To achieve an efficient degenerate four-wave-mixing (FWM) process, i.e. two pump photons converted into one signal and one idler photon, 2ωp = ωs + ωi, the phase = (ks + ki) − 2kp, P is the input pump peak power and L is the waveguide length. Graphically, when the −∆kl curve falls...