Milan Sinobad

Mid-infrared nonlinear optical response of Si-Ge waveguides with ultra-short optical pulses

We characterize the nonlinear optical response of low loss Si(0.6)Ge(0.4) / Si waveguides in the mid-infrared between 3.3 μm and 4 μm using femtosecond optical pulses. We estimate the three and four-photon absorption coefficients as well as the Kerr nonlinear refractive index from the experimental measurements. The effect of multiphoton absorption on the optical nonlinear Kerr response is evaluated and the nonlinear figure of merit estimated providing some guidelines for designing nonlinear optical devices in the mid-IR. Finally, we compare the impact of free-carrier absorption at mid-infrared wavelengths versus near-infrared wavelengths for these ultra-short pulses.

Mid-infrared nonlinear optics in SiGe waveguides

Comprehensive mid-IR nonlinear measurements of SiGe waveguides performed in the picosecond and femtosecond regime and compared to numerical calculations are reported. Nonlinear properties of SiGe waveguides in the mid-IR are extracted.

Broadband mid-infrared supercontinuum generation in low loss dispersion engineered silicon-germanium waveguide

There is a growing interest in generating mid-infrared (mid-IR) supercontinuum (SCG) using CMOS compatible platforms for applications such as, optical coherence tomography and molecular spectroscopy [1, 2]. SCG spanning from the telecom band to the SWIR (< 3 μm) has already been achieved using silicon-based platforms such as silicon-on-insulator, silicon nitride-on-insulator and silicon-germanium-on-insulator [3-6] but has been limited to up ∼3.5μm mainly due to the absorption in the silica substrate. Recently, SCG in the mid-IR up to 6 μm was reported from a silicon-on-sapphire platform [7] limited by the sapphire absorption. More recently, silicon-germanium (SiGe) alloys, with transparency potentially extending up to 15 μm depending on the Ge content [8] have emerged as an attractive alternative platform for mid-IR photonics [9-11].

Dispersion engineered air-clad SiGe waveguides with low propagation loss in the mid-infrared

Photonic devices operating in the mid-IR (3 μm to 13μm wavelength range) are of great interest for a wide range of applications, such as free-space communications, environmental monitoring or defence. Group IV-based material platforms [1], such as silicon-on-insulator (SOI)[2] and silicon-on-sapphire (SOS)[3] have attracted significant interest for mid-IR integrated photonics. However, absorption in silica beyond 3.5 μm and in sapphire beyond 5.5 μm eventually limits the operational wavelength band of these platforms. More recently, silicon-germanium (SiGe) alloys, with a transparency window potentially extending up to 13 μm depending on the Ge content [4] have emerged as an attractive alternative platform for mid-IR photonics [5-7]. In [6, 7] we reported Si0.6Ge0.4 waveguides buried-in silicon with propagation loss of around 1dB/cm at 4μm, and nonlinear properties somewhat comparable to crystalline silicon between 3.5μm and 5μm.