Abstract
Germanium optical fibers hold great promise in extending semiconductor photonics into the fundamentally important mid-infrared region of the electromagnetic spectrum. The demonstration of nonlinear response in fabricated Ge fiber samples is a key step in the development of mid-infrared fiber materials. Here we report the observation of detuning oscillations in a germanium fiber in the mid-infrared region using femtosecond dispersed pump-probe spectroscopy. Detuning oscillations are observed in the frequency-resolved response when mid-infrared pump and probe pulses are overlapped in a fiber segment. The oscillations arise from the nonlinear frequency resolved nonlinear (χ(3)) response in the germanium semiconductor. Our work represents the first observation of coherent oscillations in the emerging field of germanium mid-infrared fiber optics.
Highlights
Semiconductors are immensely attractive materials for transmission in the mid-infrared (IR) region due to their transparency and large refractive index
Given the importance of both mid-wave infrared and long-wave infrared regions for molecular spectroscopy for chemical and biological sensing,[1] hyperspectral imaging,[2] standoff detection,[3] mid-infrared astronomy[4] and astrophotonics,[5] considerable progress has been made in group IV infrared photonics using both silicon and germanium.[6,7,8]
Ge is especially suitable for mid-infrared nonlinear optics because of its exceptionally high values of important nonlinear optical coefficients
Summary
Semiconductors are immensely attractive materials for transmission in the mid-infrared (IR) region due to their transparency and large refractive index. Among the common dielectric materials and semiconductors, Ge with its small ∼ 0.67 eV band gap has the highest linear refractive index of n ∼ 4 as well as the highest nonlinear refractive index coefficient, with a Kerr coefficient n2 = 10-17 m2/W that scales inversely with the band gap in accordance with the model of Sheik-Bahae et al.[9] Among common crystalline materials, Ge has the highest third order susceptibility[10] χ(3) = 1.5 × 10 18 m2/V2 near 2500 cm-1 or at wavelengths near 4000 nm. The nonlinear properties of Ge and related materials have spurred interest in extending group IV photonics to the important longer wavelength
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