Nonlinear optics in germanium mid-infrared fiber material: Detuning oscillations in femtosecond mid-infrared spectroscopy

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.

Semiconductor core fibres: materials science in a bottle

“…While Ge has been less studied optically because the small bandgap makes it incompatible with conventional telecom test equipment, losses in the material have been reduced 89 and nonlinear behaviour has been explored 91 . Whispering gallery modes have been characterised in microspheres made from Ge core fibre 92 .…”

Recent progress in germanium-core optical fibers for mid-infrared optics

“…Figures are unique for each sample but a common color code is applied. Maximum and minimum normalized intensities are represented with red and blue respectively [24]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.…”

“…The nonlinear properties of Si-core fibers have been previously examined more thoroughly than any other semiconductorcore fibers [19]. There has been only a couple of studies of the nonlinear properties of Ge-core fibers [22,24]. The first study was focused on Raman scattering in a Ge-core borosilicate glass-cladded fiber.…”

“…The Raman gain at ~6.8 µm was observed by pumping a 4 mm-long Ge-core borosilicate glass-cladded fiber with a 5.62 µm quantum cascade laser (QCL) [22]. In a recent study, the detuning oscillations, a third-order (χ3) nonlinear off-resonance electronic response of transparent materials, were observed in the Ge-core fiber samples [24]. A femtosecond dispersed pump-probe spectroscopy setup that can also be utilized for the frequency dispersed optical heterodyne detections was used for demonstrating the nonlinearity of Ge [61].…”

Effect of Thermal Annealing on Mid-Infrared Transmission in Semiconductor Alloy-Core Glass-Cladded Fibers

“…One important application area could be related to the exploitation of the nonlinear properties of the semiconductors since semiconductors such as Si and Ge have much higher nonlinearity than the silicabased glasses. Successful experimental demonstrations of various nonlinear properties of semiconductor-core fibers are encouraging for the future studies [23,24]. Fig.…”