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Currently third harmonic generation (THG) in fibers is in focus of research, due to the prospects of enabling efficient generation of entangled photon triplets via the inverse, but spontaneous process. To date, microstructured and tapered fibers are the most prominent platforms to provide the high index contrast between the core and cladding material necessary to enable phase-matching (PM) to higher order modes (HOMs). Here, we employ a liquid core fiber (LCF) combining a silica cladding and a highly nonlinear core material, which can be temperature-tuned during operation [1].

Nonlinear light generation in optical fibers is an indispensable tool for generating light to access wavelengths away of the fundamental laser lines broadening the field of applications in biophotonics, metrology, and communications. However, most multi-wavelength sources rely on glass fibers which are static in their material properties after fabrication, thus post-tuning their properties is impossible. Complementary to the pressure-adjustable gas-filled hollow-core fibers in the high power laser regime [1], liquid-core fibers (LCF) offer a versatile platform for tunable nonlinear light generation and pulse control in the low- to medium-power regime. Recently, we demonstrated accurate control of the soliton fission process via temperature due to the large thermo-optical coefficient of the core liquid [2]. However, those experiments were performed with rather cost-intensive thulium laser technology.

Liquid core fibers offer unique features such as hybrid nonlinear responses, wide transmission windows and real-time tuning capabilities. Here I will report on hybrid temporal solitons, coherent supercontinuum generation and real-time dispersive wave tuning.

We show theoretically that microstructured optical fibers filled with nonlinear liquids are capable of generating photon-pairs with highly tunable properties, suitable for applications in quantum spectroscopy and as sources of heralded single photons.

Various applications in biophotonics require widely wavelength-selectable laser sources in the infrared(IR) with high spectral density rather than broad bandwidth. This requirement is barely covered by the recent advances in supercontinuum generation in static optical glass fibers, in which the nonlinear effects can mainly be controlled by the injected power [1]. Supercontinua in gas-core fibers ranging from the UV to visible wavelengths are additionally adjustable by the gas pressure but require complex fiber structures [2]. Due to their strong thermooptical coefficient liquid-core step-index fibers that have a high nonlinearity and wide transmission windows can be used for temperature-based supercontinuum tuning in the mid-infrared [3].