Investigation of four-wave-mixing phenomena in liquid core optical fibers

• Applicant: Professor Dr. Markus A. Schmidt, since 5/2023
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 454735729

Nonlinear light generation based on liquid-core optical fibers (LCOF) has recently received increased attention due to the unique properties offered by certain liquids. In addition to their high nonlinearity and wide spectral transparencies, liquids can exhibit a strong non-instantaneous nonlinearity arising from the slow or retarded molecular motions in response to the excitation field. This non-instantaneous nonlinear optical response varies from liquid to liquid based on their molecular response time and primarily depends on the input pulse duration. This special response largely impacts the nonlinear broadening mechanisms in LCOFs thus impacting supercontinuum generation (SCG) as well as soliton dynamics. However, the benefits of having these unique characteristics available for nonlinear parametric processes, such as four-wave mixing (FWM), is still largely unexplored and needs extensive theoretical and experimental study. FWM through nonlinear optical fiber is an extremely promising platform for nonlinear light generation in several spectral domains including mid-infrared. The aim of this project is to transfer and extent the known concepts for FWM to LCOF and to exploit the impact of the unique characteristics of liquids on the FWM nonlinear optical process both theoretically and experimentally. Based on this idea, three main topics will be addressed during the project;1. Liquids possess distinctly sharp and narrow Raman resonance lines unlike glass materials which exhibit spectrally broad Raman response. Therefore, LCOF have particular benefits over silica fibers in enabling Raman-free or Raman-enhanced (depending on the selected phase matching) generation of signal and idler bands. While Raman-free FWM plays an important role for the background-free generation of pure photon pairs, Raman-enhanced effects may allow boosting the conversion efficiencies at limited signal/idler bandwidth through the effect of gain narrowing by operating at a Raman resonance. 2. Utilizing selectively liquid-filled photonic crystal fibers offers a great flexibility for cascaded-FWM due to relaxed dispersion management provided by the binary mixtures of liquids and/or temperature sensitivity of the liquid filled fiber both of which allow fulfilling phase-matching for FWM, which are critical for cascaded-FWM process. This enables to the best of our knowledge, for the first time, a single-pump configuration of the fiber based cascaded FWM system.3. FWM in optical fibers is generated from the phase noise of the input field when pumped at long pulse durations. Whereas, a key feature of LCOF based nonlinear light generation is its spectral coherence, indicating increased susceptibility to input noise. The origin of this improved coherence property is associated with the strong influence of the high non-instantaneous nonlinearity. This makes FWM in LCOFs a great indicator to quantify the non-instantaneous response of different liquids.

• DFG Programme: Research Grants
• International Connection: Australia
• Cooperation Partner: Professorin Dr. Heike Ebendorff-Heidepriem
• Ehemalige Antragstellerin: Dr. Saher Junaid, Ph.D., until 4/2023