Exploring quasi-phase-matching through resonance-enhanced microstructured fibers: a platform for tailored light generation

• Applicant: Professor Dr. Markus A. Schmidt
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403520928

Nonlinear light-matter interactions in optical fibers enable the effective transfer of electromagnetic energy into selected spectral regions. One important effect is soliton-based supercontinuum generation, relying on the spectral broadening of ultrafast input pulses by effects such as dispersive waves (DWs). This often results in broadband features that can have low spectral densities or overspan the spectral regions of interest. One way to generate narrowband features is to combine continuous wave light and phase-matching, allowing transferring power from a fundamental wave to a short-wavelength harmonic. Material and waveguide dispersion typically cause the harmonic to be generated in a higher-order mode, which is disadvantageous for many applications. One approach to solve this issue relies on integrating a periodicity along the propagation direction, preventing backconversion of power to the fundamental wave. This process, known as quasi-phase-matching (QPM), represents a challenge in the field of Fiber Optics due to technological limitations. Hence, there is a strong demand for an efficient method to incorporate QPM in Fiber Optics to exploit the advantageous properties of optical fibers in the context of nonlinear optics. Building on the previous project, this project will investigate the concept of nonlinear frequency conversion in fibers using QPM from previously unexplored perspectives. Essential to this is a new hybrid waveguide platform - nanofilm-reinforced micro-structured fibers with exposed cores - opening up unique opportunities for the investigation of QPM in untapped scenarios. The project addresses both experimental and theoretical aspects and is divided into two parts: In the first part, QPM-induced generation of higher-order DWs with ultrashort pulses is explored in detail. Of particular interest are the dynamical and temporal properties, as well as the application potential of the narrowband comb-like sidebands in the supercontinuum spectra. In the second part of the project, QPM-based third-harmonic-generation in the fundamental mode under continuous-wave excitation is investigated. The key difference to conventional QPM-approaches is the use of fibers that have no spatial variation along the propagation direction. Overall, this basic science-oriented project explores the QPM-effect from previously inaccessible perspectives using a novel photonic platform. New physical principles and dynamics that were previously unattainable are being explored, potentially leading to innovative light sources for a variety of applications, examples of which include pump-probe spectroscopy or the generation of correlated photons.

• DFG Programme: Research Grants