Polarization-resolved nonlinear endoscopy using twisted photonic crystal fibers

• Applicant: Professor Dr. Nicolas Joly
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569004160

This experimental project aims to explore the potential of twisted microstructured fibers for endoscopic applications. The ultimate goal is to develop multiphoton endoscopes capable of measuring the orientation of biological molecules and tissues such as amyloidosis. Amyloidosis is a rare disease in which abnormal proteins, known as amyloid fibrils, build up in tissue (kidney, heart, nervous and gastric system, glands…). It is known to generate amyloid aggregates plaques that show birefringence. Diagnosis of amyloidosis generally requires tissue biopsies, which is a long process. Conventional endoscopes, which cannot resolve polarization are useless in this case. Twisted microstructured fibers offer unique opportunity to address such issue. They feature circular birefringence, enabling the preservation of right- and left-hand circular polarizations during light propagation. As a result, these chiral fibers possess optical activity: a linearly polarized wave retains its polarization state, but the orientation of this polarization is deviated, a deviation that depends only on the length of the fiber. Once calibrated, this property makes it possible to precisely determine the direction of the polarization state of the light leaving the fbre, offering the possibility of probing the orientation of molecules in a sample. The sample can then be scanned to map its molecular structure. For nonlinear endoscopy, twisted solid-core fibres require special care of the dispersion to ensure the multiphoton excitation of the sample at the end of the fibre. In this project we will design and develop dedicated twisted hollow-core fibre to prevent the potential deformation of the initial pulse. It is also important to have a channel to collect the light from the sample, which will be done through a double-clad structure of the new fibres. This research is crucial for the future development of new types of polarization-resolved multiphoton endoscopes. The project is based on the synergy between two areas of expertise: advanced multiphoton endoscopy and polarization-resolved molecular imaging techniques from Hervé Rigneault's research group at the Institut Fresnel in Marseille (FR), and microstructured optical fiber know-how from Nicolas Joly's group at the University of Erlangen (DE).

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partner: Professor Dr. Herve Rigneault