Photo-thermal nonlinearity enhancement in dye-doped liquid crystals by polymer doping

Year: 2025

Authors: Massarelli F., Wiersma DS., Riboli F., Nocentini S.

Autors Affiliation: Univ Florence, European Lab Nonlinear Spect LENS, Florence, Italy; Ist Nazl Ric Metrolog INRiM, Div Metrol Innovat Mat & Life Sci, Turin, Italy; Univ Florence, Dept Phys & Astron, Florence, Italy; Consiglio Nazl Ric Ist Nazl Ott CNR INO, Florence, Italy.

Abstract: Nonlinear photonic materials play an important role in the development of advanced optical and photonic technologies. Third-order optical nonlinearity is at the basis of effects like self-modulation and threshold phenomena and can be used for fast tuning and optical switching. Dye-doped nematic liquid crystals are characterised by outstanding values of the nonlinear refractive index. However, in resonance conditions, they suffer from energy loss due to absorption. In this work, we demonstrate large photo-thermal nonlinearity in dye-doped linear Polymer-Stabilized Liquid Crystals (PSLCs) and show how to tune their nonlinear refractive index by tailoring the chemical formulation. Dye-doped PSLC are probed with pre-resonant light at very low power and are characterised by the Z-scan technique. This approach, which strongly limits losses, proves to preserve the nonlinear response despite the pre-resonance illumination. Moreover, the linear polymeric structure turns out to enhance the third-order optical nonlinearity and make its response faster. We thus obtain a controllable nonlinear refractive index that reaches values of around 10-5 cm2 & sdot;W-1 with pre-resonant light in a characteristic time of about 1.5 ms, offering low energy loss, remarkable features in terms of nonlinearity and time response that can strongly impact integrated photonics, cryptography and optical computing applications.

Journal/Review: LIQUID CRYSTALS

More Information: Funded by the European Union [ERC, 3DnanoGiant, n. 101163799]. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. This work was also supported by the European Union with the funding of the Italian Ministry of University and Research (MUR) within the action Missione 4 Istruzione e ricerca – Componente 2 ’Dalla ricerca all’impresa’ Investimento 1.1 Fondo per il Programma Nazionale di Ricerca e Progetti di Rilevante Interesse Nazionale (PRIN) del PNRR – Financed by the European Union – NextGenerationEU under grant PHOTAG [2022T3B4HS, CUP: E53D23005320006]. This work was par-tially supported by project SERICS (PE00000014) under the MUR National Recovery and Resilience Plan funded by the European Union-NextGenerationEU and co-funded by the European Union-NextGenerationEU, ’Integrated infrastruc-ture initiative in Photonic and Quantum Sciences’-I-PHOQS [IR0000016, ID D2B8D520, CUP B53 C22001750006]. FR and SN acknowledge the funding project AFOSR/RTA2 (A.2.e. Information Assurance and Cybersecurity) project ’Highly Secure Nonlinear Optical PUFs’ [FA9550-21-1-0039].
KeyWords: Third order nonlinearity; Z-scan setup; dye-doped liquid crystals; polymer-stabilized liquid crystals; polymer concentration
DOI: 10.1080/02678292.2025.2531107