Enhancing the two-photon excited fluorescence by two-dimensional nonlinear optical-polymer photonic crystals

Abstract

We have successfully demonstrated enhancement of the two-photon excited fluorescence (TPEF) in a highly nonlinear optical polymer two-dimensional (2D) photonic crystal (PhC) waveguide, arising from resonant coupling between the external laser field and a photonic band mode. Moreover, we directly determine the experimental photonic band dispersion structure of waveguiding modes under the light line in a 2D PhC waveguide by using angle-resolved attenuated total reflection spectroscopy. Resonance coupling between the external evanescent wave from total reflection within the prism and the waveguiding modes in the 2D PhC provides clear information on individual band components by resolving the angle (i.e., wave vector <i>k</i>) and photon energy. The experimentally determined photonic band structure is essential for understanding the novel light propagation and nonlinear optical properties of PhC systems. Good agreement was obtained between the TPEF enhancements and features of the photonic band structure, indicating that active manipulation of these nonlinear TPE processes is a realistic possibility through engineering the band dispersion and band group velocity characteristics. Future work in this direction should lead to dramatic improvements in the performance of TPE applications.