Femtosecond laser additive manufacturing of nonlinear and fluorescent optical structures

• Main Author: Jiao,Jiannan
• Other Authors: Su Pei-Chen
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Mechanical engineering; Engineering::Manufacturing::Metrology
• Online Access: https://hdl.handle.net/10356/144184
• Institution: Nanyang Technological University

In the past few years, the state-of-the-art additive manufacturing (AM) via femtosecond laser direct writing (FsLDW) has become a powerful tool for flexible microfabrication of complex 3D structures and it is promising to utilize this technology to fabricate optical structures integrated into optofluidic chips, because of its unnecessary of pre-patterned masks and higher manufacturing throughput compared to traditional manufacturing methods such as mask-based photo-lithography and mask-less electron-beam lithography. Varieties of micro-sized optical structures are successfully additively fabricated and applied to real on-chip applications, which are mainly based on the linear optical phenomenon and are passive optical structures. Micro-sized nonlinear-optics-based active structure additively fabricated via FsLDW is promising for generating new flexible light sources and has not been studied too much, which is the research gap to be fulfilled in this research. In the research, on-chip optofluidic sources of small volume are the targets to be realized and the objective of this research is three-fold: (1) establishment of 3D and 2D FsLDW systems to realize additive manufacturing of basic micro-sized optical structures for optofluidic applications, (2) characterization and utility of surface third harmonics (THs) from the flexible two-photon-polymerized structures to provide coherent sources for metrology and sensing applications such as micro-interferometer for real-time monitoring of gas refractive index changes and diffractive lens for generation of Bessel-like THs with a large non-divergent range, and (3) demonstration of fabricated active optical structures that contain gain mediums (upconversion nano particles and fluorescent dye) for micro laser sources (high repetition-rate pulsed upconversion micro-laser) and waveguides to be integrated into micro-sized optofluidic chips. Our demonstrated nonlinear-optics-based active optical structures over traditional ones have three main advantages: firstly, the active optical structures containing a gain medium works well for the external photon excitation and efficient collection of the emission signals; this lowers the system complexity, optical delivery loss, and integration cost. Secondly, highly tunable small volumetric light sources can be realized in terms of beam size, output intensity, polarization, spectral position and distribution. Flexible patterned and diffracted surface optical harmonics and upconversion lasing can work as coherent light sources for micro sensing and detection applications. Finally, the need for in-coupling and out-coupling of the lights from or to the integrated photonic devices and relevant alignment issues can be much relieved with additively manufactured waveguides. In the future, complex optofluidic systems will be fabricated based on our nonlinear-optics-based active structures for applications such as sensing the micro/nano particles and chemical characterization of fluids.