Chiral Liquid-Crystalline Photonic Crystals for Advanced Photonic Applications
Open Access
- Author:
- Chen, Chun Wei
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 29, 2020
- Committee Members:
- Iam-Choon Khoo, Dissertation Advisor/Co-Advisor
Iam-Choon Khoo, Committee Chair/Co-Chair
Zhiwen Liu, Committee Member
Noel Christopher Giebink, Committee Member
Mark Maroncelli, Outside Member
Kultegin Aydin, Program Head/Chair - Keywords:
- liquid crystal
photonic crystal
chiral optics
nonlinear optics
ultrafast optics - Abstract:
- Ultrafast lasers have been powerful tools for bio-imaging, micro-fabrication, material characterization, optical communication, etc. The optical properties of most ultrafast lasers (e.g., pulse width and polarization) are fixed upon fabrication, and thus external optical modulations are often necessary for adaptation to different needs. Conventional modulation systems require long interaction length, complex optical alignment, and high peak intensity (if nonlinear interactions are needed), hindering their use outside optical laboratories. Compact single-component devices with strong and controllable optical dispersion and nonlinearity are thus highly desirable. To this end, my doctoral research focuses on the development of liquid-crystalline chiral photonic crystals (CPC) to enable efficient ultrafast optical modulations. In Chapters 2–5, we study how to direct the self-assembly of cholesteric liquid crystals (LC) into 1D CPCs containing thousands of grating periods and also the optical physics underlying their linear and nonlinear interactions with ultrashort laser pulses. On the temporal modulations, we demonstrate slow light generation, pulse stretching–recompression, and direct compression of transform-limited pulses in 1D CPCs, achievable at peak intensities of only 10–100 MW/cm^2. These 1D CPCs also exhibits giant optical rotatory powers up to ~10,000°/mm, thus enabling large polarization rotation by 100°–1000° in sub-millimeters without sacrificing the transmitted power and degree of linear polarization. In Chapters 6–8, we look into 3D liquid-crystalline CPCs (namely blue-phase LC) and their soft-matter/optical properties to access more dispersion relation options. A gradient-temperature scanning technique is developed to direct the self-assembly of blue-phase LCs into 10×10×1 mm^3-large 3D single crystals (containing ~10^11 unit cells). We have also conducted a dynamical study of the electrostrictive effects in blue-phase LCs, which then inspires us to devise a method to engender the reconfiguration of the CPCs into new lattice structures that are stable on field removal. Forming a polymer network in situ further enables temperature-invariant lattice structure and dynamic electrical tuning of the photonic bandgap over 100 nm. New possibilities of photonic-crystalline LCs as photonic materials and soft mesoscale crystals for fundamental research and practical applications are also discussed.