Novel Organic Polymeric and Molecular Thin-Film Devices for Photonic Applications
Lee, Chi H.
Herman, Warren N.
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The primary objective of this thesis is to explore the functionalities of new classes of novel organic materials and investigate their technological feasibilities for becoming novel photonic components. First, we discuss the unique polarization properties of optical chiral waveguides. Through a detailed experimental polarization analysis on planar waveguides, we show that eigenmodes in planar chiral-core waveguides are indeed elliptically polarized and demonstrate waveguides having modes with polarization eccentricity of 0.25, which agrees very well with recent theory. This is, to the best of our knowledge, the first experimental demonstration of the mode ellipticities of the chiral-core optical waveguides. In addition, we also examine organic magneto-optic materials. Verdet constants are measured using balanced homodyne detection, and we demonstrate organic materials with Verdet constants of 10.4 and 4.2 rad/T · m at 1300 nm and 1550 nm, respectively. Second, we present low-loss waveguides and microring resonators fabricated from perfluorocyclobutyl copolymer. Design, fabrication and characterization of these devices are addressed. We demonstrate straight waveguides with propagation losses of 0.3 dB/cm and 1.1 dB/cm for a buried channel and pedestal structures, respectively, and a microring resonator with a maximum extinction ratio of 4.87 dB, quality factor Q = 8554, and finesse F = 55. In addition, from a microring-loaded Mach-Zehnder interferometer, we demonstrate a modulation response width of 30 ps and a maximum modulation depth of 3.8 dB from an optical pump with a pulse duration of 100 fs and a pulse energy of 500 pJ when the signal wavelength is initially tuned close to one of the ring resonances. Finally, we investigate a highly efficient organic bulk heterojunction photodetector fabricated from a blend of P3HT and C<sub>60</sub>. The effect of multilayer thin film interference on the external quantum efficiency is discussed based on numerical modeling. We experimentally demonstrate an external quantum efficiency η<sub>EQE</sub>=87±2% under an applied bias voltage V = −10 V, leading to an internal quantum efficiency η<sub>IQE</sub>≈97%. These results show that the charge collection efficiency across the intervening energy barriers can indeed reach near 100% under a strong electric field.