Energy transduction in surface photonic crystals.

摘要

This dissertation is a detailed investigation of the fabrication, design, characterization, and understanding of physical principles of energy transduction in surface photonic crystals which are engineered for various applications. One-dimensional photonic crystals are engineered as optically tunable reflectance filters for lambda = 632.8 nm wavelength light by incorporating azobenzene liquid crystal dye molecules into the photonic crystal structure. Optical energy is transduced to accomplish mechanical work by exciting the dye molecules into different physical configurations, leading to changes in the optical properties of the dye molecules, namely their refractive index. This mechanism is used to tune the reflection resonance of the photonic crystal filter. The spectral and temporal optical tuning response of the photonic crystal filter due to excitation light at lambda = 532 nm is characterized. Modulation of the transmitted and reflected lambda = 632.8 nm light is achieved at microsecond time response. Two-dimensional photonic crystals are also investigated as reflectance filters for lambda = 532 nm wavelength light. Both optically tunable and static reflectance filters are studied. Again, azobenzene liquid crystal molecules are incorporated into the photonic crystal to achieve optical tuning of the reflectance wavelength. In this case, the lambda = 532 nm wavelength light is used for self-modulation. That is, the light serves both to optically tune the photonic crystal filter as well as to modulate its own reflection efficiency through the photonic crystal filter. Moreover, stacking of multiple photonic crystals into a single filter is studied for both static and optically tunable photonic crystal filters. It is shown that this approach improves the performance of the photonic crystal reflectance filter by increasing its optical density and its angular tolerance at the reflection wavelength of lambda = 532 nm. Additionally, surface photonic crystals are fabricated which incorporate quantum dots as light emitters. Enhancement of optical down-conversion is demonstrated. The quantum dots absorb photons at one wavelength and emit photons at a longer wavelength. The photonic crystal is used to engineer the optical emission behavior of the quantum dots such that the energy conversion between absorbed and emitted photons is controlled. Enhanced excitation of the quantum dots is achieved through resonant excitation of the quantum with photonic crystal modes. Also, enhanced extraction of the emitted photons is achieved through modifying the allowed emitted optical modes provided by the photonic crystal. Photons of certain wavelengths and propagation directions are more efficiently emitted through engineering of the photonic crystal. Normal incident emission enhancement of 7.7x at lambda = 875 nm is obtained through the extraction effect. Normal incident emission enhancement of 1.5x is obtained at normal incidence at lambda = 865 nm, and a 2x increase in optical down-conversion efficiency is achieved through enhanced excitation effects.