京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20090号 / 工博第4257号 / 新制||工||1659(附属図書館) / 33206 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 野田 進, 教授 藤田 静雄, 教授 川上 養一 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The primary objective of the presented research is to develop a class of integrated compact silicon diffractive sensors (CSDS) based on in-plane diffraction gratings. This class of sensors uses a silicon-on-insulator (SOI) substrate to limit costs, exploit established fabrication processes, enable integration of supporting electronics, and use the well-understood telecommunications wavelength of 1.55µm. Sensing is achieved by combining constant-diffraction-efficiency and highly-angularly-selective in-plane resonance-domain diffraction gratings. Detection is based on the diffraction efficiency of the highly angularly selective grating. In this research, the design processes for the constant-diffraction-efficiency and the highly angularly selective gratings are detailed. Grating designs are optimized with rigorous coupled-wave analysis (RCWA) and simulated with finite-difference time-domain (FDTD) analysis. Fabrication results are presented for the CSDS gratings. An inductively coupled plasma (ICP) Bosch etch process enables grating fabrication to within one percent of designed values with nearly vertical sidewalls. Experimental results are presented for individual CSDS gratings, the prototype sensor, and a prototype linear sensor array. The results agree well with simulation. The linear sensor array prototype demonstrates the intrinsic splitting mechanism and forms the basis of a 2-D sensor array. Finally, a toluene sensor was functionally demonstrated. The proof-of-concept device includes a polymer immobilization layer and microfluidic delivery of toluene. Toluene concentrations as low as 100ppm are measured, corresponding to a refractive index change of 3x10⁻⁴ RIU.

An enhanced thermal imaging concept made possible through the development of a gradient-indexed metamaterial infrared detector that offers broadband transmission and reflection in THz waves. This thesis proposes a proof of feasibility for a metamaterial infrared detector containing an anti-reflective coating with various geometrically varying periodic metasurfaces, a gradient-indexed dielectric multilayer for near-perfect longpass filtering, and a gradient index of refraction (GRIN) metalens for enhanced focal plane thermal imaging. 2D Rigorous Coupled-Wave Analysis (RCWA) is used for understanding the photonic gratings performance based on material selection and varying geometric structure. Finite Difference Time Domain (FDTD) is used to characterize performance for a diffractive metalens by optimizing the radius and arrangement of cylindrical nanorods to create a desired phase profile that can achieve a desired focal distance for projections on a detector for near- to far-infrared thermal imaging. Through combining a micromachined anti-reflective coating, a near-perfect longpass filter, and metamaterial GRIN metalens, infrared/THz focal plane thermal imaging can obtain faster photo-response and image quality at targeted wavelengths, which allows for scientific advancements in electro-optical devices for the Department of Defense, aerospace, and biochemical detection applications.

This thesis fills in the gaps in the existing theory of wave phenomena in thick diffraction gratings at extreme angles of scattering, i.e. when the scattered wave propagates parallel or almost parallel to the grating boundaries. A consistent theory of a new type of Bragg scattering of bulk and guided optical modes in thick uniform and non-uniform, dissipative and non-dissipative, slanted periodic gratings has been developed. This type of scattering is called extremely asymmetrical scattering (EAS). One of the main distinctive features of EAS is the strong resonant increase of the scattered wave amplitude compared to the amplitude of the incident wave. Several unique combinations of strong resonances shaping a complex multi-resonant pattern of EAS in different types of gratings have been predicted and investigated theoretically and numerically. This includes the prediction of a new resonant wave effect in non-uniform gratings with varying phase – double-resonant EAS, the discovery of several sharp and strong resonances with respect to scattering angle in gratings with the scattered wave propagating almost parallel to the grating boundaries (grazing-angle scattering (GAS)) for the case of second-order scattering, and the prediction of a new type of eigenmode in gratings with second-order scattering (especially in gratings with large amplitude). In addition, several other important practical problems that may be crucial for the experimental observation and application of EAS and GAS have been solved. These are the determination of the tolerance of EAS to small grating imperfections, e.g., fluctuations of the grating amplitude, prediction of unusually high sensitivity of second-order EAS to small variations of mean structural parameters, determination of the effect of weak dissipation on EAS, etc. Physical reasons for the predicted resonances and effects are explained. In particular, the crucial role of the diffractional divergence for EAS and GAS has been revealed, especially for non-uniform gratings. Methods of analysis involve the approximate and rigorous approaches. The approximate method is based on understanding the role of the diffractional divergence in the geometry of EAS and the two-wave approximation (valid for any types of waves). The rigorous approach is based on the rigorous coupled-wave analysis (RCWA) and, in particular, the known enhanced T-matrix algorithm (by Moharam, et al.) that is numerically stable for narrow and wide gratings with arbitrary amplitude (valid only for bulk electromagnetic waves).