Radiative properties of a material is the core of thermal science and optics, which play critical roles in modern technologies, including microelectronics, energy conversion, and nanotechnology. The key to modify or enhance radiative properties is employing one-, two-, and three-dimensional (1, 2, and 3D) periodic micro/nanostructures. Since their applications are not fully uncovered and very few comprehensive studies are available, the objective of this dissertation is to explore applications of periodic micro/nanostructures with modified radiative properties in modern technologies through both numerically and experimentally investigations. Theses representative applications include the thermal control in rapid thermal processing, the design of a wavelength-selective radiator for thermophotovoltaic systems, and the nanothermal manufacturing. The theoretical foundation of the study is built on the rigorous coupled-wave analysis (RCWA) for numerical calculation of the far-field radiative properties and the electromagnetic field distribution in the near-field regime. Measurements of diffraction efficiencies are conducted on fabricated 1D and 2D periodic silicon microstructures with a laser scatterometer/diffractometer with high angular resolution. The diffraction efficiency can be employed for non-contact surface profile inspection tool because it strongly depends on structure patterns. For better temperature control during rapid thermal processing, the dissertation performs a parametric study on radiation absorption of a generic CMOS device together with its simplified nanoscale structures. The applicability of approximation models, which homogenize micro/nanostructures into a film, is also evaluated. Next, a new concept of complex gratings is proposed for actively tailoring the radiative properties and serving as a thermophotovoltaic (TPV) radiator. The radiator exhibits a wide-band and angle-independent high transverse magnetic wave emittance matching the bandgap of TPV cells so that the energy conversion efficiency can be improved. Furthermore, the nanoscale metallic slit arrays show polarization-dependant enhanced transmission and highly localized electromagnetic energy density, which hold promising potentials in nanothermal manufacturing. Three submicrometer metallic slit arrays are fabricated on top of a silicon substrate. Their spectral transmittance is measured with a Fourier-transform infrared spectrometer and largely agrees with RCWA modeling results. In short, the dissertation clearly demonstrates that precise control and tuning of radiative properties using micro/nanofabrication are not only feasible but also may have numerous technological impacts.

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M.Ing. / This thesis, devoted to fibre optics, is primarily concerned with the utilization of fibre Bragg gratings and optical couplers to realize optical add-drop multiplexers (OADMs). A comparative study regarding various OADM configurations is undertaken on the basis of manufacturing and the performance in terms of insertion loss, channel isolation, tuning ranges, stability and cost. The heart of most of the OADMs is fibre Bragg gratings. The Runge-Kutta numerical integration method is used to solve the coupled-mode equations in order to simulate the spectral dependence of Bragg gratings numerically. Properties such as the grating strength, the grating length and the grating index profile governing the spectral dependence of Bragg gratings are investigated. In recent years, there has been an increasing interest in the dispersive properties of Bragg gratings. We investigate methods to limit the amount of dispersion induced by fibre Bragg gratings. The tuning of Bragg gratings for dynamic OADMs is also reviewed. High channel isolation Bragg gratings are theoretically and experimentally investigated. DC-apodized gratings were designed and manufactured by using the phase mask method through the use of a preconditioning technique. Bragg gratings with channel isolations of up to 24.61 dB have been realized by using this technique. The spectral dependence of DC-apodized gratings on the amount of preconditioning and the smoothness of the index envelope is simulated and in agreement with the experimental results. An athermal Bragg grating was designed and manufactured, exhibiting an average wavelength-temperature sensitivity of 2.76 pm/oC. An OADM comprising a DC-apodized Kaiser grating and an optical circulator was realized. The device showed an insertion loss of 1.84 dB and a channel isolation of 22.84 dB. The coupling mechanisms for different types of optical couplers are investigated. The distribution of power was established to be either by evanescent field coupling (etched, polished and weakly fused couplers) or due to the beating phenomenon (strongly fused couplers). The beating phenomenon of the HE11 and HE12 modes in the waist of the tapered-fused coupler is modelled and used to simulate different characteristics, such as wavelength, polarization and external refractive index dependence of tapered-fused couplers, in order to realize OADMs.

M.Ing. / Bragg gratings written in polymer optical fibres are much more sensitive to temperature and strain measurements than silica fibre with a lower Young's modules and higher temperature coefficient. The good biocompatibility of polymer fibres makes them ideal medical sensors for in vivo strain and temperature measurements as well as excellent chemical sensors that can easily be doped with organic compounds. Most of the Bragg gratings in polymer optical fibres are inscribed around 1550 nm where the attenuation is as large as 1 dB/em. Grating fabrication was investigated at 980 nm where the attenuation was discovered to be optimal (less than 0.1 dB/em). The polymer optical fibre was spliced to silica optical fibre through butt-coupling and affixed with optical adhesive to produce transmission loss of between 7 and 25 dB (at 980 nm). Preliminary results show that it may be possible to create fibre Bragg gratings in polymer optical fibre at 980 nm. Gratings inscribed in fibre with an energy density of between 80 and 150 mJ/cm2 supplied by Paradigm Optics (MORFOP3) had a repeatability of 25%. With the fibres supplied by Prof. Peng (PBzMA- PEMA- PMMA co-polymer) a success rate of more than 90% was achieved when using energy densities around 70 mJ/cm2 • However, these gratings were weak and disappeared within 48 hours. The strength of these gratings varied from grating to grating. The reason of this instability is unknown and should be further investigated. The temperature sensitivity of polymer optical fibre at 976 nm was found to be -100 ±17 pm;oc corresponding with the reported value of -94 pm;oc at 976 nm.

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An index grating is a periodic perturbation of the refractive index in a waveguide's axial direction. Gratings have important roles in optical communication as spectral filters and dispersion compensators. The spectral response characteristics of gratings can be controlled by shaping the profile of the index modulation, a process called apodization. Apodizing different layers of the grating using different apodizing functions is proposed for adding more degrees of freedom to the design. An approach to designing a two-layer separately apodized grating that yields virtually the same reflectivity and dispersion responses as an arbitrary zero-"dc", apodized, un-chirped grating is proposed. A design example is presented, and coupled-mode theory is employed to compute the reflectivity responses of the original zero-"dc" design and the nearly equivalent separately-apodized design proposed in this thesis. An approach to designing a four-layer separately apodized grating that yields virtually the same reflectivity and dispersion responses as an arbitrary chirped grating is proposed. The largest bandwidth a four-layer separately-apodized grating designed using this approach can yield is as large as the largest bandwidth a variable-period conventional design can yield. Also, a similar, less-capable design approach is proposed for two-layer separately apodized gratings that are equivalent to conventional, chirped gratings. Design examples are presented. For all of the separately apodized gratings designed, the layers have a varying "dc" index change that is proportional to the varying "ac" index change. Furthermore, the period, which is the same in every layer, is constant, i.e. independent of the position. Both considerations enhance the prospects of fabricating the separately-apodized designs using a simple, reproducible technique. One such technique is proposed that separately-apodizes halves of the waveguide, instead of layers, but the design approaches are easily adjusted to this case. / Master of Science

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In modern communications systems, the components supporting wavelength division for increased density are rapidly becoming small compared with the wavelength of light being manipulated. As the size of these devices shrinks there comes a point when the features of interest become smaller than the wavelength and thereby the fundamental properties of light interaction with such structures change dramatically. In these structures and materials, resonances, effective properties, and band-gaps arise and offer designers a new realm of possibilities for the design of high quality factor resonators, filters and switches. / The study of structures comprising two different scales compared with the wavelength of light promises interesting optical possibilities for future devices. In these structures a subwavelength size feature is used in conjunction with a super-wavelength size feature. This thesis will show how the resulting optical behavior for such structures arises from the combination of the sub- and super-wavelength diffractive effects. / Two application examples of these two-scale devices will be studied: the distributed echelle grating and the subwavelength based Fabry-Perot cavity. Both of these applications can be thought, of as distributed diffractive structures, a structure in which diffraction and subwavelength scale interference combine to produce high efficiency and versatile new devices.

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