Enhancement of infrared absorption and sensing in two- and three-dimensional photonic media

The detection of light over a broad spectrum plays a key role in a wide variety of fields ranging from imaging to communication. The ability to detect light efficiently depends on the level of absorption of the available light. At the infrared regime, where potential optical applications are abundant, the intrinsic absorption efficiency of typical absorbers (e.g. graphene) are usually low. Moreover, such absorbers have a low frequency selectivity. In other words, while the absorber is able to detect the amplitude of light, it can not sense the spectral content of it. Hence, there is a need for highly efficient frequency-selective infrared detectors. On the other hand, near-field optical detectors are required to make measurements very near the object due to the diffraction limit. However, due to the closeness of the object and the detector, the field along the object can get distorted, resulting in detrimental effects of image quality. In this thesis, the phenomenon of light trapping and sensing in engineered photonic structures has been inverstigated. In the first part of this thesis, novel photonic architectures have been proposed to achieve light trapping. The trapping of light in such structures has been achieved via the concept of slow light and non-Hermitian optics. Owing to the slow light based design principle, it has been shown that light can be trapped and be separated into its Fourier components. In result, highly efficient multicolor infrared absorption has been achieved. In another propsed photonic device, it has been shown that owing to the slow light phenomena, the trapped light can be selectively filtered with high transmission efficiency and quality factor via frequency sensitive cavities. Furthermore, it has been shown that in non-Hermitian optical media having balanced gain and loss regions, that the incoming light can be localized at predefined locations. In the second part of this thesis, various novel invisibility methods have been propsed to achieve sensor invisibility. By means of the proposed methods, the invisibility of arbitrary shaped objects (e.g. tip of a sensor) have been achieved. The proposed invisibility technique is based on the judicious tailoring of the scattering potential of a given object. Owing to such a tailoring, it has been shown that certain scattered waves can be uncoupled from the incident radiation, leading to invisibility effects. The theoretically analyzed cloaks have been experimentally realized at the microwave regime. In this regard, by measuring the steady-state electric field profiles and angular scattering patterns, the proposed methods have been experimentally verified. The proposed methods may find useful applications especially in cloaked sensor and antenna radome applications.