Non-diffractive structured light fields - Generation, properties, and applications

Propagation of light can be controlled by structuring the propagation medium or the light itself. Methods for controlling light are continuously improved and renewed to meet the requirements of modern optical and photonic devices. The work presented in this thesis advances these developments, being focused on propagation-invariant optical fields and their applications in laser beam engineering, optical imaging, and photonic chip technology. In the thesis, it is shown that diffraction-free optical beams can be structured, both spatially and spectrally, to propagate at an arbitrary group velocity in free space. Through a theoretical analysis, we find that in addition, the group velocity can be made to vary as a function of both space and time. As an example, a two-frequency Bessel beam with a spatially varying group velocity that reaches subluminal, superluminal, and negative values has been demonstrated in one of our experiments. This work also presents a design of a compound prism with an extraordinarily high angular dispersion, i.e., the ability to split the incident light into its constituent frequency components. The prism is designed for generating non-diverging two-dimensional light sheets. A common problem with such light sheets is the presence of multiple interference fringes in the beam profile, which the high angular dispersion of the prism helps remove. Non-diverging Bessel beams are also employed in this work to extend the depth of field of an optical imaging system. The system comprises two lenses and a ring-shaped aperture placed at their common focal plane. This makes the images consist of nearly diffraction-free Bessel-like beams. Consequently, the object can be displaced from the front focal plane of the system without blurring the image. The performance of the system is assessed with both coherent and incoherent light. The thesis also describes an analytical method for modeling discrete diffraction in waveguide arrays. This type of diffraction appears as a result of light leakage between neighboring waveguides in densely packed waveguide arrays. The phenomenon, known as crosstalk, limits the miniaturization of photonic integrated circuits. The presented model offers new insight into the problem of crosstalk suppression and shows that the problem can be solved by bending the waveguides. The results suggest a way to further reduce the footprint of photonic chips without hindering their performance.