Structured light generation by refractive-diffractive micro optical array illuminators

Structured light generation having broad applications in different optical fields, is the topic of this thesis. Our structured light generation strategy is based on applying periodic microoptical elements at the refraction-diffraction limit, under a focused diverging source instead of a plane wave. The high contrast pattern in the far-field is achieved for certain distances between the source and periodic structure, where the self-imaging condition is satisfied. This phenomenon is the basis of our strategy to obtain a high-contrast far-field distribution. Throughout this thesis, we analytically, numerically, and experimentally examine the self-imaging condition for our light generators. We engineer the structured light using two main strategies; modifying the periodic microoptical element surface profile and modulate the source by applying an optical element in its near-field. For surface profile modulation, we apply a sinusoidal phase grating instead of conventional periodic optical elements such as microlenses under a Gaussian beam illumination to increase the number of points in the far-field distribution. We study the far-field distribution for thin and thick sinusoidal phase gratings by comparing vectorial and scalar simulation tools for paraxial and non-paraxial diffraction angles. By properly choosing the sinusoidal phase grating thickness, large numbers of peaks with a high field of view and uniform distribution in the far-field can be achieved. We use the Two-photon Polymerization (2PP) as a rapid technique to fabricate the sinusoidal phase grating and compare the measurement results with simulations. This part of the thesis demonstrates that by properly defining the refractive-diffractive microoptical element surface profile, we can achieve even more points in far-field compared to other optical elements such as lens arrays. In the next part, we engineer the structured light in the far-field by modifying the source near-field. By bringing a dielectric microstructure in the source near-field, a source with new optical characteristics is produced. For a dielectric microparticle, for example, a hot spot i.e a photonic nanojet (PNJ) is generated in the shadow side surface of the structure that can redistribute the dots in the far-field. We first numerically investigate the PNJ optical characteristics by changing the microsphere diameter for diverging and converging sources of low and high wavefront curvatures and compare with plane wave illumination. The PNJ shows completely different behaviors under converging and diverging illuminations when changing the particle size. In some cases, no hot spot is generated in the microparticle near-field. In this way, we can generate different sources from low to high numerical apertures. For the experimental evaluation, we employ a high-resolution interference microscopy (HRIM) setup which is based on a Mach-Zehnder interferometer to record both the amplitude and phase. Our setup has the flexibility to work with different illumination conditions from plane wave to the Gaussian beam and also to observe both near-field and far-field distributions. We study the far-field distribution for a microlens array under a focused diverging source that is modulated by applying a microparticle in its near-field. With the microparticle in the source near-field, a PNJ is generated and for this reason, the pattern field of view in the far-field is modified.