Miniaturizing optical systems is necessary and useful for many different applications, such as cameras and optical sensors. Recent breakthroughs in metalenses have enabled ultra-thin optical components, driving efforts to reduce the free space propagation distances between them. This can be done using devices called spaceplates, which mimic the phase response of free space propagation within a shorter relative distance. This thesis investigates the properties of theoretical spaceplates comprised of multilayer thin film structures, designed through optimization. It explores the limits of achievable effective distances by stacking devices, ultimately demonstrating a theoretical effective distance of 23.3 mm for an NA of 0.087 and 1550 nm wavelength. It also finds manufacturing errors have a significant influence on this metric, reducing achievable effective distances to millimeter scales. Lastly, it explores combining the spaceplate function with angular stray light filtering to achieve multifunctional designs, with promising results.

The growing demand for scalable biomedical solutions calls for precise, programmable, and cost-effective manipulation techniques at the microscale. While mechanical and magnetic methods have been explored, they often face limitations in flexibility, biocompatibility, or scalability. Optical tweezers offer high precision, but suffer from thermal side effects and complex, expensive setups. Optoelectronic tweezers (OET), by contrast, utilize patterned light to induce dielectrophoretic forces, enabling flexible, energy-efficient, and scalable control of microscopic particles using relatively simple hardware.

To support advanced biomedical research at Delft University of Technology, a fully functional OET platform was developed from the ground up. It integrates a custom transparent photoconductive microfluidic chip with a DMD-based optical system for real-time, reconfigurable actuation. Custom-fabricated PDMS microgear robots were successfully manipulated under varying electrical and optical conditions. Using precise motion tracking and calibration, the generated dielectrophoretic forces were quantified, with peak values approaching 500 pN, and benchmarked against theoretical models and literature estimates.

This research demonstrates that complex-shaped microbots can be effectively actuated within a custom-built OET system, paving the way for future applications in automated diagnostics, single-cell manipulation, and intelligent lab-on-a-chip platforms. By combining hardware innovation with theoretical insight, this work lays a robust foundation for microscale robotics in next-generation biomedical technologies.

Gravitational waves predicted by Einstein have been measured in a few observatories worldwide. These detectors are complex interferometers with sizes of kilometers. Misalignments and aberrations in their optical set-up can create higher-order modes in the laser beam. These higher-order mode effects should be compensated to improve the sensitivity of the interferometer. Such a compensating control system requires a real-time wavefront sensor. The phase cameras developed for the Virgo gravitational wave detector can simultaneously create intensity and phase images of the laser wavefront at 11 demodulation frequencies. Currently, the phase images are not used due to difficulties in the interpretation. Therefore, the goal of this research is to improve the understanding of the phase images of a phase camera for the Virgo gravitational wave detector.

A prototype set-up of the phase camera was built at Nikhef. The beam is modulated and sidebands are created such that a beat signal of 80 MHz and the first upper and lower sidebands at 75 and 85 MHz are measured. Images are created by scanning the laser beam across a pinhole diode and digital demodulation. In the chosen optical set-up only one of the two beams that give the measurable beat signal is scanned. This leads to systematic phase effects caused by length differences in the optical path as a function of the scanning angle. To predict the phase images, the interference of two Gaussian beams with a scanning mirror is mathematically derived. Phase images are created with a simulation, which matches within 10 to 20% compared to measurements. To improve the results, the input parameters of the simulation should be measured more accurately and the optical set-up layout should be checked. Also, the phase stability of the prototype set-up is measured. Due to the high sensitivity of the phase camera, very small optical path length differences, for example caused by airflow or temperature differences, lead to significant phase offsets. The long timescale fluctuations in the phase measurements can be reduced by covering the optical set-up. The measured high-frequency phase resolution is Δ𝜙 = 7.1 ± 0.4 mrad and behaves as a function of power as expected.

When looking up to the sky and trying to detect the photons of far away stars that are still in formation, we can get access to knowledge we never had before. In order to do this, we must make sure we truly understand the nature of how photons behave in accordance to each other and to our detectors.In quantum optics we can see that these photons have a very dubious character. They are both particle and wave and neither. This makes studying how they are distributed over the spectrum of the submillimeter and millimeter wave astronomy a very big challenge. We know that this very particlewave duality is what makes up the noise that is fundamental to photons. This duality also makes them obey the BoseEinstein statistics. Hence due to their particlelike behavior, we have a noise component that resembles that of a Poisson distribution. Very much like raindrops falling down from the sky. On the other hand we have the wave nature of the photons, this causes them to arrive in bunches rather than these random raindrops. It is observed that photons arriving at a detector are corrrelated.
In this thesis we will be investigating how to incorporate the noise of the bunching of the photons into the model of TiEMPO. This model simulates the signal processing of a measurement done by the wideband spectrometer named DESHIMA. Due to the fact that DESHIMA operates in a wideband frequency range, we do theoretical research that explains the fundamental theory behind calculating the photon noise over this wideband range. We show that taking the wideband integral of the photon noise is mathematically equivalent of summing the narrowband approximation for infinitely many subbands and adding them up top each other. This approach is the previous method of calculating the photon noise over the wideband. Due to this method being valid, the question of how these variances over these smaller subbands can be additive?
Since we are dealing with the detection of photons which as previously stated is a correlated signal. By modeling a simplified version of wideband photon detection, we have come to the conclusion that due to the small coherence time these photons are independent in the wideband signal. The photons in these smaller subbands of the wideband signal can also be viewed as statistically independent. If we decrease the frequency bandwidth, we increase the coherence time. Thus measuring the signal over this subband equates to having a larger uncertainty in time. Hence when a photon is detected in this subband, due to the large coherence time we have that the knowledge of when this photon arrived is mostly lost. Making the time correlations irrelevant to a measurement of an integration time this long.

Phase Retrieval Problem is very common and has a lot of applications in fields such as microscope, astronomy, crystallography, optical imaging etc.. In this problem, PSF and the pupil function are given, and the goal is to reconstruct the phase of the object. For camera which has 8 bits color depth, the maximum number of colors that can be displayed at any one time is 2^8 , i.e. 256. When the minimal exposure time of the camera is longer than "correct" exposure time or the intensity is changing, e.g. dynamic focusing, too much intensity is measured by the camera and causes saturation, i.e. over-exposure. Over-exposure causes distortion of the image, thereby losing the information. However, on the other hand, the overall brightness of the PSF image will be enhanced due to over-exposure. It highlight structure and increase the number of informative pixels of the image. We can use this to enhance the information in the PSF image to offset the negative effects of noise or background in the image.
Gerchberg-Saxton algorithm is a solution to phase retrieval problem and is a nice example of projection based algorithm. The algorithm has a perfect performance in the case that the PSF is the modules square of the object, i.e. without noise or other preconditioners effect. It is demonstrated in [Nishizaki, 2019] that an over-exposure preconditioner can improve the performance for phase restoration of a machine-learning model based algorithm. In this master thesis, we propose modification of the model of PSF amplitude in Gerchbrg-Saxton algorithm to make the algorithm be able to cope with over-exposed PSF image. This approach is tested both by numerical simulation and with experimental data.

Turbulent layers high in the atmosphere cause anisoplanatic phase aberrations, that are responsible for image degradation [6, 33, 46]. Adaptive Optics (AO) aims to correct for these aberrations by sensing them with a wavefront sensor and performing the correction with phase conjugate devices [18]. Various wavefront sensors have been designed and successfully implemented over the years, including the curvature sensor, interferometers, the Shack-Hartmann (SH) sensor and the pyramid sensor [7, 32, 40, 51]. In recent work the plenoptic sensor, an intermediate between the SH and pyramid sensor designs [10, 32, 37], has been proposed to improve on modern wavefront sensing. It has been reported to be beneficial in presence of strong or complex
wavefronts, such as deep turbulence conditions [18, 47]. The goal of this thesis is to investigate the SH and plenoptic wavefront sensors, with the
specific application on the correction of anisoplanatic aberrations that vary throughout the field of view. The contribution of this thesis to the field of AO is the development of a simulation toolbox in MATLAB. This toolbox is designed to simulate the SH and plenoptic sensors, providing a comparative study between the two. The comparative simulations reinforced results obtained from a corresponding Literature Survey. The SH sensor can outperform the plenoptic sensor on many occasions. If both sensors share the same microlens array (MLA) the plenoptic sensor scores worse in terms of performance metrics. By adjusting the MLA of the plenoptic sensor its dynamic range and sensitivity can be improved, such that it outperforms the SH sensor. Additionally, it was shown that the plenoptic sensor performs best for strong aberrations, simulated using
randomly-generated Kolmogorov screens. On the other hand, it fails in the presence of weak aberrations where the SH performs best. The developed toolbox allows for iso- and anisoplanatic aberrations to be reconstructed in a single frame, by differentiating between aperture plane reconstruction and phase screen retrieval. Multiple approaches are implemented in the toolbox, such that different reconstruction methods can be selected depending on experimental conditions.

This thesis discusses developments towards a low-cost Fourier Ptychographic microscope for label free imaging of malaria parasites.
A review of the morphology and life cycle of malaria and the main diagnostic methods for its detection is followed by an introduction to Fourier Ptychography with emphasis on the underlying imaging principles and phase retrieval algorithms which are at the core of the algorithms used.
The practical realization of the Fourier Ptychographic setup with the required resolution has proven to be very challenging due to its susceptibility to errors when operating the system at its theoretical limits.
Insights from in-depth analyses of the effects of quantization noise, intensity drop-off due to angled illumination, and partial coherence are presented. These insights rule in- or out these potential error sources and help identify potential mitigations in the design.
In the final chapters the realization of the setup is described, and the results with real blood smear samples are used to illustrate the interference of the error sources. The thesis concludes with considerations for further research and recommendations for international collaboration.

In optical imaging, image quality is not only determined by the system itself but also by the media in which light traverse. Differences in the refraction index of the media encountered by a light wavefront produces phase aberrations which distort the image received from the original object. Currently, there are two main approaches for solving this problem: adaptive optics, which rely on deformable mirrors and wavefront sensors for correcting the phase aberration before it reaches the imaging sensor; and post-processing techniques, which try to estimate the object after receiving distorted images.

MFBD methods are a family of algorithms that are capable of reconstructing the object by fusing the information carried by a set of differently aberrated images. These techniques are widely used in current optical systems, allowing a notable increase in image quality in most situations. However, there are cases in which they are not applicable; for example, looking at a dynamic object (e.g., a bird flying) or looking through static aberrations (e.g., in microscopy applications); but certain modifications in the optical system can be used for solving this problem.

Actual optical devices have only one aperture, thus creating one full-size image on the imaging sensor but, by segmenting the pupil, several images can be retrieved at the same time with different aberrations (i.e., light follows a distinct path for each aperture). However, using a multi-aperture system implies that there is less imaging sensor area available for each aperture, thus obtaining images with less resolution. Nonetheless, MFBD algorithms can usually be extended in order to support SR, a technique that allows the increase of the object resolution by retrieving extra information from the displacement between images.

This thesis is focused on the development of a functional prototype of a multi-aperture optical system that can do real-time object reconstruction. As a MFBD technique is needed, the novel TIP algorithm (developed at Delft Center for Systems and Control) is selected. In order to achieve a fast and reliable reconstruction, the algorithm is: modified for increasing its robustness against noise, expanded in order to support SR and implemented efficiently in both CPU and GPU. Finally, the system is tested in a real environment, showing promising results.

Two dimensional plasmonic back reflectors have shown the ability to match the
scattering performance of standard back reflectors. However, three dimensional
plasmonic structures have not yet been thoroughly investigated. Here, the scat-
tering properties of a 3D plasmonic structure are approached at three levels of
system. First, the scattering properties of different types of particles are inves-
tigated. An optimum particle size is found for both spherical and cylindrical
silver particles. The interaction of two particles is then studied. By comparing
numerical and analytic results, the strength of different effects is explored. It is
found that dipole-dipole interactions can not be ignored within the structure.
Finally, the effect of the lattice structure on the scattering properties is probed.
A new lattice summation method is developed, revealing that only particles near
the point of interest must be considered. Several 3D devices were fabricated to
investigate the properties of self forming metal island films. It was found that
the surface morphology of layers deposited on top of these films, do not depend
on the properties of the film.