From Metasurfaces to Compact Optical Metasystems

Optical metasurfaces are a class of ultra-thin diffractive optical elements, which can control different properties of light such as amplitude, phase, polarization and direction at various wavelengths. The compatibility of optical metasurfaces with standard micro- and nano-fabrication processes makes them highly-suitable for realization of compact and planar form optical devices and systems. In addition, optical metasurfaces have achieved unique and unprecedented functionalities not possible by conventional diffractive or refractive optical elements. In this thesis, after a short review on the history and state of the art optical metasurfaces, I will discuss the systems consisting of optical metasurfaces, called optical meta-systems, which allow for implementations of complicated optical functions, such as wide field of view imaging and projection, tunable cameras, retro-reflection, phase-imaging, multi-color imaging, etc. Thereafter, the concept of folded metasurface optics is introduced and a compact folded metasurface spectrometer is showcased to demonstrate how the folded meta-systems can be designed, fabricated and practically utilized for real-life applications. Furthermore, different approaches for implementation of miniaturized hyperspectral imagers are investigated, among which the folded metasurface optics and a computational scheme using a random metasurface mask will be highlighted. Other potentials of optical metasurfaces achieved by the employment of optimization techniques to improve their multi-functional performances, as well as example applications in realizing optical vortex cornographs are studied. Finally, I will conclude the dissertation with an outlook on further applications of optical metasurfaces, where they can surpass the performance of current optical devices and systems and what limitations are still to be overcome before we can expect their wide-spread applications in our daily life.</p

MEMS-tunable dielectric metasurface lens

Varifocal lenses, conventionally implemented by changing the axial distance between multiple optical elements, have a wide range of applications in imaging and optical beam scanning. The use of conventional bulky refractive elements makes these varifocal lenses large, slow, and limits their tunability. Metasurfaces, a new category of lithographically defined diffractive devices, enable thin and lightweight optical elements with precisely engineered phase profiles. Here we demonstrate tunable metasurface doublets, based on microelectromechanical systems (MEMS), with more than 60 diopters (about 4%) change in the optical power upon a 1-μm movement of one metasurface, and a scanning frequency that can potentially reach a few kHz. They can also be integrated with a third metasurface to make compact microscopes (~1 mm thick) with a large corrected field of view (~500 μm or 40 degrees) and fast axial scanning for 3D imaging. This paves the way towards MEMS-integrated metasurfaces as a platform for tunable and reconfigurable optics

Compact folded metasurface spectrometer

An optical design space that can highly benefit from the recent developments in metasurfaces is the folded optics architecture where light is confined between reflective surfaces, and the wavefront is controlled at the reflective interfaces. In this manuscript, we introduce the concept of folded metasurface optics by demonstrating a compact spectrometer made from a 1-mm-thick glass slab with a volume of 7 cubic millimeters. The spectrometer has a resolution of -1.2 nm, resolving more than 80 spectral points from 760 to 860 nm. The device is composed of three reflective dielectric metasurfaces, all fabricated in a single lithographic step on one side of a substrate, which simultaneously acts as the propagation space for light. The folded metasystem design can be applied to many optical systems, such as optical signal processors, interferometers, hyperspectral imagers, and computational optical systems, significantly reducing their sizes and increasing their mechanical robustness and potential for integration

MEMS-tunable dielectric metasurface lens

Varifocal lenses, conventionally implemented by changing the axial distance between multiple optical elements, have a wide range of applications in imaging and optical beam scanning. The use of conventional bulky refractive elements makes these varifocal lenses large, slow, and limits their tunability. Metasurfaces, a new category of lithographically defined diffractive devices, enable thin and lightweight optical elements with precisely engineered phase profiles. Here we demonstrate tunable metasurface doublets, based on microelectromechanical systems (MEMS), with more than 60 diopters (about 4%) change in the optical power upon a 1-μm movement of one metasurface, and a scanning frequency that can potentially reach a few kHz. They can also be integrated with a third metasurface to make compact microscopes (~1 mm thick) with a large corrected field of view (~500 μm or 40 degrees) and fast axial scanning for 3D imaging. This paves the way towards MEMS-integrated metasurfaces as a platform for tunable and reconfigurable optics

Quantitative phase gradient microscope based on multifunctional metasurfaces (Conference Presentation)

Quantitative phase imaging systems enable label-free imaging of transparent bio-samples. Miniaturization of these imaging systems will extend their potentials in biomedical and diagnostic applications. Here, we demonstrate a novel quantitative phase gradient microscope using two multifunctional metasurface layers. Thanks to the multi-functionality and compactness of the dielectric metasurfaces, the device simultaneously captures three differential interference contrast images to retrieve a quantitative phase gradient image in a single shot. Imaging experiments with diverse phase samples verify the capability to capture quantitative phase gradient data, with low noise levels and single cell resolution

Quantitative phase gradient microscope based on multifunctional metasurfaces (Conference Presentation)

Quantitative phase imaging systems enable label-free imaging of transparent bio-samples. Miniaturization of these imaging systems will extend their potentials in biomedical and diagnostic applications. Here, we demonstrate a novel quantitative phase gradient microscope using two multifunctional metasurface layers. Thanks to the multi-functionality and compactness of the dielectric metasurfaces, the device simultaneously captures three differential interference contrast images to retrieve a quantitative phase gradient image in a single shot. Imaging experiments with diverse phase samples verify the capability to capture quantitative phase gradient data, with low noise levels and single cell resolution

Dielectric metasurfaces with independent angular control

We introduce dielectric metasurfaces with independent response at different angles of incidence given the same input polarization. We demonstrate a reflective metasurface grating with different effective grating pitches under two different incident angles, and a hologram that projects different images for different incidence angles