Design and fabrication of ultrathin nanophotonic devices based on metasurfaces

Wydział FizykiOd kilkuset lat badania natury światła fascynuje naukowców na całym świecie. W XVII wieku, holenderski astronom i matematyk, Willebrord Snellius zdefiniował pojęcie refrakcji światła, które później od jego nazwiska zostało nazwane prawem Snella. Prawo to wciąż jest szeroko stosowane, a jego uogólnienie w roku 2011 zaproponował prof. Capasso z Uniwersytetu Harvarda. Uogólnione prawo Snella pozwala na rozwijanie technik kontroli frontów falowych wykorzystując powierzchnie zmieniające ich fazę w transmisji lub w odbiciu, zwane metapowierzchniami. Uogólnione prawo Snella jest zgodne z zasadą Fermata a wytwarza się je przy użyciu bardzo małych struktur mogących arbitralnie modyfikować amplitudę, fazę, polaryzację fali światła. Mechanizm odpowiedzialny za to zjawisko można dostosować do konkretnych zakresów długości fali i jest szczególnie dobrze sprawdzone dla światła z zakresu widzialnego. W pracy doktorskiej przedstawiłem koncepcję wykorzystania metapowierzchni do projektowania kilku urządzeń nanofotonicznych. Zaprojektowałem w pełni dielektryczne filtry koloru na bazie krzemu, które efektywnie działają dla fal przechodzących i odbitych. Rozszerzyłem te badania również o projekt dynamicznych i przestrajalnych filtrów kolorów kontrolując polaryzację światła przy wykorzystaniu ciekłych kryształów. Następnie zaproponowałem koncepcję urządzenia wykorzystujące zjawisko impedancji powierzchniowej do sterowania transmisją i umożliwiając prowadzenie fal w płaszczyźnie falowodu kryształu fotonicznego.Light is one of the most fascinating research areas of science since the past few centuries and this century no exception. In 17th, Snell's law was introduced by Willebrord Snellius a Dutch astronomer and mathematician, which explain the properties of refraction and reflection of light. In 2011, prof. Capasso group from Harvard University generalized the Snell's law and introduce a new way to modify the wave-front of the wave using phase varying surfaces. The modified Snell's law follows the Fermat principle for the phase changing surfaces. This phase changing surface can be created using tiny nanostructures to arbitrarily modified the amplitude, phase, polarization of the wave, commonly known as metasurfaces. The concept is scalable to arbitrary wavelength range and very well followed especially in the visible range. In this thesis, I used the concept of metasurfaces to design and fabricate the different nanophotonics devices. I design and fabricate the Si-based all-dielectric color filters which can be used in transmission and reflection mode. The color filter design presented in this thesis is very efficient due to the all dielectric material approach. I also extended the research to design dynamically tunable color filters with the aid of source polarisation and liquid crystal. Furthermore, I also proposed the surface impedance approach to control the in-plane transmission within the photonic crystal waveguide

A full degree-of-freedom photonic crystal spatial light modulator

Harnessing the full complexity of optical fields requires complete control of all degrees-of-freedom within a region of space and time -- an open goal for present-day spatial light modulators (SLMs), active metasurfaces, and optical phased arrays. Here, we solve this challenge with a programmable photonic crystal cavity array enabled by four key advances: (i) near-unity vertical coupling to high-finesse microcavities through inverse design, (ii) scalable fabrication by optimized, 300 mm full-wafer processing, (iii) picometer-precision resonance alignment using automated, closed-loop "holographic trimming", and (iv) out-of-plane cavity control via a high-speed micro-LED array. Combining each, we demonstrate near-complete spatiotemporal control of a 64-resonator, two-dimensional SLM with nanosecond- and femtojoule-order switching. Simultaneously operating wavelength-scale modes near the space- and time-bandwidth limits, this work opens a new regime of programmability at the fundamental limits of multimode optical control.Comment: 25 pages, 20 figure

Event-based camera refractory period characterization and initial clock drift evaluation

Event-based camera (EBC) technology provides high-dynamic range operation and shows promise for efficient capture of spatio-temporal information, producing a sparse data stream and enabling consideration of nontraditional data processing solutions (e.g., new algorithms, neuromorphic processors, etc.). Given the fundamental difference in camera architecture, the EBC response and noise behavior differ considerably compared to standard CCD/CMOS framing sensors. These differences necessitate the development of new characterization techniques and sensor models to evaluate hardware performance and elucidate the trade-space between the two camera architectures. Laboratory characterization techniques reported previously include noise level as a function of static scene light level (background activity) and contrast responses referred to as S-curves. Here we present further progress on development of basic characterization methods and test capabilities for commercial-off-the-shelf (COTS) visible EBCs, with a focus on measurement of pixel deadtime (refractory period) including results for the 4th-generation sensor from Prophesee and Sony. Refractory period is empirically determined from analysis of the interspike intervals (ISIs), and results visualized using log-histograms of the minimum per-pixel ISI values for a subset of pixels activated by a controlled dynamic scene. Our tests of the Prophesee gen4 EVKv2 yield refractory period estimates ranging from 6.1 msec to 6.8 μsec going from the slowest (20) to fastest (100) settings of the relevant bias parameter, bias_refr. We also introduce and demonstrate the concept of pixel bandwidth measurement from data captured while viewing a static scene – based on recording data at a range of refractory period setting and then analyzing noise-event statistics. Finally, we present initial results for estimating and correcting EBC clock drift using a GPS PPS signal to generate special timing events in the event-list data streams generated by the DAVIS346 and DVXplorer EBCs from iniVation

Doctor of Philosophy

dissertationOptics is an old topic in physical science and engineering. Historically, bulky materials and components were dominantly used to manipulate light. A new hope arrived when Maxwell unveiled the essence of electromagnetic waves in a micro perspective. On the other side, our world recently embraced a revolutionary technology, metasurface, which modifies the properties of matter-interfaces in subwavelength scale. To complete this story, diffractive optic fills right in the gap. It enables ultrathin flat devices without invoking the concept of nanostructured metasurfaces when only scalar diffraction comes into play. This dissertation contributes to developing a new type of digital diffractive optic, called a polychromat. It consists of uniform pixels and multilevel profile in micrometer scale. Essentially, it modulates the phase of a wavefront to generate certain spatial and spectral responses. Firstly, a complete numerical model based on scalar diffraction theory was developed. In order to functionalize the optic, a nonlinear algorithm was then successfully implemented to optimize its topography. The optic can be patterned in transparent dielectric thin film by single-step grayscale lithography and it is replicable for mass production. The microstructures are 3?m wide and no more than 3?m thick, thus do not require slow and expensive nanopatterning techniques, as opposed to metasurfaces. Polychromat is also less demanding in terms of fabrication and scalability. The next theme is focused on demonstrating unprecedented performances of the diffractive optic when applied to address critical issues in modern society. Photovoltaic efficiency can be significantly enhanced using this optic to split and concentrate the solar spectrum. Focusing through a lens is no news, but we transformed our optic into a flat lens that corrects broadband chromatic aberrations. It can also serve as a phase mask for microlithography on oblique and multiplane surfaces. By introducing the powerful tool of computation, we devised two imaging prototypes, replacing the conventional Bayer filter with the diffractive optic. One system increases light sensitivity by 3 times compared to commercial color sensors. The other one renders the monochrome sensor a new function of high-resolution multispectral video-imaging

Hyperspectral microscopy of two-dimensional semiconductors

Here we present an interferometric wide field hyperspectral microscope based on a common-path birefringent interferometer with translating wedges, to measure photoluminescence emission from two-dimensional semiconductors. We show diffraction-limited hyperspectral photoluminescence microscopy from two-dimensional materials across millimeter areas, proving that our hyperspectral microscope is a compact, stable and fast tool to characterize the optical properties and the morphology of 2D materials across ultralarge areas