We exploit the inherent dispersion in diffractive optics to demonstrate planar chromatic-aberration-corrected lenses. Specifically, we designed, fabricated and characterized cylindrical diffractive lenses that efficiently focus the entire visible band (450 nm to 700 nm) onto a single line. These devices are essentially pixelated, multi-level microstructures. Experiments confirm an average optical efficiency of 25% for a three-wavelength apochromatic lens whose chromatic focus shift is only 1.3 μm and 25 μm in the lateral and axial directions, respectively. Super-achromatic performance over the continuous visible band is also demonstrated with averaged lateral and axial focus shifts of only 1.65 μm and 73.6 μm, respectively. These lenses are easy to fabricate using single-step grayscale lithography and can be inexpensively replicated. Furthermore, these devices are thin (<3 μm), error tolerant, has low aspect ratio (<1:1) and offer polarization-insensitive focusing, all significant advantages compared to alternatives that rely on metasurfaces. Our design methodology offers high design flexibility in numerical aperture and focal length, and is readily extended to 2D.
We demonstrate imaging over the visible band using a single planar diffractive lens. This is enabled via multi-level diffractive optics that is designed to focus over a broad wavelength range, which we refer to as an achromatic diffractive lens (ADL). We designed, fabricated and characterized two ADLs with numerical apertures of 0.05 and 0.18. Diffraction-limited focusing is demonstrated for the NA = 0.05 lens with measured focusing efficiency of over 40% across the entire visible spectrum (450 nm to 750 nm). We characterized the lenses with a monochromatic and a color CMOS sensor, and demonstrated video imaging under natural sunlight and other broadband illumination conditions. We use rigorous electromagnetic simulations to emphasize that ADLs can achieve high NA (0.9) and large operating bandwidth (300 nm in the visible spectrum), a combination of metrics that have so far eluded other flat-lens technologies such as metalenses. These planar diffractive lenses can be cost-effectively manufactured over large areas and thereby, can enable the wide adoption of flat, low-cost lenses for a variety of imaging applications.
Fiber Bragg gratings (FBGs) are key elements in modern telecommunication and sensing applications. In optical communication, with the advancement of the Erbium doped fiber amplifier (EDFA), there is a great demand for devices with wavelength tunability over the Erbium gain bandwidth (in particular, for wavelength division multiplexing (WDM) networks). The center wavelength of a FBG can be shifted by means of change of temperature, pressure or mechanical axial strain. The axial strain approach is the best method among all other techniques because it allows relatively large wavelength shifts with high speed. Axial strain of up to 4% will be required to cover the whole EDFA region (more than 40 nm of central wavelength shift). The formation of Bragg grating results in significant reduction in mechanical strength of optical fibers especially in tension. As a result, axial strain of only about 1% can be achieved by mechanical stretching of FBGs. In order to achieve the remaining 3% strain compression of FBGs has to be applied.In this thesis, the design and analysis of a novel device for achieving central wavelength shift are presented. In particular, the device has achieved, for a fiber with Further, using the piezoelectric transducer (PZT) actuator as a driver, tuning speed of around 1.5nm/ms was achieved.-iii - ACKNOWLEDGMENTSUpon the completion of this thesis, I would like to express my sincere gratitude and appreciation to my supervisors Professor Chris W.
We show that multi-level diffractive microstructures can enable broadband, on-axis transmissive holograms that can project complex full-color images, which are invariant to viewing angle. Compared to alternatives like metaholograms, diffractive holograms utilize much larger minimum features (>10 µm), much smaller aspect ratios (<0.2) and thereby, can be fabricated in a single lithography step over relatively large areas (>30 mm ×30 mm). We designed, fabricated and characterized holograms that encode various full-color images. Our devices demonstrate absolute transmission efficiencies of >86% across the visible spectrum from 405 nm to 633 nm (peak value of about 92%), and excellent color fidelity. Furthermore, these devices do not exhibit polarization dependence. Finally, we emphasize that our devices exhibit negligible absorption and are phase-only holograms with high diffraction efficiency.
We report the enhancement of photovoltaic output power by separating the incident spectrum into 3 bands, and concentrating these bands onto 3 different photovoltaic cells. The spectrum-splitting and concentration is achieved via a thin, planar micro-optical element that demonstrates high optical efficiency over the entire spectrum of interest. The optic (which we call a polychromat) was designed using a modified version of the direct-binary-search algorithm. The polychromat was fabricated using grayscale lithography. Rigorous optical characterization demonstrates excellent agreement with simulation results. Electrical characterization of the solar cells made from GaInP, GaAs and Si indicate increase in the peak output power density of 43.63%, 30.84% and 30.86%, respectively when compared to normal operation without the polychromat. This represents an overall increase of 35.52% in output power density. The potential for cost-effective large-area manufacturing and for high system efficiencies makes our approach a strong candidate for low cost solar power.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.