Optical MEMS

Optical microelectromechanical systems (MEMS), microoptoelectromechanical systems (MOEMS), or optical microsystems are devices or systems that interact with light through actuation or sensing at a micro- or millimeter scale. Optical MEMS have had enormous commercial success in projectors, displays, and fiberoptic communications. The best-known example is Texas Instruments’ digital micromirror devices (DMDs). The development of optical MEMS was impeded seriously by the Telecom Bubble in 2000. Fortunately, DMDs grew their market size even in that economy downturn. Meanwhile, in the last one and half decade, the optical MEMS market has been slowly but steadily recovering. During this time, the major technological change was the shift of thin-film polysilicon microstructures to single-crystal–silicon microsructures. Especially in the last few years, cloud data centers are demanding large-port optical cross connects (OXCs) and autonomous driving looks for miniature LiDAR, and virtual reality/augmented reality (VR/AR) demands tiny optical scanners. This is a new wave of opportunities for optical MEMS. Furthermore, several research institutes around the world have been developing MOEMS devices for extreme applications (very fine tailoring of light beam in terms of phase, intensity, or wavelength) and/or extreme environments (vacuum, cryogenic temperatures) for many years. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on (1) novel design, fabrication, control, and modeling of optical MEMS devices based on all kinds of actuation/sensing mechanisms; and (2) new developments of applying optical MEMS devices of any kind in consumer electronics, optical communications, industry, biology, medicine, agriculture, physics, astronomy, space, or defense

Momentum exchange between light and nanostructured matter

An object\u27s translational and rotational motion is associated with linear and angular momenta. When multiple objects interact the exchange of momentum dictates the new system\u27s motion. Since light, despite being massless, carries both linear and angular momentum it too can partake in this momentum exchange and mechanically affect matter in tangible ways. Due to conservation of momentum, any such exchange must be reciprocal, and the light therefore acquires an opposing momentum component. Hence, light and matter are inextricably connected and one can be manipulated to induce interesting effects to the other. Naturally, any such effect is facilitated by having strongly enhanced light-matter interaction, which for visible light is something that is obtained when nanostructured matter supports optical resonances. This thesis explores this reciprocal relationship and how nanostructured matter can be utilised to augment these phenomena.Once focused by a strong lens, light can form optical tweezers which through optical forces and torques can confine and manipulate small particles in space. Metallic nanorods trapped in two dimensions against a cover glass can receive enough angular momentum from circularly polarised light to rotate with frequencies of several tens of kilohertz. In the first paper of this thesis, the photothermal effects associated with such optical rotations are studied to observe elevated thermal environments and morphological changes to the nanorod. Moreover, to elucidate upon the interactions between the trapped particle and the nearby glass surface, in the thesis\u27 second paper a study is conducted to quantify the separation distance between the two under different trapping conditions. The particle is found to be confined ~30-90 nm away from the surface.The momentum exchange from a single nanoparticle to a light beam is negligible. However, by tailoring the response of an array of nanoparticles, phase-gradient metasurfaces can be constructed that collectively and controllably alter the incoming light\u27s momentum in a macroscopically significant way, potentially enabling a paradigm shift to flat optical components. In the thesis\u27 third paper, a novel fabrication technique to build such metasurfaces in a patternable polymer resist is investigated. The technique is shown to produce efficient, large-scale, potentially flexible, substrate-independent flat optical devices with reduced fabricational complexity, required time, and cost.At present, optical metasurfaces are commonly viewed as stationary objects that manipulate light just like common optical components, but do not themselves react to the light\u27s changed momentum. In the last paper of this thesis, it is realised that this is an overlooked potential source of optical force and torque. By incorporating a beam-steering metasurface into a microparticle, a new type of nanoscopic robot – a metavehicle – is invented. Its propulsion and steering are based on metasurface-induced optical momentum transfer and the metavehicle is shown to be driven in complex shapes even while transporting microscopic cargo

Advancing nanofabrication processes for the generation of multifunctional surfaces

Ubiquitous in the natural world, micro- and/or nano-structured surfaces can afford simultaneous control over a range of interfacial properties; providing an attractive solution for where the accumulation of fluids (fog/rain/oil) and bacteria, and the mismanaged interaction of photons, can impede the safety or efficiency of the surface. Although surfaces found in nature provide a wealth of inspiration, replicating the structures synthetically persists to be a challenge, particularly so when striving for scalability and simplicity to encourage industrial/commercial uptake. Furthermore, the fabrication challenges become amplified when aiming for sub-wavelength structures; often necessary to unlock or enhance additional functionality. In this thesis, I present novel fabrication routes based on lithography and reactive ion etching (RIE) to achieve a range of ordered structures at the nano-scale in glass and silicon, and further replicate the resultant structures into polymers. I explore scalable masking techniques including block copolymer (BCP) lithography, laser interference lithography (LIL) and nanoimprint lithography (NIL), to achieve a series of pitches from 50 – 600 nm. By coupling the masking with novel combinations of etching chemistries, and taking advantage of the etch resistivity of different materials, I fabricate high aspect ratio nanostructures through simplified processes and demonstrate their ability to target applications in wettability, photonics and anti-bacterial action. Specifically, for silicon and glass nanocones, I focus on their anti-fogging, superhydrophobic, anti-reflective and anti-bacterial properties. I also investigate the impact of the nanostructure morphology on a sub-class of water-repellent surfaces, namely, slippery liquid infused porous surfaces, and their ability to retain lubricant under dynamic conditions; continuing on the theme of smart nanostructure design and simplified fabrication to pave a route to multifunctional surfaces. It is anticipated that the surfaces and their properties will find use as car windscreens, coatings for solar panels, high-rise glass facades, and high-touch surfaces to name a few

Enhancement of Optical Properties in Artificial Metal-dielectric Structures

The thesis consists of 7 self-contained chapters. Following the introductory Chapter 1, in Chapter 2, I analyze the enhancement of radiation in HMMs by going beyond usual “effective medium” model and discovering many interesting phenomena that augment and, in some cases, contradict the established results. I discover that Purcell enhancement of radiation is always present in metal dielectric structures and that it results from the direct coupling of the energy into the free electron motion in the metal that leads to quenching of the radiative lifetime. In Chapter 3, I study the so-called hyperlensing purportedly capable of imaging sub-wavelength objects. I analyze the imaging properties of HMMs by using newly developed Eigen-mode approach as well as by transfer matrix method. In Chapter 4, I study arrays of subwavelength resonant features made form metals and dielectrics. In this arrays mid-infrared fields get greatly enhanced which is extremely important for applications in sensing. I establish that to achieve the strongest enhancement, one still needs to use metals, due to high free carrier density in them. That makes the metals preferred in fluorescence or Raman sensing. The subject of Chapter 5 is also related to the mid-infrared region where I explore the light manipulation with metasurface consisting of metal-isolator metal (MIM) resonators. Based on theoretical analysis and simulation performed by me, a metasurface was designed and fabricated using nanoimprint method and later analyzed using Fourier Transform Infrared Spectrometry. Chapter 6 is dedicated to a new material that can be greatly broaden the range of features attainable in metal dielectric structure – a two-dimensional MoS2. An origami-inspired self-folding approach is used to reversibly transform MoS2 into functional 3D optoelectronic devices. We demonstrated that the 3D self-folded MoS2 structures show enhanced light interaction and are capable of angle-resolved photodetection. Chapter 7 deals with periodically poled lithium niobate for frequency conversion for a novel application – development of non-magnetic optical isolator – a key component for application in optical communications and especially in integrated optics. The nonmagnetic isolator based on frequency converter was proposed, designed, fabricated and tested showing excellent performance characteristics in terms of isolation ratio exceeding 20dB

Complex polarization manipulation with dielectric metasurfaces

Metasurfaces are an important, developing part of modern optics. They consist of surface structures designed to shape the incident light beams through arrays of sub-wavelength nano-resonators. In this thesis, I focus on the manipulation and sensing of classical and quantum light using dielectric metasurfaces, comprising of dielectric materials such as amorphous silicon on glass. Dielectric metasurfaces are of exceptional interest due to the minimal material losses as compared to their plasmonic counterparts, for which material losses are an intrinsic part. In particular, polarization of light is of great interest in many aspects of both quantum and classical experiments, extending itself to uses such as communication, quantum communication, and quantum computation, and oft times, particular polarization manipulations are implemented using mechanically complex, space-intensive bulk optics. This is problematic for cases demanding high precision and compactness, such as fundmental quantum optical experiments, space-based installations, and quantum communications. It is thus that in the course of this thesis, I explore a fundamentally new form of polarization manipulation using metasurfaces. This new polarization manipulation concept is known as complex birefringence, and is capable of performing heretofore impossible forms of polarization transformation in a single, monolithic structure. Throughout this thesis, I develop an analytical framework utilizing an optimally minimal amount of loss, and explore it through experimental and numerical methods that this concept can implement truly arbitrary control over polarization in classical and quantum cases, and further demonstrate that this concept may be extended to a new form of polarization monitoring that allows for rapid and highly sensitive response. Finally, I extend similar concepts to the concept of singleshot polarimetry, overcoming challenges that previous approaches had considered fundamental weaknesses

Micro/Nano Structures and Systems

Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability is a comprehensive guide that explores the various aspects of micro- and nanostructures and systems. From analysis and design to manufacturing and reliability, this reprint provides a thorough understanding of the latest methods and techniques used in the field. With an emphasis on modern computational and analytical methods and their integration with experimental techniques, this reprint is an invaluable resource for researchers and engineers working in the field of micro- and nanosystems, including micromachines, additive manufacturing at the microscale, micro/nano-electromechanical systems, and more. Written by leading experts in the field, this reprint offers a complete understanding of the physical and mechanical behavior of micro- and nanostructures, making it an essential reference for professionals in this field

Directive dielectric designs for high efficiency photovoltaics

Solar energy is, together with wind, one of the main sources of renewable energy for the future, mostly coming from of solar cells based on photovoltaics. The technique has rapidly developed over the past decades, resulting in large efficiency increases and tremendous price reduction. But further improvement is needed to meet the demands for the energy transition. In this thesis we present several concepts and designs to achieve this, all based on directive light emission from dielectric nanophotonic structures. In chapter 2 we explain why not only light absorption, but also light emission in an important parameter for efficient photovoltaics. In the following chapters we present different designs that can lead to the described efficiency increases. In chapter 3 and 4 we work with a highly optimized nanophotonic microlens. We first show how this structure can give record directivity, and subsequently combine it with the new wonder material for photovoltaics, mixed halide perovskite, to create a self-optimizing system with even higher directivity. This self-optimization is exploited further in chapter 5 to make solar concentrator that exhibits self-tracking and diffuse light utilization. In the final two chapters we investigate luminescent solar concentrators that make use of directional light emitters and show a great potential for efficiency increase. Overall we show a variety of directive dielectric designs that each can lead to novel device applications