Reprogrammable Phononic Metasurfaces

Phononic metamaterials rely on the presence of resonances in a structured medium to control the propagation of elastic waves. Their response depends on the geometry of their fundamental building blocks. A major challenge in metamaterials design is the realization of basic building blocks that can be tuned dynamically. Here, a metamaterial plate is realized that can be dynamically tuned by harnessing geometric and magnetic nonlinearities in the individual unit cells. The proposed tuning mechanism allows a stiffness variability of the individual unit cells and can control the amplitude of transmitted excitation through the plate over three orders of magnitude. The concepts can be extended to metamaterials at different scales, and they can be applied in a broad range of engineering applications, from seismic shielding at low frequency to ultrasonic cloaking at higher frequency ranges.     

Adaptable and Reprogrammable Surfaces

Establishing control over chemical reactions on interfaces is a key challenge in contemporary surface and materials science, in particular when introducing well‐defined functionalities in a reversible fashion. Reprogrammable, adaptable and functional interfaces require sophisticated chemistries to precisely equip them with specific functionalities having tailored properties. In the last decade, reversible chemistries—both covalent and noncovalent—have paved the way to precision functionalize 2 or 3D structures that provide both spatial and temporal control. A critical literature assessment reveals that methodologies for writing and erasing substrates exist, yet are still far from reaching their full potential. It is thus critical to assess the current status and to identify avenues to overcome the existing limitations. Herein, the current state‐of‐the‐art in the field of reversible chemistry on surfaces is surveyed, while concomitantly identifying the challenges—not only synthetic but also in current surface characterization methods. The potential within reversible chemistry on surfaces to function as true writeable memories devices is identified, and the latest developments in readout technologies are discussed. Finally, we explore how spatial and temporal control over reversible, light‐induced chemistries has the potential to drive the future of functional interface design, especially when combined with powerful laser lithographic applications.     

Interferometric optical vortex array generator

Two new interferometric configurations for optical vortex array generation are presented. These interferometers are different from the conventional interferometers in that they are capable of producing a large number of isolated zeros of intensity, and all of them contain optical vortices. Simulation and theory for optical vortex array generation using three-plane-wave interference is presented. The vortex dipole array produced this way is noninteracting, as there are no attraction or repulsion forces between them, leading to annihilation or creation of vortex pairs.     

Extended coding for optical array logic

We present extended coding for optical array logic (OAL) to avoid the marginal effect. The marginal effect is defined as an effect caused by the finite size of the image region, and it is a problem in massively parallel processing by OAL. OAL is a paradigm of optical computing suitable for optical implementation utilizing image coding and discrete correlation. To avoid the marginal effect in the context of OAL, we propose a new coding rule and consider possible operations with this coding. With extended coding, binary data can be identified from background with the same number of pixels as that used in the original OAL. Simulation results of the operations verify the correctness of the proposed technique.     

Multilevel phase gratings for array illuminators

We describe a variety of multilevel phase structures that can be used to generate Lohmann's array illuminators. We report several experimental verifications of the synthesis of such multilevel phase structures by using simple binary curves in a conventional optical processor.     

Fourier optical analysis of gradient-index array imaging

We present theory and experiments in which Fourier optics and the generalized Fresnel-zone integral form are used to characterize the imaging both of a single gradient-index rod and an array of nine rods. For the unity magnification SELFOC imager, we show that it has both internal and external Fourier transform planes. Careful treatment of the aperture function for off-axis points leads to a theoretical point-spread function that is in close agreement with experiments. Experiments are presented to illustrate the Fourier transform patterns as well as the imaging for single rods and for the entire array.     

Planar optical array with a spatial-integration feature

A planar optical array is presented that provides a selective concentration of the light incident upon the system onto a given area. Several alternative designs are analyzed and explained geometrically. The photometric calculation is presented for three different levels of approximation. A prototype of the proposed system is tested, showing good accordance with the theoretical predictions.     

Nanowire array fabricated by Al-Ge phase separation

Phase-separated Al-Ge films, composed of Al nanowire array with diameters ranging from less than 10 to 18 nm embedded in an amorphous Ge matrix, have been prepared by a sputtering method. Similar to lateral phase separation of Al-Si system, sputtered Al and Ge form an Al nanowire array surrounded by a Ge matrix during film growth when the preparation conditions are optimized. Removal of the Al nanowires from the phase-separated Al-Ge films by etching in acid solution provides nanoporous films with a pore density on the order of 10¹⁵ pores/m². Template-assisted growth of Ni nanowires into the nanopores was carried out to increase the potential applications of the phase-separated Al-Ge films.     

Engineering optical response through gold bowtie nanoantennas array

We propose the coupled gold bowtie nanoantennas array and investigate its plasmonic properties theoretically. The bowtie antenna consists of a pair of opposing truncated cones. We calculate the transmission spectra and the electric field distributions. The evolution of the transmission spectrum with the gap width of the bowtie, the diameter of the tip of the cone and the distance between adjacent bowties is directly visualized. Furthermore, the sensitivity of the antennas array to dielectric constant changes of the environment is also investigated in detail. We show the electric field distribution of this nanostructure and find that E_x is mainly located at the corners of the cross section, especially at the extremity of the cone. As for the E_y, the electric field enhancement localizes at the external edges and the gap of the bowtie. Our work elucidates further the plasmonic interactions can be useful in the design of optimized, sensitive optical sensors, and the enhancement of the fluorescence of molecules.     

Nanopin plasmonic resonator array and its optical properties

A one-step electron-beam lithography process for the fabrication of a high-aspect ratio nanopin array is presented. Each nanopin is a metal-capped dielectric pillar upon a ring-shaped metallic disc. Highly tunable optical properties and the electromagnetic interplay between the metallic components were studied by experiment and simulation. The two metallic pieces play asymmetrical roles in their coupling to each other due to their drastic size difference. The structure can lead to ultrasensitive surface-enhanced Raman scattering chemical sensor arrays, etc.     

Frequency-multiplexed and pipelined iterative optical systolic array processors

Optical matrix processors using acoustooptic transducers are described with emphasis on new systolic array architectures using frequency multiplexing in addition to space and time multiplexing. A Kalman filtering application is considered as our case study from which the operations required on such a system can be defined. This also serves as a new and powerful application for iterative optical processors. The importance of pipelining the data flow and the ordering of the operations performed in a specific application of such a system are also noted. Several examples of how to effectively achieve this are included. A new technique for handling bipolar data on such architectures is also described.     

Tunable coupled-ring-resonator of thermally actuated optical switch array

In this research, we design tunable micro-ring resonators and propose the employment of an integrated control circuit to compensate for the fabrication error, and tune as well as lock the wavelength in a thermal-actuated ring-type optical switch through an amplitude modulation scheme. Additional functionalities can also be added in this circuit by tailoring externally the roundtrip loss or coupling constants of the ring. The design concept can be easily scaled up for a large array optical switch system without much change to the terminal numbers thanks to the three-dimensional hierarchy of the high gray-scale control circuit design, which effectively reduces the terminal numbers to the cubic root of the total control unit numbers. The integrated circuit has been designed, simulated, as well as fabricated, and demonstrated a decent performance with free spectral range (FSR) equal to 1.5 nm at 1532 nm and very accurate wavelength modulation to 0.3 nm within 0.01 nm fluctuation for a thermal actuated ring type optical switch.     

Microstrip antenna array controlled with active phase shifter

Abstract

A two‐element microstrip antenna array controlled with active phase shifters has been fabricated and tested. The phase and amplitude of the active phase shifter output can be continuously changed by controlling the gate voltages of the dual gate FET. This array can be mounted on aircraft or missiles and be used in the direction finder or adaptive array systems.

The mutual couplings between microstrip patches are also experimentally studied. It is found that the self‐impedance and resonant frequencies depend highly on the separation if the patches are separated less than 0.4 wavelength and become constant as the separation is greater than 0.5 wavelength. The effect of mutual coupling in the E‐plane is less prominent than that in the H‐plane. In array patterns synthesis, the mutual coupling can be neglected if the separation is greater than 0.5 wavelength. However, if the separation becomes smaller, the mutual coupling must be considered such that the calculated patterns are in good agreement with the experimental results.     

Microfluidic sorting with a moving array of optical traps

Optical sorting was demonstrated by selective trapping of a set of microspheres (having specific size or composition) from a flowing mixture and guiding these in the desired direction by a moving array of optical traps. The approach exploits the fact that whereas the fluid drag force varies linearly with particle size, the optical gradient force has a more complex dependence on the particle size and also on its optical properties. Therefore, the ratio of these two forces is unique for different types of flowing particles. Selective trapping of a particular type of particles can thus be achieved by ensuring that the ratio between fluid drag and optical gradient force on these is below unity whereas for others it exceeds unity. Thereafter, the trapped particles can be sorted using a motion of the trapping sites towards the output. Because in this method the trapping force seen by the selected fraction of particles can be suitably higher than the fluid drag force, the particles can be captured and sorted from a fast fluid flow (about 150 μm/s). Therefore, even when using a dilute particle suspension, where the colloidal trafficking issues are naturally minimized, due to high flow rate a good throughput (about 30 particles/s) can be obtained. Experiments were performed to demonstrate sorting between silica spheres of different sizes (2, 3, and 5 μm) and between 3 μm size silica and polystyrene spheres.     

Kilohertz scanning optical delay line employing a prism array

A kilohertz scanning optical delay line is demonstrated by means of employing a prism array formed by identical wedge prisms. The wedge prisms are lined up with one another and uniformly disposed on a rotational wheel. The optical path length of a light beam can thus be scanned as the prisms pass through the beam periodically. Scanning rate of 2 kHz, scanning amplitude of 3.5 mm, linearity of 99%, and duty cycle of 95% can be achieved simultaneously. Simplicity and rigidity are embedded in the design. Preliminary test results are presented.     

Silicon planar-apertured probe array for high-density near-field optical storage

We propose a novel, to our knowledge, silicon planar-apertured probe array as an optical head for high-density near-field optical storage. In comparison with a conventional fiber probe employed for near-field optical storage the apertured probe array has a higher readout data-transmission rate and better mechanical durability. A probe array with an aperture size of 100 nm was fabricated by use of photolithography and wet etching of a silicon wafer. Subwavelength-readout capability was demonstrated by use of one aperture of the probe array. Furthermore, we achieved a 16 times increase in the light-transmission efficiency of the probe array by installing glass-sphere microlenses on each aperture. The increase was confirmed by measurement of the near-field optical intensity.     

Finite-difference time-domain simulation of a liquid-crystal optical phased array

Accurate modeling of a high-resolution, liquid-crystal-based, optical phased array (OPA) is demonstrated. The modeling method is extendable to cases where the array element size is close to the wavelength of light. This is accomplished through calculating an equilibrium liquid-crystal (LC) director field that takes into account the fringing electric fields in LC OPAs with small array elements and by calculating the light transmission with a finite-difference time-domain method that has been extended for use in birefringent materials. The diffraction efficiency for a test device is calculated and compared with the simulation.     

Two-dimensional photonic-crystal vertical-cavity array for nonlinear optical image processing

We investigate the electromagnetic properties of a two-dimensional (2-D) photonic-crystal array of vertical cavities for use in nonlinear optical image processing. We determine the 2-D photonic band structure of the array, and we discuss how it is influenced by the degree of interaction between cavities. We study the properties of defects in the 2-D lattice and show that neighboring cavities interact through their overlapping wave functions. This interaction can be used to produce nearest-neighbor nonlinear Boolean functions such asand, or, and xor, which are useful for optical image processing. We demonstrate the use of 2-D photonic bandgap structures for image processing by removing noise from a sample image with a nearest-neighbor and function.