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A multileveled tunable silicon grating array is designed and fabricated on a large-scale-integration (LSI) substrate. The grating consists of 250 single crystalline silicon ribbons of 260 nm in thickness, 400 μm in length, and 10 μm in period. The LSI substrate generates voltages to vary the heights of respective grating ribbons addressed by digital signal input. Each grating ribbon is attracted by an electrostatic force generated by 6-bit applied voltage in the range from 0 to 5 V. In the fabrication, the LSI substrate and a silicon-on-insulator wafer are bonded by the two kinds of polymers. A photosensitive polyimide polymer is used for patterning the bonding pads and also for bonding the wafers at the pressure of 0.25 MPa and the temperature of 350°C. Another epoxy polymer fills the space underneath the grating ribbons for subsequent process, which is finally removed by sacrificial etching to make the grating ribbons freestanding. The tunability of the grating is examined experimentally under the basic operation conditions.
We discuss several recent advances in the development of methodologies and techniques used to structurally and morphologically engineer chalcogenide (ChG) materials. We introduce two ChG patterning techniques both offering spatial resolution beyond the classical single-photon diffraction limit: multiphoton lithography and thermal scanning probe lithography (TSPL). The former was applied to produce nanoscale modifications in thermally deposited As2S3, and we realized gradient refractive index (GRIN) effective medium lens fabrication in multilayer As2S3-As2Se3 films with features as small as 120 nm using this approach. The GRIN lens was shown to be optically functional. ChG Ge-Sb-Se-Te (GSST) material was also explored for its potential as a phase-change material (PCM). We demonstrated nanoscale feature patterning using TSPL in PCMs with critical dimensions below 100 nm. In addition, new patterning methods, we also report solution processing of GSST PCMs as an alternative route for ChG film deposition. These new material processing and structuring techniques will offer new pathways for creating functional planar optical and photonic devices.
Current microscopy systems for the imaging of microorganisms are expensive because of their optimized design toward resolution maximization and aberration correction. In situations where such an optimization is not needed, for instance to merely detect the presence of pathogens in liquids for on-site analyses, a potential approach is to use highly refractive spheres in combination with low-magnification objectives to increase the resolution and the sensitivity of the optical sensing system in a cost-effective fashion. Indeed, for point-of-need assays, integration of optical elements on a microfluidic device can bring several advantages, such as test parallelization/automation and low-volume consumption. We report a study on BaTiO3 spheres that are partially embedded in thin polymeric membranes of mismatched refractive index. We computed the transformation that the polymeric membrane/dielectric sphere assembly (PMDSA) mediates on the light originating from the sample toward the optical detector and shows its enhanced-detection potential for a low-magnification objective. We then propose a method to easily fabricate chips with custom designs and precise location of such dielectric spheres relative to the microfluidic structures for enhanced imaging of microorganisms. We applied this concept to the detection of living fluorescent bacteria, either flowing in aqueous medium or immobilized in hydrodynamic traps. We quantified the contrast gain provided by the PMDSA for short exposure when used with a low-magnification objective. By comparing with a high-magnification objective, we also show how longer-term imaging can be still reliably performed with a more cost-effective system. Since the present PMDSA concept combines the optical enhancement of low-magnification systems with the flexibility of microfluidic handling, it can be highly suitable for portable and cost-effective systems for on-site analysis, from flow cytometry to longer-term antibiotic testing.
We present high-speed, traveling-wave (TW) Si Mach–Zehnder modulators and Si sub-bandgap photodetectors (SBPD) monolithically integrated on an Si-only photonics platform without incorporation of Ge epitaxial growth process. Through constructing a detailed equivalent circuit model on the components, we design the device structure and TW electrodes for operating the device with bandwidth beyond 40 GHz. The experimental results show the 3-dB bandwidths of the Si modulator and photodetectors are 35 and 44 GHz, respectively, generally agreeing well with our design. The measured photoresponsivity of the SBPD varies from 0.1 A / W to nearly 1 A / W, depending on the bias voltage. These two components potentially can be utilized for an integrated optical transceiver operating for 50 Gbit / s data transmission.
An adaptive driving beam (ADB) for vehicle headlights has been developed using a microelectromechanical systems optical scanner. A piezoelectric scanner is constructed using thin-film lead-zirconate-titanate oxide (PbZrTiO3, PZT) on a bonded silicon-on-insulator (SOI) wafer, respectively, processed by ion-milling and deep reactive ion etching. The PZT layer is laminated in metal films on the SOI layer to form a piezoelectric unimorph actuator, which are then arranged as a pair of twisting suspensions to drive the scanner at resonance. The same piezoelectric actuators are also arranged into another form of meandering suspensions to generate a large deflection angle. By the combination of these two mechanisms, two-dimensional optical scanner is constructed in a single chip. The scanner is used to draw a Lissajous pattern of a blue laser light on a phosphor material to create a structured light source that is projected forward for illumination. The lighting patterns and positions are electronically controlled and reconfigured depending upon the location of leading/oncoming vehicles, pedestrians, road signs, and the cruising speed of the vehicle. The paper discusses on the design of the piezoelectrically driven optical scanner along with the optomechanical performances. We also report on the road-test result of the developed on-vehicle ADB module.
Micro-opto-electro-mechanical systems (MOEMS) micromirror and shutter arrays have gained huge interest in research and applications. Our study starts with an overview on the technological achievements and experimental results of groups that have been working on this field. The main part of our study is revealing the MOEMS micromirror array technology for light steering via smart glazing for buildings. The mirror array is actuated electrostatically and integrated between the panes of insulation glazing. Depending on user activity as well as daytime and season requirements, the MOEMS micromirror arrays shall enable personalized light steering, energy saving, and reduction of CO2 emission. Technological fabrication of subfield addressing up to 64 fields inside the arrays is presented. Experimental characterization results such as actuation voltages, maximum and minimum transmission, contrast, and energy saving potential are reported. Using an industrial window module fabrication process, a laboratory demonstrator and a function demonstrator have been implemented. Rapid aging tests including vibrations, extreme temperatures, multiple temperature cycles, and long-term electrostatic actuation of micromirror structure were performed to evaluate reliability and lifetime. These results validate extrapolated lifetimes—in future applications as active windows—far beyond 40 years, as well as their robustness during transportation, installation, and against all vibration influences in buildings.