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Net acceleration of attosecond-scale electron pulses is critical to the development of on-chip accelerators. We demonstrate a silicon-based laser-driven two-stage accelerator as an injector stage prototype for a Dielectric Laser Accelerator (DLA). The first stage converts a 57-keV ($500\ifmmode\pm\else\textpm\fi{}100$)-fs (FWHM) electron pulse into a pulse train of $700\ifmmode\pm\else\textpm\fi{}200$ as (FWHM) microbunches. The second stage harnesses the tunability of dual-drive DLA to perform both a net acceleration and a streaking measurement. In the acceleration mode, the second stage increases the net energy of the electron pulse by 200 eV over $12.25\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. In the deflection mode, the microbunch temporal profile is analyzed by a direct streaking measurement with 200 as resolution. This work provides a demonstration of a novel, on-chip method to access the attosecond regime, opening new paths towards attosecond science using DLA.

Linear micromechanical optical phased arrays solve many of the problems facing their two-dimensional counter parts. In this paper we cover the basics of linear micromechanical phased arrays and show how their fundamental properties lead to desirable functional characteristics for optical applications. Experimental results on sheet microscopy with improved axial resolution demonstrates how the scanning performance of linear phased arrays can be combined with other scanning elements to create three dimensional images with high resolution at high speed.

Universal unitary photonic devices can apply arbitrary unitary transformations to a vector of input modes and provide a promising hardware platform for fast and energy-efficient machine learning using light. We simulate the gradient-based optimization of random unitary matrices on universal photonic devices composed of imperfect tunable interferometers. If device components are initialized uniform-randomly, the locally-interacting nature of the mesh components biases the optimization search space towards banded unitary matrices, limiting convergence to random unitary matrices. We detail a procedure for initializing the device by sampling from the distribution of random unitary matrices and show that this greatly improves convergence speed. We also explore mesh architecture improvements such as adding extra tunable beamsplitters or permuting waveguide layers to further improve the training speed and scalability of these devices., Comment: 18 pages, 2 tables, 14 figures, 6 videos (videos provided in Appendix via external URL link)

Monolithic-silicon fiber-based pressure sensors offer high resolution over a broad frequency range with minimal footprint. We fabricate these devices using scalable single frontside mask silicon nanofabrication. Our sensors consist of a sealed 1 μm cavity under a 1 μm thick silicon diaphragm only 100 μm in diameter. For static pressures from 0.3 to 1.4 atm, our sensors showed a standard deviation of 2.6×10−3 atm from the reference. For dynamics pressures out to 50 kHz, our sensors show a pressure resolution of 1.1×10−6 atm/√Hz.

Miniaturizing particle accelerators Particle accelerators are usually associated with large national facilities. Because photons are able to impart momentum to electrons, there are also efforts to develop laser-based particle accelerators. Sapra et al. developed an integrated particle accelerator using photonic inverse design methods to optimize the interaction between the light and the electrons. They show that an additional kick of around 0.9 kilo–electron volts (keV) can be given to a bunch of 80-keV electrons along just 30 micrometers of a specially designed channel. Such miniaturized dielectric laser accelerators could open up particle physics to a number of scientific disciplines. Science , this issue p. 79

International journal of modern physics / A 34(36), 1942031 - (2019). doi:10.1142/S0217751X19420314, Dielectric Laser Acceleration (DLA) achieves the highest gradients among structure-based electron accelerators. The use of dielectrics increases the breakdown field limit, and thus the achievable gradient, by a factor of at least 10 in comparison to metals. Experimental demonstrations of DLA in 2013 led to the Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation. In ACHIP, our main goal is to build an accelerator on a silicon chip, which can accelerate electrons from below 100 keV to above 1 MeV with a gradient of at least 100 MeV/m. For stable acceleration on the chip, magnet-only focusing techniques are insufficient to compensate the strong acceleration defocusing. Thus, spatial harmonic and Alternating Phase Focusing (APF) laser-based focusing techniques have been developed. We have also developed the simplified symplectic tracking code DLAtrack6D, which makes use of the periodicity and applies only one kick per DLA cell, which is calculated by the Fourier coefficient of the synchronous spatial harmonic. Due to coupling, the Fourier coefficients of neighboring cells are not entirely independent and a field flatness optimization (similarly as in multi-cell cavities) needs to be performed. The simulation of the entire accelerator on a chip by a Particle In Cell (PIC) code is possible, but impractical for optimization purposes. Finally, we have also outlined the treatment of wake field effects in attosecond bunches in the grating within DLAtrack6D, where the wake function is computed by an external solver., Published by World Scientific Publ., Singapur

We report an optoelectromechanical vibratory gyroscope inspired by halteres of dipteran flies. The gyroscope utilizes optical displacement sensing to achieve a Brownian-motion-limited displacement sensitivity without mechanical resonant amplification in the sense mode. This yields a threefold difference between the resonance frequencies of the drive and sense modes, corresponding to a theoretical bandwidth of over 200 Hz, without compromising the sensitivity. Our measurements show a noise-equivalent rotation rate of 3°/h/Hz $^{\mathrm {1/2}}$ under atmospheric-pressure conditions.

A Fabry–Perot fiber hydrophone with improved fluidics over a previous design to increase the pressure sensitivity by two orders of magnitude and the response at low frequencies is reported. The interferometer is made of a photonic-crystal diaphragm placed at the tip of a single-mode fiber coated with a dielectric reflector. To increase the sensitivity, the water that fills the sensor head is connected to the surrounding environment through holes in the protective housing. The response extends below 100 Hz, with a measured average sensitivity of $\sim 0.23$ Pa $^{\mathrm {-1}}$ and a record average minimum detectable pressure of $\sim 90~\mu $ Pa/ $\surd $ Hz from 100 Hz to 2.5 kHz.

To be useful for most scientific and medical applications, compact particle accelerators will require much higher average current than enabled by current architectures. For this purpose, we propose a photonic crystal architecture for a dielectric laser accelerator, referred to as a multi-input multi-output silicon accelerator (MIMOSA), that enables simultaneous acceleration of multiple electron beams, increasing the total electron throughput by at least 1 order of magnitude. To achieve this, we show that the photonic crystal must support a mode at the Γ point in reciprocal space, with a normalized frequency equal to the normalized speed of the phase-matched electron. We show that the figure of merit of the MIMOSA can be inferred from the eigenmodes of the corresponding infinitely periodic structure, which provides a powerful approach to design such devices. Additionally, we extend the MIMOSA architecture to electron deflectors and other electron manipulation functionalities. These additional functionalities, combined with the increased electron throughput of these devices, permit all-optical on-chip manipulation of electron beams in a fully integrated architecture compatible with current fabrication technologies, which opens the way to unconventional electron beam shaping, imaging, and radiation generation.

Unlike existing silicon, CIGS, and multi-junction cells that exhibit remarkable mechanical durability, perovskite solar cells have been shown to delaminate when subjected to the mechanical loads that occur during processing and field exposures, limiting their potential as a reliable solar technology. Mechanical reinforcement is thus essential for durable and reliable perovskite technologies. A recent strategy to overcome the thermomechanical fragility of perovskite solar cells is to extrinsically shield them by introducing reinforcing scaffolds which partition the cell into many distinct microcells, but improvements in mechanical stability coincide with a reduced device efficiency due to parasitic absorption by the scaffold. We address this reduced efficiency by integrating concentrating immersion-lens arrays (CILAs) into scaffold-reinforced solar cells. These scaffolds are lithographically patterned by a maskless process, in which ultraviolet light is used to pattern the scaffolds through the CILAs, ensuring self-alignment and optical contact with the microcells. This process creates mm-scale scaffold patterns with a line edge roughness of 17.5 ± 4.3 µm and line width roughness of 26.4 ± 8.5 µm. Perovskite devices are deposited into the microcells, and during operation, light is concentrated into the microcells and away from the insulating scaffolds, resulting in mechanically resilient solar cells with efficiencies comparable to planar devices. The devices with the strongest lenses—i.e., lower radius of curvature—recover up to 89 ± 15% of photocurrent and 91 ± 29% power conversion efficiency that would have been otherwise lost to parasitic absorption. Ray-tracing simulations of the CILAs also demonstrate passive tracking of incident light which is critical for optimal power output as the sun moves across the sky during the day. In these simulations, devices with CILAs showed improved passive tracking compared to devices without CILAs out to 60° off-normal. The UV stability of CILAs are experimentally verified through aging tests which show no change in their mechanical integrity after 1000 h of UV exposure. The simplicity of the fabrication process and the efficiency of the resulting scaffolded devices show that a lens-integrated scaffold-reinforced structure is a potential pathway to high-performance, robust, commercially viable perovskite solar cells.

Single-photon light detection and ranging (LiDAR) techniques use emerging single-photon detectors (SPADs) to push 3D imaging capabilities to unprecedented ranges. However, it remains challenging to robustly estimate scene depth from the noisy and otherwise corrupted measurements recorded by a SPAD. Here, we propose a deep sensor fusion strategy that combines corrupted SPAD data and a conventional 2D image to estimate the depth of a scene. Our primary contribution is a neural network architecture—SPADnet—that uses a monocular depth estimation algorithm together with a SPAD denoising and sensor fusion strategy. This architecture, together with several techniques in network training, achieves state-of-the-art results for RGB-SPAD fusion with simulated and captured data. Moreover, SPADnet is more computationally efficient than previous RGB-SPAD fusion networks.

This paper describes two surface treatments for silicon dual-pillar dielectric laser accelerators (DLAs), which increase the laser-induced damage threshold (LIDT) and therefore the maximum achievable acceleration gradient. Hydrogen annealing reduces the surface roughness of the silicon pillars and mesa, making the LIDT less dependent on surface perturbations incurred during fabrication, as well as causing damage to occur at predictable locations. Hydrogen annealing decreases the range of the measured LIDT from 5.3 − 10 m J / c m 2 to 9.5 − 10.2 m J / c m 2 with 1960 nm 300 fs pulses. Additionally, 90 nm of low-stress silicon nitride film coating on the annealed DLA improves the damage fluence by 27%. Smoother interfaces, possibly combined with charge transfer from the pillars to the nitride coating, decrease the range of the LIDT and increase the damage fluence. The surface-treated DLAs accelerate 97 keV electrons with an acceleration gradient of 178 ± 1.8 M e V / m , an increase of 11% over the previous maximal gradient achieved with dual-pillar DLAs.

We demonstrate a laser-driven, tunable electron lens fabricated in monolithic silicon. The lens consists of an array of silicon pillars pumped symmetrically by two 300 fs, 1.95 $\mu$m wavelength, nJ-class laser pulses from an optical parametric amplifier. The optical near-field of the pillar structure focuses electrons in the plane perpendicular to the pillar axes. With 100 $\pm$ 10 MV/m incident laser fields, the lens focal length is measured to be 50 $\pm$ 4 $\mu$m, which corresponds to an equivalent quadrupole focusing gradient $B'$ of 1.4 $\pm$ 0.1 MT/m. By varying the incident laser field strength, the lens can be tuned from a 21 $\pm$ 2 $\mu$m focal length ($B'>3.3$ MT/m) to focal lengths on the cm-scale.

Focusing combined with translation in one transversal plane is demonstrated using a high-speed linear MEMS phased array. Total scan ranges of 80 mm in the depth dimension and 16 mrad in the transversal dimension are demonstrated.

Low-loss photonic crystal (PC) mirrors exhibit positive and negative Goos–Hanchen shift (GHS) due to the strong angular and wavelength dependencies of their reflected phase. This Letter demonstrates the existence of large positive and negative GHS in PC mirrors through theoretical, numerical, and experimental approaches. A simple algebraic relation shows that positive effective thickness yields positive (negative) GHS for resonances that blue (red) shift with angle, while the opposite is true for interfaces with negative effective thickness. Spatiotemporal coupled-mode theory demonstrates the above relation for simple systems with one or two resonance modes, and it also shows the existence of both positive and negative GHS. These effects are numerically and experimentally verified in complex PCs with several resonance modes.

We present the demonstration of phase-dependent laser acceleration and deflection of electrons using a symmetrically driven silicon dual pillar grating structure. We show that exciting an evanescent inverse Smith–Purcell mode on each side of a dual pillar grating can produce hyperbolic cosine acceleration and hyperbolic sine deflection modes, depending on the relative excitation phase of each side. Our devices accelerate sub-relativistic 99.0 keV kinetic energy electrons by 3.0 keV over a 15 μm distance with accelerating gradients of 200 MeV/m with 40 nJ, 300 fs, 1940 nm pulses from an optical parametric amplifier. These results represent a significant step towards making practical dielectric laser accelerators for ultrafast, medical, and high-energy applications.

An optimization algorithm for preparing display-ready holographic elements (hogels) to synthesize a light field is outlined, and proof of concept is experimentally demonstrated. This method allows for higher-rank factorization, which can be used for time-multiplexing multiple frames for improved image quality, using phase-only and fully complex modulation with a single spatial light modulator.

We present phase-dependent laser acceleration and deflection of electrons using a symmetrically driven silicon dual pillar grating. We demonstrate cosh accelerator modes and sinh deflecting modes at gradients of 200 MeV/m over 15 μm distance.

The cytoskeleton controls cellular morphology and mediates the mechanical interactions between a cell and its environment. Atomic force microscopy (AFM) has the unique capability to map cytoskeletal mechanics and structures with nanometer resolution. However, whole-cell cytomechanical imaging with conventional AFM techniques is limited by low imaging speed. Here, we present fast nanomechanical mapping of cells using high-bandwidth AFM (HB-AFM), where10(6) nanoindentation measurements were acquired in ∼10 min-a task that would take weeks to finish using conventional AFM. High-bandwidth measurements enabled capture of the entire tip-sample interaction for each tap on cells, engendering a new measurement ("force phase") that exceeds the contrast of conventional tapping mode and enabling spectral visualization of10 harmonics. The abundance of measurements allowed discovery of subtle cytomechanical features, including the stiffness of fibers of the cellular spectrin network in situ. This approach bridges HB-AFM and high-harmonic imaging and opens future opportunities for measuring the dynamic mechanical properties of living cells.

The combination of high-mechanical flexibility and high-optical reflectivity makes planar photonic crystal diaphragms excellent mirrors for optical resonators used in fiber-optic pressure sensing. We have developed a standard silicon process to construct a monolithic photonic crystal-based crystalline silicon membrane. We report on three photonic crystal pressure sensors with different compliances, and discuss the following figures of merit: 1) spectral shift sensitivity; 2) optical sensitivity; 3) pressure sensitivity; 4) resolution; and 5) dynamic range. When compared with a sensor made with an oxide diaphragm, each of our sensors is at least an order of magnitude more sensitive, with a spectral shift sensitivity magnitude of up to 8.6 nm/kPa. We show that the fabrication can be tailored to optimize figures of merit depending on the needs of the application. [2014-0151]

Complex optical devices including aspherical focusing mirrors, solar concentrator arrays, and immersion lenses were 3D printed using commercial technology and experimentally demonstrated by evaluating surface roughness and shape. The as-printed surfaces had surface roughness on the order of tens of microns. To improve this unacceptable surface quality for creating optics, a polymer smoothing technique was developed. Atomic force microscopy and optical profilometry showed that the smoothing technique reduced the surface roughness to a few nanometers, consistent with the requirements of high-quality optics, while tests of optical functionality demonstrated that the overall shapes were maintained so that near theoretically predicted operation was achieved. The optical surface smoothing technique is a promising approach towards using 3D printing as a flexible tool for prototyping and fabrication of miniaturized high-quality optics.

This paper describes an acoustic sensor based on a single-crystal silicon diaphragm with an integrated Photonic Crystal (PC) mirror, whose deflection is measured in a Fabry-Perot resonator formed between the PC mirror and a gold coated single-mode fiber. The sensors are fabricated on standard silicon wafers, yielding monolithic, low-stress sensing diaphragms. The packaged sensor exhibits a minimum detectable pressure of 17μPa/√Hz in the 8.5kHz to 18kHz frequency range.

Waveguide evanescent fields enable lysing of selected red blood cells. Cells are trapped on waveguides and are lysed by rapidly reducing the trapping forces. Red blood cells of different age require different levels of lysing power, allowing selective lysing of crenate cells.

Quantitative phase imaging enables precise characterization of cellular shape and motion. Variation of cell volume in populations of cardiomyocytes can help distinguish their types, while changes in optical thickness during beating cycle identify contraction and relaxation periods and elucidate cell dynamics. Parameters such as characteristic cycle shape, beating frequency, duration and regularity can be used to classify stem-cell derived cardiomyocytes according to their health and, potentially, cell type. Unlike classical patch-clamp based electrophysiological characterization of cardiomyocytes, this interferometric approach enables rapid and non-destructive analysis of large populations of cells, with longitudinal follow-up, and applications to tissue regeneration, personalized medicine, and drug testing.

We present a single-mask process that combines isotropic and anisotropic etching with selective removal of passivation layers followed by hydrogen annealing to yield monolithic crystalline silicon (c-Si) devices. The process is demonstrated by creating pressure sensors that combine photonic crystal (PC) mirror pressure-sensing diaphragms with silicon-on-nothing (SON) reference cavities. The first generation sensors were tested with fiber-optic readout and showed high sensitivity. The single-mask process has sufficient flexibility for application-specific optimization of the PC, diaphragm, and cavity. The monolithic silicon structure gives the sensor potential for good stability. The simple process, robust structure, and integration of all critical components simplifies packaging, which could lead to low-cost mass production.

We propose an on-chip optical power delivery system for dielectric laser accelerators based on a fractal 'tree-branch' dielectric waveguide network. This system replaces experimentally demanding free-space manipulations of the driving laser beam with chip-integrated techniques based on precise nano-fabrication, enabling access to orders of magnitude increases in the interaction length and total energy gain for these miniature accelerators. Based on computational modeling, in the relativistic regime, our laser delivery system is estimated to provide 21 keV of energy gain over an acceleration length of 192 um with a single laser input, corresponding to a 108 MV/m acceleration gradient. The system may achieve 1 MeV of energy gain over a distance less than 1 cm by sequentially illuminating 49 identical structures. These findings are verified by detailed numerical simulation and modeling of the subcomponents and we provide a discussion of the main constraints, challenges, and relevant parameters in regards to on-chip laser coupling for dielectric laser accelerators., Comment: 14 pages

Characterizing cardiomyocytes' activity is important for drug development, but traditional patch clamping analysis is destructive and slow. A label-free method for extracting timing and motion characteristics of cardiomyocytes using quantitative phase imaging is presented.

Microelectromechanical system (MEMS) technology, and surface micromachining in particular, have led to the development of miniaturized optical devices with a substantial impact in a large number of application areas. The reason is the unique MEMS characteristics that are advantageous in fabrication, systems integration, and operation of micro-optical systems. The precision mechanics of MEMS, microfabrication techniques, and optical functionality all make possible a wide variety of movable and tunable mirrors, lenses, filters, and other optical structures. In these systems, electrostatic, magnetic, thermal, and pneumatic actuators provide mechanical precision and control. The large number of electromagnetic modes that can be accommodated by beam-steering micromirrors and diffractive optical MEMS, combined with the precision of these types of elements, is utilized in fiber-optical switches and filters, including dispersion compensators. The potential to integrate optics with electronics and mechanics is a great advantage in biomedical instrumentation, where the integration of miniaturized optical detection systems with microfluidics enables smaller, faster, more-functional, and cheaper systems. The precise dimensions and alignment of MEMS devices, combined with the mechanical stability that comes with miniaturization, make optical MEMS sensors well suited to a variety of challenging measurements. Micro-optical systems also benefit from the addition of nanostructures to the MEMS toolbox. Photonic crystals and microcavities, which represent the ultimate in miniaturized optical components, enable further scaling of optical MEMS. [2013-0297]

This letter describes the manufacture and performance of a monolithic double-layer silicon photonic crystal temperature sensor. The sensor is fabricated on standard silicon wafers using oxide passivation and a combination of isotropic and anisotropic etching, and mounted on the facet of a standard single-mode optical fiber using template-assisted epoxy bonding. The double-layer configuration leads to coupling of the guided resonances in the two photonic crystals and enables sharper resonances and consequently higher temperature sensitivity and better detection limit (0.011 °C) than the single-layer counterpart. We experimentally demonstrate that the sensor has a twofold increased temperature sensitivity in terms of reflectivity change at a fixed wavelength (-0.00576/°C), and report on electromagnetic simulations explaining the enhanced sensor operation. The photonic crystal fabrication method and template-assisted bonding enable batch-fabrication of the sensors. Their small size, robust construction, and fiber interface make the sensors promising for numerous applications, including sensing in harsh environments.

We demonstrate improved optical sectioning in light sheet fluorescence microscopy using tunable structured illumination (SI) frequencies to optimize image quality in scattering specimens. The SI patterns are generated coherently using a one-dimensional spatial light modulator for maximum pattern contrast, and the pattern spatial frequency is adjustable up to half the incoherent cutoff frequency of our detection objective. At this frequency, we demonstrate background reductions of 2 orders of magnitude.

This paper discusses recent developments in fiber acoustic sensors utilizing a miniature Fabry–Perot (FP) interferometer fabricated at the tip of a fiber. The FP is made of a high-reflectivity photonic-crystal membrane placed ∼30 μm from the reflective end of a single-mode fiber. When exposed to an acoustic wave the compliant membrane vibrates, and this vibration is detected as a modulation of the optical power reflected by the FP. The interferometer is enclosed in a sensor head designed, with the assistance of an electro-mechanical model, to minimize squeezed-film damping of the thin air gap between the reflectors and obtain a good acoustic response. The sensor head is fabricated out of silica elements and assembled with silicate bonding to minimize thermal expansion and ensure thermal stability. In the first sensor of this type the reflector at the fiber tip is a gold coating. It exhibits an average minimum detectable pressure (MDP) of 33 μPa/√Hz (1–30 kHz), a high thermal stability, and a weak polarization dependence. The second sensor incorporates several improvements, including a larger membrane for increased vibration amplitude, and higher reflectivity mirrors (PC and fiber tip) for increased displacement sensitivity. Its measured response is flat between ∼600 Hz and 20 kHz, with a normalized sensitivity as high as ∼0.17 Pa −1 . Between 1 kHz and 30 kHz its average MDP is ∼2.6 μPa/√Hz, the lowest reported value for a fiber acoustic sensor this small. These results demonstrate the promising potential of this class of stable and compact optical sensors for highly sensitive detection in the audible range.

We propose and experimentally demonstrate a time-division-multiplexed acoustic sensor array employing multiple low-gain Er-doped fiber amplifiers to multiplex ten compact Fabry-Perot acoustic sensors. We show that the ten sensors can be interrogated with a single laser diode at a single wavelength, and exhibit the same measured SNR within $\pm$ 0.95 dB of each other. We present a model to identify the dominant noise contributions, and their dependence on the number of multiplexed sensors. This model predicts that more than 350 sensors can be multiplexed with the proposed architecture.

Due to the high mechanical bandwidth of an integrated diffraction-grating-based force sensor, interdigitated AFM probes enable probing the nanomechanical properties of the sample by measuring fast varying tip-sample interaction forces while operating in tapping mode. To explain the mechanical frequency response obtained from finite-element analysis, we developed an analytical model that incorporates the higher order flexural modes of a cantilever. To enable flexibility necessary to use the probes in different imaging environments, a step is introduced into the batch fabrication where high-stress nitride is used. This step allows the probe to be used in various optical conditions such as different laser wavelengths (in the light-lever configuration), incident angles, and ambient refractive indices (such as air and water). We demonstrate that the probe can operate in both air and fluid and measure fast varying tip-sample interactions by imaging a sputtered gold film in both conditions.

A methodology allows fabrication of silicon-photonic devices in standard silicon wafers, eliminating the need for silicon-on-insulator (SOI) wafers. Using this technology, the authors demonstrate low-loss silicon waveguides (2.34 dB/cm), comparable to conventional SOI channel waveguides. The ease and flexibility of this fabrication method simplify integration of electronics and photonics and make it a possible alternative to SOI-based technology for implementation of silicon-photonic devices and systems.

Optical particle trapping and separation are essential techniques in the fields of biology and chemistry. In many applications, it is important to identify passive separation techniques that only rely on intrinsic forces in a system with a fixed device geometry. We present a dual-waveguide sorter that utilizes the loss of metal-insulator-metal (MIM) waveguides for completely passive particle trapping and separation and is created using a unique angle sidewall deposition process. Our experiments show that an inner Au–Si3N4–Au waveguide is able to trap particles within the propagation distance of its dominant modes and release the particles into an outer Au–H2O–Au waveguide. The outer waveguide then propels the particles and separates them by size. The separation results are accurately modeled by a first-principles, analytical model.

Compared with conventional planar optical image sensors, a curved focal plane array can simplify the lens design and improve the field of view. In this paper, we introduce the design and implementation of a segmented, hemispherical, CMOS-compatible silicon image plane for a 10-mm diameter spherical monocentric lens. To conform to the hemispherical focal plane of the lens, we use flexible gores that consist of arrays of spring-connected silicon hexagons. Mechanical functionality is demonstrated by assembling the 20-μm-thick silicon gores into a hemispherical test fixture. We have also fabricated and tested a photodiode array on a silicon-on-insulator substrate for use with the curved imager. Optical testing shows that the fabricated photodiodes achieve good performance; the hemispherical imager enables a compact 160 ° field of view camera with >80% fill factor using a single spherical lens. US researchers have developed a curved photodetector array that could lead to miniature monocentric imagers. Silicon imagers in cell-phone cameras are planar grids of photodetectors, requiring flat imaging planes and complex lens designs to correct for aberrations. The curved imager would allow a simple, compact, and wide field-of-view spherical lens to be used instead of conventional lens stacks. Roger Howe and co-workers from Stanford University, California, have created a tessellated thin silicon array of optoelectronic devices that can conform to a 10-mm-diameter ball lens. The team constructed the photodetectors on a silicon-on-insulator substrate. The 20-μ-thick device layer was etched into gore segments consisting of arrays of spring-connected hexagons. These interconnected, compliant segments were released from the substrate and assembled onto the hemispherical mounting surface for the ball lens.

Asymmetric, low-loss, Photonic Crystal mirrors exhibit negative Goos-Hanchen shift up to −16.2 μm at 1532 nm wavelength. The shift is a strong function of wavelength, polarization and incident angle.

We present the demonstration of high gradient (370 MeV/m) laser acceleration and deflection of sub-relativistic electrons with silicon dual pillar grating structures using both evanescent inverse Smith-Purcell modes and coupled cosh-like modes.

A thermally stable high-sensitivity compact fiber acoustic sensor with a large bandwidth and a high dynamic range is introduced. The device is based on a photonic crystal fabricated on a compliant single-crystal silicon diaphragm, which is placed near the metalized end of a single-mode fiber to form a Fabry-Perot (FP) cavity. High reproducibility in operating wavelength (±1 nm) is enabled by assembling the sensor in a SiO2 chip using room-temperature sodium silicate oxide bonding. We demonstrate ten FP sensors with measured displacement sensitivities within ±0.6 dB. The response is shown to be polarization independent and thermally stable, with a thermal coefficient of the operating wavelength of 2.9pm/°C over more than 50 °C. An experimental sensor is shown to measure acoustic pressures down to a record low of 5.6 μPa/√Hz at 12.5 kHz with a flatband response greater than 8 kHz and a sensitivity extending down to at least 100 Hz. The dynamic range in pressure is greater than 100 dB. An electromechanical model of the device response is presented and shown to be in good agreement with experimental results.

In this paper, we introduce a 2-D microelectromechanical systems scanner for 3.2-mm-diameter dual-axis confocal microendoscopes, fabricated exclusively by front-side processing. Compared to conventional bulk micromachining that incorporates back-side etching, the front-side process is simple and thus enables high device yield. By eliminating the back-side etch window, the process yields compact and robust structures that facilitate handling and packaging. An important component of our front- side fabrication is a low-power deep reactive ion etching (DRIE) process that avoids the heating problems associated with standard DRIE. Reducing the RF etch coil power from 2400 to 1500 W leads to elimination of the spring disconnection problem caused by heat-induced aggressive local etching. In our scanner, the outer frame of the gimbal is split and noncontinuous to allow the scanner to be diced along the very edge of the scanning mirror in order to minimize the chip size (1.8 mm × 1.8 mm). The maximum optical deflection angles in static mode are ±5.5° and ±3.8° for the outer and inner axes, respectively. In dynamic operation, the optical deflection angles are ±11.8° at 1.18 kHz for the outer axis and ±8.8° at 2.76 kHz for the inner axis.

We demonstrate a temperature sensor consisting of a 2-D, Silicon (Si), Photonic Crystal (PC) attached to the facet of a standard single-mode optical fiber. The 2-D PC sensors are fabricated on standard Si wafers, using a single mask and a combination of isotropic and anisotropic etching, and microassembled onto the facets of the optical fibers by Si-welding. The temperature of the Si-PC sensor is monitored by measuring its reflectance spectrum in the 1250 to 1650 nm wavelength range. The measured reflectivity peak shift is 0.11 nm°C in the 100°C to 700°C temperature range. The observed spectral shift and temperature sensitivity are significantly higher than high-temperature fiber Bragg grating sensors, and comparable to long-period fiber gratings sensors. The high sensitivity, combined with compactness and robust structure, give these sensors strong potential for use in harsh environments.

In this paper, we demonstrate high-resolution mapping of composite surfaces based on their nanomechanical properties by employing an atomic force microscope probe that can resolve high-frequency tip-sample interaction forces in tapping-mode atomic force microscopy (AFM) (TM-AFM). Time-resolved force measurements are achieved by a small integrated interferometric high-bandwidth grating force sensor at the end of the cantilever beam. The probes are batch fabricated using optical lithography and are used in an AFM system with no further modification. The fabricated devices are characterized and grating-force-sensor signals and their measured spectra confirm that probes with integrated high-bandwidth force sensors can successfully resolve high-frequency tip-sample interaction forces. We utilize the capability of our probes to form images by recording the amplitude of the higher harmonics of the time-resolved tip-sample interaction forces with lock-in detection. These images show that our probes can successfully map, with high spatial resolution, the mechanical contrast due to different materials and structural differences in composite surfaces.

Fiber optic sensors have applications in the measurement of a wide range of physical properties such as temperature, pressure, and refractive index. These sensors are immune to electromagnetic interference, made of high temperature dielectric materials and hence can be deployed in harsh environments where conventional electronics would fail. Photonic crystal (PC) fiber tip sensors are highly sensitive to changes in the refractive index and temperature while remaining compact and robust. In comparison to conventional fiber sensors such as fiber Bragg gratings (FBG) or long period fiber gratings (LPFG), they are attractive in several aspects. PC fiber tip sensors have better sensitivity to refractive index and temperature than FBG sensors and are have much smaller sensing volumes than FBGs and LPFGs. Their small size allows them to combine high sensitivity and structural robustness. The most attractive feature may be that PC fiber tip sensors also return a spectrally rich signal with independently shifting resonances that can be used to extract multiple physical properties of the measurand and distinguish between them. In this paper, we show that the PC fiber tip sensor is highly sensitive to the refractive index and temperature of the environment and that both parameters can be simultaneously determined using multiple wavelengths.

This work reports on an optical hydrophone that is insensitive to hydrostatic pressure, yet capable of measuring acoustic pressures as low as the background noise in the ocean in a frequency range of 1 Hz to 100 kHz. The miniature hydrophone consists of a Fabry-Perot interferometer made of a photonic-crystal reflector interrogated with a single-mode fiber and is compatible with existing fiber-optic technologies. Three sensors with different acoustic power ranges placed within a sub-wavelength sized hydrophone head allow a high dynamic range in the excess of 160 dB with a low harmonic distortion of better than -30 dB. A method for suppressing cross-coupling between sensors in the same hydrophone head is also proposed. A prototype was fabricated, assembled, and tested. The sensitivity was measured from 100 Hz to 100 kHz, demonstrating a sound-pressure-equivalent noise spectral density down to 12 μPa/Hz(1/2), a flatband wider than 10 kHz, and very low distortion.

Fiber based access networks are recognized as promising technologies for solving broadband bandwidth bottlenecks. TDM-PONs, which are passive and non-reconfigurable, are the most widely deployed type of fiber access networks today. However, due to their passive nature, TDM-PONs encounter several issues such as inflexible coverage, lack of intelligence for control, and inability to counter security attacks. Based on current issues in optical access networks, we propose a novel non-volatile, reconfiguration node. The proposed remote node can reconfigure the network to adapt to varying degrees of deployment conditions and/or network attacks. Moreover, the proposed remote node incorporates a novel quasi-passive device that reconfigures using remotely supplied energy from CO. This quasi-passive device technology does not consume any energy once it reconfigures into a new latching states. Therefore, the proposed remote node has very low energy consumption and does not require local power supply to preserve the passivity of the passive distribution network. In particular, the proposed quasi-passive device technology is implemented using a novel tri-state Micro- Electro-Mechanical System (MEMS) actuator structure and the device demonstrates very small energy consumption requirement to enable energy be remotely supplied from CO. Also, the MEMS structure is shown to demonstrate acceptable insertion losses to makes it suitable for flexible energy distribution. Simulation study shows the proposed reconfigurable device would outperform traditional passive splitter in terms of maximum number of supportable users under realistic deployment conditions.