Photonic signal processing offers the prospect of realizing extremely high multigigahertz sampling frequencies, overcoming inherent electronic limitations. This stems from the intrinsic excellent delay properties of optical delay lines. These processors provide new capabilities for realizing high time-bandwidth operation and high-resolution performance. In-fiber signal processors are inherently compatible with fiber-optic microwave systems and can provide connectivity with built-in signal conditioning. Fundamental principles of photonic signal processing, including sampling, tuning, and noise, are discussed. Structures that can extend the performance of photonic signal processors are presented, including methods for improving the filter shape characteristics of interference mitigation filters, techniques to increase the stopband attenuation of bandpass filters, and methods to achieve large free spectral range. Several photonic signal processors, including high-resolution microwave filters, widely tunable filters, arbitrary waveform generators, and fast signal correlators, are discussed. Techniques to solve the fundamental noise problem in photonic signal processors are described, and coherence-free structures for few-tap notch filters are discussed. Finally, a new concept for realizing multiple-tap coherence-free processor filters, based on a new frequency-shifting technique, is presented. The structure not only eliminates the phase-induced intensity noise limitation, but can also generate a large number of taps to enable the achievement of processors with high performance and high resolution.

Photonic signal processing of microwave signals

Mounting of the acute inflammatory response is crucial for host defense and pivotal to the development of chronic inflammation, fibrosis, or abscess formation versus the protective response and the need of the host tissues to return to homeostasis. Within self-limited acute inflammatory exudates, novel families of lipid mediators are identified, named resolvins (Rv), protectins, and maresins, which actively stimulate cardinal signs of resolution, namely, cessation of leukocytic infiltration, counterregulation of proinflammatory mediators, and the uptake of apoptotic neutrophils and cellular debris. The biosynthesis of these resolution-phase mediators in sensu stricto is initiated during lipid-mediator class switching, in which the classic initiators of acute inflammation, prostaglandins and leukotrienes (LTs), switch to produce specialized proresolving mediators (SPMs). In this work, we review recent evidence on the structure and functional roles of these novel lipid mediators of resolution. Together, these show that leukocyte trafficking and temporal spatial signals govern the resolution of self-limited inflammation and stimulate homeostasis.

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Lipid Mediators in the Resolution of Inflammation

Amplifiers are ubiquitous in electronics and play a fundamental role in a wide range of scientific measurements. From a user's perspective, an ideal amplifier has very low noise, operates over a broad frequency range, and has a high dynamic range - it is capable of handling strong signals with little distortion. Unfortunately, it is difficult to obtain all of these characteristics simultaneously. For example, modern transistor amplifiers offer multi-octave bandwidths and excellent dynamic range. However, their noise remains far above the fundamental limit set by the uncertainty principle of quantum mechanics. Parametric amplifiers, which predate transistor amplifiers and are widely used in optics, exploit a nonlinear response to transfer power from a strong pump tone to a weak signal. If the nonlinearity is purely reactive, ie. nondissipative, in theory the amplifier noise can reach the quantum-mechanical limit. Indeed, microwave frequency superconducting Josephson parametric amplifiers do approach the quantum limit, but generally are narrow band and have very limited dynamic range. In this paper, we describe a superconducting parametric amplifier that overcomes these limitations. The amplifier is very simple, consisting only of a patterned metal film on a dielectric substrate, and relies on the nonlinear kinetic inductance of a superconducting transmission line. We measure gain extending over 2 GHz on either side of an 11.56 GHz pump tone, and we place an upper limit on the added noise of the amplifier of 3.4 photons at 9.4 GHz. Furthermore, the dynamic range is very large, comparable to microwave transistor amplifiers, and the concept can be applied throughout the microwave, millimeter-wave and submillimeter-wave bands.

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A wideband, low-noise superconducting amplifier with high dynamic range

Stereolithography is a solid freeform technique (SFF) that was introduced in the late 1980s Although many other techniques have been developed since then, stereolithography remains one of the most powerful and versatile of all SFF techniques It has the highest fabrication accuracy and an increasing number of materials that can be processed is becoming available In this paper we discuss the characteristic features of the stereolithography technique and compare it to other SFF techniques The biomedical applications of stereolithography are reviewed, as well as the biodegradable resin materials that have been developed for use with stereolithography Finally, an overview of the application of stereolithography in preparing porous structures for tissue engineering is given

A review on stereolithography and its applications in biomedical engineering

Diameter-controlled Growth of Single-crystalline In2O3 Nanowires and Their Electronic Properties

Presented is a micromachined WR-3 waveguide filter with two embedded H-plane back-to-back bends fabricated using thick SU-8 photoresist micromachining technology. The filter was constructed with four silver-coated SU-8 layers with a thickness of 0.432 mm for each layer. These layers were then bonded on top of each other to form the filter. This layered WR-3 waveguide filter with bends exhibited a minimum insertion loss of 3.3 dB and an 8.8 3 dB fractional bandwidth at a central frequency of 293.2 GHz. The measured return loss is better than 16 dB across the whole passband.

Micromachined WR-3 waveguide filter with embedded bends

This paper implements wideband, low-loss, and via-free left-handed transmission lines (LH-TLs) using superconductor thin films. Introducing superconductors greatly reduces the loss inherited in the constituent series capacitors and shunt inductors of such planar LH-TLs. The measured results agree very well with design expectations. The bandwidth of left-handed characteristics is 4.9-10.9 GHz, with a minimum insertion loss of 0.03 dB at 30 K. Open-ended LH-TL resonators are also characterized at the different harmonics; of special interest are those with zero or negative phase constants, which are not possible when using any conventional transmission lines. Temperature-dependence measurements of the LH-TLs reveal the effect of the superconductor kinetic inductance

High-Temperature Superconducting Coplanar Left-Handed Transmission Lines and Resonators

A low profile, high gain 32 × 64-slot array antenna with unequal beamwidths in the E- and H-planes and low sidelobes is proposed for vehicular applications in the 71–81 GHz band. The antenna is composed of 512 (16 × 32) 2 × 2-slot subarrays arranged with equal spacing and excited by a nonuniform corporate-feed-network. A two dimensional amplitude-tapering (complying with Taylor distribution) is used to achieve the low sidelobe levels (SLLs). Combined with the different dimensions of the array, the sidelobes and the beamwidths in the E- and H-planes are independently controlled. A prototype slotted waveguide array is fabricated to verify the array properties. Measurements show that the matching of the array is better than −14 dB over the entire bandwidth. The first SLL is lower than −18.9 dB/−24 dB with the maximum 3-dB beamwidth of 2.3°/1.3° in the E-/H-plane, respectively. The peak gain of over 39.4 dBi and the cross-polarization discrimination (XPD) of below −36.2 dB are also achieved. The demonstrated features of high gain, low SLL, and independent controllability of the beam in the E- and H-planes are most desirable for vehicular communications and radars.

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Millimeter-Wave Slotted Waveguide Array With Unequal Beamwidths and Low Sidelobe Levels for Vehicle Radars and Communications

This paper presents a novel method of designing the compact dual-sense circularly polarized (CP) microstrip antenna/array with improved impedance bandwidth, axial ratio (AR) bandwidth, and interpolarization isolation. The left-hand and right-hand CP characteristics are achieved simultaneously by conceiving a vertically coupled resonant structure for the first time. Different from traditional methods, the antenna shows a compact size but exhibits the wide impedance and 3 dB AR bandwidths. For each input, two coupling paths are purposely designed to excite the TM10 and TM01-mode of the patch, respectively. By composing different coupling units in the two paths, an intrinsic ±90° phase difference over a broadband can be obtained, resulting in the broadband CP characteristics. In addition, a novel method of using the neutralization line between the two feeds is investigated to improve the isolation between the polarizations. Based on the dual-sense CP element, a $1 \times 4$ dual-sense CP array is composed to exemplify its potential applications in large arrays. Compared with traditional CP antennas, the proposed antennas have the advantages of compact size, simplified feed, broad impedance and 3 dB AR bandwidths, and improved isolation. Experimental results verify the predictions.

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Compact Broadband Dual-Sense Circularly Polarized Microstrip Antenna/Array With Enhanced Isolation

Two 25-ns high-temperature superconductor delay lines with novel double-spiral meander line structures were fabricated and measured, one based on the conventional coplanar waveguide (CPW) and the other based on the conductor-backed CPW. Compared with other published studies, the performance of the Conductor-backed CPW delay line is among the best in terms of the widest resonance-free band (2-18 GHz), low insertion loss (0.06 dB/ns at 60 K and 10 GHz), small ripple (<1 dB up until 16 GHz), and small dispersion (<2 ns in the variation of group delay between 2-18 GHz). This is also the first coplanar delay line successfully demonstrated without using wire bonding. The reflecting elements in the delay lines were identified through time-domain measurements. Full-wave simulations were performed to compare the double-spiral meander-line structure with conventional double-spiral line, and to identify the geometric factors restricting the bandwidth of the double-spiral meander line.

Yi Wang

Papers

Micromachined WR-3 waveguide filter with embedded bends

High-Temperature Superconducting Coplanar Left-Handed Transmission Lines and Resonators

Millimeter-Wave Slotted Waveguide Array With Unequal Beamwidths and Low Sidelobe Levels for Vehicle Radars and Communications

Compact Broadband Dual-Sense Circularly Polarized Microstrip Antenna/Array With Enhanced Isolation

Wide-band superconducting coplanar delay lines