Designing the optical interface of a transcutaneous optical telemetry link

Optical telemetry has long been an option for transcutaneous data transfer and has been used in various types of implanted systems. This telemetry modality and the efficiency of these optical links are becoming ever more important as higher bandwidth sources such as cortical recording arrays are being implemented in implanted systems. The design of the transmitter-skin-receiver interface (the "optical interface") is paramount to the operation of a transcutaneous optical telemetry link. This interface functions to achieve sufficient receiver signal power for data communication. This paper describes a mathematical analysis and supporting data that quantitatively describes the relationship between the primary interface design parameters. These parameters include the thickness of the skin through which the light is transmitted, the size of the integration area of the optics, the degree of transmitter-receiver misalignment, the efficiency of the optics system, and the emitter power. The particular combination of these parameters chosen for the hardware device will determine the receiver signal power and, therefore, the data quality for the link. This paper demonstrates some of the tradeoffs involved in the selection of these design parameters and provides suggestions for link design. This analysis may also be useful for transcutaneous optical powering systems.     

A Queuing Theory-Enabled Dynamic Bandwidth Allocation Algorithm for a Wired-Wireless Converged Network

Multi-sink wireless sensor networks (WSNs) are being increasingly deployed in an ever-widening range of application scenarios, especially as they are reliable and exhibit low power consumption. Providing a backhaul for WSN traffic has become an important issue because the sensor data must usually be sent to the Internet or the core network. Passive optical networks (PONs) represent one next-generation access network technology which is appropriate for such a backhaul, however existing research appears to have concentrated on either WSN performance or PON performance, without considering the overall performance of both networks converged together. This paper proposes a new architecture which converges multi-sink WSNs and PONs, then provides a novel queuing-theory analysis of the converged network performance. Results from this analytical model are then used to motivate a new a DBA algorithm which optimizes grant size allocation. Numerical results show that this algorithm outperforms existing proposals when minimizing the system queue length in the converged network, while providing shorter end-to-end packet delay and higher throughput. We believe that this first resource allocation algorithm which considers the performance of both networks as one converged unit.     

Microwave filters-applications and technology

This paper describes the development of microwave filter technology from an applications perspective. Military applications required wide-band and tunable devices for electronic support measures receivers, which led to the development of highly selective wide-band waveguide filters, coaxial resonator and suspended-substrate multiplexers, and electronically tunable filters. The satellite communications industry created demand for low-mass narrow-band low-loss filters with severe specifications on amplitude selectivity and phase linearity. These requirements resulted in the development of dual-mode waveguide and dielectric-resonator filters, and advances in the design of contiguous multiplexers. Cellular communications base-stations demanded low-loss high power-handling selective filters with small physical size, capable of being manufactured in tens of thousands at a reasonable cost. These demands led to advances in coaxial resonator, dielectric resonator, and superconducting filters, and also to methods of cost-reduction, including computer-aided alignment. Cellular radio handsets have required the manufacture of hundreds of millions of extremely small very low-cost filters, still with reasonably low loss and high selectivity. This has driven significant advances in integrated ceramic, surface, and bulk acoustic-wave active filters and filters using micromachined electromechanical systems     

A photonic technique for microwave frequency measurement

A novel photonic technique for microwave frequency measurement utilizing dispersion in a multichannel chirped fiber Bragg grating is presented. The technique is based on the amplitude comparison of power fading functions generated by double sideband modulated optical carriers propagating through a dispersive medium.     

Improved Optoelectronic Properties of Rapid Thermally Annealed Dilute Nitride GaInNAs Photodetectors

We investigate the optical and electrical characteristics of GaInNAs/GaAs long-wavelength photodiodes grown under varying conditions by molecular beam epitaxy and subjected to postgrowth rapid thermal annealing (RTA) at a series of temperatures. It is found that the device performance of the nonoptimally grown GaInNAs p ⁺–i–n ⁺ structures, with nominal compositions of 10% In and 3.8% N, can be improved significantly by the RTA treatment to match that of optimally grown structures. The optimally annealed devices exhibit overall improvement in optical and electrical characteristics, including increased photoluminescence brightness, reduced density of deep-level traps, reduced series resistance resulting from the GaAs/GaInNAs heterointerface, lower dark current, and significantly lower background doping density, all of which can be attributed to the reduced structural disorder in the GaInNAs alloy.     

Grouping and partner selection in cooperative wireless networks

Various results to date have demonstrated the advantages of one or several relay nodes assisting transmissions in a wireless network. In many practical scenarios, not all nodes in the network are simultaneously involved in every transmission; therefore, protocols are needed to form groups or subsets of nodes for the purposes of cooperation. We consider this problem in the context of regenerative nodes and non-altruistic cooperation (all nodes have data of their own to transmit). For a network-wide diversity advantage, the protocol must provide each transmitting node with enough "partners" that can decode its message with high-enough probability. Assuming that the nodes cannot communicate their control decisions (distributed scenario), and that each node chooses to help n other nodes, we point out a simple, static selection strategy that guarantees diversity n+1 for all transmissions. We then consider centralized control strategies and study the additional gains that arise from a central control, under various amounts of information being available to the central controller     

Tunable microwave photonic passive delay line based on multichannel fibre grating matrix

A discretely tunable passive microwave photonic delay line based on a multichannel grating matrix is demonstrated. This topology demonstrates high-speed high-resolution time delaying of microwave signals, along with requiring a reduced number of discrete gratings for any given delay range. High channel isolation and low insertion loss are also features of this topology, making this suitable for many wideband applications.     

Surface and interface properties of PdCr/SiC Schottky diode gas sensor annealed at 425°C

The surface and interface properties of Pd_0.9Cr_0.1/SiC Schottky diode gas sensors both before and after annealing are investigated using Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). At room temperature the alloy reacted with SiC and formed Pd_xSi only in a very narrow interfacial region. After annealing for 250 h at 425°C, the surface of the Schottky contact area has much less silicon and carbon contamination than that found on the surface of an annealed Pd/SiC structure. Palladium silicides (Pd_xSi) formed at a broadened interface after annealing, but a significant layer of alloy film is still free of silicon and carbon. The chromium concentration with respect to palladium is quite uniform down to the deep interface region. A stable catalytic surface and a clean layer of Pd_0.9Cr_0.1 film are likely responsible for significantly improved device sensitivity.     

International intercomparison of horn gain at X-band

An international intercomparison of horn gain and polarization measurements at X-band has previously been completed. There were seven participating laboratories with the National Institute of Standards and Technology serving as the pilot laboratory. Two X-band pyramidal standard gain horns with a nominal gain of 22 dB served as the traveling standards. Quantities measured included on-axis fixed frequency gain at 8, 10, and 12 GHz, swept frequency gain between 8-12 GHz and polarization characteristics at the three fixed frequencies. All laboratories performed the fixed frequency-gain measurements. The swept-frequency and polarization measurements were optional, with four laboratories performing swept-frequency measurements and three laboratories measuring polarization. The results of the gain measurements generally agreed within the reported uncertainties which were of the order of 0.1 dB or less     

Noise Equivalent Power of Background Limited Thermal Detectors at Submillimeter Wavelengths

With the advent of large submillimeter telescopes at high, dry sites, the atmospheric background noise in a moderate bandwidth can be low enough to challenge the ability of instrument designers to produce sufficiently low noise bolometers to be background limited. We compare the predictions for the noise power of a bolometer observing through an emissive atmosphere, considering the effect of atmospheric absorption, telescope optical efficiency, and detector optical efficiency, with measurements through the atmosphere over Mauna Kea.