Information Technology : Telecommunications


More for Less: Higher Throughput, Lower Energy Communications Made Possible In Mobile Devices

UW–Madison researchers have developed a new device and method that brings the benefits of MIMO systems to energy-constrained mobile devices.

The researchers discovered that they could increase the amount of data wirelessly transmitted to an RF receiver without significantly increasing energy consumption by switching between transmit antennas of an RF transmitter on a sub-symbol basis and by adaptively determining how often antenna switching occurs.

In the new system, a transmitter runs on a single RF chain but switches between multiple passive antennas. A data symbol, consisting of waveform patterns, is broken into parts and sent using the multiple antennas. The index of the antennas may be used to convey extra bits of information on top of the original data symbols being transmitted. The receiver, which may use a single antenna, then deciphers the transmit antenna’s index inside each symbol to successfully decode the data signals.

Phased-Array Antenna Concept Reduces Cost, Improves Power Handling

UW–Madison researchers have developed a new concept for designing low-complexity, low-cost phased-array antennas. The design consists of a collimating surface, a feed antenna and a macro electromechanical system (MaEMS) used to dynamically change the properties of the collimating surface. This surface can act in the transmitting mode (a lens) or in the reflecting mode (a reflectarray).

The researchers have explored several MaEMS tuning mechanisms to dynamically change the phase shift gradient and control the direction of the main beam of the antenna. Very small mechanical movements help achieve this tenability and the entire process can be performed extremely rapidly. Most existing solutions try to tune the capacitors.

Wideband Transceiver for Antenna Array

UW–Madison researchers have developed a hardware/software-based solution. Their new method quantifies and corrects degradation due to beam-squint, and introduces several small design changes to beamspace MIMO (B-MIMO) systems.

The researchers identified a channel dispersion factor that can be used to quantify the severity of the problem and to select the beams for maximum performance.

New MIMO Transceiver Cuts Costs, Complexity

UW–Madison researchers have designed a MIMO transceiver for improved interference suppression. The new design eliminates the need for a phase-coherent local oscillator.

More specifically, the new architecture – called differential MIMO or D-MIMO – enables linear interference suppression between multiple spatially multiplexed and differentially encoded data streams. In particular, it is based on a novel approach to quasi-coherent channel measurement from differential measurements that do not require phase coherence between transmitter and receiver. A number of system architectures – with different tradeoffs – are enabled by the invention.

Improved Mobile User Localization

A UW–Madison researcher has developed a localization method using sparse angle-delay channel signatures. The new method exploits both LoS and non-LoS propagation paths for improved performance.

Using measured channel signatures, a statistical pattern classifier is designed to determine a device’s location from the signals that it sends to the base station. Pattern matching is performed on the signal received at the base station using a database of statistical classifier information, and finally a location is computed. The database is based on various ‘cells’ or ‘regions’ that are used to decrease complexity during the pattern matching.

Ultrawide Band, Low-Profile ‘Stacked’ Antenna System

UW–Madison researchers have developed a compact, ultrawide band antenna system with monopole-like radiation characteristics and a bandwidth of 10:1. The system is designed with two antennas wherein one is a scaled-down version of the other. The two antennas can ‘stack’ or ‘nest’ to be less conspicuous. A feed network feeds the appropriate antenna based on the frequency of the input signal. This enables the design to work as a single, ultrawide band system.

Enhanced Traveling Wave Tube

UW–Madison researchers have designed a slow wave structure that can enhance the gain and output power of a TWT.

The modified slow wave structure has ports to receive and output amplified radiofrequency (RF) signals. It is made of two different materials that repeat at periodic intervals, e.g., the first material may be a vacuum and the second material may be a metal plate or wire mesh. The second material has a real part of permittivity that is negative and a real part of permeability that is positive at an operational frequency of the RF signal. An electron beam vacuum tube runs through the center of the slow wave structure.

More Efficient Semiconductor Lasers

UW–Madison researchers have taken a new approach and developed QCLs configured for symmetric longitudinal mode (single-lobe beams) with no loss in efficiency. Instead of relying on phase shifters, the new lasers work by suppressing undesired antisymmetric longitudinal modes.

The lasers are made of layers of cladding, metal (such as gold or silver) and indium phosphide-based semiconductor material. The interface of the metal and semiconductor layers forms a corrugated, second-order distributed feedback grating, which absorbs the undesired antisymmetric longitudinal modes. This configuration eliminates the need for cleaved facets.

Low-Profile, Ultrawide Band Antenna

UW–Madison researchers have developed an electrically small ultrawide band antenna that radiates in every direction like a monopole. The unique structure of the antenna relies on the placement and shape of the arms and slot. It is composed of a top-loaded, multifolded planar structure placed vertically on a ground plane. The structure is loaded with a top hat conductor that is short circuited to the ground plane at two locations.

Electrically Small, Super-Directive Antennas Inspired by Insect Anatomy

A UW–Madison researcher has developed an electrically small array that converts super-resolving antennas to super-directive antennas by utilizing a phase shifter. The resolution enhancement increases the total amount of collected power and the overall signal-to-noise output.

The receiver system includes two antennas and a processing circuit with a differential phase shifter (DPS). The second antenna receives a signal, which then is phase shifted as a function of its angle of incidence relative to the array’s boresight axis. An output signal can be configured by combining the phase-shifted signal with the first antenna’s original signal.

Three distinct DPS methods can achieve the same result. Active DPS can be implemented using a mixer, filters, amplifiers and voltage controlled phase shifter. Direct DPS is another analog process, while digital DPS samples and processes the antenna signals digitally.

Ultrawideband, Frequency-Selective Transceiver Lens for Less Distortion

UW–Madison researchers have developed a microwave lens for ultrawideband signals that doesn’t introduce major distortion in the radiated pulse.

The design utilizes low-pass FSS layers of metallic grids. The grids are formed by inductive-capacitive (IC) cells that resonate in response to incoming electromagnetic radiation at frequencies that vary with cell shape. The two-dimensional grids are mounted on both sides of stacked dielectric sheets in alignment with each other to form a time-delay circuit, or filter.

To receive and transmit a pulse, a processor first receives a digital data stream and transforms it into an analog signal. An electromagnetic wave feed element, like a dipole antenna, receives the signal and radiates a spherical radio wave toward the first capacitive grid. The time-delay circuit is selected to reradiate the wave in the form of a second radio wave. Consistent time delays across the desired band and calculated phase shifts ensure that the incident wave is not distorted.

Steering and Tuning Lasers Formed by Nanoscale Microtubes

UW–Madison researchers have developed semiconductor microtube lasers that are wavelength-tunable and can be steered when an electromagnetic field is applied.

The microtube is a heterostructure of various group III/V alloys integrated for different purposes. The structuring involves three essential components: a strained layer to make the tube curl, an optically active lattice to emit laser light (interband or intersubband), and a grating structure to provide optical feedback. Thickness of the layers may range from five to 2000 nm.

Unlike existing lasers, the diameter of the microtube can be altered to produce different wavelengths of light. Through piezoelectric coupling or the addition of an insulating layer that leads to a change in lattice spacing, the tube can be made to expand or contract, corresponding to modulated emissions.

Additionally, the microtubes can be anchored in devices with electrodes that cause them to rise and tilt, steering the direction in which their light is given off.

Electrically-Small, Super-Resolving Antennas and Arrays

UW–Madison researchers have developed a small-scale electromagnetic antenna array capable of resolving the direction of arrival of an electromagnetic wave using principles based in nature. The design is based on directional hearing in insects that have two ears with minimal space between them. These insects use small differences in the time of arrival of sound between their two ears and amplify these minute differences to detectable levels.

This electrically-small antenna array design is a second-order coupled resonator network that includes two antenna inputs and two outputs. The design allows directional sensitivity by increasing the small phase difference between the almost-identical input signals. This allows the sensitivity pattern of the small array to become significantly more directional than that of a regular receiving array occupying the same area. Achieving the same sensitivity and output phases from regular arrays is only possible if the array size is increased and more antenna elements are used, making this an ideal design for small antenna arrays.

Prioritized Data Mapping to Recover High Usefulness Data for Improved Wireless Communications

UW-Madison researchers have developed a wireless communication system with a physical transmitter that transmits symbols mapped to multiple bits under an encoding system that allows data in an incorrectly received symbol to be salvaged. This encoding system exploits predictable expectations in error rates of different bit positions of symbols to promote transmission of high usefulness data. By placing the high usefulness data preferentially in bit positions that have fewer errors, the likelihood that high usefulness data can be recovered even after symbol errors occur is increased. The system recovers data by harvesting a portion of the bits of erroneous symbols rather than discarding the bits.

The entire system consists of a transmitter, a prioritizer, an encoder and an interleaver. The wireless transmitter transmits the symbols. The prioritizer divides received multibit data units into categories of relatively high and low usefulness, and creates mixed multibit data units made up of high and low usefulness bits. The encoder maps the mixed multibit data units to symbols and provides the symbols to the transmitter for transmission. The interleaver and encoder work together to map high usefulness bits to positions within the symbols having lower data error rates.

Improved Delivery of Rich Media Content over Wireless Networks

UW-Madison researchers have developed a wireless system that provides a new approach for media delivery using existing systems, such as the 802.11 wireless protocol. This approach, which is achieved through simple software changes, promises to improve the delivery of HD media over wireless networks and enhance the user experience.

The system identifies priorities of data units and assigns physical transmission parameters based on usefulness of the data. The usefulness of each data unit is used to control the transmitter parameters for the data unit. These parameters include the transmission rates of the bits of the data unit, the order of transmission of the data units and/or the number of retransmission attempts of the data units. This system provides both an ordering and a quantitative difference in usefulness between data units, permitting adjustment of the transmission parameters for different data units and a simple method of scheduling data units for transmission.

Algorithm Improves Resolution of Time-Frequency Analysis for Medical Diagnostics, Telecommunications

UW-Madison researchers have developed a pseudo-wavelet algorithm known as the “damped-oscillator oscillator detector” (DOOD). This algorithm is unique among all wavelet and pseudo-wavelet algorithms in that it is the only algorithm that is explicitly based on modeling data as a “driving force” that interacts with a hypothetical set of mathematical oscillators. In the DOOD algorithm, an entirely new spectral density can be defined as the time rate of change in the energy specifically due to interaction with the data driving force, referred to as the data power. The data power measure is more sensitive to the presence or absence of data oscillators than traditional energy measures.

The DOOD algorithm allows an enormous frequency range to be spanned over as many orders of magnitude as desired. The instantaneous phase of oscillation and correlation functions can be calculated easily. The inverse of the DOOD transform is accomplished readily, which means that the DOOD algorithm also can be used to compress data. Any time-frequency or correlation analysis that can be accomplished by conventional means also can be accomplished using the DOOD algorithm, with the advantages of greater flexibility in defining the frequency range and better time resolution.

Hybrid Analog-Digital Transceiver for Enhanced Wireless Communications

UW-Madison researchers have developed a hybrid analog-digital wireless transceiver architecture that improves wireless link capacity while providing gains in power and bandwidth efficiency. The improved transmitter system, known as a continuous aperture phased MIMO (CAP MIMO) system, employs a signal processor, a plurality of feed elements and an aperture. The hybrid architecture provides the lowest complexity analog-digital interface.

The system integrates analog and digital processing rather than employing only digital processing. The signal processor is configured to simultaneously receive digital data streams and transform them into analog signals. A number of the digital data streams are selected for transmission to a single receive antenna based on the transmission environment. The feed elements are configured to receive the analog signals, and in response, to radiate radio waves toward the aperture. The aperture is configured to receive the radiated radio waves and radiate a second plurality of radio waves toward the single receive antenna in response. This allows independent data streams for typically disjointed communication modes. The result is an improved wireless communication system with high power efficiency, high wireless capacity and improved bandwidth efficiency.

Ultrawide Band, Compact Antenna for Low Frequency Applications, Including Military Vehicles and Wireless Communications

UW-Madison researchers have developed a low-profile, ultrawide band antenna with improved performance at low frequencies. The antenna contains a ground plane substrate and a radiating element. The radiating element includes at least two loop sections, which are electrically connected to a feed network and to the ground plane substrate to seamlessly combine two modes of operation. The radiating element is configured to radiate over a first frequency band when the feed network provides an in-phase input signal to the loop sections and to radiate over a second frequency band when the network provides an out-of-phase input. The second frequency band includes a lower frequency than the first frequency band, enabling the compact antenna to cover a wide range of frequencies.

Method for Reducing Power Consumption of Mobile Devices

UW-Madison researchers have developed a technique to increase energy efficiency of network communications by determining an “energy profile” of the transmitting device that models energy consumption at different transmission rates and powers. The energy profile is used to adjust operating conditions of a digital radio transmitter to reduce energy consumption during transmission. The profiling technique may be enhanced by using a modified communication protocol that reduces the amount of data that must be transmitted by using data compression and/or a remote proxy device to handle network protocol data not required by the mobile device. By reducing the amount of data sent through transmission control, data compression and utilization of remote devices, the energy efficiency of wireless devices may be improved dramatically.

Packet Router with Improved Packet Classification Abilities

UW–Madison researchers have developed a computer-implemented system similar to a smart rule cache to classify received packets. The system uses a comparison of a hardware cache of evolving rules and a software cache of the original rule set. This allows for faster cache updating, searching algorithms and conflict resolution, thereby achieving significantly better packet classification performance than current rule cache computation algorithms.

Centralized Scheduling for Interference Mitigation in Wireless Local Area Networks

UW-Madison researchers have developed a centralized scheduling framework to design efficient channel access for WLANs with exposed and hidden terminals. Based on known characteristics of the network, scheduling is performed using speculative scheduling tactics concentrated within the central controller, which has contact with a significant portion of the traffic on the network. The role of the scheduler is to decide, for each channel and packet, which in-range access point assigned to the channel should send the packet. 

The method includes determining whether a computing device receiving a data packet through a wireless access point is in conflict with another computing device associated with a different access point. Furthermore, the method determines whether such conflicts in transmittal are scheduled to forward the packet to an access point at a rescheduled time. Through the use of the centralized speculative scheduling method, network throughput is maximized by coordinating transmittals based on groups of packets being sent within defined time periods. Interference due to conflicting transmittal of data packets is reduced and network traffic management is improved.

Multi-Rate Data Transmission Using Standard Hardware for Continuous Mobility in Wireless Devices

UW-Madison researchers have developed a transmission protocol to obtain intra-packet rate variations and vary the effective rate of transmission within individual data packets.  A transceiver then provides for the variable intra-packet bit rates for high-speed adaptation to variations in the quality of wireless connection. This allows for a faster, proactive approach to adapt to varying link qualities, which is necessary for continuous mobility applications.

An Improved Method for Analyzing Wireless Broadcasts

UW-Madison researchers have developed a more efficient method for recovering CSI. This method uses a non-linear reconstruction algorithm that learns multipath channels in time, frequency and space. By tailoring training signals and estimation strategies to the anticipated characteristics of the underlying channel, the researchers were able to yield better estimates than conventional procedures.

This approach improves the accuracy of learning the receiver channel response by focusing on two critical aspects of training-based channel learning methods, sensing and estimation. Sensing relates to the design and placement of training signals that are used to probe the channel. This method defines the most suitable transmitter training signals for exploiting multipath sparsity in angle, delay and/or Doppler. Estimation refers to the signal analysis process implemented at the receiver to recover the channel response. Researchers implemented non-linear reconstruction algorithms, based on convex/linear programming, that come within a logarithmic factor of the performance of an ideal channel estimator. This new approach clearly reveals how the relationship between the training signals and the accuracy of this algorithm efficiently estimates the CSI, resulting in faster channel responses at the receiver.

Improved High-Power Transistor Amplifier for Wireless Communications

UW-Madison researchers have optimized a high-power amplifier utilizing HBTs with a CB configuration to provide significant improvements in gain and power handling capacity. Although it is widely believed that CB and CE HBT amplifiers should provide identical power, the inventors determined that the power handling capabilities for HBTs are significantly affected by whether they are used in a CB or CE configuration. In voltage source biasing configurations, CE amplifiers provide higher output power than CB configurations. However, if an active current source biasing is used to bias the output of the amplifier, CB amplifiers will outperform CE amplifier configurations using identical parameters.

By taking advantage of the difference between CB and CE configurations, this method provides an increase in power handling for HBT transistor amplifiers without changing the HBT device and most significantly, without increasing the area of the device. In comparison to voltage source biasing configurations, the current source biasing arrangement allows the application of higher voltages since it is not limited by breakdown voltage. The ability to apply higher voltages further expands the opportunities with this new amplifier design, such as an increase in the amplifier gain for improved receiver applications. The amplifier seamlessly integrates with voltage source biasing systems by making the current source bias conversion within the amplifier itself. This improvement in power handling capacity will have a substantial influence on the manufacture and miniaturization of RF amplifiers.

Nested Waveguides for Generating or Detecting Radiation, Including Terahertz Radiation

UW Madison researchers have recently demonstrated a room temperature, tunable THz source operating at 1.3 THz with an extremely narrow linewidth (< 200 kHz; < 7 x 10-6 cm-1) and record conversion efficiency.  This source takes advantage of a new nested waveguide structure to produce continuously phase-matched difference frequency mixing between spectrally pure, amplified diode laser pumps.  The thin film active medium for this source (LiNbO3 ) is interchangeable with other nonlinear materials operating at other frequency ranges (e.g., AlGaAs for 3.5 THz).  It can be designed to generate ultra-narrow band radiation across a range of frequencies. The device also may be designed to detect THz radiation.

The nested waveguides are fabricated using well established lithography and semiconductor fabrication techniques, such as chemical vapor deposition. A smaller waveguide can be embedded within a larger waveguide.  The smaller waveguide provides guidance for radiation of a shorter wavelength, while the larger waveguide provides a transition to radiation of a longer wavelength. The waveguides enhance the efficiency at which the nonlinear process converts the radiation to the desired frequency by providing strong optical confinement of the input and output radiation, reducing diffraction and improving phase matching. Nested waveguides also have a small footprint, making them ideal for creating small THz-based systems.

Microscale High-Frequency Vacuum Electrical Device

A UW-Madison researcher has developed a mechanically tunable, microscale vacuum electrical device with a high frequency range. This device uses mechanical modulation to tune the electron beam, making it better suited for microscale fabrication by eliminating complicated tuning components and avoiding interference with the emitted electrons. In addition, using mechanical, rather than voltage, modulation may enable the device to use less power at around 50 to 100V.

Distributed Scheduling Method for Multi-Antenna Wireless Data Communication System

UW-Madison researchers have developed a method of scheduling the use of antennas in a MIMO wireless communication system that addresses the problems of mathematical intractability and communication overhead. The method offloads the optimization process to the individual base station receivers, dynamically allocating communication channels between a base station and a group of mobile stations. As a result, as the number of users increases, the potential computational power also increases, improving the scalability of the optimization process. Also, by distributing the optimization process among these base station receivers, the amount of communication overhead is significantly reduced. The invention matches most of the existing schemes in performance, while having a limited overhead.

Use of Overlapping Channels for Expanded Wireless Communications

UW-Madison researchers have developed a method for the simultaneous use of overlapping wireless communication channels, providing substantially higher throughput. They developed criteria for characterizing the interference levels that can arise as a result of any given arrangement of wireless communication devices operating at different channels. This provides a method for controlling interference levels, allowing the overlap of channels while keeping interference within acceptable, predetermined bounds.

Method of Producing Short-Wavelength Quantum-Entangled Light Beams

UW-Madison researchers have developed a new approach to generating quantum-entangled light beams using second harmonic generation to provide entanglement at short wavelengths. The science is in its infancy, but as it develops, entanglement generated at shorter wavelengths may be important for applications in quantum measurements, quantum-enhanced lithography and ultra-secure quantum communication. Entangled light could also lead to more sensitive medical diagnoses, more powerful computer chips and scalable quantum computing.

Apparatus and Algorithms for Channel Management in Wireless Local Area Networks

UW-Madison researchers have developed a method of assigning channels to a plurality of access points of a wireless local area network to provide enhanced bandwidth usage, interference minimization and load balancing. The method identifies a range set and an interference set for each client of a WLAN. Using a hierarchy of importance for each AP, it then calculates a respective interference level that would be experienced by that AP in at least two channels, and stores that information. The analysis cycles until AP assignment results in optimized throughput and interference.

Method for Improving Performance in a Sparse Multipath Environment Using Reconfigurable Arrays

UW-Madison researchers have developed a wireless communication system and method that use reconfigurable multi-element antenna arrays to support improved performance in sparse multipath environments that are commonly encountered in practice. To maximize the information capacity of a wireless link, the antenna spacings are systematically adapted at the transmitter and/or receiver arrays based on the sparsity of the multipath environment and the operating signal-to-noise ratio (SNR). The method involves two basic steps: 1) channel sounding or estimation at a critical antenna spacing to determine the number of spatial degrees of freedom (DoF) available for communication, and 2) adjusting the antenna spacing at the transmitter and receiver as a function of the estimated number of DoF and the operating SNR to optimize the capacity of the wireless link at that SNR.

High-Power-Gain, Bipolar Transistor Amplifier

UW-Madison researchers have developed a silicon-based bipolar transistor and an associated configuration that allow for maximum power performance at high frequencies. The transistor can be either a silicon bipolar junction transistor or a silicon-germanium heterojunction bipolar transistor. The invention uses a common-base amplifier design rather than a common-emitter design with easy and effective ballast-resistor-free control of current hogging to provide maximum power gain and efficiency at radio frequencies, including microwave frequencies.

Left-Handed Non-Linear Transmission Line Device for Efficient Harmonic Generation

A team of UW-Madison electrical engineers has developed a device that can generate microwaves at very high frequencies and with greater efficiency than current technologies. Known as a left-handed non-linear transmission line, the device makes use of left-handed materials concepts. It is designed for use as an efficient harmonic generator; as such, it can take an input signal at a frequency of 3-4 gigahertz (GHz) and generate an output signal in the third harmonic, or 9-12 GHz, range. It is also scalable to higher frequencies.

The device can be constructed from inexpensive electronic parts that are easy to obtain, such as capacitors, inductors and varactor diodes. And along with harmonic generation, the device can be used to increase the intensity of an input signal at the same frequency (parametric amplification), or to generate an output signal of a lower frequency than the input (fractional frequency generation).

Type II Quantum Well Laser Devices

UW-Madison researchers have developed a low-cost, gallium arsenide-based laser device that exhibits high performance operation in the 1.55-micron region, up to elevated temperatures. The laser’s active region is deposited on a substrate of GaAs and includes electron quantum well layers of GaAsN or InGaAsN, and a hole layer quantum well of GaAsSb with a type II alignment. The composition of these quantum well layers can be selected to provide light emission at wavelengths ranging from 1.3 to 3.0 microns.

Machining of Lithium Niobate by Laser Fracturing

UW-Madison researchers have developed a method for rapidly dicing lithium niobate wafers into a variety of shapes, including curved shapes. The edges cut with this method are nearly atomically smooth, allowing direct attachment of fiber optic pigtails without further polishing.

The process uses a commercially available laser to create and guide a fracture through the wafer to cut it. Under different beam conditions, the same laser can also ablate features on the wafer surface, such as alignment marks, gratings and microwave and optical cavities. Model calculations have shown that ablated features can significantly improve the performance of devices, such as the traveling wave modulator.

Electro-Optic Optical Elements

UW-Madison researchers have developed electro-optic elements formed in metal oxide films, particularly lithium niobate, for use in electro-optic devices. These elements are fabricated through a process in which lithium niobate is deposited as an amorphous thin-film onto a lithium niobate substrate, patterned and etched by conventional techniques, and then annealed to a crystalline state suitable for electro-optic applications (see WARF reference number P01007US). Because amorphous lithium niobate is easily etched and otherwise manipulated, trenches and other features in the electro-optic elements can be easily designed to improve device performance. In particular, this invention includes traveling wave modulators whose topographical features can be selected to achieve higher bit rate functioning than conventional devices.

Layered Space Time Processing Reduces Interference in a Multiple Antenna Wireless Communications System

UW-Madison researchers have developed a system and method for performing space-time processing, which efficiently and reliably remove interference for multiple antenna array systems.  This invention uses baseline algorithms that significantly simplify signal processing at the receiver compared to BLAST. Furthermore, the invention includes extended algorithms that can eliminate the bottleneck in BLAST performance caused by error propagation. The extended algorithms can be applied to existing systems employing BLAST-type processing, without altering their structure.

Channel Aware Space-Time Signaling for Wireless Communication over Wideband Multipath Channels

UW-Madison researchers have developed a method for reducing the computational resources required to enhance signal transmissions. Specifically, the method enables management of the usage of a space-time channel having a plurality of orthogonal sub-channels in a communication system. The system includes a transmitter, a receiver and one or more signal propagation paths between the transmitter and receiver.

Vertical-Cavity, Surface-Emitting Semiconductor Laser Arrays

UW-Madison researchers have developed a method of coupling arrays of VSELs that overcomes the problems of prior technologies and provides a stable, diffraction limited output at high power levels. The array contains at least four core elements arranged in a 2-D rectangular array. The core elements are separated and surrounded by a matrix region to provide an array of antiguided phase-locked VCSELs.

Bi-Directional, Micromechanical Linear Actuator for Optical Switching

UW-Madison researchers have developed a micromechanical linear actuator that provides ultra precise, rectilinear displacements at the high forces needed for optical fiber switching. Using this actuator the researchers achieved lower optical losses (i.e., better performance) during switching than any single-mode optical fiber switch currently on the market. Another key feature is the switch’s magnetic latching mechanism, which holds the actuator at either end of its travel after switching is complete without requiring standby power.

Method and System for Multi-Carrier Multiple Access Reception in the Presence of Imperfections

UW–Madison researchers have now developed a system that addresses current limitations of multicarrier modulation schemes by using a universal receiver structure. This system processes signals from multiple users in a manner that compensates for imperfections, and in fact exploits some of these imperfections to significantly improve the accuracy of received data.

Vertical-Cavity Surface-Emitting Lasers with Anti-Resonant Reflecting Optical Waveguides

UW–Madison researchers have developed a VCSEL that uses an anti-resonant reflecting optical waveguide (ARROW) to reduce the edge radiation losses for the fundamental mode. This structure is capable of providing single-mode output at higher powers than conventional VCSEL devices.