Publications
Impact of semiconductor optical amplifiers in coherent down-conversion microwave photonic links
June 6, 2012
Conference Paper
Published in:
CLEO: Conf. on Lasers and Electro-Optics, 6-11 June 2012.
Summary
We compare the impact of conventional semiconductor optical amplifiers (SOAs) and high linearity slab-coupled optical waveguide amplifiers (SCOWAs) on the SFDR of carrier-suppressed coherent down-conversion microwave photonic links.
Summary
We compare the impact of conventional semiconductor optical amplifiers (SOAs) and high linearity slab-coupled optical waveguide amplifiers (SCOWAs) on the SFDR of carrier-suppressed coherent down-conversion microwave photonic links.
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Dynamical decoupling and dephasing in interacting two-level systems
June 6, 2012
Journal Article
Published in:
Phys. Rev. Lett., Vol. 109, No. 1, 6 June 2012, 010502.
Summary
We implement dynamical decoupling techniques to mitigate noise and enhance the lifetime of an entangled state that is formed in a superconducting flux qubit coupled to a microscopic two-level system. By rapidly changing the qubit's transition frequency relative to the two-level system, we realize a refocusing pulse that reduces dephasing due to fluctuations in the transition frequencies, thereby improving the coherence time of the entangled state. The coupling coherence is further enhanced when applying multiple refocusing pulses, in agreement with our 1/f noise model. The results are applicable to any two-qubit system with transverse coupling and they highlight the potential of decoupling techniques for improving two-qubit gate fidelities, an essential prerequisite for implementing fault-tolerant quantum computing.
Summary
We implement dynamical decoupling techniques to mitigate noise and enhance the lifetime of an entangled state that is formed in a superconducting flux qubit coupled to a microscopic two-level system. By rapidly changing the qubit's transition frequency relative to the two-level system, we realize a refocusing pulse that reduces dephasing...
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A stochastic system for large network growth
June 1, 2012
Journal Article
Published in:
IEEE Signal Process. Lett., Vol. 19, No. 6, June 2012, pp. 356-359.
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Summary
This letter proposes a new model for preferential attachment in dynamic directed networks. This model consists of a linear time-invariant system that uses past observations to predict future attachment rates, and an innovation noise process that induces growth on vertices that previously had no attachments. Analyzing a large citation network in this context, we show that the proposed model fits the data better than existing preferential attachment models. An analysis of the noise in the dataset reveals power-law degree distributions often seen in large networks, and polynomial decay with respect to age in the probability of citing yet-uncited documents.
Summary
This letter proposes a new model for preferential attachment in dynamic directed networks. This model consists of a linear time-invariant system that uses past observations to predict future attachment rates, and an innovation noise process that induces growth on vertices that previously had no attachments. Analyzing a large citation network...
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NextGen surveillance and weather radar capability (NSWRC) siting analysis
May 22, 2012
Project Report
Published in:
Project Report ATC-391, MIT Lincoln Laboratory
Summary
As the current radars that perform weather and aircraft surveillance over the United States age, they must be sustained through service life extension programs or replaced. In the latter case, the radars can be replaced by multiple types of radars with different missions or they can be replaced by scalable multifunction phased array radars (MPARs). State-of-the-art active phased array systems have the potential to provide improved capabilities such as earlier detection and better characterization of hazardous weather phenomena, 3D tracking of noncooperative aircraft, better avoidance of unwanted clutter sources such as wind farms, and more graceful performance degradation with component failure. As the U.S. aviation community works toward realizing the Next Generation Air Transportation System (NextGen), achieving improved capabilities for aircraft and weather surveillance becomes critical, because stricter observation requirements are believed to be needed. Hence, the Federal Aviation Administration (FAA) is considering the MPAR as a possible solution to their NextGen Surveillance and Weather Radar Capability (NSWRC). Cost is one hurdle to the deployment of a modern phased array radar network. One way of lowering the overall cost is to reduce the total number of radars. Because of the overlap in coverage provided by the current radar networks, a unified MPAR replacement network can potentially decrease the total number of radars needed to cover the same airspace. An earlier analysis conducted by MIT Lincoln Laboratory concluded that 510 legacy radars could be effectively replaced by 334 MPARs over the contiguous United States (CONUS). There was, however, some uncertainty whether the spatial resolution used in the terrain blockage calculations was fine enough to accurately depict radar coverage, and also if terminal area coverage was being adequately addressed. This study revisits the siting analysis using a much finer spatial resolution, expands the coverage domain to include all fifty states and U.S. territories, adds the Air Force long-range surveillance radars (FPSs) to the legacy pool, and allows scaling by number of faces per radar. The aim is to provide an estimate of the minimum number of MPARs needed to replace the existing radar coverage. We also provide an extensive statistical compilation of legacy versus MPAR coverage for various observational performance parameters.
Summary
As the current radars that perform weather and aircraft surveillance over the United States age, they must be sustained through service life extension programs or replaced. In the latter case, the radars can be replaced by multiple types of radars with different missions or they can be replaced by scalable...
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Continuous security metrics for prevalent network threats - introduction and first four metrics
May 22, 2012
Project Report
Published in:
MIT Lincoln Laboratory Report IA-3
Topic:
R&D area:
R&D group:
Summary
The goal of this work is to introduce meaningful security metrics that motivate effective improvements in network security. We present a methodology for directly deriving security metrics from realistic mathematical models of adversarial behaviors and systems and also a maturity model to guide the adoption and use of these metrics. Four security metrics are described that assess the risk from prevalent network threats. These can be computed automatically and continuously on a network to assess the effectiveness of controls. Each new metric directly assesses the effect of controls that mitigate vulnerabilities, continuously estimates the risk from one adversary, and provides direct insight into what changes must be made to improve security. Details of an explicit maturity model are provided for each metric that guide security practitioners through three stages where they (1) Develop foundational understanding, tools and procedures, (2) Make accurate and timely measurements that cover all relevant network components and specify security conditions to test, and (3) Perform continuous risk assessments and network improvements. Metrics are designed to address specific threats, maintain practicality and simplicity, and motivate risk reduction. These initial four metrics and additional ones we are developing should be added incrementally to a network to gradually improve overall security as scores drop to acceptable levels and the risks from associated cyber threats are mitigated.
Summary
The goal of this work is to introduce meaningful security metrics that motivate effective improvements in network security. We present a methodology for directly deriving security metrics from realistic mathematical models of adversarial behaviors and systems and also a maturity model to guide the adoption and use of these metrics...
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Rational design and optimization of plasmonic nanoarrays for surface enhanced infrared spectroscopy
May 21, 2012
Journal Article
Published in:
Opt. Express, Vol. 20, No. 11, 21 May 2012, pp. 11953-11966.
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Summary
We present an approach for rational design and optimization of plasmonic arrays for ultrasensitive surface enhanced infrared absorption (SEIRA) spectroscopy of specific protein analytes. Motivated by our previous work that demonstrated sub-attomole detection of surface-bound silk fibroin [Proc. Natl. Acad. Sci. U.S.A. 106, 19227 (2009)], we introduce here a general framework that allows for the numerical optimization of metamaterial sensor designs in order to maximize the absorbance signal. A critical feature of our method is the explicit compensation for the perturbative effects of the analyte's refractive index which alters the resonance frequency and line-shape of the metamaterial response, thereby leading to spectral distortion in SEIRA signatures. As an example, we leverage our method to optimize the geometry of periodic arrays of plasmonic nanoparticles on both Si and CaF2 substrates. The optimal geometries result in a three-order of magnitude absorbance enhancement compared to an unstructured Au layer, with the CaF2 substrate offering an additional factor of three enhancement in absorbance over a traditional Si substrate. The latter improvement arises from increase of near-field intensity over the Au nanobar surface for the lower index substrate. Finally, we perform sensitivity analysis for our optimized arrays to predict the effects of fabrication imperfections. We find that
Summary
We present an approach for rational design and optimization of plasmonic arrays for ultrasensitive surface enhanced infrared absorption (SEIRA) spectroscopy of specific protein analytes. Motivated by our previous work that demonstrated sub-attomole detection of surface-bound silk fibroin [Proc. Natl. Acad. Sci. U.S.A. 106, 19227 (2009)], we introduce here a general...
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A compressed sensing analog-to-information converter with edge-triggered SAR ADC core
May 20, 2012
Journal Article
Published in:
ISCAS 2012: IEEE Int. Symp. on Circuits and Systems, 20-23 May 2012, pp. 3162-3165.
Summary
This paper presents the design and implementation of an analog-to-information converter (AIC) based on compressed sensing. The core of the AIC is an edge-triggered charge-sharing SAR ADC. Compressed sensing is achieved through random sampling and asynchronous successive approximation conversion using the ADC core. Implemented in 90nm CMOS, the prototype SAR ADC core achieves a maximum sample rate of 9.5MS/s, an ENOB of 9.3 bits, and consumes 550 mu W from a 1.2V supply. Measurement results of the compressed sensing AIC demonstrate effective sub-Nyquist random sampling and reconstruction of signals with sparse frequency support suitable for wideband spectrum sensing applications. When accounting for the increased input bandwidth compared to Nyquist, the AIC achieves an effective FOM of 10.2fJ/conversion-step.
Summary
This paper presents the design and implementation of an analog-to-information converter (AIC) based on compressed sensing. The core of the AIC is an edge-triggered charge-sharing SAR ADC. Compressed sensing is achieved through random sampling and asynchronous successive approximation conversion using the ADC core. Implemented in 90nm CMOS, the prototype SAR...
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Dallas/Fort Worth field demonstration #2 (DFW-2) final report for Tower Flight Data Manager (TFDM)
May 16, 2012
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-393
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R&D area:
Summary
The Tower Flight Data Manager (TFDM) is the next generation air traffic control tower (ATCT) information system that integrates surveillance, flight data, and other sources, which enables advanced decision support tools (DSTs) to improve departure and arrival efficiency and reduce fuel burn at the airport. TFDM was exercised as a prototype installed at the Dallas / Fort Worth International Airport (DFW) during a two-week demonstration in the spring of 2011 termed DFW-2. MIT Lincoln Laboratory conducted this demonstration for the FAA in coordination with DFW air traffic control (ATC) and the DFW airport authority. The objective of this TFDM field demonstration was to validate the operational suitability and refine production system requirements of the Tower Information Display System (TIDS) surface surveillance display and Flight Data Manager (FDM) electronic flight data display and to evaluate the first iteration of the Supervisor Display and DSTs. These objectives were met during the two-week field demonstration. Results indicated that the TIDS and FDM exhibited capabilities considered operationally suitable for the tower as an advisory system and as a primary means for control given surface surveillance that is approved for operational use. Human factors data indicated that TIDS and FDM could be beneficial. The prototype Supervisor Display and DSTs met a majority of the technical performance criteria, but fewer than half of the human factors success criteria were met. As this was the first iteration of the Supervisor Display and DST capabilities, subsequent prototype iterations to achieve the target concept of operations, functionality and information presentation with accompanying field demonstrations to evaluate these honed capabilities were recommended and expected. FLM/TMC feedback will help refine subsequent system design.
Summary
The Tower Flight Data Manager (TFDM) is the next generation air traffic control tower (ATCT) information system that integrates surveillance, flight data, and other sources, which enables advanced decision support tools (DSTs) to improve departure and arrival efficiency and reduce fuel burn at the airport. TFDM was exercised as a...
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Vertically stacked RF switches by wafer-scale three-dimensional integration
May 10, 2012
Journal Article
Published in:
Electron. Lett., Vol. 48, No. 10, 10 May 2012.
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R&D area:
Summary
Vertically stacked RF switches implemented by wafer-scale three-dimensional (3D) integration of three completely fabricated silicon-on-insulator wafers are demonstrated. The individual switch performance was maintained through the 3D integration process while the signal path is shortened by vertical interconnects. The footprint of the switch can be shrunk in proportion to the number of tiers it is distributed between, demonstrating the potential of significant size reduction of multiple-throw switches commonly required in many applications.
Summary
Vertically stacked RF switches implemented by wafer-scale three-dimensional (3D) integration of three completely fabricated silicon-on-insulator wafers are demonstrated. The individual switch performance was maintained through the 3D integration process while the signal path is shortened by vertical interconnects. The footprint of the switch can be shrunk in proportion to the...
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The MIT IAP radar course: build a small radar system capable of sensing range, Doppler, and synthetic aperture (SAR) imaging
May 7, 2012
Conference Paper
Published in:
Proc. of the 2012 IEEE Radar Conf., 7-11 May 2012.
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R&D area:
Summary
MIT Lincoln Laboratory sponsored a radar short course at MIT campus during the January 2011 Independent Activities Period (IAP). The objective of this course was to generate student interest in applied electromagnetics, antennas, radio frequency (RF) electronics, analog circuits, and signal processing by building a short-range radar sensor and using it in a series of field tests. Lectures on the fundamentals of radar, modular RF design, antennas, pulse compression and synthetic aperture radar (SAR) imaging were presented. Teams of three students built a radar system from a kit. This kit was developed by the authors and uses a frequency modulated continuous wave (FMCW) architecture. To save costs, empty metal coffee cans are used for antennas, components are mounted on a wood block, the system uses only six coaxial microwave parts, analog circuitry on a solderless breadboard, and runs on eight AA batteries. Analog data is acquired by the audio input port on a laptop computer. The total cost of each kit was $360 which made this radar technology accessible to students. Of the nine student groups, all succeeded in building their radar, acquiring Doppler vs. time and range vs. time plots, seven succeeded in acquiring SAR imagery, and some groups improved the radar system. By presenting these difficult topics at a high level while at the same time making a radar kit and performing field experiments, students became self motivated to explore these topics and much interest in radar design was generated.
Summary
MIT Lincoln Laboratory sponsored a radar short course at MIT campus during the January 2011 Independent Activities Period (IAP). The objective of this course was to generate student interest in applied electromagnetics, antennas, radio frequency (RF) electronics, analog circuits, and signal processing by building a short-range radar sensor and using...
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