Browsing by Author "Mittleman, Daniel"

Now showing 1 - 5 of 5
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    A terahertz two-wire waveguide with low bending loss
    (2009) Mbonye, Marx; Mittleman, Daniel
    We present experimental and theoretical evidence for low loss terahertz propagation along a two-wire waveguide. We find that the mode pattern at the end of the waveguide resembles that of a dipole consistent, with the expected fundamental mode of the structure. We experimentally observe that the two-wire configuration can be used to efficiently excite the radial mode (Somerfield wave) of a single wire, by adiabatically separating the two wires into two single wires. We observe for the first time that a commercial 300-Ω TV twin-lead antenna cable can be used to propagate low loss THz radiation, guiding frequency components up to 0.2 THz even though they are designed only to operate to about 800 MHz. We find this to be the case even at considerable wire-bend angles.
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    Focused terahertz waves generated by a phase velocity gradient in a parallel-plate waveguide
    (Optical Society of America, 2015) McKinney, Robert W.; Monnai, Yasuaki; Mendis, Rajind; Mittleman, Daniel
    We demonstrate the focusing of a free-space THz beam emerging from a leaky parallel-plate waveguide (PPWG). Focusing is accomplished by grading the launch angle of the leaky wave using a PPWG with gradient plate separation. Inside the PPWG, the phase velocity of the guided TE1ﾠmode exceeds the vacuum light speed, allowing the wave to leak into free space from a slit cut along the top plate. Since the leaky wave angle changes as the plate separation decreases, the beam divergence can be controlled by grading the plate separation along the propagation axis. We experimentally demonstrate focusing of the leaky wave at a selected location at frequencies of 100 GHz and 170 GHz, and compare our measurements with numerical simulations. The proposed concept can be valuable for implementing a flat and wide-aperture beam-former for THz communications systems.
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    High-speed Track and Hold Amplifiers in CMOS for Enabling Pulse-based Direct Modulation, Secure Communication and Precision Localization
    (2015-08-06) Aggrawal, Himanshu; Babakhani, Aydin; Cavallaro, Joseph; Mittleman, Daniel
    Last few decades have seen a puissant desire for fast communication links that has shaped the evolution of high-speed circuits and silicon- based technology. This desire accompanied with a large consumer market has fueled the development of ever-shrinking, faster technology nodes. These advanced nodes open doors for designers to develop new ways of transferring data with unprecedented speed and accuracy. There are a number of challenges in building high-speed, secure communication links, one being the lack of availability of fast Analog to Digital Converters (ADCs), which form the front end of a receiver. Even in advanced technology nodes, the leakage in the transmission gate due to parasitic source-drain capacitance provides an alternate path for signals to pass, thus lowering the performance of the ADCs at high frequencies. Second, the current communication schemes use beam-forming or Direct Antenna Modulation (DAM) to narrow the information beam and point it in the direction of communication. Such techniques still have a wide information beam compared pulse-based directional modulation, as discussed in this thesis. In this dissertation, we address the issue of parasitic leakages in the transmission gate of a fast sampler by introducing active cancellation. A track-and-hold amplifier with active cancellation is designed and fabricated in 45nm CMOS SOI technology, which can operate at 40GSample/second real-time. In addition to this, we also study a pulse-based directional modulation scheme which can be used for secure communication, imaging and localization. Two coherent pulse generators with pulse width less than 200ps were used to attain an information beamwidth of less than 1 degree and localize objects with millimeter accuracy.
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    Location information from a receiver in a wireless network
    (2024-08-27) Mittleman, Daniel; Knightly, Edward; Rice University; Brown University; United States Patent and Trademark Office
    A multi-frequency wireless access device including a first waveguide having a pair of parallel metal plates with open sides and a slot in one of the metal plates, the slot permitting radiation to leak out, the leaked radiation illuminating a range of angles depending on frequency.
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    Superfluorescence from a Two-Dimensional Electron-Hole System: Magnetic Field, Temperature, and Density Dependence
    (2014-10-30) Cong, Kankan; Kono, Junichiro; Mittleman, Daniel; Natelson, Douglas
    In the phenomenon of superfluorescence (SF), a macroscopic polarization spontaneously builds up from an initially incoherent ensemble of excited dipoles and then cooperatively decays, producing giant pulses of coherent radiation. SF arising from electron-hole recombination has recently been observed in semiconductor quantum wells, but its observability conditions have not been fully understood. Here, by fully mapping out the magnetic field (B), temperature (T), and electron-hole pair density (n) dependence of SF intensity and linewidth, we have constructed a ‘phase’ diagram, showing the B-T-n region in which SF is observable. In general, SF can be observed only at low enough temperatures, high enough magnetic fields, and high enough laser powers with characteristic threshold behaviors. These results lay the foundation of our understanding of electron-hole SF and provide guidelines for our search for a Bardeen-Cooper-Schrieffer state of excitons.