Browsing by Subject "Electrical and computer Engineering"

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    Electronic post-compensation of optical fiber nonlinearity in high-speed long-haul wavelength division multiplexed transmission systems.
    (2010-01) Ahmed, Nisar
    A vast majority of optical fiber infrastructure deployed today utilizes 10 Gb/s transmission technology which is falling short of demands for current communication networks. To fulfill the ever increasing needs of bandwidth, the research trend since past few years has been in the direction of increasing the per channel data rate to ≥ 40 Gb/s. The transmission of optical pulses over ≥ 40 Gb/s data rates greatly suffers from degradations arising from interaction of dispersion and optical fiber nonlinearity. The work presented in this thesis focuses on the development and evaluation of a novel electronic signal processing technique that can undo the degradations already caused by the interaction between dispersion and intra-channel nonlinearities. The proposed technique tends to compensate degrading nonlinear effects by incorporating the knowledge of the neighboring bits and exploiting the fact that for a given bit pattern, the nonlinear degradation, deterministically, depends upon dispersion map and operating channel power. We have tested our proposed technique in WDM transmission systems using return-to-zero (RZ), carrier suppressed RZ (CSRZ) and differential phase-shift keying modulation formats, and have analyzed the system performance by using computer simulations. Our analysis shows that the proposed scheme can significantly undo the degradation caused by fiber nonlinearity and can significantly increase the overall system margin of a 40 Gb/s WDM system.
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    Optical system design of a laser-based stethoscope
    (2012-06) Sileshi, Girum A.
    In this paper, we demonstrate the development of a new type of stethoscope using laser technology to visualize the heart beat signal. This heartbeat detection technique could overcome the limitation of the acoustic stethoscope brought by the poor ability of human ears to hear low frequency heart sounds. This is important, as valuable information from sub-audio sounds is present at frequencies below the human hearing range. Moreover, the diagnosis accuracy of the acoustic stethoscope is also very sensitive to noise from the immediate environment. In this laser-based stethoscope, the heartbeat signal is correlated to the optical spot of a laser beam reflected from a thin mirror attached to the patient’s chest skin. The motion of the mirror with the chest skin is generated by heartbeat and breathing. A linear optical sensor is applied to detect and record the motion of the optical spot, from which the heart sound signal in time-domain is extracted. The heart sound signal is subsequently transformed to frequency domain through digital signal processing. Both time domain and frequency-domain signals are analyzed in order to classify different types of heart murmurs. A digital filter is designed to remove other activities associated with the movement of chest skin, such as respiration. We developed the prototype of the system and tested the prototype on a dummy human body with various heartbeat patterns and breathing. We compared the laser generated results with the concurrent testing results from phonocardiography. Results reveal that the laser based heart sound detection approach has the advantage over the phonocardiography for low frequency sounds (≤ 50Hz) while the phonocardiography is more sensitive to higher frequency sounds ≥ 200Hz).