Browsing by Author "Arya, Vivek"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Analysis, Design and Performance Evaluation of Optical Fiber Spectrum-Sliced WDM Systems
    Arya, Vivek (Virginia Tech, 1997-06-03)
    This dissertation investigates the design and performance issues of a recently demonstrated technique, termed as spectrum-slicing, for implementing wavelength-division-multiplexing (WDM) in optical fiber systems. Conventional WDM systems employ laser diodes operating at discrete wavelengths as carriers for the different data channels that are to be multiplexed. Spectrum-slicing provides an attractive low-cost alternative to the use of multiple coherent lasers for such WDM applications by utilizing spectral slices of a broadband noise source for the different data channels. The principal broadband noise source considered is the amplified spontaneous emission (ASE) noise from an optical amplifier. Each slice of the spectrum is actually a burst of noise that is modulated individually for a high capacity WDM system. The stochastic nature of the broadband source gives rise to excess intensity noise which results in a power penalty at the receiver. One way to minimize this penalty, as proposed and analyzed for the first time in this work, is to use an optical preamplifier receiver. It is shown that when an optical preamplifier receiver is used, there exists an optimum filter bandwidth which optimizes the detection sensitivity (minimizes the average number of photons/bit) for a given error probability. Moreover the evaluated detection sensitivity represents an order of magnitude ( > 10 dB) improvement over conventional PIN receiver-based detection techniques for such spectrum-sliced communication systems. The optimum is a consequence of signal energy fluctuations dominating at low values of the signal time bandwidth product (m), and the preamplifier ASE noise dominating at high values of m. Operation at the optimum bandwidth renders the channel error probability to be a strong function of the optical bandwidth, thus providing motivation for the use of forward error correction coding (FEC). System capacity (for BER = ) is shown to be 23 Gb/s without coding, and 75 Gb/s with a (255,239) Reed Solomon code. The effect of non-rectangular spectra on receiver sensitivity is investigated for both OOK and FSK transmission, assuming the system (de)multiplexer filters to be N'th order Butterworth bandpass. Although narrower filters are recommended for improving power budget, it is shown that system penalty due to filter shape may be kept < 1 dB by employing filters with N > 2. Moreover spectrum-sliced FSK systems using optical preamplifier receivers are shown, for the first time, to perform better in a peak optical power limited environment. Performance-optimized spectrum-sliced WDM systems have potential use in both local loop and long-distance fiber communication systems which require low-cost WDM equipment for high data rate applications.
  • Thumbnail Image
    Investigation And Application Of The Frustrated-Total-Internal-Reflection Phenomenon in Optical Fibers
    Rahnavardy, K.; Arya, Vivek; Wang, A.; Weiss, J. M. (Optical Society of America, 1997-12-01)
    A detailed investigation of the frustrated-total-internal-reflection (FTIR) phenomenon in silica-glass-based optical fibers and its application to simple intensity-modulated strain and pressure sensors is presented. Such sensors may be readily fabricated with silica-based fibers and can be easily modified with sapphire fibers for high-temperature industrial applications where conventional silica-based fiber sensors are not feasible. We present the all-fiber FTIR sensor and show good correlation between theory and experiment. We also present results for the design and implementation of a prototype FTIR-based fiber pressure sensor. (C) 1997 Optical Society of America.
  • Thumbnail Image
    Microbending effects in singlemode optical fibers: investigation and novel applications
    Arya, Vivek (Virginia Tech, 1994-12-04)
    Microbends are axial distortions on the optical fiber that have a spatial wavelength small enough to effect coupling between guided and radiation or cladding modes. The magnitude of this wavelength-dependent coupling is a function of the nature and the number of microdefonnations. Since these periodic perturbations lead to an attenuation in signal level, they are avoided in fiber-based communication systems. However, controlled induction and signal processing of microbending losses has led to the fabrication of novel optical fiber~based sensors, devices, and components. A systematic study of microbending effects in singlemode optical fibers is presented in this thesis. The theoretical analysis is based on the coupling between the fundamental LP01 mode to discrete cladding modes. An algorithm is developed to characterize optical attenuation as a function of the spatial period of the microbend defonnation. Optical attenuation peaks are described in terms of central wavelength, amplitude and spectral width. An excellent correlation is shown between the experimental results and the theoretical predictions, with nominal errors less than 2.5%. The algorithm developed may be used with any commercially available singlemode fiber, and any kind of microbend de former apparatus, provided the microbend defonnation function ⠱(z) is known accurately. Based on the above analysis, a wavelength-tunable fiber polarizer is proposed and demonstrated. The polarizer is fabricated by inducing a periodic perturbation on a high birefringence singlemode optical fiber. The fiber thus exhibits polarization· selective attenuation characteristics. The operating wavelength is shown to be tunable by changing the spatial period of the defonnation. A polarization extinction ratio of 25 dB is obtained with an attenuation of 1.3 dB, at an operating wave length of 1177 nm.