by Hung Wing-yiu. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves 98-103.

Recently, Coherent Optical Orthogonal Frequency-division Multiplexing (CO-OFDM) has been considered as a promising technology for high-speed optical transmission due to its easiness of dispersion compensation, high optical spectral efficiency and superior scalability over the channel dispersion and data rate. In this thesis, we conduct analysis on the transceiver nonlinearity impact on a coherent optical Orthogonal Frequency-division Multiplexing (OFDM) system and the feasibility of transmitting up to 1 Tb/s per channel data rate over CO-OFDM WDM systems. / We investigate the optimum design for a CO-OFDM transmitter using an optical In-phase/Quadrature (I/Q) modulator and show by simulation that in contrast to the direct-detected system, the optimal modulator bias point for the coherent system is π, or the null point of the modulator. We also propose and demonstrate through simulation a transmitter side digital signal processing technique including digital clipping and digital pre-distortion to compensate the nonlinearity induced by the OFDM peak-to-average power ratio effect and Mach–Zehnder modulator (MZM). Furthermore, we conduct analysis on the study of nonlinearity and dynamic range for a CO-OFDM receiver induced by the imbalance between the two ports of a balanced receiver. The input power dynamic range and tolerance to the relative-intensity-noise (RIN) are analyzed for the coherent balanced-receiver. / We then explore the transmission performance for high speed wavelength-division multiplexing (WDM) CO-OFDM systems with up to 1Tb/s per channel data rate under the impact of fiber nonlinearity. We find that the optimum fiber launch power increases almost linearly with the increase of data rate. A 7 dB optimum launch power difference is observed between 107-Gb/s and 1.07-Tb/s CO-OFDM systems. We also investigate the dispersion compensation fiber impact and filter concatenation effect issues when upgrading the 10-Gb/s to the future 100-Gb/s CO-OFDM systems. We identify three contributions to the Q degradation for the inline dispersion compensated WDM systems. We show that due to the high spectral efficiency, 100-Gb/s CO-OFDM signals have very high tolerance to the filter narrowing effect, and are resilient to the group ripples from the filter concatenation effect.

Optical source generation has attracted significant attention recently, especially in fiber optical communications. Today there is a growing a demand for optical source generation beyond conventional telecommunication wavelength bands. However, high quality and versatile optical source is generally not available over those wavelength bands due to the lack of efficient gain medium. Thanks to fiber optical parametric amplifier (FOPA), which is based on the third order nonlinear susceptibility of optical fibers, offers ultrafast response, wide-gain bandwidth, high gain and large frequency detune from the pump, serves as a promising candidate for signal amplification over those wavelength bands. By using the corresponding fiber optical parametric oscillator (FOPO) configuration, widely tunable source from continuous-wave (CW) to sub-picosecond pulses can be potentially generated to serve different applications from communication to biomedical imaging. In this thesis, we first demonstrate an all-fiber widely-tunable picosecond FOPO using highly-nonlinear fiber (HNLF). The tuning range is as wide as 250 nm, which is higher than previous picosecond FOPOs reported in the 1550-nm region. Second, time-dispersion tuning of the FOPO is investigated with fixed pump wavelength. It is a relatively simple and economic approach, and there will be no filter induced cavity loss. We then describe using FOPO to generated nearly-transform limited sub-picosecond pulses with a 60-nm tuning range. Another FOPO with a tuning range of 440-nm with dispersion-shifted fiber (DSF) as the gain medium is proposed and demonstrated. Compared with FOPOs demonstrated using HNLF as the gain medium, the use of DSF offers two key advantages: a wider tuning range and a narrower linewidth. In addition to picosecond FOPO, CW FOPO is also of great interest in fiber optical communications and biomedical imaging. We also demonstrate an all-fiber CW single-longitudinal-mode (SLM) FOPO with tuning range covers the S and L bands. SLM oscillation with a side-mode suppression ratio greater than 43 dB is achieved, which has been extended to 1-μm region under stable operation. Apart from static tuning, dynamic wavelength tuning of the FOPO is also discussed in this thesis with a cumulative speed exceeds 4,000,000 nm/s, which is higher than previous work reported in wavelength-swept FOPOs. The high-speed swept source would be useful in biomedical imaging and sensing applications. The amplification of the sub-picosecond pulses of the FOPO output is also investigated, for the first time to our knowledge, by using a fiber optical parametric chirped pulse amplifier(FOPCPA).The totally fiber-integrated nature of the whole system allows complete self-alignment and further integration to other fiber-based systems. All these research effort will show the versatility of FOPO techniques for generating wide range of optical sources for varies applications. These schemes may be useful in generating CW and short pulse for potential optical communication and biomedical imaging in non-conventional wavelength bands. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

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A theoretical study of an electrically passive, loss-compensated, optical position sensor is the goal of this project. Optical fiber sensors exploit light as the information carrier. Fiber-optic sensors consist of a constant light source launched into an optical fiber and transmitted to another point at which a measurement is made.In the proposed optical position sensor, a Light Emitting Diode (LED) produces a constant beam of light, which is channeled through an optical fiber to a Graded Index (GRIN) lens. This lens makes all the light rays parallel to one another, a process called collimation. The light then enters a polarizer which is a lens that further orders the light rays in a process called polarization.Then the light enters a chamber in which a doubly refracting (birefringent) crystal is situated. The crystal is a wedge, and thus has a varying thickness throughout its length. The light beam strikes the crystal, sending a spectrum, or spectral signature, that is distinct to the particular thickness of the crystal. That signature goes directly from the chamber housing the crystal into a lens called an analyzer which orders the light again through polarization. Then the light goes into another GRIN lens, and this GRIN lens focuses the light onto an optical fiber, which transmits the particular spectral signature of this light to an optical spectrum analyzer (OSA). The OSA uses a Photodiode Array to accept the incoming light, a device that takes in light and redistributes it to a monitor for display by the user. Such a device is called a detector. The thickness of the crystal that the light travels through is determined by the crystal's position.If the crystal rests on a platform which is connected to an object whose position must always be monitored, then the crystal will move as the object moves. The different spectral signatures shown on a monitor reveal different thicknesses of the crystal, which reveal different positions of the monitored object. The object whose position is measured is the measurand.The selected crystal is quartz. It has a 12.5-mm length, a width of 10.8-mm at its thinnest end, and a taper angle to the thickest end of only 0.008 degrees, which corresponds to a 0.17-micron difference between the two. This angle is called the polishing angle of the quartz. The quartz itself is called the active cell. The Photodiode Array Detector receives the spectral signature from the optical fiber, and that signature is projected on an OSA, which is software built-in to the computer. A mathematical program is used to evaluate the signature, and the position of the measurand is thereby revealed. How accurate the measurement is can be revealed by use of a control device. If the quartz crystal is moved by a measuring device, such as a micrometer, the distance that the crystal moved may be measured by the micrometer, as well as by the OSA. By comparing the two, the accuracy of the spectrograph, and the position it reveals, can be known. / Department of Physics and Astronomy

Graduation date: 1997

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: fiber amplifier; erbium; excited state absorption; rare earth fluorescence; neodymium. Includes bibliographical references (leaves 70-72).

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Joe C. Campbell. Vita. Includes bibliographical references.