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 Title
 STABLE OPTICAL FREQUENCY COMB GENERATION AND APPLICATIONS IN ARBITRARY WAVEFORM GENERATION, SIGNAL PROCESSING AND OPTICAL DATA MINING.
 Creator

Ozharar, Sarper, Delfyett, Peter, University of Central Florida
 Abstract / Description

This thesis focuses on the generation and applications of stable optical frequency combs. Optical frequency combs are defined as equally spaced optical frequencies with a fixed phase relation among themselves. The conventional source of optical frequency combs is the optical spectrum of the modelocked lasers. In this work, we investigated alternative methods for optical comb generation, such as dual sine wave phase modulation, which is more practical and cost effective compared to modelocked...
Show moreThis thesis focuses on the generation and applications of stable optical frequency combs. Optical frequency combs are defined as equally spaced optical frequencies with a fixed phase relation among themselves. The conventional source of optical frequency combs is the optical spectrum of the modelocked lasers. In this work, we investigated alternative methods for optical comb generation, such as dual sine wave phase modulation, which is more practical and cost effective compared to modelocked lasers stabilized to a reference. Incorporating these comblines, we have generated tunable RF tones using the serrodyne technique. The tuning range was ±1 MHz, limited by the electronic waveform generator, and the RF carrier frequency is limited by the bandwidth of the photodetector. Similarly, using parabolic phase modulation together with time division multiplexing, RF chirp extension has been realized. Another application of the optical frequency combs studied in this thesis is real time data mining in a bit stream. A novel optoelectronic logic gate has been developed for this application and used to detect an 8 bit long target pattern. Also another approach based on orthogonal Hadamard codes have been proposed and explained in detail. Also novel intracavity modulation schemes have been investigated and applied for various applications such as a) improving rational harmonic modelocking for repetition rate multiplication and pulse to pulse amplitude equalization, b) frequency skewed pulse generation for ranging and c) intracavity active phase modulation in amplitude modulated modelocked lasers for supermode noise spur suppression and integrated jitter reduction. The thesis concludes with comments on the future work and next steps to improve some of the results presented in this work.
Show less  Date Issued
 2008
 Identifier
 CFE0002388, ucf:47744
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0002388
 Title
 InjectionLocked Vertical Cavity Surface Emitting Lasers (VCSELs) for Optical Arbitrary Waveform Generation.
 Creator

Bhooplapur, Sharad, Delfyett, Peter, Li, Guifang, Christodoulides, Demetrios, Malocha, Donald, University of Central Florida
 Abstract / Description

Complex optical pulse shapes are typically generated from ultrashort laser pulses by manipulating the optical spectrum of the input pulses. This generates complex but periodic timedomain waveforms. Optical Arbitrary Waveform Generation (OAWG) builds on the techniques of ultrashort pulse?shaping, with the goal of making non?periodic, truly arbitrary optical waveforms. Some applications of OAWG are coherently controlling chemical reactions on a femtosecond time scale, improving the performance...
Show moreComplex optical pulse shapes are typically generated from ultrashort laser pulses by manipulating the optical spectrum of the input pulses. This generates complex but periodic timedomain waveforms. Optical Arbitrary Waveform Generation (OAWG) builds on the techniques of ultrashort pulse?shaping, with the goal of making non?periodic, truly arbitrary optical waveforms. Some applications of OAWG are coherently controlling chemical reactions on a femtosecond time scale, improving the performance of LADAR systems, high?capacity optical telecommunications and ultra wideband signals processing.In this work, an array of Vertical Cavity Surface Emitting Lasers (VCSELs) are used as modulators, by injectionlocking each VCSEL to an individual combline from an optical frequency comb source. Injectionlocking ensures that the VCSELs' emission is phase coherent with the input combline, and modulating its current modulates mainly the output optical phase. The multiGHz modulation bandwidth of VCSELs updates the output optical pulse shape on a pulsetopulse time scale, which is an important step towards true OAWG. In comparison, it is about a million times faster than the liquidcrystal modulator arrays typically used for pulse shaping! Novel components and subsystems of Optical Arbitrary Waveform Generation (OAWG) are developed and demonstrated in this work. They include:1.Modulators An array of VCSELs is packaged and characterized for use as a modulator for rapid?update pulse?shaping at GHz rates. The amplitude and phase modulation characteristics of an injection?locked VCSEL are simultaneously measured at GHz modulation rates.2.Optical Frequency Comb SourcesAn actively mode?locked semiconductor laser was assembled, with a 12.5 GHz repetition rate, ~ 200 individually resolvable comblines directly out of the laser, and high frequency stability. In addition, optical frequency comb sources are generated by modulation of a single frequency laser.3.Highresolution optical spectral demultiplexersThe demultiplexers are implemented using bulk optics, and are used to spatially resolve individual optical comblines onto the modulator array. 4.Optical waveform measurement techniques Several techniques are used to measure generated waveforms, especially for spectral phase measurements, including multiheterodyne phase retrieval. In addition, an architecture for discriminating between ultrashort encoded optical pulses with record high sensitivity is demonstrated.
Show less  Date Issued
 2014
 Identifier
 CFE0005466, ucf:50402
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005466
 Title
 DESIGN OF POLYNOMIALBASED FILTERS FOR CONTINUOUSLY VARIABLE SAMPLE RATE CONVERSION WITH APPLICATIONS IN SYNTHETIC INSTRUMENTATION AND SOFTWARE DEFINED RADIO.
 Creator

Hunter, Matthew, Mikhael, Wasfy, University of Central Florida
 Abstract / Description

In this work, the design and application of PolynomialBased Filters (PBF) for continuously variable Sample Rate Conversion (SRC) is studied. The major contributions of this work are summarized as follows. First, an explicit formula for the Fourier Transform of both a symmetrical and nonsymmetrical PBF impulse response with variable basis function coefficients is derived. In the literature only one explicit formula is given, and that for a symmetrical even length filter with fixed basis...
Show moreIn this work, the design and application of PolynomialBased Filters (PBF) for continuously variable Sample Rate Conversion (SRC) is studied. The major contributions of this work are summarized as follows. First, an explicit formula for the Fourier Transform of both a symmetrical and nonsymmetrical PBF impulse response with variable basis function coefficients is derived. In the literature only one explicit formula is given, and that for a symmetrical even length filter with fixed basis function coefficients. The frequency domain optimization of PBFs via linear programming has been proposed in the literature, however, the algorithm was not detailed nor were explicit formulas derived. In this contribution, a minimax optimization procedure is derived for the frequency domain optimization of a PBF with timedomain constraints. Explicit formulas are given for direct input to a linear programming routine. Additionally, accompanying Matlab code implementing this optimization in terms of the derived formulas is given in the appendix. In the literature, it has been pointed out that the frequency response of the ContinuousTime (CT) filter decays as frequency goes to infinity. It has also been observed that when implemented in SRC, the CT filter is sampled resulting in CT frequency response aliasing. Thus, for example, the stopband sidelobes of the DiscreteTime (DT) implementation rise above the CT designed level. Building on these observations, it is shown how the rolloff rate of the frequency response of a PBF can be adjusted by adding continuous derivatives to the impulse response. This is of great advantage, especially when the PBF is used for decimation as the aliasing band attenuation can be made to increase with frequency. It is shown how this technique can be used to dramatically reduce the effect of alias build up in the passband. In addition, it is shown that as the number of continuous derivatives of the PBF increases the resulting DT implementation more closely matches the ContinuousTime (CT) design. When implemented for SRC, samples from a PBF impulse response are computed by evaluating the polynomials using a socalled fractional interval, µ. In the literature, the effect of quantizing µ on the frequency response of the PBF has been studied. Formulas have been derived to determine the number of bits required to keep frequency response distortion below prescribed bounds. Elsewhere, a formula has been given to compute the number of bits required to represent µ to obtain a given SRC accuracy for rational factor SRC. In this contribution, it is shown how these two apparently competing requirements are quite independent. In fact, it is shown that the wordlength required for SRC accuracy need only be kept in the µ generator which is a single accumulator. The output of the µ generator may then be truncated prior to polynomial evaluation. This results in significant computational savings, as polynomial evaluation can require several multiplications and additions. Under the heading of applications, a new Wideband Digital Downconverter (WDDC) for Synthetic Instruments (SI) is introduced. DDCs first tune to a signal's center frequency using a numerically controlled oscillator and mixer, and then zoomin to the bandwidth of interest using SRC. The SRC is required to produce continuously variable output sample rates from a fixed input sample rate over a large range. Current implementations accomplish this using a prefilter, an arbitrary factor resampler, and integer decimation filters. In this contribution, the SRC of the WDDC is simplified reducing the computational requirements to a factor of three or more. In addition to this, it is shown how this system can be used to develop a novel computationally efficient FFTbased spectrum analyzer with continuously variable frequency spans. Finally, after giving the theoretical foundation, a real Field Programmable Gate Array (FPGA) implementation of a novel Arbitrary Waveform Generator (AWG) is presented. The new approach uses a fixed DigitaltoAnalog Converter (DAC) sample clock in combination with an arbitrary factor interpolator. Waveforms created at any sample rate are interpolated to the fixed DAC sample rate in realtime. As a result, the additional lower performance analog hardware required in current approaches, namely, multiple reconstruction filters and/or additional sample clocks, is avoided. Measured results are given confirming the performance of the system predicted by the theoretical design and simulation.
Show less  Date Issued
 2008
 Identifier
 CFE0002292, ucf:47844
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0002292