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ABSTRACT: Microwave photonic filters utilizing optical frequency combs have been shown to achieve narrow bandwidths, high stopband attenuation as well as easy tunability of center frequency and bandwidth. The ability to achieve smooth apodization of optical frequency comb spectrum to specific spectral profiles is important to obtain high stopband attenuations. Previously, by utilizing an optical pulse shaper to crease a Gaussian profile spectrum, filters with high stopband attenuation and Gaussian passbands were demonstrated. However this technique is flexible and can be used to easily program the filter passband profile. We demonstrate this by creating filters with a flat top passband. We also demonstrate that the stopband attenuation can be significantly enhanced by utilizing frequency combs which achieve the necessary spectral shapes directly from the source. By generating an optical comb with a smooth quasi-Gaussian profile, we demonstrate filters with a record >;60dB stopband attenuation.
Microwave Symposium Digest (MTT), 2011 IEEE MTT-S International; 07/2011
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ABSTRACT: We report, for the first time to the best of our knowledge, spectral phase
characterization and line-by-line pulse shaping of an optical frequency comb
generated by nonlinear wave mixing in a microring resonator. Through
programmable pulse shaping the comb is compressed into a train of
near-transform-limited pulses of \approx 300 fs duration (intensity full width
half maximum) at 595 GHz repetition rate. An additional, simple example of
optical arbitrary waveform generation is presented. The ability to characterize
and then stably compress the frequency comb provides new data on the stability
of the spectral phase and suggests that random relative frequency shifts due to
uncorrelated variations of frequency dependent phase are at or below the 100
microHertz level.
03/2011;
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ABSTRACT: We use intensity and phase modulators to develop a 10-GHz optical frequency comb whose shape can be easily switched between extremely flat-topped (38-lines within 1-dB) and Gaussian (36-lines over 15-dB dynamic range).
IEEE Photonics Society, 2010 23rd Annual Meeting of the; 12/2010
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ABSTRACT: We demonstrate the application of optical combs to implement tunable programmable microwave photonic filters. We design well-known multi-tap microwave photonic filters; however, the utilization of an optical comb with a dispersive medium enables scaling of these filters to a large number of taps. We use optical line-by-line pulse shaping to program tap weights, which allows us to shape the filter's bandpass. Our scheme is simple and easily implementable, which provides filters with arbitrary tap weights. As an example, we implement filters with Gaussian apodized tap weights, which achieve more than 35-dB sidelobe suppression. Our experiments provide usable bandwidth, free of sampling spurs, over a Nyquist zone of 5 GHz, equal to half of our 10-GHz comb repetition frequency. Furthermore, we introduce a simple new technique, based on a programmable optical delay line, to uniformly tune the passband center frequency across the free spectral range (FSR) of the filter, ideally without changing the bandpass shape. We demonstrate this scheme by tuning the filter over a full FSR, equal to 10.4 GHz in our experiments.
IEEE Transactions on Microwave Theory and Techniques 12/2010; · 1.85 Impact Factor
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ABSTRACT: We present an optical frequency comb with, to the best of our knowledge, unprecedented flatness, high stability and a large number of spectral lines, which allows for high quality pulse compression using single mode fiber.
Microwave Photonics (MWP), 2010 IEEE Topical Meeting on; 11/2010
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ABSTRACT: We demonstrate for the first time 2.5V RF arbitrary waveform generation, at frequencies of interest to ultra-wideband (UWB) applications, enabled by high power handling photodiodes. The effect of the photodiodes' amplitude & phase linearity is also explored.
Microwave Photonics (MWP), 2010 IEEE Topical Meeting on; 11/2010
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ABSTRACT: We demonstrate tunable programmable microwave photonic filters based on optical frequency combs. The utilization of optical comb enables to scale multi tap filters to large number of taps. By using optical line-by-line pulse shaping to program tap weights, we shape the filter's bandpass. In contrast to our previous work, we demonstrate a much simplified technique based on intensity modulator biased at its minimum transmission which results in double sideband with carrier suppression. We use a programmable optical delay line to uniformly tune the bandpass filter center frequency uniquely across half of the free spectral range. Our new scheme is very simple and easily implementable which provides filters with arbitrary tap weights. As an example we implement a filter with Gaussian apodized tap weights which we tune over 0-5.2 GHz with sidelobe suppression in the range 26-31 dB.
Microwave Photonics (MWP), 2010 IEEE Topical Meeting on; 11/2010
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ABSTRACT: For the first time, we report lightwave system experiments testing a concept for all-order polarization-mode-dispersion (PMD) compensation based on optical pulse shaping. Our results demonstrate compensation of PMD with > 50-ps average differential group delay, well into the all-order regime, in a 40-Gb/s return-to-zero on-off keying experiment.
IEEE Photonics Technology Letters 09/2010; · 2.19 Impact Factor
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ABSTRACT: By using wavelength-parallel polarimetry and hyperfine optical pulse shaping for sensing and compensation of the frequency-dependent Jones matrix, optical compensation of all-order polarisation mode dispersion is experimentally demonstrated with >40 ps mean differential group delay in a 10 Gbit/s à 2 Pol-Mux system (10% RZ).
Electronics Letters 06/2010; · 0.96 Impact Factor
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ABSTRACT: We demonstrate a simple scheme which uses only an intensity modulator and an OSA to achieve low-power (~100 nW, 10 aJ/pulse at 10 GHz), self-referenced, amplitude and phase characterization of optical frequency combs and 100% duty factor arbitrary waveforms.
Optical Fiber Communication (OFC), collocated National Fiber Optic Engineers Conference, 2010 Conference on (OFC/NFOEC); 04/2010
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ABSTRACT: Developing a full-fledged cost-based XQuery optimizer is a fairly complex task. Nowadays, there is little knowledge concerning suitable cost formulae and optimization strategies for exploring and constraining the tremendously large search space. To allow for a fair assessment of different optimization strategies, physical algebra operators, and indexing approaches, we developed an extensible optimization framework. The framework is accompanied by a supportive visual explain tool that enables user interactions to refine the inspection and the comprehension of the query plans proposed. Using this tool, the optimizer can be dynamically reconfigured and the impact of different optimization strategies on the final query execution plan can be immediately visualized.
Data Engineering (ICDE), 2010 IEEE 26th International Conference on; 04/2010
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ABSTRACT: We demonstrate fast characterization ( ~ 1.4 ??s) of both the dispersion and dispersion slope of long optical fiber links ( ~ 25 km) using dual quadrature spectral interferometry with an optical frequency comb. Compared to previous spectral interferometry experiments limited to fiber lengths of meters, the long coherence length and the periodic delay properties of frequency combs, coupled with fast data acquisition, enable spectral interferometric characterization of fibers longer by several orders of magnitude. We expect that our method will be useful to recently proposed lightwave techniques like coherent wavelength-division multiplexing and to coherent modulation formats by providing a real-time monitoring capability for the link dispersion. Another area of application would be in stabilization of systems which perform frequency and timing distribution over long fiber links using stabilized optical frequency combs.
IEEE Photonics Technology Letters 03/2010; · 2.19 Impact Factor
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ABSTRACT: We present an electric-field cross-correlation technique that uses a pair of frequency combs to sweep phase and group delays independently without a mechanical stage. We demonstrate this technique for characterization of optical arbitrary waveforms composed of ~30 spectral lines from a 10 GHz frequency comb. Rapid data acquisition (tens of microseconds) enables interferometric spectral phase measurement of pulses subject to propagation over 20 km of optical fiber.
Optics Letters 12/2009; 34(24):3875-7. · 3.40 Impact Factor
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ABSTRACT: Millimeter-wave (MMW) electrical power spectra are flexibly synthesized by integrating fast wavelength switching, optical frequency comb generation, spectral line-by-line pulse shaping, and optical-to-electrical conversion. Control over generated RF power spectra is exercised through the choice both of the optical parent waveforms and of the wavelength switching patterns. Discrete or comb-like MMW power spectra are generated using periodic wavelength switching, while nearly continuous MMW spectra can be obtained when wavelengths are switched according to a pseudorandom bit stream.
IEEE Photonics Technology Letters 10/2009; · 2.19 Impact Factor
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ABSTRACT: In summary we demonstrate the application of programmable microwave photonic phase filters to compensate a broadband antenna dispersion at a receiver front which enables to increase data rate by overcoming distortion due to antenna nonlinear spectral phase. We also show that dispersion-compensation combined with matched filtering arbitrary waveforms can be used in waveform detection. Our scheme is programmable and broadband and can be used to enhance the performance of ultrawideband wireless systems, in particular satellite communications and radar systems.
Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
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ABSTRACT: We report the first quantitative study of intensity noise induced in line-by-line pulse shaping in response to time-varying changes in the comb frequency offset. Controllable comb linewidth broadening is synthesized through frequency dithering of a continuous-wave laser that is fed to a phase modulator. An electrical spectrum analyzer is used to examine the current power spectra of shaped time-domain intensity waveforms subject to comb frequency noise. A theoretical model predicting a 20 dB/decade scaling relation between the dither-induced noise and the frequency dither amplitude is presented. A numerical simulation method capable of predicting the precise form of the RF power spectrum in the presence of optical frequency dithering is explained. Two line-by-line shaping cases are considered in detail. Experimental data are in excellent agreement with the simulated results down to frequency dithers of a few tenths of a percent of the comb spacing. Tolerances to laser frequency fluctuations are given for several simple pulse shaping examples. The effect of pulse shaper parameters is also discussed.
IEEE Journal of Quantum Electronics 07/2009; · 1.88 Impact Factor
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ABSTRACT: We demonstrate experimental post-compensation of ultra-wideband (UWB) antenna dispersion at a receiver front-end by using programmable microwave photonic phase filtering. After the received RF signal is modulated onto an optical carrier, we utilize a hyperfine resolution optical pulse shaper to apply the conjugate of its spectral phase in the optical domain. After optical-to-electronic conversion, this yields an electrical waveform, which is compressed to bandwidth-limited duration. Further we use this technique in two schemes: a radar configuration in which we resolve two close echoes from different paths, which initially interfere and mask each other due to the dispersed response of the antenna link, and a spread-time UWB transmission configuration in which we retrieve and compress a distorted signal received in line-of-sight. To our knowledge, this is the first experimental demonstration of dispersion post-compensation of UWB RF waveforms to approach the ultimate bandwidth-limited resolution, as well as identification of such signals by matched filtering and compression. Our technique is programmable and offers potential to enhance performance in UWB radar and communications.
IEEE Transactions on Microwave Theory and Techniques 05/2009; · 1.85 Impact Factor
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ABSTRACT: We demonstrate ultra-compact spectral shaping via thermo-optically tunable multiple-channel micro-ring resonators on a silicon chip, and combine it with frequency-time mapping to achieve controllable photonic radio-frequency waveform generation.
IEEE Lasers and Electro-Optics Society, 2008. LEOS 2008. 21st Annual Meeting of the; 12/2008
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ABSTRACT: A new self-referenced technique for measuring the amplitude and phase of individual optical frequency comb lines is demonstrated. Spectral frequency shear is obtained from sum frequency generation of a signal comb with wavelength separated reference tones.
IEEE Lasers and Electro-Optics Society, 2008. LEOS 2008. 21st Annual Meeting of the; 12/2008
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ABSTRACT: The performance of asynchronous coherent time-spreading optical code-division multiple-access (OCDMA) systems is evaluated semi-analytically and the results are compared with those of spectral coding OCDMA systems using ultrashort pulses. The fundamental multi-access interference limited performances are predicted to be identical.
Journal of Lightwave Technology 09/2008; · 2.78 Impact Factor
