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William Shieh - One of the best experts on this subject based on the ideXlab platform.
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duobinary pulse shaping for Frequency Chirp enabled complex modulation
Optics Letters, 2016Co-Authors: Feng Yuan, Hamid Khodakarami, William ShiehAbstract:The Frequency Chirp of optical direct modulation (DM) used to be a performance barrier of optical transmission system, because it broadens the signal optical spectrum, which becomes more susceptible to chromatic dispersion induced inter-symbol interference (ISI). However, by considering the Chirp as Frequency modulation, the single DM simultaneously generates a 2-D signal containing the intensity and phase (namely, the time integral of Frequency). This complex modulation concept significantly increases the optical signal to noise ratio (OSNR) sensitivity of DM systems. This Letter studies the duobinary pulse shaping (DB-PS) for Chirp enabled DM and its impact on the optical bandwidth and system OSNR sensitivity. DB-PS relieves the bandwidth requirement, at the sacrifice of system OSNR sensitivity. As DB-PS induces a controlled ISI, the receiver requires one more tap for maximum likelihood sequence estimation (MLSE). We verify this modified MLSE with a 10-Gbaud duobinary PAM-4 transmission experiment.
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Towards high-order PAM utilizing large Frequency Chirp of directly modulated lasers
2016 Optical Fiber Communications Conference and Exhibition (OFC), 2016Co-Authors: Feng Yuan, William ShiehAbstract:We demonstrate the first dual-polarization PAM-8 transmission over 320-km SSMF with record electrical spectral-efficiency of 6-bit/s/Hz for optical PAM. SNR sensitivity of directly modulated laser based system can be greatly improved utilizing larger Frequency Chirp.
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Reinventing Optical Direct Modulation by Frequency Chirp
2016 Asia Communications and Photonics Conference (ACP), 2016Co-Authors: Feng Yuan, Qi Yang, Hamid Khodakarami, Yifei Wang, Jian Fang, William ShiehAbstract:Frequency Chirp used to be a transmission barrier for optical direct modulation (DM) systems. We reinvent DM by treating the Chirp as complex modulation, which significantly increases the OSNR sensitivity of DM based coherent systems.
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Frequency Chirp Supported Complex Modulation of Directly Modulated Lasers
Journal of Lightwave Technology, 2016Co-Authors: Feng Yuan, Qian Hu, William ShiehAbstract:The Frequency Chirp of the directly modulated lasers (DML) has long been regarded as the performance barrier preventing the DML from being employed in high-speed optical transmissions. In contrast, we regard the Chirp as the combination of intensity modulation (IM) and Frequency modulation in this paper. By utilizing coherent detection which provides a wavelength reference by the local oscillator, FM can be converted to phase modulation via time integral. Namely, we realize a 2 dimensional complex modulation (CM) using a single DML. The channel of a complex modulation of directly modulated lasers (CM-DML) is convolutional due to the integral operation. The maximum likelihood sequence estimation can be applied for demodulation. CM-DML offers more than 10-dB system OSNR sensitivity advantages over the conventional IM-DML using coherent detection, which shrinks the sensitivity penalty to 1000-km transmission of the standard single mode fiber. This reach record of the optical PAM reveals the great potentials of the CM-DML to replace the commercialized DP-QPSK products for medium reach applications.
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Enabling complex modulation using the Frequency Chirp of directly modulated lasers
2015 European Conference on Optical Communication (ECOC), 2015Co-Authors: Qian Hu, Feng Yuan, William ShiehAbstract:We demonstrate the first complex modulation and detection of PAM-4 and PAM-8 using a directly modulated laser with Frequency Chirp. Through coherent detection and differential phase assisted Viterbi decoding, PAM-4 system shows >9-dB OSNR sensitivity advantage over the intensity-only decision.
K.g.h. Baldwin - One of the best experts on this subject based on the ideXlab platform.
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control of Frequency Chirp in nanosecond pulsed laser spectroscopy 3 spectrotemporal dynamics of an injection seeded optical parametric oscillator
Journal of The Optical Society of America B-optical Physics, 2007Co-Authors: Richard T White, Yabai He, Mitsuhiko Kono, K.g.h. BaldwinAbstract:Complicated spectrotemporal processes are associated with the generation of signal and idler output pulses on a nanosecond timescale in an injection-seeded optical parametric oscillator (OPO). The mechanisms of such spectrotemporal dynamics are revealed by numerical simulation, including innovative modeling of instantaneous-Frequency profiles and Frequency Chirp. These simulations are in satisfactory agreement with optical-heterodyne measurements of output from a nanosecond-pulsed OPO system that is based on periodically poled KTiOPO4, pumped at 532 nm by a Nd:YAG laser and injection-seeded at a signal wavelength of ∼842 nm. Frequency Chirp in narrowband signal output pulses from such an OPO system has previously been observed to depend on phase mismatch between the pump, signal, and idler waves, and also on the pump-pulse energy. Our simulations accurately predict this behavior and yield realistic estimates of the Frequency Chirp, optical bandwidth, and spectral purity of the signal output pulse as it evolves, including effects that are not readily observed directly. This approach provides insight into instrumental conditions that facilitate continuously tunable, single-longitudinal-mode operation of such a pulsed OPO system, with optical bandwidth as close as possible to the Fourier-transform limit.
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control of Frequency Chirp in nanosecond pulsed laser spectroscopy 1 optical heterodyne Chirp analysis techniques
Journal of The Optical Society of America B-optical Physics, 2004Co-Authors: Richard T White, Yabai He, Mitsuhiko Kono, K.g.h. BaldwinAbstract:We evaluate ways to analyze optical-heterodyne measurements of Frequency Chirp in pulsed, single-longitudinal-mode output from lasers (or other coherent light sources) that operate on nanosecond time scales. The instantaneous Frequency is extracted from the beat signal generated between a continuous-wave reference beam and the output of the pulsed source. Three analysis techniques are tested: Fourier-transform, direct curve fitting, and electronic mixing. We use synthetic beat waveforms based on actual experimental parameters to evaluate the three methods and apply these Chirp-measurement techniques to an injection-seeded optical parametric oscillator system.
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pulsed injection seeded optical parametric oscillator with low Frequency Chirp for high resolution spectroscopy
Optics Letters, 2003Co-Authors: Richard T White, Yabai He, Mitsuhiko Kono, K.g.h. BaldwinAbstract:An injection-seeded optical parametric oscillator (OPO), based on periodically poled KTiOPO4 and pumped by a Frequency-doubled, nanosecond-pulsed Nd:YAG laser, generates continuously tunable, single-longitudinal-mode, pulsed output at ~842nm for high-resolution spectroscopy. Optical-heterodyne measurements show that the OPO Frequency Chirp increases linearly with detuning from the free-running (unseeded) OPO Frequency and can be maintained as low as 10 MHz. Other factors affecting Chirp are identified.
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Frequency Chirp in a pulsed, single-longitudinal-mode, injection-seeded optical parametric oscillator
2003 European Quantum Electronics Conference. EQEC 2003 (IEEE Cat No.03TH8665), 2003Co-Authors: R.t. White, Y. He, M. Kono, K.g.h. BaldwinAbstract:Heterodyne technique is used to measure the optical phase characteristics of a ns-pulsed periodically poled KTiOPO/sub 4/ (PPKTP) OPO that is injection-seeded by a cw tunable diode laser (TDL). How Frequency Chirp in a TDL-seeded PPKTP OPO is affected by various experimental conditions is investigated.
Didier Erasme - One of the best experts on this subject based on the ideXlab platform.
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Frequency Chirp stabilization in semiconductor distributed feedback lasers with external control
Proceedings of SPIE, 2012Co-Authors: Frederic Grillot, Jean-Guy Provost, Khalil Kechaou, Bruno Thedrez, Didier ErasmeAbstract:It is well known that current modulation in diode lasers generates amplitude (AM) and optical Frequency (FM) modulations. The Frequency Chirp under direct current modulation originates from variations in the carrier density and from the finite difference in carrier density between the laser on and off states. Modulation of the carrier density modulates the gain and the optical index causing the resonant mode to shift. This Frequency Chirp broadens the spectrum, which is a serious limitation for high-speed applications and optical fiber communications. At low frequencies, thermal effects also alter the Frequency Chirp. The aim of this paper is to show that the laser's Frequency Chirp can be modified using an external control technique. The Chirp response is evaluated via the determination of the Chirp-to-power ratio (CPR) through a Mach-Zehnder interferometer. Experiments demonstrate that when an external optical feedback is properly adjusted, the CPR can be severely decreased over a wide range of modulation frequencies as compared to the free-running case. These preliminary results obtained on quantum well distributed feedback lasers (QW DFB) with low normalized coupling coefficient (κL) demonstrate how to stabilize the CPR through the DFB facet phase effects or parameters such as the linewidth enhancement factor. In order to confirm this Frequency Chirp engineering, selfconsistent calculations based on the transfer matrix method are also presented.
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Self-injected semiconductor distributed feedback lasers for Frequency Chirp stabilization
Optics Express, 2012Co-Authors: Khalil Kechaou, Jean-Guy Provost, Bruno Thedrez, Frederic Grillot, Didier ErasmeAbstract:It is well known that semiconductor distributed feedback lasers (DFB) are key devices for optical communications. However direct modulation applications are limited by the Frequency Chirp induced by current modulation. We demonstrate that a proper external control laser operation leads to Chirp-to-power ratio (CPR) stabilization over a wide range of modulation frequencies as compared to the free-running case. Under experimentally selected optical feedback conditions, the CPR decreases significantly in the adiabatic regime from about 650 MHz/mW in the solitary case down to 65 MHz/mW. Experimental results are also confirmed by numerical investigations based on the transfer matrix method. Simulations point out the possible optimization of the CPR in the adiabatic regime by considering a judicious cavity design in conjunction with a proper external control. These results demonstrate important routes for improving the transmission performance in optical telecommunication systems.
Randolph L. Moses - One of the best experts on this subject based on the ideXlab platform.
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EUSIPCO - Sparse target recovery performance of multi-Frequency Chirp waveforms
2011Co-Authors: Emre Ertin, Lee C. Potter, Randolph L. MosesAbstract:Imaging radars employ wideband linear Frequency modulation (LFM) waveforms to achieve high resolution while maintaining moderate sampling rates through restricting the target support to a known range interval and using stretch (deramp) processing. In recent work motivated by compressive sensing principles, multi-Frequency extensions of the Chirp waveforms were proposed to obtain randomized projections of range profiles. This paper considers the sparse target recovery problem with Chirp transmit waveforms and their multi-Frequency extensions. We derive the sensing matrix for multi-Frequency Chirp waveforms and study its coherence properties. We show that multi-Frequency Chirp waveforms result in sensing matrices with lower coherence between the columns resulting in improved target estimation performance compared to the standard LFM waveform.
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Sparse target recovery performance of multi-Frequency Chirp waveforms
2011 19th European Signal Processing Conference, 2011Co-Authors: Emre Ertin, Lee C. Potter, Randolph L. MosesAbstract:Imaging radars employ wideband linear Frequency modulation (LFM) waveforms to achieve high resolution while maintaining moderate sampling rates through restricting the target support to a known range interval and using stretch (deramp) processing. In recent work motivated by compressive sensing principles, multi-Frequency extensions of the Chirp waveforms were proposed to obtain randomized projections of range profiles. This paper considers the sparse target recovery problem with Chirp transmit waveforms and their multi-Frequency extensions. We derive the sensing matrix for multi-Frequency Chirp waveforms and study its coherence properties. We show that multi-Frequency Chirp waveforms result in sensing matrices with lower coherence between the columns resulting in improved target estimation performance compared to the standard LFM waveform.
Feng Yuan - One of the best experts on this subject based on the ideXlab platform.
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duobinary pulse shaping for Frequency Chirp enabled complex modulation
Optics Letters, 2016Co-Authors: Feng Yuan, Hamid Khodakarami, William ShiehAbstract:The Frequency Chirp of optical direct modulation (DM) used to be a performance barrier of optical transmission system, because it broadens the signal optical spectrum, which becomes more susceptible to chromatic dispersion induced inter-symbol interference (ISI). However, by considering the Chirp as Frequency modulation, the single DM simultaneously generates a 2-D signal containing the intensity and phase (namely, the time integral of Frequency). This complex modulation concept significantly increases the optical signal to noise ratio (OSNR) sensitivity of DM systems. This Letter studies the duobinary pulse shaping (DB-PS) for Chirp enabled DM and its impact on the optical bandwidth and system OSNR sensitivity. DB-PS relieves the bandwidth requirement, at the sacrifice of system OSNR sensitivity. As DB-PS induces a controlled ISI, the receiver requires one more tap for maximum likelihood sequence estimation (MLSE). We verify this modified MLSE with a 10-Gbaud duobinary PAM-4 transmission experiment.
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Towards high-order PAM utilizing large Frequency Chirp of directly modulated lasers
2016 Optical Fiber Communications Conference and Exhibition (OFC), 2016Co-Authors: Feng Yuan, William ShiehAbstract:We demonstrate the first dual-polarization PAM-8 transmission over 320-km SSMF with record electrical spectral-efficiency of 6-bit/s/Hz for optical PAM. SNR sensitivity of directly modulated laser based system can be greatly improved utilizing larger Frequency Chirp.
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Reinventing Optical Direct Modulation by Frequency Chirp
2016 Asia Communications and Photonics Conference (ACP), 2016Co-Authors: Feng Yuan, Qi Yang, Hamid Khodakarami, Yifei Wang, Jian Fang, William ShiehAbstract:Frequency Chirp used to be a transmission barrier for optical direct modulation (DM) systems. We reinvent DM by treating the Chirp as complex modulation, which significantly increases the OSNR sensitivity of DM based coherent systems.
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Frequency Chirp Supported Complex Modulation of Directly Modulated Lasers
Journal of Lightwave Technology, 2016Co-Authors: Feng Yuan, Qian Hu, William ShiehAbstract:The Frequency Chirp of the directly modulated lasers (DML) has long been regarded as the performance barrier preventing the DML from being employed in high-speed optical transmissions. In contrast, we regard the Chirp as the combination of intensity modulation (IM) and Frequency modulation in this paper. By utilizing coherent detection which provides a wavelength reference by the local oscillator, FM can be converted to phase modulation via time integral. Namely, we realize a 2 dimensional complex modulation (CM) using a single DML. The channel of a complex modulation of directly modulated lasers (CM-DML) is convolutional due to the integral operation. The maximum likelihood sequence estimation can be applied for demodulation. CM-DML offers more than 10-dB system OSNR sensitivity advantages over the conventional IM-DML using coherent detection, which shrinks the sensitivity penalty to 1000-km transmission of the standard single mode fiber. This reach record of the optical PAM reveals the great potentials of the CM-DML to replace the commercialized DP-QPSK products for medium reach applications.
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Enabling complex modulation using the Frequency Chirp of directly modulated lasers
2015 European Conference on Optical Communication (ECOC), 2015Co-Authors: Qian Hu, Feng Yuan, William ShiehAbstract:We demonstrate the first complex modulation and detection of PAM-4 and PAM-8 using a directly modulated laser with Frequency Chirp. Through coherent detection and differential phase assisted Viterbi decoding, PAM-4 system shows >9-dB OSNR sensitivity advantage over the intensity-only decision.