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The Analysis and Optimization of Broadband Fiber Optical Parametric Amplifiers Pumped by Chirped Pulses
摘要： The broadband gain properties of fiber optical parametric amplifiers pumped both by one and two chirped pump pulses are investigated for the amplification of ultrashort pulses, analytically with the gain spectrum calculated in both the anti-Stokes and Stokes side. The influence of chirp rate and time delay on the gain spectrum of fiber-based optical parametric chirped pulse amplification is mainly explored. It is shown that, the chirp rate and time delay distinctly affect the second order dispersion and phase mismatching, leading to the gain variation, the two pump scheme provides broader gain bandwidth, especially under the condition of the two chirp rate with low absolute value, a genetic algorithm is employed to optimize the gain characteristics for realizing a flatter and wider, high gain that is useful for the ultrashort pulse system.
关键词： chirped pulse,ultrashort pulse,Broadband fiber optical parametric amplifiers,gain optimization
更新于2025-09-23 15:23:52
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Dynamic Behavioral Modeling of RF Power Amplifier Based on Time-Delay Support Vector Regression
摘要： A new, dynamic behavioral modeling technique, based on a time-delay support vector regression (SVR) method, is presented in this paper. As an advanced machine learning algorithm, the SVR method provides an effective option for behavioral modeling of radio frequency (RF) power amplifiers (PAs), taking into account the effects of both device nonlinearity and memory. The basic theory of the proposed modeling technique is given, along with a detailed model extraction procedure. Unlike traditional artificial neural network (ANN) techniques, which take time to determine the best configuration of the model, the SVR method can obtain the optimal model in short time, using the grid-search technique. An example of an optimal SVR model selection applied to an RF PA is also given; the performance of the selected model presents a big improvement when compared with the default SVR model. Experimental validation is performed using an LDMOS PA, a single device gallium nitride (GaN) PA, and a Doherty GaN PA, revealing that the new modeling methodology provides very efficient and extremely accurate prediction. Compared with traditional Volterra models, canonical piecewise linear models, and ANN-based models, the proposed SVR model gives improved performance with reasonable complexity. In addition, it is shown that the model can predict accurately the behavior of the PA under input power levels that are different from those under which it is extracted.
关键词： time delay,radio frequency (RF) power amplifiers (PAs),machine learning,Dynamic behavioral model,support vector regression (SVR)
更新于2025-09-23 15:23:52
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Exceptional Points of Degeneracy Induced by Linear Time-Periodic Variation
摘要： We present a general theory of exceptional points of degeneracy (EPD) in periodically time-variant systems. We show that even a single resonator with a time-periodic component is able to develop EPDs, contrary to parity-time- (PT) symmetric systems that require two coupled resonators. An EPD is a special point in a system parameter space at which two or more eigenmodes coalesce in both their eigenvalues and eigenvectors into a single degenerate eigenmode. We demonstrate the conditions for EPDs to exist when they are directly induced by time-periodic variation of a system without loss and gain elements. We also show that a single resonator system with zero time-average loss-gain exhibits EPDs with purely real resonance frequencies, yet the resonator energy grows algebraically in time since energy is injected into the system from the time-variation mechanism. Although the introduced concept and formalism are general for any time-periodic system, here, we focus on the occurrence of EPDs in a single LC resonator with time-periodic modulation. These findings have significant importance in various electromagnetic and photonic systems and pave the way for many applications, such as sensors, amplifiers, and modulators. We show a potential application of this time-varying EPD as a highly sensitive sensor.
关键词： exceptional points of degeneracy,time-periodic systems,sensors,modulators,LC resonator,amplifiers
更新于2025-09-23 15:23:52
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Optimization of a supercontinuum source based on tapered ordinary fibers
摘要： In this paper the generation of visible spectrum via optimized supercontinuum generation (SCG) in tapered ordinary fibers by ultrashort laser pulses is presented. The tunability of the visible part of the spectra is achieved by changing the pump pulse duration during operation. The optimization of the SCG is carried out by the investigation of the taper geometry with the emphasis on the downtapering section length. Its increase is found to be correlated to higher intensity in the visible part of the spectra. This is further supported by the results on spectra evolution before it enters the taper waist where an important transfer of the pump power to the shorter wavelengths is found.
关键词： fiber lasers,ytterbium-doped fiber amplifiers,supercontinuum generation
更新于2025-09-23 15:23:52
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A Square-Root-Based Memory Polynomial Model for Concurrent Dual-Band Digital Predistortion
摘要： In this letter, a novel 2-D square-root-based memory polynomial behavioral model is proposed. A new set of square-root-based basic functions is adopted to describe the characteristic of the predistorter. Since the proposed model has only two nested summations, the number of coefficients of the proposed model is greatly reduced compared with models which have three nested summations. The experimental results show that the proposed model can reduce the coefficients by more than 66.7% compared with the 2-D digital predistortion (2D-DPD) model. Moreover, the proposed model can achieve better adjacent channel power ratio (ACPR) performance. Compared with the 2D-DPD model and the simple online coefficient update model, the proposed model can improve the normalized mean-square error by 11 dB. Compared with the 2-D modified memory polynomial model, the proposed model can obtain similar ACPR performance with a shorter running time.
关键词： power amplifiers (PAs),Digital predistortion (DPD),dual band
更新于2025-09-23 15:22:29
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Characterization of Polarization Pulling in Fiber Optical Parametric Amplifiers
摘要： In fiber optical parametric amplifiers (FOPAs), the output states of polarization (SOPs) of both the signal and the idler are affected by the pump SOP through the polarization pulling effect. We proposed a normalized model to characterize the general dynamics of polarization pulling in degenerated pump FOPAs. By using this model, we determined the relationship between the output degree of polarization (DOP) and the gain of the FOPAs over three orders of magnitude changes in polarization-mode dispersion (PMD) coefficient. We demonstrated numerically that when fibers with typical PMD coefficients are used, the output signals of the FOPAs can achieve higher DOP than those of co-propagating fiber Raman amplifiers, which depends on whether the parametric gain is sufficiently large to compensate the PMD-induced phase mismatch. We also found that for FOPAs using different types of fibers with moderate PMD coefficients, this DOP-gain relationship exhibits highly similar behaviors. We thus adopted a set of modified empirical formulas to analyze this relationship. This formula can also describe the relationship between the output DOP and the conversion efficiency of the idler. The results indicate that in all cases studied, FOPAs achieve much stronger polarization pulling to the idlers than the signals.
关键词： Nonlinear optics,parametric oscillators and amplifiers,polarization-selective devices
更新于2025-09-23 15:22:29
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On-chip Optical Vector Quadrature De-multiplexer Proposal for QAM De-aggregation by Single Bi-directional SOA-based Phase-sensitive Amplifier
摘要： In this paper, a simple optical vector quadrature de-multiplexer (QD) scheme is proposed for de-aggregating input 10 Gbaud 16/32/64 quadrature amplitude modulation (QAM) signals into two pulse amplitude modulation (PAM) streams. The proposed QD is based on a single bi-directional degenerate phase-sensitive amplifier (PSA), where the wavelength and the polarization status of the extracted in-phase and quadrature components stay the same as the input signal. Since the proposed QD is realized using PSA based on semiconductor optical amplifier (SOA), it is also possible to realize an on-chip QD system, providing an integrated platform for optical signal processing. Through numerical simulation, the transfer characteristics of the proposed QD system show that the SOA-based PSA has a high phase-sensitive gain extinction ratio of 44.1 dB. The constellations, error vector magnitudes (EVMs), and bit-error rates (BERs) of the data streams after the de-aggregation are numerically investigated to verify the proposed QD scheme. For the 10 Gbaud 16/32/64 QAM signals with an input optical signal-to-noise ratio (OSNR) of 25 dB, the de-aggregated PAM4/PAM6/PAM8 signals show 6.1, 5.6, and 8.2 dB receiver OSNR improvements at the BER of 10?3, respectively. Also, to optimize the performance of the subsystem, the BER performance dependence on the phase difference between two arms in the subsystem is also examined. The simulation results reveal that the proposed QD can accomplish the function of optical vector de-aggregation well for the high-level QAM signals. The proposed QD can be applied to information de-aggregation, format conversion, and direct detection for optical vector signals, which may have great potential values for the flexible optical networks.
关键词： Optical fiber communication,semiconductor optical amplifiers,nonlinear optical devices,optical signal processing
更新于2025-09-23 15:22:29
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Repeater-enhanced distributed quantum sensing based on continuous-variable multipartite entanglement
摘要： Entanglement is a unique resource for quantum-enhanced applications. When employed in sensing, shared entanglement between distributed quantum sensors enables a substantial gain in the measurement sensitivity in estimating global parameters of the quantum sensor network. Loss incurred in the distribution of entanglement, however, quickly dissipates the measurement-sensitivity advantage enjoyed by the entangled quantum sensors over sensors supplied with local quantum resources. Here we present a viable approach to overcome the entanglement-distribution loss and show that the measurement sensitivity enabled by entangled quantum sensors beats that afforded by the optimum local resource. Our approach relies on noiseless linear amplifiers (NLAs) to serve as quantum repeaters. We show that, unlike the outstanding challenge of building quantum repeaters to suppress the repeaterless bound for quantum key distribution, NLA-based quantum repeaters for distributed quantum sensing are realizable by available technology. As such, distributed quantum sensing would become an application instance that benefits from quantum repeaters.
关键词： quantum repeaters,distributed quantum sensing,entanglement,quantum sensing,noiseless linear amplifiers
更新于2025-09-23 15:22:29
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Single-mode large-mode-area Er–Yb fibers with core based on phosphorosilicate glass highly doped with fluorine
摘要： Single-mode Er–Yb fibers with the core based on a phosphorosilicate glass matrix (up to 6.5 mol.% P2O5) highly doped with fluorine (up to 0.9 wt.%) were fabricated using an all-gas-phase modified chemical vapor deposition method. The core numerical aperture was in the range of 0.07–0.08 relative to the pure silica, which allowed us to increase the single-mode core diameter up to 20 μm. The slope efficiency in lasers based on the fabricated fibers reached 34% relative to the launched pump power.
关键词： fiber lasers,optical fibers,erbium–ytterbium fibers,erbium-doped fiber amplifiers
更新于2025-09-23 15:22:29
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Gain and bandwidth of the TM-mode gyrotron amplifiers
摘要： This work discusses the feasibility of gyrotron amplifiers using TM modes by investigating their dispersion relations starting with the relativistic Vlasov equation. For an input signal carrying a real frequency x, the complex wave number kz solved from the dispersion relation tells us the growth rate and the bandwidth of an amplifier. Three modes (TE01, TM11, and TM01) operating at the fundamental cyclotron harmonic (s ? 1) with the same cutoff frequency will be discussed. The results show that the TM11- and TM01-mode gyrotrons require much higher beam current than the TE01-mode gyrotron traveling-wave tube (gyro-TWT) amplifier. The TM modes are unsuitable for the gyro-TWT amplifier as discovered by other authors. The gyrotron backward-wave (gyro-BW) amplifier is also examined. The dispersion relations indicate that the TM modes are as good as the TE modes. The gain and bandwidth of the TM11-mode gyrotron backward-wave amplifier (gyro-BWA) are studied by changing either the magnet field or the beam voltage. The TM11 mode is suitable and has a decent bandwidth for the operation of the gyro-BW amplifier.
关键词： relativistic Vlasov equation,TE01 mode,TM modes,gyro-BW amplifier,TM11 mode,gyrotron amplifiers,gyro-TWT amplifier,TM01 mode,dispersion relations
更新于2025-09-23 15:21:21