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Narrow linewidth DBR laser based on high order Bragg grating defined by i-line lithography
摘要： In order to obtain narrow linewidth semiconductor laser around 1564 nm, we design a distributed Bragg reflector (DBR) laser with high-order Bragg gratings (HOBGs) using butterfly encapsulation. The DBR laser is fabricated only by i-line lithography technology with grating period of 4.84 μm, groove width of 1.5 μm and grating length of 72 μm on a strip width of 4 μm. The 1mm-long devices achieved an output power of 9.9 mW and a side mode suppression ratio (SMSR) more than 30 dB without facet coating at an injection current of 80 mA. The lasers showed ultra-narrow Lorentz linewidth of 70 KHz. This paper provides a simple method for large-scale production of narrow linewidth semiconductor lasers.
关键词： narrow linewidth spectrum,Semiconductor laser,high-order grating,distributed Bragg reflector laser
更新于2025-11-28 14:23:57
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Research on Spatially Adaptive High-Order Total Variation Model for Weak Fluorescence Image Restoration
摘要： Confocal laser scanning microscopy (CLSM) has emerged as one of the most advanced ?uorescence cell imaging techniques in the ?eld of biomedicine. However, ?uorescence cell imaging is limited by spatial blur and additive white noise induced by the excitation light. In this paper, a spatially adaptive high-order total variation (SA-HOTV) model for weak ?uorescence image restoration is proposed to conduct image restoration. The method consists of two steps: optimizing the deconvolution model of the ?uorescence image by the generalized Lagrange equation and alternating direction method of multipliers (ADMM); using spatially adaptive parameters to balance the image ?delity and the staircase e?ect. Finally, an comparison of SA-HOTV model and Richardson-Lucy model with total variation (RL-TV model) indicates that the proposed method can preserve the image details ultimately, reduce the staircase e?ect substantially and further upgrade the quality of the restored weak ?uorescence image.
关键词： weak ?uorescence,spatially adaptive high-order total variation (SA-HOTV),image restoration,confocal microscopy
更新于2025-09-23 15:23:52
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Pressure dependence of high order harmonic generation in nitrogen molecular gas and atmospheric air
摘要： The effect of the variation of the gas pressure on the high harmonic generation (HHG) from nitrogen molecular gas (N2) and atmospheric air with ultrashort intense laser pulses is measured. The optimum pressure in the interaction region of a gas jet for maximizing the HHG yield is determined for both gases. Enhancement of the HHG output and its extension to higher harmonic orders are observed around the optimum pressure value of 0.33 bar. Theoretical calculations based on one-dimensional models explain this effect and provide reasonable agreement with experimental results.
关键词： Femtosecond laser,Conversion efficiency,High-order harmonic generation (HHG),Phase matching,XUV radiation,Pressure optimization
更新于2025-09-23 15:23:52
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High-spectral-efficiency 600-Gbps/carrier Transmission Using PDM-256QAM Format
摘要： High-capacity carrier signals with high-order modulation are being considered for data center interconnection (DCI) applications as they can reduce the cost per bit by decreasing the number of devices and increasing fiber capacity. However, signal quality degradation due to device imperfections affecting the frequency response has limited the capacity per carrier of PDM-256QAM signals to under 400 Gbps. Here, it is possible to use a calibration method for dealing with device imperfections wherein a fixed equalizer separately calibrates the frequency response of the transmitter and receiver. Our previous study showed that PDM-256QAM signals at up to 48 GBaud could be transmitted over 100 km, while it used an experimental setup with total 3-dB analog bandwidth of 13 GHz and 20 GHz for transmitter and receiver, respectively. A micro-integrable tunable laser assembly (μITLA) with a typical linewidth of 20 kHz, maximum under 100 kHz. Actual data center interconnection (DCI) applications, however, are expected to use dense wavelength division multiplexing (WDM), so in this study, we examined transmission of 10-WDM 48-GBaud PDM-256QAM signals in a 50-GHz grid and evaluated the WDM penalties. The resulting spectral efficiency (SE) of 600-Gbps/carrier WDM transmissions was as high as 12.02 bit/s/Hz.
关键词： optical,digital coherent,fiber,optical transmission,signal processing,digital communication,high-order quadrature amplitude modulation
更新于2025-09-23 15:23:52
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High order harmonic generation in solids: a review on recent numerical methods
摘要： Interaction of intense lasers with solid materials offers an alternative way to achieve high-order harmonic generation (HHG). Since the underlying mechanisms of the harmonic emission remain uncertain, a large number of theoretical studies have been proposed to explain the experimental findings in this fast-growing field. Here, we review the primary numerical methods and present a brief perspective of HHG in solids.
关键词： Ultrafast laser,strong field,numerical simulations,laser-crystal interaction,solid materials,high-order harmonic generation
更新于2025-09-23 15:23:52
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Dynamical distortions of structural signatures in molecular high-order harmonic spectroscopy
摘要： We study the signature of two-center interferences in molecular high-order harmonic spectra, with an emphasis on the spectral phase. With the help of both ab initio computations based on the time-dependent Schr?dinger equation and the molecular strong-field approximation (SFA) as developed by Chiril? et al. [Phys. Rev. A 73, 023410 (2006)] and Faria [Phys. Rev. A 76, 043407 (2007)], we observe that the phase behavior is radically different for the short and the long trajectory contributions. By means of Taylor expansions of the molecular SFA, we link this effect to the dynamics of the electron in the continuum. More precisely, we find that the value of the electric field at recombination time plays a crucial role in the shape of the destructive interference phase jump.
关键词： molecular spectroscopy,spectral phase,strong-field approximation,two-center interferences,time-dependent Schr?dinger equation,high-order harmonic generation
更新于2025-09-23 15:23:52
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New Current-Mode Multipliers by CNTFET-Based n-Valued Binary Converters
摘要： This paper presents new Binary Converters (or current-mode compressors) by the usage of carbon nanotube field effect transistors. The new designs are made of three parts: 1) the input currents which are converted to voltage; 2) threshold detectors; and 3) the output current flow paths. In addition, an 8×8-bit multiplier is considered as a bench mark to estimate their efficiency degrees. The first approach is based on high-order Binary Converters, and the second one is only composed of 4BCs and Half Adders.
关键词： high-order compressor,current-mode logic,multiplier,CNTFET,Binary Converter
更新于2025-09-23 15:22:29
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Modulational instability and homoclinic orbit solutions in vector nonlinear Schr?dinger equation
摘要： Modulational instability has been used to explain the formation of breathers and rogue waves qualitatively. In this paper, we show modulational instability can be used to explain the structure of them in a quantitative way. In the first place, we develop a method to derive general forms for Akhmediev breathers, rogue waves and their multiple or high order ones in a N-component nonlinear Schr?dinger equations. The existence condition for each pattern is clarified clearly with a compact algebraic equation. Moreover, we show that the existence condition of ABs and RWs is consistent with the dispersion relation of the linear stability analysis on the background solution. The results further deepen our understanding on the quantitative relations between modulational instability and homoclinic orbits solutions.
关键词： general multi-high-order rogue wave,vector nonlinear Schr?dinger equation,modulational instability analysis,Akhmediev breathers
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Saint Petersburg, Russia (2018.10.22-2018.10.23)] 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Band-Pass ARC-Filter Based on the Classical Wien Bridge with the Pole Frequency Rise and Independent Adjustment of the Main Parameters
摘要： A new topology of the band-pass active RC filter (BP) based on the classic Wien bridge is proposed. This scheme, implemented on two Op-Amps, is recommended for the use as a second-order link in more complex BPs. The analysis of the modified band-pass ARC filter is carried out, the main parameters of the BP are found. The computer simulation of the developed PF tuning algorithm is completed. The graphs of changes in the frequency response and phase response when changing various parameters of the BP are obtained. It is shown that in the considered BP an independent adjustment of the main parameters is ensured - transmission coefficient in the passband, pole attenuation and pole frequency.
关键词： ARC filter,trimming,active RC filter,band-pass RC filter,high-order BP,Wien bridge,parameter adjustment
更新于2025-09-23 15:22:29
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Correlation Properties of Additive Linear High-Order Markov Chains
摘要： The aim of this paper is to study the statistical properties of the Nth order correlated Markov chains, which have a large application area in the UWB signal generation, transmission and processing. The state space of the chain under consideration is supposed to be a finite set of real numbers. The transition probability function is assumed to be homogeneous, additive and linear with respect to the values of random variable. The equations relating the correlation functions of the sequence to the memory function, which determined by the transition probability function, are derived and solved. The obtained analytical solutions for the correlation functions are compared with the results of numerical simulations. Examples of possible correlation scenarios in additive linear chains of higher orders are given. The obtained results can be useful both in analytical and simulative context, for example, for the modeling of the UWB transmission channels, for the refinement of transmitter and receiver design, for the enhancement of coding methods suitable for the UWB communication systems.
关键词： UWB channels,higher order Markov chain,memory function,linear additive high-order Markov chain,correlation function
更新于2025-09-23 15:21:21