Pulse Shaping Technology Research Articles

Pulse shaping, high average power narrow linewidth Er, Yb co-doped fiber amplifier

We demonstrate a high repetition rate, high average power narrow-linewidth fiber amplifier at 1.55 μm eye-safe waveband by using a very-large-mode-area active fiber doping Er and Yb, having a 60-μm-diameter core and a 600-μm-diameter inner cladding. A maximum average power reaches 16 W at a 10 kHz repetition rate for 600 ns pulses in the stimulated Brillouin scattering (SBS) free operation, which calculates to a 1.6 mJ pulse energy and 2.7 kW peak power. In addition, the peak power rises to 4.9 kW with 148 ns pulses at the onset of SBS. The signal peak is located at 1,551.15 nm with a 36 dB signal-to-noise ratio (SNR). In order to eliminate the pulse steepening, the pulse shaping technology using a triangular-like wave with a slower rising edge is applied on the input pulses. The half-width of the frequency-intensity spectrum from high-average-power fiber amplifier is about 1.02 MHz, approaching the Fourier transform limit.

Distance controlled resonant radiation from modulated Airy pulses

We investigate the dynamic evolution of resonant radiation (RR) emitted from modulated Airy pulses in an optical fiber with emphasis on the third-order dispersion. We show that the process of RRs emission strongly depends on the parameters of the predesigned spectral phase imposed on the Airy pulses, which is attributed to its linear focusing behaviors. A localized pulse formed at the distance-controlled focusing can effectively generate a large amount of RR after a prescribed propagation distance. At variance with the case of fundamental soliton, the minimum value of third-order dispersion required for the onset of RRs emission becomes much smaller for the modulated Airy pulse. The conversion efficiency of RRs increases with an increasing linear focusing point, but decreases with an increasing truncated coefficient. There is an optimal value of the truncated coefficient for the RRs having highest peak intensity and largest frequency shift. The impact of Raman effects on the RRs is also revealed. Our results not only provide a simply route to actively manipulate the efficient emission of RRs in conventional optical fiber, also could have significant implications of pulse shaping technology in novel highly efficient light sources based on the RRs emission for a variety of application.

Enhanced Dispersive Waves Generation via Sinusoidally Spectral Phase‐Modulated Pulses

AbstractThe dispersive waves (DWs) emitted from a Gaussian pulse with an initial sinusoidally spectral phase (SSP) modulation are investigated. By tailoring the modulation depth and frequency, the SSP results in complex pulses shape with a multipulses structure ranging from Airy‐like to pulse sequences having controllable delay and phase. These salient features are able to control and enhance the radiation frequency and energy conversion efficiency of the DWs. The resonant frequencies based on a modified phase‐matching condition are given, which agree with the numerical results obtained by solving the nonlinear Schrödinger equation directly. The results not only further extend the application of the pulse shaping technology in fiber optics, but also provide an alternative approach to manipulate the process of DWs emission which is relevant to the generation broadband supercontinuum as well as frequency comb.

Research on Dynamic Compressive Performance of Polypropylene Fiber-Reinforced High-Strength Concrete under Freeze-Thaw Environment

Existing studies have proved that the incorporation of polypropylene fiber can effectively improve the impact resistance of concrete. In this paper, the split Hopkinson pressure bar and digital pulse shaping technology are used to further study the dynamic compression performance and constitutive relationship of concrete in the cold regions under the deteriorating effect of freeze-thaw cycle, and obtain the dynamic increase factor. Studies have shown that polypropylene fiber-reinforced high-strength concrete has a strain rate enhancement effect. The number of freeze-thaw cycle times at low strain rates has an obvious effect on concrete deterioration, and the effect is weaker at higher strain rates. By comparing three typical dynamic strength growth factor models with the test results, after revising the model, the dynamic increase factor equations under different freeze-thaw circulation times were fitted. This research provides a basis for the design of durability and robustness of building structures in cold regions.

Effect of the Laser Processing Parameters on the Selective Laser Melting of TiC–Fe-Based Cermets

The influence of laser pulse shaping on the formation of TiC-Fe-based cermets with different laser process parameters is investigated. The impact of pulse shaping and laser melting peak power on the microstructural development and mechanical properties of SLM-built parts is addressed. This research focuses primarily on the process parameters required to produce crack-free components and includes investigations of mechanical properties such as microhardness and fracture toughness. To acquire optimal process parameters, samples were manufactured using pulse shaping technology with varying laser melting peak power and exposure time. The influence of laser melting peak power and pulse shape on microstructure development and phases was analyzed using a scanning electron microscope and X-ray diffraction.

Spectral Hump Formation in Visible Region of Supercontinuum from Shaped Femtosecond Laser Filamentation in Fused Silica

We investigate experimentally the local intensity control in the visible region of the supercontinuum (SC) generated from femtosecond laser filamentation in fused silica by using pulse shaping technology. Based on the genetic algorithm, we show that a distinct spectral hump at any preset wavelength can be formed in the blue-side extension. The local intensity control in the SC could improve the abilities of the SC applications.

Dynamic compression property of distill-water ice and impurity-water ice at high strain rates

The dynamic strength of three kinds of ice specimens at −18 ℃ were tested by the split Hopkinson pressure bar (SHPB) method. The pulse-shaping technology was used to achieve constant strain rate loading and stress equalization. The double-peak phenomena of reflection wave and transmission wave were explained by comparing with stress waveforms. The compression stress of distill-water ice in the strain rate range from 700 to 2 700 s−1 is 14.5−49.3 MPa, and it is much higher than the static data. Generally, the dynamic compression stress of the impurity-water ice is higher than that of the distill-water ice, this indicate that the ice specimens become harder after adding impurities, and the capability to resist deformation is enhanced. Compared with a-type and c-type specimens, the crack stress of b-type specimens becomes higher and its dispersiveness is lower. This indicates that the adhesive forces between impurities and ice crystals become stronger, and the expending and nucleate process of cracks is restrained.

Frequency-domain two-dimensional infrared spectroscopy using an acousto-optic programmable dispersive filter.

We report on multidimensional spectroscopy in the mid-infrared, performed using a calomel-based acousto-optic programmable dispersive filter. Although the associated spectral resolution is currently not as good as what has been previously reported using time-domain interferometers or other pulse-shaping technologies, the extreme compactness of the calomel crystal allows a straightforward implementation in a pre-existing pump-probe setup. Furthermore, the frequency-domain approach allows easy measurement of 2D slices of the multidimensional spectrum associated with a given pump frequency. We demonstrate our method with the measurement of the mid-infrared spectrum of carboxy-hemoglobin in three spectro-temporal dimensions.

A novel illumination‐efficient dimming control scheme based on reversed unipolar return‐to‐zero coding and circular (7, 1) modulation in high‐speed visible light communication

AbstractVisible light communication (VLC) is an emerging optical wireless communication, which combines lighting and communication simultaneously. In indoor VLC systems, the brightness of LEDs should be dimmed to a certain level to support the illumination function. In this article, we propose a novel dimming control scheme based on Reversed Unipolar Return‐to‐Zero (RURZ) coding and circular (7, 1) modulation. The dimming level is determined by the duty cycle ratio (DCR) of the RURZ codes. Contrary to traditional RZ coding, with the decrease of DCR, the component of high‐level signal in RURZ codes increases and could constantly keep LEDs on. Therefore, when the DCR is smaller, the time that the LED is on keeps longer and the illumination efficiency is higher. A special shaped 8‐QAM modulation scheme called circular (7, 1) is employed to obtain a wider dimming range and higher communication quality for its superiority in operation range and bit error ratio (BER) performance. Furthermore, pulse shaping technology is utilized to suppress the wide spectrum extended by RURZ coding and increase the spectral efficiency (SE) and the data rate. Theoretical analysis and experimental investigation demonstrate that the RURZ coded and circular (7, 1) modulated VLC system could achieve a wide dimming range with high illumination efficiency and high communication speed. An illumination efficiency improvement of 0.63 is successfully achieved at 30% DCR with a data rate of 1.35 GB/s over 1 m free space transmission.

Multielectron dissociative ionization of methane and formaldehyde molecules with optimally tailored intense femtosecond laser pulses

The multielectron dissociative ionization of CH4 and CH2O molecules has been investigated using optimum convolution of different dual tailored short laser pulses. Based on three dimensional molecular dynamics simulations and TDDFT approach, the dissociation probability is enhanced by designing the dual chirped-chirped laser pulses and chirped-ordinary laser pulses for formaldehyde molecule. However, it is interesting to notice that the sensitivity of enhanced dissociation probability into different tailored laser pulses is not significant for methane molecule. In this presented modifications, time variation of bond length, velocity, time dependent electron localization function and evolution of the efficient occupation states are presented to analyze the time evolution of molecular dynamics. This work is proved to be a potential way to reduce the controlling costs with a currently available pulse shaping technology.

Optical Modulator With a Near-Linear Field Response

The principle and characteristics of a linear optical modulator (LOM), which has a high field-response linearity, are discussed. A conventional Mach–Zehnder modulator (MZM) shows a nonlinear (sinusoidal) field response. This nonlinearity causes some problems in advanced digital coherent optical transmission systems that employ advanced multilevel modulation or pulse-shaping technologies. To solve this, we devised the LOM, which has a two-stage asymmetric lattice configuration with two MZMs driven with a pair of complementary voltage signals. The key idea of the LOM is to utilize the complementary output from the first MZM for generating the compensation signal. This enables us to improve the linearity without losing much optical power. Theoretical characteristics of the LOM are discussed in detail for the first time. To verify the LOM concept, we fabricated a linear in-phase-and-quadrature modulator (LIQM) with a hybrid configuration of silica planar lightwave circuits and a LiNbO3 chip with a high-speed phase-modulator array. Using the LIQM, we experimentally proved that the LOM provides a better loss-linearity trade-off than the conventional MZM does. The LIQM was also tested for 12.5-GBd 16-QAM modulation, and it generated a clear constellation where the nonlinearity of the MZM was compensated well.

Invited Review Article: Pump-probe microscopy.

Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.

Digital-Preprocessed Analog-Multiplexed DAC for Ultrawideband Multilevel Transmitter

High-speed digital-to-analog converters (DACs) are essential in advanced optical transmission systems, utilizing multilevel modulation formats and pulse-shaping technologies. Analog bandwidth of DACs is one of the major limiting factors for the system capacity. In this paper, we present an idea to extend the analog bandwidth of DACs by utilizing a digital preprocessor, two sub-DACs, and an analog multiplexer (AMUX). The AMUX is a high-speed linear selector, and a frequency-domain interpretation of the AMUX's function has led us to devise the digital preprocessing for a seamless extension of the analog bandwidth. This configuration, which we call a digital-preprocessed analog-multiplexed DAC, provides nearly doubled analog bandwidth compared to that of each subDAC with a symmetric configuration. The idea was verified by a transmission experiment with 160-Gb/s 80-Gbaud Nyquist four-level pulse amplitude modulation. In the experiment, we used subDACs with an analog bandwidth of ∼20 GHz in combination with an AMUX fabricated with InP heterojunction bipolar transistor technology.

Performance Optimization of Nyquist Signaling for Spectrally Efficient Optical Access Networks [Invited

In this work, Nyquist pulse-shaping technology is exploited for future implementations of optical access networks. The paper first presents technical issues regarding digital implementation of Nyquist spectral shaping for low-symbol-rate systems. Second, the potential benefits regarding mitigation of cross talk (linear and nonlinear) of Nyquist pulse shaping in symmetric and bidirectional wavelength-division multiplexing passive optical networks (WDM-PONs) are presented. Lastly, the paper proposes a WDM-PON solution employing self-coherent detection at the optical network unit and heterodyne coherent detection at the optical line terminal. In this proposed architecture, a multi-objective optimization strategy is developed to enhance the transmission performance of the Nyquist-shaped bands in full-duplex mode.

Femtosecond pulse shaping technology and its applications

By controlling the spectral amplitude, phase and polarization of the femtosecond laser pulse in the frequency domain, a shaped femtosecond laser pulse with almost arbitrary pulse shape in time domain can be obtained, and this femtosecond laser pulse shaping technique provides a new experimental tool to study the nonlinear interaction between light and atoms or molecules. In this paper, we introduce the development history, technical method, control technique and relevant applications of the femtosecond laser pulse shaping technique, and also carry out a prospect on the research trends of this technique.

The influence of ultra-fast temporal energy regulation on the morphology of Si surfaces through femtosecond double pulse laser irradiation

The effect of ultrashort laser-induced morphological changes upon irradiation of silicon with double pulse sequences is investigated under conditions that lead to mass removal. The temporal delay between twelve double and equal-energy pulses (Ep=0.24J/cm2 each, with pulse duration tp=430fs, 800nm laser wavelength) was varied between 0 and 14ps and a decrease of the damaged area, crater depth size and periodicity of the induced subwavelength ripples (by 3-4%) was observed with increasing pulse delay. The proposed underlying mechanism is based on the combination of carrier excitation and energy thermalization and capillary wave solidification and aims to provide an alternative explanation to the control of ripple periodicity by temporal pulse tailoring. This work demonstrates the potential of pulse shaping technology to improve nano/micro processing.

PAPR reduction based on improved Nyquist pulse shaping technology in OFDM-RoF systems

High peak-to-average power ratio (PAPR) is the main disadvantage in orthogonal frequency-division multiplexing (OFDM) communication systems, which also exists in OFDM-radio over fiber (RoF) systems. In this paper, we firstly analyze the impact of high PAPR on a 40 GHz OFDM-RoF system, and then describe the theory of Nyquist pulse shaping technology for reducing PAPR. To suppress PAPR further, an improved Nyquist pulse shaping technology is proposed, in which the distribution of original-data amplitude is changed by properly selecting the time-limited waveforms of the different subcarriers. We firstly apply the improved Nyquist pulse shaping technology to an OFDM-RoF system. The simulation results show that PAPR is effectively reduced by more than 2 dB with the bit error rate (BER) declining by about 0.125%.

Pulse shaping fiber laser at 15 μm

In this paper we present, for the first time to our knowledge, a new pulse shaping technology (modulation schemes for seed laser) used to mitigate pulse narrowing effect and SBS effect in a high energy Er:Yb codoped fiber master oscillator power amplifier system at 1.5 μm to obtain longer pulse duration and higher energy. An average power of over 1.3 W and a pulse energy of over 0.13 mJ were obtained at 10 kHz repetition rate with a pulse duration of 200 ns and near-diffraction-limited beam quality (M(2)<1.2).

整形飞秒脉冲的应用&lt;br&gt;Applications of Femtosecond Pulse Shaping

飞秒脉冲整形技术通过时空变换对飞秒脉冲进行处理，以产生可满足需要的各种波形，已经广泛应用在生物及医学成像、信号处理、飞秒化学等领域。介绍了整形飞秒脉冲在显微成像、飞秒化学和通信领域的应用，对比了应用整形飞秒脉冲后的实验效果较之前的改进。 The femtosecond pulse shaping technology, which transforms the femtosecond pulse through temporal-spatial conversion to generate various kinds of wave form in need, has been widely applied in the areas including image processing in biomedicine, signalling, femtochemistry, etc. The applications of femtosecond pulse shaping technology in the areas of microscopic imaging, femtochemistry and communications are introduced. The improvement in the results of experiments with the femtosecond pulse shaping technology compared to the former experiments without the technology is found out.

Low repetition rate high energy 15 µm fiber laser

In this paper, we report, for the first time, that by modulating pump beam to suppress ASE effect we realized ultra-low repetition rate output in an all fiber based Er:Yb codoped master oscillator power amplifiers (MOPA) system. Combined with pulse shaping technology, pulses with up to 205 µJ pulse energy and 200 ns pulse duration were obtained at Hz level.