Nonlinear Pulse Shaping Research Articles

Ultrafast reverse saturable absorption and all-optical computing with boron dipyrromethene (BODIPY) chromophore derivatives

Ultrafast reverse saturable absorption (RSA) in chromophore-based borondipyrro-methenes (BODIPYs) derivatives, 1,7-Diphenyl-3,5-bis(9,9-dimethyl-9H-fluoren-2-yl)-boron-diuoride-azadipyrromethene (ZL-61) and 1,7-Diphenyl-3,5-bis(4-(1,2,2-triphenyl-vinyl)phenyl)-boron-diuoride azadipyrromethene (ZL-22), has been theoretically analyzed with femtosecond (fs) laser pulses at 800 nm and 850 nm. The results are in good agreement with the reported experimental results. The effect of input pulse intensity, pulse width, nonlinear absorption (NLA) coefficients, sample thickness and laser pulse shaping on transmittance has been studied and optimized for high contrast and low-power operation. All-optical fs NOT and the universal NOR and NAND Boolean logic gates have been designed with ZL-61 and ZL-22. The logic gates with top-hat input pulse profile have a sharp switch ON/OFF time compared to the Gaussian input laser profile. Ultrafast operation at relatively low pump intensities opens up exciting prospects for the applicability of BODIPY derivatives for ultrafast low-power all-optical computing and information processing.

Design of nonlinear pulse shaper for flexible repetition rate ultrashort pulse generation

Nonlinear pulse shaping based on Mamyshev regenerator is a powerful approach for ultrashort pulse generation. The performance strongly depends on the initial seed parameters. We investigate and design a nonlinear pulse shaper seeded by a long pulsed gain-switched laser diode for generation of high quality ultrashort pulses with flexible repetition rate. The shaper architecture provides more flexibility on the input diode requirements and can yield shorter pulses with the improved laser relative intensity noise. The system optimization is based on numerical simulations mapping the favourable parameters at each stage of the system and enabling identification of limiting factors.

Massive MIMO Precoding and Spectral Shaping With Low Resolution Phase-Only DACs and Active Constellation Extension

Nonlinear precoding and pulse shaping are jointly considered in multi-user massive multiple-input multiple-output (MIMO) systems with low resolution D/A-converters (DACs) in terms of algorithmic approach as well as large system performance. Two design criteria are investigated: the mean squared error (MSE) with active constellation extension (ACE) and the symbol error rate (SER). Both formulations are solved based on a modified version of the generalized approximate message passing (GAMP) algorithm. Furthermore, theoretical performance results are derived based on the state evolution analysis of the GAMP algorithm. The MSE based technique is extended to jointly perform over-the-air (OTA) spectral shaping and precoding for frequency-selective channels, in which the spectral performance is characterized at the transmitter and at the receiver. Simulation and analytical results demonstrate that the MSE based approach yields the same performance as the SER based formulation in terms of uncoded SER. The analytical results provide good performance predictions up to medium SNR. Substantial improvements in detection, as well as spectral performance, are obtained from the proposed combined pulse shaping and precoding approach compared to standard linear methods.

Modelling self-similar parabolic pulses in optical fibres with a neural network

We expand our previous analysis of nonlinear pulse shaping in optical fibres using machine learning [Opt. Laser Technol., 131 (2020) 106439] to the case of pulse propagation in the presence of gain/loss, with a special focus on the generation of self-similar parabolic pulses. We use a supervised feedforward neural network paradigm to solve the direct and inverse problems relating to the pulse shaping, bypassing the need for direct numerical solution of the governing propagation model.

Artificial neural networks for nonlinear pulse shaping in optical fibers

We use a supervised machine-learning model based on a neural network to predict the temporal and spectral intensity profiles of the pulses that form upon nonlinear propagation in optical fibers with both normal and anomalous second-order dispersion. We also show that the model is able to retrieve the parameters of the nonlinear propagation from the pulses observed at the output of the fiber. Various initial pulse shapes as well as initially chirped pulses are investigated.

Frequency Comb Generation at 800 nm in Waveguide Array Quantum Well Diode Lasers

A traveling wave model for a semiconductor diode laser based on quantum wells is presented as well as a comprehensive theoretical model of the lasing dynamics produced by the intensity discrimination of the nonlinear mode-coupling in a waveguide array. By leveraging a recently developed model for the detailed semiconductor gain dynamics, the temporal shaping effects of the nonlinear mode-coupling induced by the waveguide arrays can be characterized. Specifically, the enhanced nonlinear pulse shaping provided by the waveguides are capable of generating stable frequency combs wavelength of 800 nm in a GaAs device, a parameter regime not feasible for stable combline generation using a single waveguide. Extensive numerical simulations showed that stable waveform generation could be achieved and optimized by an appropriate choice of the linear waveguide coupling coefficient, quantum well depth, and the input currents to the first and second waveguides. The model provides a first demonstration that a compact, efficient and robust on-chip comb source can be produced in GaAs.

High-energy femtosecond pulse shaping, compression, and contrast enhancement using multicore fiber

Nonlinear spatiotemporal dynamics of femtosecond pulses in a hexagonal seven-core silica fiber pumped by a sub-μJ 370fs Er:fiber chirped pulse amplification (CPA) system were studied. Nonlinear pulse shaping and compression in the central core and pedestal coupling to the outer cores were directly measured by frequency-resolved optical gating. Further compression of the pulses spectrally broadened in the multicore fiber down to 53fs was demonstrated. Two orders of magnitude contrast enhancement of the pulses after compression was observed.

Nonlinear sculpturing of optical pulses with normally dispersive fiber-based devices

We present a general method to determine the parameters of nonlinear pulse shaping systems based on pulse propagation in a normally dispersive fiber that are required to achieve the generation of pulses with various specified temporal properties. The nonlinear shaping process is reduced to a numerical optimization problem over a three-dimensional space, where the intersections of different surfaces provide the means to quickly identify the sets of parameters of interest. We also show that the implementation of a machine-learning strategy can efficiently address the multi-parameter optimization problem being studied.

Application of nonlinear pulse shaping of femtosecond pulse generation in a fiber amplifier at 500 MHz repetition rate

We numerically and experimentally demonstrate that a nonlinear pulse shaping technique based on pre-chirping management in a short gain fiber can be exploited to improve the quality of a compressed pulse. With prior tuning of the pulse chirp, the amplified pulse express different nonlinear propagating processes. A spectrum with s flat top and more smooth wings, showing a similariton feature, generates with the optimal initial pulse chirp, and the shortest pulses with minimal pulse pedestals are obtained. Experimental results show the ability of nonlinear pulse shaping to enhance the quality of compressed pulses, as theoretically expected.

Second harmonic generation and pulse shaping in positively and negatively spatially dispersive nanowaveguides: comparative analysis

Comparative analysis of second harmonic generation in ordinary and backward-wave settings is presented. Extraordinary properties of frequency doubling nonlinear optical reflectivity and pulse shaping through phase matching of ordinary and backward electromagnetic waves in the nanowaveguides with mixed negative/positive spatial dispersion is demonstrated with numerical simulations.

Nonlinear pulse shaping-assisted ultrashort optical pulse generation

An ultrashort optical pulse generator based on nonlinear pulse shaping is proposed and demonstrated. With a spatial light modulator placed prior to a high nonlinearity fiber, \((\mu +\lambda )\)-evolution strategy is introduced to dynamically adjust the transfer function of spatial light modulator both in phase and in amplitude. Nearly chirp-free 2.2-ps optical Gaussian pulse and 0.73-ps optical Nyquist pulse with a repetition rate of 25 GHz are both achieved in simulation. The scheme also has a certain tolerance to phase quantization error of the spatial light modulator and power fluctuation.

Ultrafast Nonlinear Fiber Optics: Single-Pulse Supercontinua and Specialty-Shape Pulses

Needs of science and technology for compact laser sources with specially shaped pulse waveforms or ultra-broad spectrum can be satisfied on the fiber-optic platform. Here we address transformation of ultrashort optical pulses in a variety of optical fibers aiming synthesis of specially shaped pulses and single-pulse flat-top supercontinuum. Results are discussed in the context of possible applications and experimental implementations. Full Text: PDF References J. M. Dudley, G. Genty, and S. Coen, "Supercontinuum generation in photonic crystal fiber", Rev. Mod. Phys. 78(4), 1135?1184 (2006). CrossRef A. M. Heidt, A. Hartung, G. W. Bosman, P. Krok, E. G. Rohwer, H. Schwoerer, and H. Bartelt, "Coherent octave spanning near-infrared and visible supercontinuum generation in all-normal dispersion photonic crystal fibers", Opt. Express, 19(4), pp. 3775?3787, (2011). CrossRef A. M. Heidt, J. Rothhardt, A. Hartung, H. Bartelt, E. G. Rohwer, J. Limpert, and A. Tünnermann, "High quality sub-two cycle pulses from compression of supercontinuum generated in all-normal dispersion photonic crystal fiber", Opt. Express 19, 13873-13879 (2011). CrossRef A. Hartung, A. M. Heidt, and H. Bartelt, "Design of all-normal dispersion microstructured optical fibers for pulse-preserving supercontinuum generation", Opt. Express 19, 7742-7749 (2011). CrossRef S. Boscolo and C. Finot, "Nonlinear Pulse Shaping in Fibres for Pulse Generation and Optical Processing", International Journal of Optics 2012, 159057 (2012) CrossRef J. M. Dudley, C. Finot, D. J. Richardson, G. Millot, "Self-similarity in ultrafast nonlinear optics", Nature Physics 3, pp. 597-603, (2007). CrossRef C. Finot, J.M. Dudley, B. Kibler, D.J. Richardson, G. Millot, "Optical Parabolic Pulse Generation and Applications", IEEE J. Quantum Electron. 45, pp. 1482-1489 (2009). CrossRef C. Finot, S. Pitois, and G. Millot, "Regenerative 40 Gbit/s wavelength converter based on similariton generation", Opt. Lett. 30, 1776?1778 (2005). CrossRef Parmigiani, P. Petropoulos, M. Ibsen, and D. J. Richardson, "Pulse retiming based on XPM using parabolic pulses formed in a fiber Bragg grating", IEEE Photon. Technol. Lett. 18, 829?831 (2006). CrossRef S. Boscolo, S. K. Turitsyn, and K. J. Blow, "Time domain all-optical signal processing at a RZ optical receiver", Opt. Express 13, 6217?6227 (2005). CrossRef T. T. Ng, F. Parmigiani, M. Ibsen, Z. Zhang, P. Petropoulos, and D. J. Richardson, "Compensation of Linear Distortions by Using XPM With Parabolic Pulses as a Time Lens", IEEE Photon. Technol. Lett. 20, 1097?1099 (2008). CrossRef S. O. Iakushev, O. V. Shulika, and I.A. Sukhoivanov, "Passive nonlinear reshaping towards parabolic pulses in the steady-state regime in optical fibers", Opt. Commun. 285, 4493?4499, (2012). CrossRef I. A. Sukhoivanov, S. O. Iakushev, O. V. Sulika, A. Díez, M. Andrés, "Femtosecond parabolic pulse shaping in normally dispersive optical fibers", Opt. Express, 21, pp. 17769-17785, (2013). CrossRef S. O. Iakushev, O. V. Shulika, I. A. Sukhoivanov, V. I. Fesenko, M. V. Andres, and H. Sayinc, "Formation of ultrashort triangular pulses in optical fibers", Opt. Express, 22(23), pp. 29119- 29134 CrossRef

Nonlinear polarization rotation-induced pulse shaping in a stretched-pulse ytterbium-doped fiber laser

We report on controllable pulse shaping in a Yb-doped stretched-pulse fiber laser followed by a high-power chirped pulse amplifier. We demonstrate that the pulses after an extra-cavity grating pair change their intensity profile from Lorentz to Gaussian and then to sech2 shapes by adjusting the intra-cavity polarization through a quarter-wave plate inside the fiber laser cavity. The laser pulses with different pulse shapes exhibit pulse-to-pulse amplitude fluctuation of ∼ 1.02%, while the sech2-shaped pulse train is provided with a more stable free-running repetition rate as a result of the stronger self-phase modulation in the fiber laser cavity than Lorentz- and Gaussian-shaped pulse trains.

Nonlinear Load and RLC Pulse Shaping Surge Generator Models in Simulation Environment

The present study was performed in order to understand how a nonlinear load affects the characteristics of the RLC pulse shaping surge generator waveforms under simulation studies. The obtained results were compared when analytical equations were used as source models for both 1.2/50 µs voltage & 8/20 µs current impulses. Three circuit models; Capacitor Bank generator, Combination waveform generator and Schaffner generator were evaluated under nonlinear loads varied from 10Ω to 106 Ω for voltage impulses and for current impulses it was from 10-4 Ω to 1 Ω. As it can perceive from the analysis, delay time, rise time and FWHM remain unchanged throughout the tested impedance range when used model equations as generator sources. It was found that for voltage impulses, these values were 4.95 μs, 1.20 μs and 81.8 μs respectively. For current impulses, these values were 16.2 μs, 8.02 μs and 20.7 μs respectively. However results obtained for generator circuit models shows that delay time, rise time and FWHM deviated from above values up to maximum of 35.15 %, 106.67 % & 115.16 % respectively for voltage impulses. For current impulses these deviations were up to maximum of 79.63 %, 48.75 % & 39.61 % respectively. The deviations were due to influence caused by the nonlinear load to the generator circuit parameters and effective internal impedance.

Nonlinear Load and RLC Pulse Shaping Surge Generator Models in Simulation Environment

The present study was performed in order to understand how a nonlinear load affects the characteristics of the RLC pulse shaping surge generator waveforms under simulation studies. The obtained results were compared when analytical equations were used as source models for both 1.2/50 µs voltage & 8/20 µs current impulses. Three circuit models; Capacitor Bank generator, Combination waveform generator and Schaffner generator were evaluated under nonlinear loads varied from 10Ω to 106 Ω for voltage impulses and for current impulses it was from 10-4 Ω to 1 Ω. As it can perceive from the analysis, delay time, rise time and FWHM remain unchanged throughout the tested impedance range when used model equations as generator sources. It was found that for voltage impulses, these values were 4.95 μs, 1.20 μs and 81.8 μs respectively. For current impulses, these values were 16.2 μs, 8.02 μs and 20.7 μs respectively. However results obtained for generator circuit models shows that delay time, rise time and FWHM deviated from above values up to maximum of 35.15 %, 106.67 % & 115.16 % respectively for voltage impulses. For current impulses these deviations were up to maximum of 79.63 %, 48.75 % & 39.61 % respectively. The deviations were due to influence caused by the nonlinear load to the generator circuit parameters and effective internal impedance.

Nonlinear pulse shaping and polarization dynamics in mode-locked fiber lasers

We review our recent progress on the study of new nonlinear mechanisms of pulse shaping in passively mode-locked fiber lasers. These include a mode-locking regime featuring pulses with a triangular distribution of the intensity, and spectral compression arising from nonlinear pulse propagation. We also report on our recent experimental studies unveiling new types of vector solitons with processing states of polarization for multi-pulse and tightly bound-state soliton (soliton molecule) operations in a carbon nanotube (CNT) mode-locked fiber laser with anomalous dispersion cavity.

Flattop pulse generation based on the combined action of active mode locking and nonlinear polarization rotation

A pulse-width-tunable 10GHz flattop pulse (FTP) train is generated based on the combined action of active mode locking and nonlinear polarization rotation pulse shaping. Although the setup was previously used for other applications, the mechanism of FTP generation based on it is first analyzed and confirmed in the experiment. An FTP with pulse width tunable from 12 to 20ps by changing polarization controllers is generated within the wavelength tuning range of 20nm. The generated pulse reveals good stability, with the side mode suppression ratio of 65dB, timing jitter of 92fs, and amplitude fluctuation of 0.36%.

Spectrally Equalized Frequency Comb Generation in Multistage Parametric Mixer With Nonlinear Pulse Shaping

A novel approach to improve the flatness of wide-band parametric frequency combs is presented. The method relies on nonlinear pulse shaping prior to parametric mixing in a comb-generating device. The parametric comb is generated in a cavity-less multistage shock-wave mixer, using continuous-wave (CW) laser as comb seed. The pulse shaping is accomplished in a regenerative stage incorporating nonlinear optical/amplifying loop mirror (NOLM/NALM) and provides near-ideal seeds for spectrally equalized frequency comb generation in the output mixing stage. The new technique was implemented separately on two comb generators with a coarse (100 GHz) and dense (10 GHz) tone spacing. A 4 dB flatness over 100 nm is achieved with wide-pitched comb, while the fine-pitched device yielded 1500 tones and possessed sub-2 dB spectral flatness over 120 nm bandwidth.

Nonlinear Pulse Shaping in Fibres for Pulse Generation and Optical Processing

The development of new all-optical technologies for data processing and signal manipulation is a field of growing importance with a strong potential for numerous applications in diverse areas of modern science. Nonlinear phenomena occurring in optical fibres have many attractive features and great, but not yet fully explored, potential in signal processing. Here, we review recent progress on the use of fibre nonlinearities for the generation and shaping of optical pulses and on the applications of advanced pulse shapes in all-optical signal processing. Amongst other topics, we will discuss ultrahigh repetition rate pulse sources, the generation of parabolic shaped pulses in active and passive fibres, the generation of pulses with triangular temporal profiles, and coherent supercontinuum sources. The signal processing applications will span optical regeneration, linear distortion compensation, optical decision at the receiver in optical communication systems, spectral and temporal signal doubling, and frequency conversion.

Experimental research of triangular optical pulse generation in normal dispersive fiber

Generation of triangular optical pulses in conventional normal dispersive (ND) fiber is experimentally realized using a passive nonlinear pulse shaping method based on a combination of pulse pre-chirping, group-velocity dispersion and self-phase modulation in a section of ND fiber. It is found that by optimizing the parameters of launching pulse power level and ND fiber length, high-quality triangular optical pulses with nearly constant gradients of leading and trailing edges and linear frequency chirp profiles can be obtained for a wide range of different pulse pre-chirping values. For different pulse pre-chirpings, high launch power is required for triangular optical pulse generation. The tolerance of triangular pulse formation to ND fiber length and launch power level is improved with the increase of pulse pre-chirping, which means that it is easy to obtain triangular pulses for higher pulse pre-chirping.