Fission Of Higher-order Solitons Research Articles

Neuromorphic Computing via Fission-based Broadband Frequency Generation.

The performance limitations of traditional computer architectures have led to the rise of brain-inspired hardware, with optical solutions gaining popularity due to the energy efficiency, high speed, and scalability of linear operations. However, the use of optics to emulate the synaptic activity of neurons has remained a challenge since the integration of nonlinear nodes is power-hungry and, thus, hard to scale. Neuromorphic wave computing offers a new paradigm for energy-efficient information processing, building upon transient and passively nonlinear interactions between optical modes in a waveguide. Here, an implementation of this concept is presented using broadband frequency conversion by coherent higher-order soliton fission in a single-mode fiber. It is shown that phase encoding on femtosecond pulses at the input, alongside frequency selection and weighting at the system output, makes transient spectro-temporal system states interpretable and allows for the energy-efficient emulation of various digital neural networks. The experiments in a compact, fully fiber-integrated setup substantiate an anticipated enhancement in computational performance with increasing system nonlinearity. The findings suggest that broadband frequency generation, accessible on-chip and in-fiber with off-the-shelf components, may challenge the traditional approach to node-based brain-inspired hardware design, ultimately leading to energy-efficient, scalable, and dependable computing with minimal optical hardware requirements.

Physical origin of higher-order soliton fission in nanophotonic semiconductor waveguides

Supercontinuum generation in Kerr media has become a staple of nonlinear optics. It has been celebrated for advancing the understanding of soliton propagation as well as its many applications in a broad range of fields. Coherent spectral broadening of laser light is now commonly performed in laboratories and used in commercial “white light” sources. The prospect of miniaturizing the technology is currently driving experiments in different integrated platforms such as semiconductor on insulator waveguides. Central to the spectral broadening is the concept of higher-order soliton fission. While widely accepted in silica fibers, the dynamics of soliton decay in semiconductor waveguides is yet poorly understood. In particular, the role of nonlinear loss and free carriers, absent in silica, remains an open question. Here, through experiments and simulations, we show that nonlinear loss is the dominant perturbation in wire waveguides, while free-carrier dispersion is dominant in photonic crystal waveguides.

Tunable Supercontinuum Generated in a Yb3+-Doped Microstructure Fiber Pumped by Ti:Sapphire Femtosecond Laser**Supported by the National Natural Science Foundation of China under Grant No 61735011, the Natural Science Foundation of Hebei Province under Grant Nos F2016203389 and F2018105036, the Science and Technology Research Project of College and University in Hebei Province under Grant No BJ2017108, the Open Subject of Jiangsu

We experimentally demonstrate that a tunable supercontinuum (SC) can be generated in a Yb3+-doped microstructure fiber by the concept of wavelength conversion with a Ti:sapphire femtosecond (fs) laser as the pump. Experimental results show that an emission light around 1040nm in an anomalous dispersion region is first generated and amplified by fs pulses in the normal dispersion region. Then, SC spectra from 1100 to 1380nm and 630 to 840nm can be achieved by combined effects of higher-order soliton fission and Raman soliton self-frequency shift in the anomalous dispersion region and self-phase modulation, dispersive wave, and four-wave mixing in the normal dispersion region. It is also demonstrated that the 20nm change of pump results in a 280nm broadband shift of soliton and the further red-shift of soliton is limited by OH− absorption at 1380 nm.

Experimental observation of mid-infrared higher-order soliton fission in a tapered tellurite microstructured optical fiber

The evolution of mid-infrared (MIR) higher-order soliton fission in a tapered tellurite microstructured optical fiber (TMOF) is experimentally investigated. From ∼30 to 80 mW, the redshift of the first fundamental soliton is obvious. From ∼80 to 120 mW, two fundamental solitons are obtained by the fission of higher-order solitons. The redshift of the first fundamental soliton almost stops because the increased pump power is preferentially distributed to the second fundamental soliton. From ∼120 to 180 mW, an obvious redshift of the first fundamental soliton is observed again, and a third fundamental soliton is obtained at ∼180 mW. The evolution of each soliton is determined by the power distribution, which is, to the best of our knowledge, reported for the first time.

Theoretical and experimental research of supercontinuum generation in an ytterbium-doped fiber amplifier.

The theoretical research of supercontinuum (SC) generation in a fiber amplifier system has been seldom reported. For the purpose of further understanding the mechanism of SC generation in fiber amplifiers, we propose a combined numerical model of the laser rate equations and the generalized non-linear Schrödinger equation to simulate the amplification of 1060 nm picosecond pulses and their spectral broadening in an ytterbium-doped fiber amplifier. The calculation results of this model are compared with the experimental results under the same conditions and a good agreement is achieved. We find that the pulse is gain amplified initially, and then dominated by stimulated Raman scattering in the normal dispersion region. In anomalous dispersion region, modulation instability, higher-order soliton fission and soliton self-frequency shift dominates the spectral broadening. It is found numerically and experimentally that the length of the gain fiber and the 976 nm pump power are the most imperative parameters to control the output power, spectral range and flatness of the SC. The pulse width of signal pulse also plays a part in influencing SC generation. The results verify that our model is promising for analyzing the physical processes of pulse evolution and SC generation in a fiber amplifier system.

Nonlinear fiber optics: its history and recent progress [Invited

This review begins with an historical introduction to the field of nonlinear fiber optics and then focuses on the propagation of short optical pulses inside optical fibers. The underlying nonlinear Schrodinger equation is used to discuss the nonlinear phenomenon of self-phase modulation that leads to the formation of solitons in the presence of anomalous dispersion. Recent work on supercontinuum generation is reviewed with emphasis on the important nonlinear processes, such as the fission of higher-order solitons and intrapulse Raman scattering. Applications of fiber-based supercontinuum sources are also discussed in diverse areas ranging from biomedical imaging to frequency metrology. The last part describes applications resulting from nonlinear phenomena, such as cross-phase modulation, stimulated Raman scattering, and four-wave mixing.

On-chip two-octave supercontinuum generation by enhancing self-steepening of optical pulses

Dramatic advances in supercontinuum generation have been made recently using photonic crystal fibers, but it is quite challenging to obtain an octave-spanning supercontinuum on a chip, partially because of strong dispersion in high-index-contrast nonlinear integrated waveguides. We show by simulation that extremely flat and low dispersion can be achieved in silicon nitride slot waveguides over a wavelength band of 500 nm. Different from most of previously reported supercontinua that were generated either by higher-order soliton fission in anomalous dispersion regime or by self-phase modulation in normal dispersion regime, a two-octave supercontinuum from 630 to 2650 nm (360 THz in total) can be generated by enhancing self-steepening in pulse propagation in nearly zero dispersion regime, when an optical shock as short as 3 fs is formed.

Ultraviolet-enhanced supercontinuum generation in tapered photonic crystal fiber

We investigate numerically and experimentally the propagation of visible sub-50 fs pulses in a tapered small core photonic crystal fiber. The fiber has anomalous dispersion between two closely spaced zero dispersion wavelengths at 509 and 640 nm, and the excitation wavelength was varied within this range. We find that the spectral evolution in the low power regime is dominated by higher-order soliton fission, soliton self-frequency shift, and dispersive wave generation. At higher powers, extremely wide spectral broadening of the input pulse occurs within the first few millimeters of fiber. The wavelength conversion into the blue and red spectral ranges is studied as a function of the input power and excitation wavelength. Conversions into the spectral range 300-470 nm at efficiencies as high as 40% are observed when pumping at 523 nm.

Supercontinuum generation based on fission of higher-order solitons in bi-refringent photonic crystal fibers

The nonlinear propagation of 100 fs Ti:sapphire laser pulses in a bi-refringent photonic crystal fiber is experimentally investigated. Super-continuum generation with spectra extending from 450—1050 nm was obtained and the spectra consist of distinct peaks. The spectral broadening is shown to be caused by the mechanism of spectral broadening through fission of higher-order solitons into red-shifted fundamental solitons and blue-shifted dispersion waves. The simulation of light propagation property in the waveguide can explain well the experimental results.

Anomalous pulse breakup in small-core photonic crystal fibers

Detailed numerical and experimental studies of propagation of 110 fs laser pulses at 800 nm in small-core photonic crystal fibers (γ≈100 W-1 km−1) reveal that pulse breakup occurs in two distinct regimes defined by the input power. At low peak power (soliton order N≤7) higher-order soliton fission occurs: individual solitons being ejected from the input pulse one after the other and are arranged in wavelength and in time by peak power. At higher levels of peak power (N>8), pulse breakup results in ejection of bound soliton pairs and the formation of single solitons that collide during propagation.

Experimental study and numerical analysis of femtosecond pulse propagation and supercontinuum generation in highly nonlinear photonic crystal fiber

Femtosecond laser pulse propagation and supercontinuum generation in a highly nonlinear photonic crystal fiber is investigated experimentally and numerically. Consistent results of continuum generation measured and calculated for 790, 800, and 820 nm pump wavelengths are presented. It is shown that when the pump wavelength overlaps with the zero-dispersion wavelength self-phase modulation and third-order dispersion play an important role, and the oscillation structure appears in the temporal waveform of the propagating pulses, whereas in anomalous dispersion region, the formation and the red-shift of solitons are evident, and the self phase modulation plays a dominant role only in the initial stage. Further spectral broadening is due to solitons self-frequency shift, fission of higher-order solitons and four-wave mixing. It is also found that four-wave mixing occurs more easily in anomalous dispersion region than at the zero-dispersion wavelength.

Supercontinuum Generation Using a Polarization-MaintainingPhotonic Crystal Fibre by a Regeneratively Amplified Ti:Sapphire Laser

Supercontinuum with an ultra-broad bandwidth in the range from 380 nmto 1750 nm was generated by injecting 250 kHz 200 fs optical pulsesproduced by a regeneratively amplified Ti:sapphire laser into a2.5-m-long polarization-maintaining photonic crystal fibre (PCF). It isindicated that the mechanism for the supercontinuum generation in theanomalous dispersion region of the PCF are directly related to theRaman effect, the fission of higher-order solitons, nonsolitonicradiation, and the coinstantaneous effect of four-wave mixing. Thefrequency components beyond 1.4 μm were also observed. It isinterpreted that the energy of solitons is shifted beyond the OHabsorption with a higher input power.

Continuous-wave pumping in the anomalous- and normal-dispersion regimes of nonlinear fibers for supercontinuum generation

Supercontinuum (SC) growth in highly nonlinear fibers is compared for cw pumping in the anomalous- and normal-dispersion regimes. For anomalous-dispersion pumping, the combined effects of modulation instability (MI) and stimulated Raman scattering (SRS) contribute to spectral broadening. Furthermore, breakup of the cw light into ultrashort pulses by MI leads to the formation of a Raman pulse that evolves into a soliton, as evidenced by the observation of soliton self-frequency shift. Blueshifted, nonsolitonic radiation associated with the fission of higher-order solitons is also present in the SC spectra. For normal-dispersion pumping, SRS seeds the SC growth by generating several cascaded Stokes orders. When the Stokes orders are shifted into the anomalous-dispersion regime at higher launch powers, MI again causes soliton formation. Broadband continua are generated when the laser is positioned as far away as 191 nm from the zero-dispersion wavelength in normal dispersion.

Soliton Induced Supercontinuum Generation in Photonic Crystal Fiber

Soliton induced supercontinuum (SC) generation using an index-guiding triangular photonic crystal fiber (PCF) is experimentally studied by pumping with 140-fs pulses at several wavelengths in the positive slope anomalous dispersion region. The focused beam incident upon the PCF core is first confirmed by in situ observation based on the reflection method to make sure accurate input coupling conditions. The influence of pumping wavelength on the spectral profile of SC is examined as a function of input peak power P/sub 0/. Processes initiating SC generation are governed by the fission of higher-order solitons, which lead to the soliton self-frequency shift (SSFS) by intrapulse Raman scattering associated with blue-shifted Cherenkov type phase matched radiation. The fission of higher-order solitons is clearly observed in the input P/sub 0/ dependent spectrum and a plot of the square root of frequency shift versus input P/sub 0/. Further increase of input P/sub 0/ leads to a new SSFS accompanied by an additional blue-shifted peak located at shorter wavelength than that of the previous one. These processes continue to develop successive blue-shifted and SSFS peaks as increasing the input P/sub 0/, which determine the spectral width of SC. Spectral profile of SC is also dominated by these initial and growth processes. SC spectra obtained in the vicinity of zero dispersion wavelength shows smooth but relatively narrow, while SC generation at deep anomalous dispersion site exhibits broad bandwidth at relatively low P/sub 0/. The input P/sub 0/ required for approaching a saturated SC which is almost the same feature within the tuning pump wavelengths is decreased as increasing the degree of anomalous dispersion.

Intensity and polarization dependences of the supercontinuum generation in birefringent and highly nonlinear microstructured fibers

We present experimental results highlighting the physica mechanism responsible for the initial spectral broadening of femtosecond Ti:Sapphire pulses in a highly birefringent microstructured fiber having a small effective area. By rotating the input polarization and varying the injected power while monitoring the resulting changes in the output spectrum, we are bringing clear evidences that the initial broadening mechanism leading to a broadband supercontinuum is indeed the fission of higher-order solitons into redshifted fundamental solitons along with blueshifted nonsolitonic radiation.

Blue light and infrared continuum generation by soliton fission in a microstructured fiber

The nonlinear propagation of ultrashort pulses in a microstructured fiber is experimentally investigated. By working around 800 nm, in the anomalous dispersion region, clear evidence of pulse break-up and soliton propagation is obtained. This is consistent with the recently suggested mechanism of spectral broadening based upon the fission of higher order solitons into red-shifted fundamental solitons and blue-shifted dispersion waves. When 190-fs pulses at high input intensities are used, the output spectrum is made of a broad infrared supercontinuum coexisting with a sharp and very intense blue peak that takes up to 24% of the input power. We tentatively propose an explanation of this effect by invoking pulse-trapping phenomena controlled by the group-velocity matching of infrared and visible pulses.

Supercontinuum generation, four-wave mixing, and fission of higher-order solitons in photonic-crystal fibers

The nonlinear propagation of femtosecond pulses in photonic-crystal fibers is investigated theoretically without the use of the slowly varying envelope approximation. Low-intensity supercontinuum generation caused by fission of higher-order solitons into red-shifted fundamental solitons and blue-shifted nonsolitonic radiation is studied in a large range of fiber and pulse parameters. It is shown that phase matching of degenerate four-wave mixing can be achieved in an extremely broad frequency range from the IR to the UV. Spontaneous generation of new frequency components and parametric amplification by four-wave mixing as well as its possible overlap with soliton fission are studied in detail.

Experimental evidence for supercontinuum generation by fission of higher-order solitons in photonic fibers.

We report on an experimental study of supercontinuum generation in photonic crystal fibers with low-intensity femtosecond pulses, which provides evidence for a novel spectral broadening mechanism. The observed results agree with our theoretical calculations carried out without making the slowly varying envelope approximation. Peculiarities of the measured spectra and their theoretical explanation demonstrate that the reason for the white-light generation in photonic crystal fibers is fission of higher-order solitons into redshifted fundamental solitons and blueshifted nonsolitonic radiation.

Supercontinuum generation of higher-order solitons by fission in photonic crystal fibers.

The nonlinear pulse propagation in photonic crystal fibers without slowly varying envelope approximation is studied using an improved variant of first-order wave equation. Supercontinuum generation is shown to be caused by a novel mechanism of spectral broadening through fission of higher-order solitons into redshifted fundamental solitons and blueshifted nonsolitonic radiation. Good agreement with experimental observations is found, and subcycle pulse compression is studied.