Raman Dissipative Solitons Research Articles

Investigation of Raman dissipative solitons parameters generated near 1.7 μm

This work demonstrates a study Raman dissipative solitons parameters at wavelengths of 1.6-1.7 μm as a function of pump pulse energy and external cavity quality factor. In the presented scheme of the Raman dissipative solitons generator, pulses with a repetition rate of 6.54 MHz, an energy in range of 4.3-7.2 nJ, and slope efficiency of about 83% at a wavelength of 1.66 μm were obtained. Numerical simulation of an external cavity and analysis of pulse compression in an optical fiber with anomalous dispersion are presented. It is shown that an increase in the fraction of diverted radiation from the external cavity from 50% to 80% may allow increasing the quality of generated pulses.

Raman dissipative soliton source of ultrashort pulses in NIR-III spectral window.

We present a novel fiber source of ultrashort pulses at the wavelength of 1660 nm based on the technique of external cavity Raman dissipative soliton generation. The output energy of the generated 30 ps chirped pulses is in the range of 0.5-3.6 nJ with a slope efficiency of 57%. Numerical simulations are in excellent agreement with the experimental results and the shape of the compressed pulses. The compressed pulses consist of a central part with a duration of 300 fs and a weak pedestal. Our results clearly demonstrate the potential to extend the spectral range of the Raman-assisted technique for generating ultra-short pulses to new frequency regions, including biomedical windows. This paves the way for the development of new dissipative soliton sources in these bands.

Self-steepening and intrapulse Raman scattering in the presence of nonlinear gain and its saturation

In this paper we present the results of a detailed numerical investigation of the influence of the self-steepening effect on the parameters of the Raman dissipative solitons in the presence of nonlinear gain and its saturation. It has been established that when the effect of self-steepening prevails under the intrapulse Raman scattering it leads to nonlinear changes in the parameters of the Raman dissipative solitons. Comparing the impact of the intrapulse Raman scattering and self-steepening in the presence of nonlinear gain and its saturation on the dissipative solitons, the following differences have been identified: a much slighter change of the amplitude in the presence of self-steepening; different types of nonlinear dependencies of the frequency and velocity in the presence of intrapulse Raman scattering; and a substantial increase of the velocity under the influence of self-steepening. We have found that under the influence of the saturation of the nonlinear gain the observed nonlinear changes of the parameters of Raman dissipative solitons in the presence of the self-steepening effect are weaker. There has been observed a reduction of the maximum values of the amplitude and velocity as well as the maximum absolute values of the frequency of the Raman dissipative solitons.

Raman dissipative solitons generation near 1.7 μm by synchronous pumping

Raman dissipative solitons generation near 1.7 μm by synchronous pumping

Higher-order correction terms to the nonlinear amplification or absorption, the nonlinear refractive index, and the intrapulse Raman scattering.

In this paper we have investigated through the numerical solution of the basic equation as well as through the dynamic model the influence of higher-order correction terms to the nonlinear amplification (absorption) and to the nonlinear refractive index on the self-frequency shift of Raman dissipative solitons. We have found a nonlinear dependence of the self-frequency shift of Raman dissipative solitons on the parameter describing intrapulse Raman scattering in the presence of the saturation of the nonlinear gain. With the increase of the absolute value of the saturation of the nonlinear gain, the maximum absolute value of the frequency shift decreases and its position moves to larger values of the parameter describing intrapulse Raman scattering. The increase in the value of the nonlinear gain leads to an increase in the maximum absolute value of the frequency shift, without changing its position. We have also observed the nonlinear dependence of the absolute value of the frequency shift on the parameter describing intrapulse Raman scattering in the presence of higher-order correction term to the nonlinear refractive index. The discovered nonlinear dependence of the self-frequency shift on the value of the saturation of the nonlinear gain as well as on the higher-order correction term to the nonlinear refractive index can be used for the better understanding and control of the spectral characteristics of Raman dissipative solitons. The dynamic model correctly describes all the features of the observed phenomena.

Raman dissipative solitons generator near 1.3 mkm: limiting factors and further perspectives

Raman dissipative solitons (RDS) have been investigated numerically. It was found that the area of stable generation is bounded in terms of pump spectral bandwidth and pulse energy. Existing optimum is strongly affected by the net cavity dispersion. The spectral bandwidth of the generated RDS linearly depends on its energy and reaches more than 50 nm in the 5-meters long cavity. Developed numerical model reproduces all the effects observed experimentally. It predicts ability to generate high-quality pulses with energy up to 6 nJ compressible down to ∼100 fs duration. The work shows that RDS generation technique can produce high-energy ultrashort pulses at wavelengths not covered by typical active mediums.

Intrapulse Raman scattering and dissipative solitons with extreme spikes

We have studied numerically the influence of intrapulse Raman scattering (IRS) on the dissipative solitons with extreme spikes (DSES). The following scenarios of the influence of IRS have been identified. In the anomalous dispersion regime, there has been found a transformation of the single spike DSES and pulsating in x and t DSES into Raman dissipative solitons. We should mention a good performance of the finite-dimensional system in the description of all pulse parameters in the first case. In the other scenario, the DSES moving with fixed velocity pulsating in x and t transforms into single spike DSES moving with fixed velocity. We have also observed a transformation of double spike DSES into single spike moving DSES as well as a transformation of a single spike DSES into a single spike moving DSES accompanied by the change in the period of the spikes appearance. In the normal dispersion regime, we have found a transformation of a single spike DSES into a single spike moving DSES and the change of the period of the spikes appearance. For a large strength of IRS, an appearance of a chaotic DSES has been observed.

Study on harmonic generation regimes of Raman dissipative solitons in an external fibre cavity in a spectral region of 1.3 μm

We have studied the harmonic generation regimes in a pulsed SRS laser with synchronous pumping. The use of phosphosilicate polarisation-maintaining fibre made it possible to obtain stable generation of Raman dissipative solitons (RDS’s) with a wavelength of 1.3 μm, and a fold increase in the length of the external cavity relative to that of the pump laser cavity by a dispersion-shifted fibre allowed us to raise the threshold for the transition to noise-like pulses and to increase the RDS energy up to 2.5 nJ with an estimated duration of a transform-limited pulse of about 200 fs.

Raman dissipative soliton fiber laser mode locked by a nonlinear optical loop mirror.

Raman dissipative soliton is generated in a mode locked polarization maintaining fiber laser with a nonlinear optical loop mirror. Ultrafast Raman laser with a repetition rate of 1.23 MHz is obtained. Signal to noise ratio of the radio frequency spectrum of the Raman dissipative soliton is as high as 85 dB. As the pump power increasing, the pulse energy and the spectral width increase, while the pulse width decreases. The highest pulse energy and lowest pulse width is 1.23 nJ and 63 ps, respectively. It is the first report of Raman dissipative soliton generation from an all polarization maintaining mode locked fiber laser to the best of our knowledge. This configuration provides a method to obtain linearly-polarized ultrafast laser at flexible wavelengths.

Generation of Raman dissipative solitons near 1.3 microns in a phosphosilicate-fiber cavity.

An external-cavity generation of powerful ultrashort pulses in an all-fiber scheme by using a new type of phosphosilicate polarization maintaining fiber is investigated. The phosphorus-related Stokes shifted Raman pulse near 1.3 microns is observed. Optimization of Stokes output spectrum depending on pump pulse duration (chirp), energy and output coupling ratio of the cavity is performed. As result, the output energy of highly-chirped pulses compressible to 570 fs reaches 1.6 nJ.

Transitions of stationary to pulsating solutions in the complex cubic-quintic Ginzburg-Landau equation under the influence of nonlinear gain and higher-order effects.

In this paper we study the transitions of stationary to pulsating solutions in the complex cubic-quintic Ginzburg-Landau equation (CCQGLE) under the influence of nonlinear gain, its saturation, and higher-order effects: self-steepening, third-order of dispersion, and intrapulse Raman scattering in the anomalous dispersion region. The variation method and the method of moments are applied in order to obtain the dynamic models with finite degrees of freedom for the description of stationary and pulsating solutions. Having applied the first model and its bifurcation analysis we have discovered the existence of families of subcritical Poincaré-Andronov-Hopf bifurcations due to the intrapulse Raman scattering, as well as some small nonlinear gain and the saturation of the nonlinear gain. A phenomenon of nonlinear stability has been studied and it has been shown that long living pulsating solutions with relatively small fluctuations of amplitude and frequencies exist at the bifurcation point. The numerical analysis of the second model has revealed the existence of Poincaré-Andronov-Hopf bifurcations of Raman dissipative soliton under the influence of the self-steepening effect and large nonlinear gain. All our theoretical predictions have been confirmed by the direct numerical solution of the full perturbed CCQGLE. The detailed comparison between the results obtained by both dynamic models and the direct numerical solution of the perturbed CCQGLE has proved the applicability of the proposed models in the investigation of the solutions of the perturbed CCQGLE.

Raman dissipative soliton fiber laser pumped by an ASE source: publisher’s note

This publisher's note corrects a typo in the affiliations in Opt. Lett.42, 5162 (2017)OPLEDP0146-959210.1364/OL.42.005162.

Raman dissipative soliton fiber laser pumped by an ASE source

The mode locking of a Raman fiber laser with an amplified spontaneous emission (ASE) pump source is investigated for performance improvement. Raman dissipative solitons with a compressed pulse duration of 1.05 ps at a repetition rate of 2.47 MHz are generated by utilizing nonlinear polarization rotation and all-fiber Lyot filter. A signal-to-noise ratio as high as 85 dB is measured in a radio-frequency spectrum, which suggests excellent temporal stability. Multiple-pulse operation with unique random static distribution is observed for the first time, to the best of our knowledge, at higher pump power in mode-locked Raman fiber lasers.

Spectral comb of highly chirped pulses generated via cascaded FWM of two frequency-shifted dissipative solitons

Dissipative solitons generated in normal-dispersion mode-locked lasers are stable localized coherent structures with a mostly linear frequency modulation (chirp). The soliton energy in fiber lasers is limited by the Raman effect, but implementation of the intracavity feedback at the Stokes-shifted wavelength enables synchronous generation of a coherent Raman dissipative soliton. Here we demonstrate a new approach for generating chirped pulses at new wavelengths by mixing in a highly-nonlinear fiber of these two frequency-shifted dissipative solitons, as well as cascaded generation of their clones forming in the spectral domain a comb of highly chirped pulses. We observed up to eight equidistant components in the interval of more than 300 nm, which demonstrate compressibility from ~10 ps to ~300 fs. This approach, being different from traditional frequency combs, can inspire new developments in fundamental science and applications such as few-cycle/arbitrary-waveform pulse synthesis, comb spectroscopy, coherent communications and bio-imaging.

Cascaded generation of coherent Raman dissipative solitons.

The cascaded generation of a conventional dissipative soliton (at 1020nm) together with Raman dissipative solitons of the first (1065nm) and second (1115nm) orders inside a common fiber laser cavity is demonstrated experimentally and numerically. With sinusoidal (soft) spectral filtering, the generated solitons are mutually coherent at a high degree and compressible down to 300fs. Numerical simulation shows that an even higher degree of coherence and shorter pulses could be achieved with step-like (hard) spectral filtering. The approach can be extended toward a high-order coherent Raman dissipative soliton source offering numerous applications such as frequency comb generation, pulse synthesis, biomedical imaging, and the generation of a coherent mid-infrared supercontinuum.

Four wave mixing of conventional and Raman dissipative solitons from single fiber laser.

Conventional (1015 nm) and Raman (1055 nm) dissipative solitons generated in an all-fiber Yb laser are mixed in an external photonic crystal fiber (PCF) at pulse energy of up to 4 nJ at the input. It has been found that red-shifted ~20 ps pulses with energy up to 1 nJ are generated in the parametric process. Their peak wavelength is tunable from 1084 to 1102 nm by means of the delay variation between the input pulses. At that, the parametric pulses are shown to be coherent with the input ones and compressible to ~2 ps that is useful in applications. The performed modeling explains the main features of generated pulses.

Feedback-controlled Raman dissipative solitons in a fiber laser.

Energy of chirped dissipative solitons (DS) generated in fiber lasers may exceed a threshold of stimulated Raman scattering (SRS) leading to formation of a noisy Raman pulse (RP). As we demonstrated recently, a feedback loop providing re-injection of the Raman pulse into the laser cavity can form a Raman dissipative soliton (RDS) with similar characteristics to those of the main dissipative soliton. Here, we present the results of feedback optimization of the generated RDS spectra. First experimental results of coherent combining of DS and RDS are also shown.

Multicolour nonlinearly bound chirped dissipative solitons.

The dissipative soliton regime is one of the most advanced ways to generate high-energy femtosecond pulses in mode-locked lasers. On the other hand, the stimulated Raman scattering in a fibre laser may convert the excess energy out of the coherent dissipative soliton to a noisy Raman pulse, thus limiting its energy. Here we demonstrate that intracavity feedback provided by re-injection of a Raman pulse into the laser cavity leads to formation of a coherent Raman dissipative soliton. Together, a dissipative soliton and a Raman dissipative soliton (of the first and second orders) form a two (three)-colour stable complex with higher total energy and broader spectrum than those of the dissipative soliton alone. Numerous applications can benefit from this approach, including frequency comb spectroscopy, transmission lines, seeding femtosecond parametric amplifiers, enhancement cavities and multiphoton fluorescence microscopy.