Soliton-effect Pulse Compression Research Articles

All-Fiber High-Power 3 GHz Ultrafast Laser System At 2.0 μm

In this work, we report on a high-power all-fiber ultrafast laser system at 2.0 μm that delivers femtosecond pulses with a fundamental repetition rate of 3.0 GHz and a maximum output power of 33.1 W. In order to obtain high-power femtosecond pulse laser directly output from the optical fiber, the evolutions of the pulsewidths and optical spectra of the amplified pulses are carefully investigated by leveraging the soliton-effect pulse compression. The performances of power stability, phase noise and intensity noise are also characterized to insight the limitations for practical applications. It is anticipated that this all-fiber laser system can be a promising source for various applications at 2.0 μm that require outstanding performances on compactness, power, pulsewidth, repetition rate, etc.

Highly Nonlinear Composite-Photonic Crystal Fibers with Simplified Manufacturing Process and Efficient Mid-IR Applications

This paper reveals special design features of the proposed highly nonlinear circular-lattice-silicon-core and silica-doped-with-fluorine (1%) cladding-composite photonic crystal fiber (PCF) in the Mid-infrared region of the spectrum. A region of small negative group velocity dispersion (GVD), managed higher order dispersions (HODs), and unique nonlinearity of silicon have been used to demonstrate a supercontinuum broadening from 1500 nm to 4700 nm with consumption of low input power of 400 W over short fiber distances. It will be also shown that the fiber’s high-level engineered structure finally results in a simple manufacturing process compared with other designed nano-sized silicon PCFs. The designed fiber could have massive potential in gas sensing, soliton effect pulse compression, spectroscopy, material processing, etc.

Soliton-effect compression of picosecond pulses on a photonic chip.

We report soliton-effect pulse compression of low energy (∼25pJ), picosecond pulses on a photonic chip. An ultra-low-loss, dispersion-engineered 40-cm-long waveguide is used to compress 1.2-ps pulses by a factor of 18, which represents, to our knowledge, the largest compression factor yet experimentally demonstrated on-chip. Our scheme allows for interfacing with an on-chip picosecond source and offers a path towards a fully integrated stabilized frequency comb source.

Tuning the soliton-effect compression via stretching of the pump

We investigate numerically the effect of introducing stretching-induced initial chirp on the soliton-effect pulse compression. We find both the positive and negative initial chirps can lead to improved compression, but through different mechanisms. With the positive initial chirp, the amount of stretching that yields the best achievable compression decreases for an increasing soliton number, whereas with the negative initial chirp, it increases. Moreover, we observe that the compression length can be substantially altered by stretching the pump, and it can even be shorter than that for the transform-limited pump within a small range of positive initial chirp. We note also, the stretching factor that gives the shortest pulse output extends the compression length by 1.23 times for any given soliton order. This study demonstrates that the soliton-effect compression can be readily controlled and optimised by placing a variable stretching element beforehand. It is useful especially in experimental setups where the length of the compressor cannot be readily modified.

Emergence of breathers in non-linear pulse compression

We report on the universality of the emergence of Akhmediev breathers in soliton effect pulse compression dynamics by using explicit analytic solutions of breathers and solitons in the non-linear Schrödinger equation. We show that at maximum compression point, a higher-order soliton and a breather solution are equivalent with a nearly identical full-width at half maximum duration. From this, we demonstrate numerically how breathers that develop in the initial stage of continuous wave supercontinuum generation transform into an ensemble of solitons in the presence of system perturbation.

Adjustable enhancement of higher order soliton effect pulse compression by using optimized active dispersion decreased nonlinear fiber loop mirror

In this paper, four common dispersion profiles have been investigated for obtaining as high as possible wings free compressed pulse in nonlinear fiber loop mirror. Results show that linear profile can be considered as the best choice. Also, as the importance for enhanced adjustability of higher order soliton effect pulse compression, we propose a new simple method, as active fiber loop. According to our investigation it can be seen that when the amplification factor changes from 3dB to 4dB in an active linear profile dispersion decreased fiber loop mirror, the compression factor can be adjusted to any desired value between 140 and 170 where it is approximately two times higher than passive loop.

Silicon Nanowire Embedded Spiral Photonic Crystal Fiber for Soliton-Effect Pulse Compression

In this paper, we propose a new type of optical waveguide called silicon nanowire embedded equai-angular spiral photonic crystal fiber (SN-SPCF) using fully vectorial finite element method, where closely arranged arrays of air holes act as cladding and nanosize silicon material at the centre acts as core. We show that the proposed nanowire embedded PCF of 400 nm core diameter exhibits high anomalous group velocity dispersion (-3148 ps2/km), small third order dispersion (-8.6591 ps3/km) and high nonlinearity (443.2 W-1m-1) at 1550 nm wavelength. Soliton-effect pulse compression of femtosecond pulses in a silicon nanowire-spiral photonic crystal fiber at 1550 nm is numerically studied. We demonstrate a pulse compression of 75 fs input pulse to about 4 fs by the simultaneous actions of both linear effects (a large anomalous group velocity dispersion and a small third order dispersion) and the nonlinear effect (an effective high nonlinearity).

Observation of soliton compression in silicon photonic crystals

Solitons are nonlinear waves present in diverse physical systems including plasmas, water surfaces and optics. In silicon, the presence of two photon absorption and accompanying free carriers strongly perturb the canonical dynamics of optical solitons. Here we report the first experimental demonstration of soliton-effect pulse compression of picosecond pulses in silicon, despite two photon absorption and free carriers. Here we achieve compression of 3.7 ps pulses to 1.6 ps with <10 pJ energy. We demonstrate a ~1-ps free-carrier-induced pulse acceleration and show that picosecond input pulses are critical to these observations. These experiments are enabled by a dispersion-engineered slow-light photonic crystal waveguide and an ultra-sensitive frequency-resolved electrical gating technique to detect the ultralow energies in the nanostructured device. Strong agreement with a nonlinear Schrödinger model confirms the measurements. These results further our understanding of nonlinear waves in silicon and open the way to soliton-based functionalities in complementary metal-oxide-semiconductor-compatible platforms.

Higher-order soliton-effect pulse compression in a nonlinear left-handed transmission line

This work introduces a method of pulse compression based on a higher-order soliton effect in a left-handed nonlinear (LH-NL) transmission line with series nonlinear capacitances. A circuit simulation of the LH-NL transmission line which is based on a finite-difference method shows that if a higher-order soliton is replaced by a fundamental soliton launched into the line, the self-phase modulation (SPM) will dominate the group velocity dispersion (GVD). As a result, the pulse compression is realized in a specific length dependent on the soliton order.

Soliton-effect pulse compression in the single-cycle regime in broadband dielectric-coated metallic hollow waveguides

We study soliton-effect pulse compression in the single-cycle region in dielectric-coated metallic hollow waveguides filled with a noble gas exploiting the broad region of anomalous dispersion in these waveguides. We predict the compression of a 20-fs pulse to a FWHM duration of 1.7 fs with an energy of 6 muJ and study the physical factors determining the limitations on shortest pulses in the single-cycle regime.

Soliton-number analysis of soliton-effect pulse compression to single-cycle pulse widths

We demonstrate that the soliton-effect compression to few- and single-cycle pulse widths in a highly nonlinear fiber can be optimized by properly choosing the input soliton number. Soliton compression to a $2\text{\ensuremath{-}}\mathrm{fs}$ pulse width with a compression ratio up to 50 is demonstrated for light pulses with an initial central wavelength of $1070\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ by solving the generalized nonlinear Schr\odinger equation for a dispersion profile typical of a small-core photonic-crystal fiber.

Analytic study on soliton-effect pulse compression in dispersion-shifted fibers with symbolic computation

The soliton-effect pulse compression of ultrashort solitons in a dispersion-shifted fiber (DSF) is investigated based on solving the higher-order nonlinear Schrödinger equation with the effects of third-order dispersion (TOD), self-steepening (SS) and stimulated Raman scattering (SRS). By using Hirota's bilinear method with a set of parametric conditions, the analytic one-, two- and three-soliton solutions of this model are obtained. According to those solutions, the higher-order soliton is shown to be compressed in the DSF for the pulse with width in the range of a few picoseconds or less. An appealing feature of the soliton-effect pulse compression is that, in contrast to the second-order soliton compression due to the combined effects of negative TOD and SRS, the third-order soliton can significantly enhance the soliton compression in the DSF with small values of the group-velocity dispersion (GVD) at the operating wavelength.

Simultaneous measurement of anomalous group-velocity dispersion and nonlinear coefficient in optical fibers using soliton-effect compression

We present a novel and simple method to measure both the value of the second-order dispersion coefficient and the nonlinear coefficient in optical fibers. This method is based on the higher-order soliton-effect pulse compression phenomenon and is valid for dispersion values greater than 0.5ps/km/nm. A non-zero dispersion-shifted fiber, a standard single-mode fiber and a highly-dispersive highly-nonlinear fiber have been measured using this method.

Sub-two-cycle soliton-effect pulse compression at 800 nm in photonic crystal fibers

The possibility of soliton self-compression of ultrashort laser pulses down to the few-cycle regime in photonic crystal fibers is numerically investigated. We show that efficient sub-two-cycle temporal compression of nanojoule-level 800 nm pulses can be achieved by employing short (typically 5 mm long) commercially available photonic crystal fibers and pulse durations of around 100 fs, regardless of initial linear chirp, and without the need of additional dispersion compensation techniques. We envision applications in a new generation of compact and efficient sub-two cycle laser pulse sources.

Soliton compression in quadratic media: high-energy few-cycle pulses with a frequency-doubling crystal

We present a soliton effect pulse compression technique that uses self-defocusing cascaded-quadratic nonlinearities, with no fundamental limit to its scalability to high pulse energies and the capability of generating few-cycle pulses with only a frequency-doubling crystal. The conditions for which group-velocity mismatch causes an acceptable perturbation to soliton compression are analyzed and underlie optimization of the compressor. Calculations predict compression to near-single-cycle durations, with compression ratios as high as 100. Initial experiments closely agree with calculations, demonstrating compression to durations under three optical cycles (12 fs) and generation of 600 nm bandwidths.

Optical pulse compression using a nonlinear optical loop mirror constructed from dispersion decreasing fiber

A novel scheme to compress optical pulses is proposed and demonstrated numerically, which is based on a nonlinear optical loop mirror constructed from dispersion decreasing fiber (DDF). We show that, in contrast to the conventional soliton-effect pulse compression in which compressed pulses are always accompanied by pedestals and frequency chirps owning to nonlinear effects, the proposed scheme can completely suppress pulse pedestals and frequency chirps. Unlike the adiabatic compression technique in which DDF length must increase exponentially with input pulsewidth, the proposed scheme does not require adiabatic condition and therefore can be used to compress long pulses by using reasonable fiber lengths. For input pulses with peak powers higher than a threshold value, the compressed pulses can propagate like fundamental solitons. Furthermore, the scheme is fairly insensitive to small variations in the loop length and is more robust to higher-order nonlinear effects and initial frequency chirps than the adiabatic compression technique.

Ultrashort soliton generation through higher-order soliton compression in a nonlinear optical loop mirror constructed from dispersion-decreasing fiber

A novel technique to generate ultrashort fundamental solitons is proposed and demonstrated numerically. The technique utilizes both the multisoliton pulse-compression effect and the switching characteristics of a nonlinear optical loop mirror constructed from dispersion-decreasing fiber. We show that, in contrast to the conventional soliton-effect pulse compression in which compressed pulses are always accompanied by broad pedestals, the proposed technique can completely suppress pulse pedestals, and the compressed pulses propagate like fundamental solitons. Unlike the adiabatic-compression technique based on dispersion-decreasing fibers that are limited to input pulse widths &lt;5 ps, the proposed technique does not require the adiabatic condition and therefore can be used to compress long pulses by use of reasonable fiber lengths. Furthermore, the scheme is more tolerant of initial frequency chirps than the adiabatic-compression technique, and it is shown that positive chirps are beneficial to ultrashort soliton generation. The influences of higher-order effects such as Raman self-scattering and third-order dispersion on soliton generation are also investigated, and it is found that Raman self-scattering can significantly enhance pulse compression under certain conditions.

Soliton-Effect Optical Pulse Compression in Bulk Media with X^(3) Nonlinearity

Self-compression of visible optical pulse in bulk χ(3) medium has been demonstrated taking the advantage of negative group-velocity dispersion of tilted pulses.

Enhanced soliton-effect pulse compression by cross-phase modulation in optical fibers

A new technique is proposed to enhance the soliton-effect compression of optical pulses. It consists of copropagating two optical pulses with close wavelengths in the negative group-velocity dispersion regime of single-mode fibers. When compared with the conventional soliton-effect pulse compression technique in which only one pulse is involved, this technique, as shown by numerical simulations, can not only dramatically increase the compression ratio but also decrease the optimum fiber length, by utilizing cross-phase modulation between copropagating pulses. It is also shown that the above cross-phase modulation induced enhancement of pulse compression is more significant in the sub-picosecond regime than in the picosecond regime. This scheme is particularly useful for the case in which the peak powers of the pulses obtained from lasers are not high enough for efficient conventional soliton-effect compression to take place.

Soliton-effect compression and dispersive radiation

Soliton-effect pulse compression is investigated using two approximate methods which do not include the dispersive radiation shed as the soliton evolves and by one approximate method which does. Results derived from the approximate equations are compared with full numerical solutions of the governing equation. It is found that while the methods without radiation can be used to predict the position of optimal compression, to also have accurate prediction of the pulse amplitude requires inclusion of the dispersive radiation. A careful analysis of the solutions of the various approximate equations shows that care must be taken in using length predictions derived from approximate methods. This is because there are phase differences between the numerical and approximate solutions. Such phase differences are not predicted by the approximate methods. While approximate methods do exist to determine phase evolution, these methods do not predict the initial phase, which is of importance when distance predictions are made.