Adiabatic Soliton Compression Research Articles

Early optical soliton research at Imperial College London

The early work of the Femtosecond Optics Group at Imperial College on optical soliton generation in fibres is reviewed that commenced with studies of ultrashort pulse generation using high order soliton compression for the production of pulses of 18 fs. Also described are seminal studies of soliton Raman generation using long pulse pumping where evolution from modulational instability led to continuum generation and tunable femtosecond generation. Early investigations of seeding modulational instability for enhanced soliton generation and spectral extension are described, as is the work on seeding of noise, soliton generation from noise bursts and soliton generation from amplified noise bursts. The first study of femtosecond soliton amplification in Er fibre amplifiers is described as well as synchronous Raman amplification of solitons. Various schemes reviewing our investigations of adiabatic soliton compression and amplification are included for the generation of pulsewidth and wavelength tunable soliton sources in fully fibre integrated geometries.

Pre-Chirp-Managed Adiabatic Soliton Compression in Pressure-Gradient Hollow-Core Fibers

Post-pulse-compression is demanded to produce energetic few-cycle pulses. We propose pre-chirp-managed adiabatic soliton compression (ASC) in gas-filled pressure-gradient hollow-core fibers to suppress the detrimental pedestals and therefore significantly improve the compressed pulse quality. We show that two-stage ASC can compress 125 μJ, 130 fs pulses at 2 μm to a nearly two-cycle pulse 15 fs in duration. Our analytical analysis suggests that ASC is in favor of compressing pulses centered at a longer wavelength. As an example, a 280 μJ, 220 fs Gaussian pulse at 4 μm is compressed to 60 fs with minimal pedestals. We expect that the resulting high-quality, energetic few-cycle pulses will find important applications in high-field science.

Ionization-induced adiabatic soliton compression in gas-filled hollow-core photonic crystal fibers.

We investigate in the experiments the ionization-induced adiabatic soliton compression process in a short length of He-filled single-ring photonic crystal fiber. We observe that the plasma-driven blueshifting solitons show little residual light near the pump wavelength in a certain pulse energy region, leading to a high-efficiency frequency upconversion process. In contrast, at high pulse energy levels, we observe that the quality of the frequency upshifting process is impaired due to the existence of a dynamical loss channel induced by the coupling of the soliton to linear modes near the pump wavelength. In addition, through adjusting the input pulse energy, the central wavelength of blueshifting solitons can be continuously tuned over 300nm. These experimental results, confirmed by numerical simulations, not only offer a deep insight into ionization-induced soliton-plasma dynamics in gas-filled hollow-core photonic crystal fibers, but also develop highly tunable ultrafast light sources at visible wavelengths, which may have many applications in ultrafast spectroscopy.

PHz-Wide Spectral Interference Through Coherent Plasma-Induced Fission of Higher-Order Solitons.

We identify a novel regime of soliton-plasma interactions in which high-intensity ultrashort pulses of intermediate soliton order undergo coherent plasma-induced fission. Experimental results obtained in gas-filled hollow-core photonic crystal fiber are supported by rigorous numerical simulations. In the anomalous dispersion regime, the cumulative blueshift of higher-order input solitons with ionizing intensities results in pulse splitting before the ultimate self-compression point, leading to the generation of robust pulse pairs with PHz bandwidths. The novel dynamics closes the gap between plasma-induced adiabatic soliton compression and modulational instability.

Adjustable pulse compression scheme for generation of few-cycle pulses in the midinfrared.

A novel adjustable adiabatic soliton compression scheme is presented, enabling a coherent pulse source with pedestal-free, few-cycle pulses in the infrared or midinfrared regime. This scheme relies on interaction of a dispersive wave and a soliton copropagating at nearly identical group velocities in a fiber with enhanced infrared transmission. The compression is achieved directly in one stage, without the necessity of an external compensation scheme. Numerical simulations are employed to demonstrate this scheme for silica and fluoride fibers, indicating ultimate limitations as well as the possibility of compression down to the single-cycle regime. Such output pulses appear to be ideally suited as seed sources for parametric amplification schemes in the midinfrared.

Combined soliton pulse compression and plasma-related frequency upconversion in gas-filled photonic crystal fiber

We numerically investigate self-frequency blueshifting of a fundamental soliton in a gas-filled hollow-core photonic crystal fiber. Because of the changing underlying soliton parameters, the blueshift gives rise to adiabatic soliton compression. Based on these features, we propose a device that enables frequency shifting over an octave and pulse compression from 30 fs down to 2.3 fs.

Femtosecond pulses at 20 GHz repetition rate through spectral masking of a phase modulated signal and nonlinear pulse compression

We present a laser system capable of producing 190 femtosecond pulses at a repetition rate of 20 GHz. The spectral masking of a phase modulated diode laser is used to produce a train of picosecond pulses which are compressed using a fibre-grating compressor followed by subsequent adiabatic soliton compression to the femtosecond regime using a tapered photonic crystal fiber.

High speed ultra short pulse fiber ring laser using photonic crystal fiber nonlinear optical loop mirror

A scheme to generate high speed optical pulse train with ultra short pulse width is proposed and experimentally studied. Two-step compression is used in the scheme: 20GHz and 40GHz pulse trains generated from a rational harmonic actively mode-locked fiber ring laser is compressed to a full width at half-maximum (FWHM) of ~1.5ps using adiabatic soliton compression with dispersion shifted fibers (DSF). The pulse trains then undergo a pedestal removal process by transmission through a cascaded two photonic crystal fiber (PCF)-nonlinear optical loop mirrors (NOLM) realized using a double-ring structure. The shortest output pulse width obtained was ~610fs for 20GHz pulse train and ~570fs for 40GHz pulse train. The signal to noise ratio of the RF spectrum of the output pulse train is larger than 30dB. Theoretical simulation of the NOLM transmission is conducted using split-step Fourier method. The results show that two cascaded NOLMs can improve the compression result compared to that for a single NOLM transmission.

Cascaded higher-order soliton for non-adiabatic pulse compression

Non-adiabatic pulse compression of cascaded higher-order optical soliton is investigated. We demonstrate high degree compression of pulses with soliton orders N=2, 3, 4, and 5 in two or three nonlinear fibers with different second-order dispersion coefficients. Each fiber length is shorter than half of its soliton period. This compression technique has significant advantages over the widely reported adiabatic and higher-order soliton compression.

Theory of adiabatic pressure-gradient soliton compression in hollow-core photonic bandgap fibers

Adiabatic soliton compression by means of a pressure gradient in a hollow-core photonic bandgap fiber is investigated theoretically and numerically. It is shown that the duration of the compressed pulse is limited mainly by the interplay between third-order dispersion and the Raman-induced soliton frequency shift. Analytical expressions for this limit are derived and compared with results of detailed numerical simulations for a realistic fiber structure.

Broadband wavelength-tunable ultrashort pulse source using a Mach–Zehnder modulator and dispersion-flattened dispersion-decreasing fiber

The broadband wavelength tunability of femtosecond pulse generation using a Mach-Zehnder-modulator-based flat-comb generator (MZ-FCG) and a dispersion-flattened dispersion-decreasing fiber (DF-DDF) was demonstrated. Near-Fourier-transform-limit picosecond pulses generated from the MZ-FCG were compressed into femtosecond pulses by adiabatic soliton compression. By tuning the wavelength of the input cw light, 200 fs, 10 GHz pulses were generated in the wavelength range of 1,535 to 1,570 nm. Such wide-range wavelength tunability was realized by both the independence of a comb-flattening condition from the inputted wavelength and the dispersion flatness of the DF-DDF.

High-Quality Ultrashort Pulse Generation Utilizing a Self-Phase Modulation-Based Reshaper

An ultrashort 10-GHz pulse generation scheme was successfully demonstrated using a bulk material InGaAsP electroabsorption modulator to generate the seed pulse. A self-phase modulation-based reshaper was used after the adiabatic soliton compression in a comb-like dispersion profiled fiber. Experiments and simulations confirm that the reshaper effectively removes the pulse pedestal and improves the pulse extinction ratio. As a result, the 10-GHz pulse had no pedestal, a high extinction ratio, and a pulse width of only 1.4 ps.

Optical pulse compression in dispersion decreasing photonic crystal fiber

Improvements to tapered photonic crystal fiber (PCF) fabrication have allowed us to make up to 50 m long PCF tapers with loss as low as 30 dB/km. We discuss the design constraints for tapered PCFs used for adiabatic soliton compression and demonstrate over 15 times compression of pulses from over 830 fs to 55 fs duration at a wavelength of 1.06 lm, an order of magnitude improvement over previous results.

Stationary rescaled pulse in dispersion-decreasing fiber for pedestal-free pulse compression

By using the concept of a stationary rescaled pulse (SRP), we analyze an adiabatic soliton compression system based on dispersion-decreasing fiber (DDF). We show that a SRP can exist in a DDF with a linearly decreasing dispersion profile and that the SRP resembles a linearly chirped sech2 pulse. According to the analysis, we show numerically that pedestal-free pulse compression is possible by using the SRP.

Wavelength and Duration-Tunable 10-GHz 1.3-ps Pulse Source Using Dispersion Decreasing Fiber-Based Distributed Raman Amplification

We experimentally demonstrate a novel pulse compression scheme using dispersion decreasing fiber (DDF)-based distributed Raman amplification. We adiabatically compress 10-GHz 13-ps seed pulses generated using a commercially available electroabsorption modulator into high-quality 1.3-ps pulses in a 20-km DDF-based diode-pumped Raman amplifier. The usual DDF adiabatic soliton compression process is assisted by the distributed Raman gain along the fiber and by control of the input pulse chirp. Both wavelength tunability of about 30 nm and pulse-duration tunability from 1 to 5 ps are also demonstrated.

Study on pulse compression in dispersion-decreasing fibers

This paper studies the adiabatic soliton compression of pulses in dispersion dec reasing fibers(DDF).We indicate that although high quality compressed pulse coul d be achieved from ps fundamental soliton by using DDF with linear profile,the r equired fiber length is too long to be useful.As a result,higher order soliton c ompression in DDF is proposed to achieve large compression factor and high quali ty compression with relatively short fiber lengths.

40 GHz adiabatic compression of a modulator based dual frequency beat signal using Raman amplification in dispersion decreasing fiber

We demonstrate the use of distributed Raman amplification (DRA) in a dispersion decreasing fiber (DDF) for the efficiency enhancement of adiabatic soliton compression of a dual frequency beat signal. We compress a 40 GHz beat signal generated from a LiNbO3 modulator at a driving RF frequency of 20 GHz into ~ 2.2 ps soliton pulses using DRA in a 20 km DDF. The generation of high quality of soliton pulses from the 40 GHz sinusoidal beat signal is readily achieved with a significantly enhanced efficiency using DDF based DRA, compared to the case of using a DDF without DRA or a DSF with DRA.

10-GHz 1.3-ps pulse generation using chirped soliton compression in a Raman gain medium

The authors demonstrate a novel pulse compression technique that is capable of producing high-quality 1.3-ps pulses at a repetition rate of 10 GHz. The technique begins with 20-ps pulses carved by a commercially available external modulator and achieves up to 15-fold compression using a combination of phase modulation and distributed Raman amplification. Unlike adiabatic soliton compression, the scheme takes advantage of an exact solution to the nonlinear Schrodinger equation for chirped soliton evolution. As such, high-quality low-pedestal compressed pulses can be produced in a shorter span of fiber than would be needed for adiabatic compression. Because the system uses external modulation, the source is inherently tunable. Furthermore, the degree of pulse compression can be adjusted by varying the amount of Raman gain and phase modulation.

Ultrashort Pulse Generation at High Repetition Rate from Mode-Locked Fiber Lasers.

A stable optical short pulse source with a high repetition rate is very important for realizing future ultrahigh speed optical communication. Of the many potential techniques, an actively mode-locked fiber laser is one of the most attractive sources for generating high quality picosecond pulses at GHz repetition rates. In this paper, we report a regeneratively mode-locked fiber laser which emits a 1-3 ps transform limited pulse at 10 GHz in the 1.53 to 1.55μm wavelength region. This laser can be locked to an external signal by operating a phase-locked loop technique. By using this pulse source and an adiabatic soliton compression technique, a 170 fs pulse train at 10 GHz was generated. Finally, we show the excellent jitter characteristics of the laser.

Adiabatic Bragg soliton compression in nonuniform grating structures

Adiabatic soliton compression is an attractive optical pulse compression scheme that relies on monotonic decreasing of the fiber dispersion along the soliton’s propagation path. This scheme requires kilometers of specialty fiber, and only a few dispersion profiles are practically feasible. We propose adiabatic soliton compression in a nonuniform fiber Bragg grating. The Bragg soliton propagates in the passband of a grating, where one or more of its parameters (e.g., the grating pitch) varies along the propagation direction. The capability of manufacturing almost arbitrary grating profiles and hence engineering practically any dispersion profile makes this all-fiber pulse compressor, which is to our knowledge novel, a very versatile component. Additionally, the large dispersion in the spectral vicinity of the grating stop band leads to very short devices (tens of centimeters as opposed to kilometers).