All-fiber passively mode-locked Tm-doped NOLM-based oscillator operating at 2-μm in both soliton and noisy-pulse regimes

A self-starting all-fiber passively mode-locked Tm-doped fiber laser based on nonlinear loop mirror (NOLM) is demonstrated. Stable soliton pulses centered at 2017.33 nm with 1.56 nm FWHM were produced at a repetition rate of 1.514 MHz with pulse duration of 2.8 ps and pulse energy of 83.8 pJ. As increased pump power, the oscillator can also operate at noise-like (NL) regime. Stable NL pulses with coherence spike width of 341 fs and pulse energy of up to 249.32 nJ was achieved at a center wavelength of 2017.24 nm with 21.33 nm FWHM. To the best of our knowledge, this is the first 2 μm region NOLM-based mode-locked fiber laser operating at two regimes with the highest single pulse energy for NL pulses. © 2014 Optical Society of America.

Conversion of a chirped Gaussian pulse to a soliton or a bound multisoliton state in quasi-lossless and lossy optical fiber spans

The formation of single-soliton or bound-multisoliton states from a single linearly chirped Gaussian pulse in quasi-lossless and lossy fiber spans is examined. The conversion of an input-chirped pulse into soliton states is carried out by virtue of the so-called direct Zakharov-Shabat spectral problem, the solution of which allows one to single out the radiative (dispersive) and soliton constituents of the beam and determine the parameters of the emerging bound state(s). We describe here how the emerging pulse characteristics (the number of bound solitons, the relative soliton power) depend on the input pulse chirp and amplitude. © 2007 Optical Society of America.

Pulse shaping in mode-locked fiber lasers by in-cavity spectral filter

We numerically show the possibility of pulse shaping in a passively mode-locked fiber laser by inclusion of a spectral filter into the laser cavity. Depending on the amplitude transfer function of the filter, we are able to achieve various regimes of advanced temporal waveform generation, including ones featuring bright and dark parabolic-, flat-top-, triangular- and saw-tooth-profiled pulses. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for controlling the dynamics of mode-locked fiber lasers. © 2014 Optical Society of America.

Role of plasma in femtosecond laser pulse propagation

This paper describes physics of nonlinear ultra‐short laser pulse propagation affected by plasma created by the pulse itself. Major applications are also discussed. Nonlinear propagation of the femtosecond laser pulses in gaseous and solid transparent dielectric media is a fundamental physical phenomenon in a wide range of important applications such as laser lidars, laser micro‐machining (ablation) and microfabrication etc. These applications require very high intensity of the laser field, typically 1013–1015 TW/cm2. Such high intensity leads to significant ionisation and creation of electron‐ion or electron‐hole plasma. The presence of plasma results into significant multiphoton and plasma absorption and plasma defocusing. Consequently, the propagation effects appear extremely complex and result from competitive counteraction of the above listed effects and Kerr effect, diffraction and dispersion. The theoretical models used for consistent description of laser‐plasma interaction during femtosecond laser pulse propagation are derived and discussed. It turns out that the strongly nonlinear effects such self‐focusing followed by the pulse splitting are essential. These phenomena feature extremely complex dynamics of both the electromagnetic field and plasma density with different spatio‐temporal structures evolving at the same time. Some numerical approaches capable to handle all these complications are also discussed.

Pulse shaping by phase-modulated fiber gratings in transmission

We propose a novel approach to pulse shaping using a phase-modulated fiber Bragg gratings (FBGs) in transmission. This enables the simplification of the device fabrication while retaining the substantial advantages of FBGs in transmission. © 2013 OSA.

Modelling, simulation and validation of a twelve-pulse autotransformer rectifier for aerospace applications

A microcap SPICE circuit-level model of a 12-pulse autotransformer based rectifier for an aircraft fuel-pump motor drive is described. The importance of including the nonlinear magnetising inductance of the interphase transformers is illustrated. Small supply voltage distortions are seen to result in current imbalance in the interphase transformers, degrading the rectifier input current, and may lead to infringement of the power quality specification. The model has been validated for various operating supply voltages, frequencies and output powers, against measurements from a 3.75 kW unit.

Spectrally controlled, picosecond pulse generation from an InGaN violet diode laser

Self-seeded, gain-switched operation of an InGaN multi-quantum-well diode laser is reported for the first time. Narrow-line, wavelength-tunable, picosecond pulses have been generated from a standard, uncoated diode laser in an external cavity.

Accurate modelling of pulse transformation by adjustable-in-time medium parameters

A possibility of a strong change of an electromagnetic signal by a short sequence of time cycles of pulses that modulate the medium parameters is shown. The backward wave is demonstrated to be an inevitable result of the medium time change. Dependence of the relation between backward and forward waves on the parameters of the medium modulation is investigated. The finite statistical complexity of the electromagnetic signal transformed by a finite sequence of modulating cycles is calculated. Increase of the complexity with the number of cycles is shown.

Calculation of non-Gaussian statistics and bit error rate degradation due to pulse-to-pulse interaction

We develop a theoretical method to calculate jitter statistics of interacting solitons. Applying this approach, we have derived the non-Gaussian probability density function and calculated the bit-error rate as a function of noise level, initial separation and phase difference between solitons.

Rectangular pulse generation based on pulse reshaping using a superstructured fiber Bragg grating

In this paper, we present a technique for the shaping of short pulses based on the use of superstructured fiber Bragg gratings (SSFBGs), We apply this technique to demonstrate the generation of 20-ps rectangular pulses by phase and amplitude profiling of 2.5-ps soliton pulses. Numerical calculations validate our experimental findings.

Tailored waveform generation in mode-locked fiber lasers by in-cavity pulse shaper

We numerically show the possibility of pulse shaping in a mode-locked fiber laser by inclusion of an amplitude-phase spectral filter into the laser cavity. Various advanced temporal waveforms are generated, including parabolic, flat-top and triangular pulses. © 2014 OSA.

Model of the femtosecond laser inscription by a single pulse

A comprehensive model of processes involved in femtosecond laser inscription and the subsequent structural material modification is developed. Different time scales of the pulse-plasma dynamics and thermo-mechanical relaxation allow for separate numerical treatments of these processes, while linking them by an energy transfer equation. The model is illustrated and analysed on examples of inscription in fused silica and the results are used to explain previous experimental observations. © 2007 Springer Science+Business Media, LLC.

In-cavity transformations for new nonlinear regimes of pulse generation in mode-locked fibre lasers

We review recent progress in the research on nonlinear mechanisms of pulse generation in passively mode-locked fibre lasers. These include parabolic self-similar pulse mode-locking, 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 the possibility of achieving various regimes of advanced temporal waveform generation in a mode-locked fibre laser by inclusion of a spectral filter into the laser cavity.