High peak and average power Yb-doped ps-pulse fiber amplifiers are of high demand for different micromachining tools. Most of commercial lasers are designed for operation near 1030 nm, which is due to high gain at this wavelength. An ultimately high peak power of ∼ MW just after the fiber amplifier and ∼3.8 GW after pulse compression [1] was achieved in lasers operated near 1030 nm by utilization of rod-type photonic crystal fibers (PCF). However, such fibers have a well-known problem: they could not be spliced with standard fibers, and also it must be kept perfectly straight. As a result, lasers based on PCF lose most of the advantages of fiber lasers – reliability, compactness and a low production cost.

We have developed a cladding pumped tapered erbium-doped fibre with a record-high core diameter for erbium-doped fibres (100 mm) and a near diffraction-limited beam quality ( μ 2 ∼ 1.3). Optimisation of the tapered fibre parameters provided a high (18 %) efficiency of pump radiation conversion at a wavelength of 976 nm into signal radiation at a wavelength of 1560 nm.

We demonstrate Kerr self-cleaning of beams in an Ytterbium doped multimode fiber taper with exponentially decreasing nonlinearity, with no accompanying frequency conversion or spectral broadening.

We demonstrate beam self-cleaning in a tapered Ytterbium-doped graded-index multimode fiber in both active and passive configurations, without accompanying self-phase modulation induced spectral broadening or frequency conversion.

We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index profile when 1064 nm pulsed beams propagate from wider (122 µm) into smaller (37 µm) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm. By taper cut-back, we observed that the dissipative landscape, i.e., a non-monotonic variation of the average beam power along the MMF, leads to modal transitions of self-cleaned beams along the taper length.

We consider a fibre laser system generating ∼10-μJ, ∼500-fs pulses with a peak power of ∼10 MW at a repetition rate of 100 kHz and emission wavelength of 1.56 μm. The system is based on a master oscillator – power amplifier configuration. The amplifier ensures chirped-pulse amplification. The pulses are then compressed by a dispersive grating compressor. The output amplifier stage is based on a specially designed tapered large mode area erbium-doped fibre for suppressing nonlinear effects. The experimental data agree with numerical simulation results for the stretcher, amplifier and compressor. The stretcher and amplifier have been simulated using a generalised nonlinear Schrödinger equation. In addition, numerical simulation results suggest that optimising the stretcher and compressor will potentially allow the peak power of the system to be scaled up to ∼30 MW.

A novel tapered Er3+-doped fiber design for high peak power amplification has been developed and tested. The core diameter was changing along 2.5 meters from 22.5 μm (single-mode operation) to 86 μm. Amplification of 2 ns pulses has resulted in peak power of 105 kW (0.25 mJ) with nearly diffraction-limited beam quality (M2<;1.27).

A novel tapered Er-doped fiber design for high peak power amplification has been developed and tested. The fiber core was based on P2O5-Al2O3-SiO2 glass matrix, which allowed simultaneous achievement of low NA and high Er content. The core diameter was changing along the fiber length from 22.5 μm (singlemode operation) to 86 μm along 2.5 meters. Amplifier based on counter propagation signal (coupled to the thin tapered fiber end) and pump (coupled into thick fiber end) was developed and a nearly diffractionlimited beam quality (M<1.27) of the output signal has been achieved. Amplification of 80 ns single frequency Gaussian-shaped pulses has resulted in peak power of 20 kW in 55 ns pulses (1.5 mJ) limited by available pump power.

We report a new ytterbium-doped active tapered fibre used in the output amplifier stage of a fibre laser system for the generation of megawatt peak power ultrashort pulses in the micro-joule energy range. The tapered fibre is single-mode at its input end (core and cladding diameters of 10 and 80 mu m) and multimode at its output end (diameters of 45 and 430 mu m), but ultrashort pulses are amplified in a quasi-single-mode regime. Using a hybrid Er/Yb fibre system comprising an erbium master oscillator and amplifier at a wavelength near 1.5 mu m, a nonlinear wavelength converter to the 1 mu m range and a three-stage ytterbium-doped fibre amplifier, we obtained pulses of 1 mu J energy and 7 ps duration, which were then compressed by a grating-pair dispersion compressor with 60% efficiency to a 130 fs duration, approaching the transform-limited pulse duration. The present experimental data agree well with numerical simulation results for pulse amplification in the three-stage amplifier.

A soliton-type erbium-doped all-fiber ring laser hybrid mode-locked with a co-action of arc-discharge single-walled carbon nanotubes (SWCNTs) and nonlinear polarization evolution (NPE) is demonstrated. For the first time, to the best of our knowledge, boron nitride-doped SWCNTs were used as a saturable absorber for passive mode-locking initiation. Moreover, the NPE was introduced through the implementation of the short-segment polarizing fiber. Owing to the NPE action in the laser cavity, significant pulse length shortening as well as pulse stability improvement were observed as compared with a SWCNTs-only mode-locked laser. The shortest achieved pulse width of near transform-limited solitons was 222 fs at the output average power of 9.1 mW and 45.5 MHz repetition frequency, corresponding to the 0.17 nJ pulse energy.

Acoustic sensitivity of the novel negative curvature hollow core fiber (NCHCF) has been investigated both experimentally and theoretically. The normalized response of NCHCF is shown to be 6 dB higher than in case of the conventional fiber.

A novel birefringent microstructured fibre (BMF) design is proposed, and its birefringence and dispersion characteristics are analysed using the finite element method. The results indicate that the proposed BMF design ensures high birefringence (∼5×10-3) at a low mode asymmetry. At a certain core ellipticity, the BMF configurations considered may have equal mode field sizes along two orthogonal axes.

Efficient wavelength conversion between telecommunication bands at 0.8 and 1.55 µm would allow these transparency windows to be more fully utilized in fibre network. Parametric wavelength converter based on four-wave mixing (FWM) in a silica microstructure fibre is very promising for solving this problem. The desired dispersion shape with the zero dispersion wavelength (ZDW) in the region of 1–1.1 µm is readily achieved with this fibre [1]. However, the nonlinear coefficient is relatively small for the pure silica fibre with the required dispersion characteristic [2]. With the goal of enhancing the FWM efficiency, we fabricated and studied the microstructure fibre with a germanosilicate core. Our fibre has a technologically simple design of 2 rings of air holes in hexagonal symmetry with the hole diameter of 2.7 µm and the pitch of 3.1 µm. The center of the core region with the diameter of 1.7 µm was doped with 24 mol % GeO 2 . A dispersion characteristic with ZDW at 1.09 µm allowed us to achieve phase matched anti-Stokes and Stokes wavelengths in the region of 0.8 and 1.55 µm, respectively, upon pumping at 1.064 µm. The measured loss did not exceed 20-30 dB/km in the bands of 0.8 and 1.55 µm. The evaluated nonlinear coefficient was 40 (W km) −1 at λ=1.064 µm (7 times higher than for a fibre with a pure silica core and the same dispersion characteristic [2]).

The dispersion and waveguide characteristics of two-layer microstructure fibres with different layer filling factors are studied theoretically and experimentally. It is shown that by changing the filling factor of the second layer, it is possible to achieve lower effective cross sections for a mode and to control dispersion characteristics in a broader range. Frequency conversion during four-wave mixing with a frequency shift of 5460 cm-1 (1098–687 nm) and efficiency of 0.1% at 200 mW of cw pump power was obtained for the first time in two-layer fibres fabricated for experiments.

Based on the interferometric technique, a setup is built for measuring the spectral dependence of chromatic dispersion in fibres with a microstructure cladding. The setup provides measurements in a broad spectral range from 670 to 1550 nm taking birefringence in the fibre into account. The results of measurements of dispersion in a standard fibre with this setup and a commercial device are in good agreement.

A pulsed fibre laser is fabricated which is based on an active fibre with a multielement cladding and an additional single-mode fibre providing nonlinear feedback. The peak output power of the laser is ∼1 kW for 20-ns pulses. The emission spectra of the laser with additional fibres having different nonlinear and dispersion properties are investigated.