Point-by-point femtosecond laser inscribed chirped Bragg gratings are good candidates for use in fiber chirped pulse amplification systems due to the high flexibility of their dispersion properties, low cost, and no length limitation. However, such gratings have two significant drawbacks: high losses and distortions of the shortwavelength part of the spectrum when operating in the normal group velocity dispersion mode. We propose a novel approach based on writing such gratings in a highly doped active fiber, which allows us to correct both shortcomings. We have also demonstrated, for the first time to our knowledge, a successful use of such gratings as stretchers in a fiber chirped pulse amplification system.

We present a high-power erbium-doped all-fiber source that generates rectangular-shaped pulses with durations ranging from 200$\mu$s to 5 ms and pulse energies up to 130 mJ.The laser has a stable single-mode output, a compact size and was designed for fractional photorejuvenation procedures.

Broadband supercontinuum (SC) fiber sources covering the mid-IR range have many significant applications, largely due to their compactness, reliability, and ease of use. However, most of the existing SC fiber sources cannot boast of either high reliability or a wide bandwidth. Thus, supercontinuum sources based on silica fibers are robust, but are not capable of generating SC in the mid-IR range. Sources based on soft glasses (tellurite, chalcogenide, etc.) generate broadband SC in the mid-IR range but are not used commercially, due to the poor mechanical and chemical characteristics of such fibers. In this work, we propose a new approach consisting of cascade generation of a supercontinuum sequentially in a silica photonic crystal fiber (PCF) and a germanate fiber. Using a standard ytterbium chirped-pulse amplification (CPA) laser system for pumping, we have demonstrated a supercontinuum in the range of 450–2950 nm in PCF and germanate fiber firmly connected by a standard fusion splicing technique. Further optimization of the cascade pump will make it possible to create a compact and reliable all-fiber SC source from the visible to mid-IR range.

An all-fiber high-power erbium-doped fiber laser (EDFL) source generating optical pulses from 200 µs to 5 ms with a stable rectangular envelope for fractional photo-rejuvenation is proposed and experimentally demonstrated. A master oscillator power amplifier (MOPA) configuration composed of a master oscillator, an acousto-optic modulator (AOM), and a one-stage amplifier is designed and employed in the EDFL to serve as an efficient laser system with excellent output performance. To avoid multistage amplifiers, the master oscillator generates 1.5 W, and a Yb-free Er-doped large-mode-area (LMA) active fiber is used for a one-stage power amplifier. There are two benefits to this approach: first, modulation of both pump and seed pulses is used to achieve clear rectangular shaped pulses without amplified spontaneous emission (ASE) growth; and second, there are no power limitations in the amplifier and undesirable 1 µm ASE compared to Er/Yb systems. We have reached 28.6 W of peak power with 26% slope efficiency limited only by available pump power, so the system can be easily scaled for achieving a higher peak power.

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.

We propose two-color pump schemes for CW Er-doped tellurite fiber lasers and amplifiers in the 2.7-2.8 mu m range at the I-4(11/2 )-> I-4(13/2) transition. The use of the first pump wavelength of 0.98 mu m (I-4(15/2 )-> I-4(11/2)) or 1.56 mu m (I-4(15/2) -> I-4(13/2)) and the second pump wavelength of 1.7 mu m (I-4(13/2 ->) I-4(9/2)) allows obtaining gain at relatively low powers. We have performed a theoretical study of laser operation under two-color pump on the basis of the experimentally measured parameters of the specially prepared Er-doped tellurite fiber from TeO2-ZnO-La2O3-Na2O glass. It has been shown numerically that, for an optimal fiber length, the small-signal gain may exceed 18 dB and laser generation may be achieved with a relatively low threshold of a few hundreds of mW and a maximum slope efficiency can be similar to 40%. In addition, we have demonstrated in experiment a prototype of the power-scalable Er silica fiber source generating simultaneously near 1.56 and 1.7 mu m, which may be used for implementing the proposed two-color pumped laser and amplifier.

We manufactured and characterized a low-loss gain fiber based on high-purity TeO2 -ZnO-La2O3-Na2O undoped glass for 100-mu m cladding and TeO2 -ZnO-La2O3-Na2O glass for 10-mu m core doped with 0.24 mol% Er2O3. To confirm that the produced fiber is a promising active element for the infrared range, we demonstrated experimentally broadband laser amplification and CW generation at the I-4(13/2) -> I-4(15/2) transition at 1555 nm with a single-mode diode pump at 975 nm at the I-4(15/2) -> I-4(11/2) transition. We developed a numerical model calibrated to the experimental data for prediction and optimization of laser characteristics in schemes with different parameters. The model describes single- wavelength lasing as well as dual-wavelength cascade lasing at 1555 nm and 2800 nm. It was shown numerically that for the optimized parameters, the maximum slope efficiency at 2800 nm at the I-4(11/2) -> I-4(13/2) transition can reach similar to 20%. The maximum calculated efficiency at 1555 nm exceeds 30%.

We designed and developed tapered suspended-core fibers of high-purity As39Se61 glass for supercontinuum generation in the mid-IR with a standard fiber laser pump source at 2μm. It was shown that microstructuring allows shifting a zero dispersion wavelength to the range shorter than 2μm in the fiber waist with a core diameter of about 1μm. In this case, supercontinuum generation in the 1–10μm range was obtained numerically with 150-fs 100-pJ pump pulses at 2μm. We also performed experiments on wavelength conversion of ultrashort optical pulses at 1.57μm from Er: fiber laser system in the manufactured As-Se tapered fibers. The measured broadening spectra were in a good agreement with the ones simulated numerically.

Ultrabroadband amplification and two-color CW lasing simultaneously near 1.9 μm and 2.3 μm in a Tm3+-doped tellurite fiber were demonstrated experimentally, for the first time to the best of our knowledge. A low-loss Tm3+-doped core fiber from TeO2–ZnO–La2O3–Na2O glasses stable against crystallization was produced by a special technique, providing a low concentration of hydroxyl groups. Supercontinuum from a highly GeO2 doped silica fiber pumped by an Er fiber laser system was used as a seed for an amplifier. A maximum gain of 30 dB and 7 dB was measured at 1.9 μm and 2.3 μm, respectively. We report detailed experimental and theoretical studies, which are in a very good agreement, of laser amplification and generation in the manufactured fiber with carefully measured and calculated parameters. A quantitatively verified numerical model was used to predict power scalability at 2.3 μm in schemes with optimized parameters at increased pump power. The presented results show that a high-quality tellurite fiber is a promising candidate for developing lasers in the 2.3 μm atmospheric window which are particularly relevant for applications in gas sensing, eye-safe laser radars, breath analysis, remote sensing and stand-off trace gas detection.

The amplification of ultrashort signals in the range 2.7 – 3 μm in active tellurite glass fibres with high Kerr nonlinearity and high concentration of erbium ions in the core is theoretically investigated under diode pumping at a wavelength of 0.975 μm. The possibility of producing pulses with the energy ∼10 nJ and the duration smaller than 100 fs with ∼20 dB gain is shown. Moreover, using a specially developed iterative computer algorithm, the possibility of determining the intensity and phase of the generated pulses by measuring their fundamental spectra and two additional spectra obtained by means of nonlinear-optical conversion in short pieces of these optical fibres is demonstrated. Optical fibre samples are made of high-purity TeO2 – ZnO – La2O3 – Na2O glasses with 1021 cm−3 concentration of erbium ions in the core and a low content of hydroxyl groups that causes small losses in the spectral range under consideration. The group velocity dispersions, effective mode fields, nonlinear coefficients and field overlap integrals of the LP01 fundamental modes with a doped core for optical fibres with different core diameters are calculated, and the emission and absorption cross sections are calculated basing on the experimental luminescence spectrum. The optimal parameters of the amplifier are determined by numerically modelling the dynamics of ultrashort pulses using the measured and calculated characteristics.

Chirped pulse monolithic fiber amplifier based on a newly developed tapered polarization maintaining Yb-doped fiber has been developed and optimized. A novel amplification regime in a relatively long (220 cm) tapered fiber of improved design, which has been theoretically predicted, allowed us to achieve an ultimate high peak power. In this regime, the signal propagates most of the fiber without amplification and growths very rapidly only in the last 80 cm of the tapered fiber, which has a mode field area of approximately 1000 mu m(2) near the output. We have demonstrated amplification of 20 ps chirped pulses centered at 1056-nm with spectral width of 20 nm to 0.7 MW peak power directly from the tapered fiber amplifier. The pulses had a diffraction limited quality (M-2 similar to 1.124) and could be compressed down to 350 fs with 50% efficiency. In addition, amplification of narrow-band 9 ps pulses centered at 1064 nm to a peak power of 1.8 MW directly from the tapered fiber amplifier was demonstrated.

We demonstrate a novel amplification regime in a counter-pumped, relatively long (2 meters), large mode area, highly Yb-doped and polarization-maintaining tapered fiber, which offers a high peak power directly from the amplifier. The main feature of this regime is that the amplifying signal propagates through a thin part of the tapered fiber without amplification and experiences an extremely high gain in the thick part of the tapered fiber, where most of the pump power is absorbed. In this regime, we have demonstrated 8 ps pulse amplification to a peak power of up to 0.76 MW, which is limited by appearance of stimulated Raman scattering. In the same regime, 28 ps chirped pulses are amplified to a peak power of 0.35 MW directly from the amplifier and then compressed with 70% efficiency to 315 ± 10 fs, corresponding to an estimated peak power of 22 MW.

A new variant of the fiber laser for generation of ultrashort pulse bunches and sequences with repetition rate in the range of 8-260 GHz, which combines a nonlinear amplifying loop mirror and a comb spectral filter for stabilization of the pulse separation, was demonstrated. We showed that a well-ordered and equidistant structure of the pulse sequence is maintained on a nanosecond timescale.

In this study, we propose a widely tunable in the 1.6-2.65 μm range femtosecond fiber laser source, generating high-quality sech-shaped pulses with the duration of order 100 fs. Experimental setup contains hybrid all-fiber Er/Tm pump laser generating 150 fs pulses of 2 nJ in Erbium (1.56 μm) channel and 125 fs pulses of 4 nJ in Thulium (2 μm) channel respectively. This laser source was coupled to a 50 cm piece of suspended-core microstructured TeO2-WO3- La2O3 glass fiber with launching efficiency of about 10%. We have observed Raman self-frequency shifting solitons in this fiber with maximum red shift of 2.25 μm for Erbium channel and 2.65 μm for Thulium channel. By varying energy of pump pulses, solitons can be tuned in broadband spectral region. We have made theoretical studies of nonlinear pulse dynamics in the tellurite fiber with carefully measured and calculated parameters. Numerical simulation is in a very good agreement with the experiment

We have investigated a new fibre laser configuration for the generation of ultrashort pulses at a repetition rate far exceeding the fundamental cavity frequency. The laser configuration includes a nonlinear amplifying mirror as an artificial saturable absorber for mode locking and a spectral comb filter for pulse separation stabilisation. Generation of trains and sequences of ultrashort pulses at a repetition rate tunable in the range 8 - 200 GHz has been demonstrated experimentally. The pulses generated by the laser have been shown to retain an ordered, equidistant structure on a nanosecond timescale.

We demonstrate a fibre laser source generating ultrashort pulses tunable in the range 2-2.5 μm. The source is based on a hybrid Er/Tm fiber laser system and microstructured suspended-core tellurite fiber where Raman soliton shifting occurs. Nonlinear soliton dynamics is studied and possibility of tuning beyond 3 μm is shown.

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.

In this study, we present a novel monolithic ytterbium-doped fiber amplifier with more than 0.5 MW peak power output power. The amplifier is based on a 2.1 m long tapered fiber with core/cladding diameters changing from 10/80 mu m (at the signal input end) to 50/430 mu m (signal output, pump input). The fiber has all-glass polarization-maintaining design, that make possible utilization of conventional FC adapter and standard angle polishing to 7 degrees for thick end. Pump absorption was measured to be 8 dB at 915 nm for the whole fiber length. Despite a very large mode area (similar to 30 mu m) the tapered fiber demonstrates low bend sensitivity (it is possible to coil tapered fiber with 9 cm radius) and a diffraction limited beam quality. In the amplifier the pump power was coupled through the thick end by means of collimating and focusing lenses. Dichroic mirror employed to separate output signal and counter-propagating pump power. We obtained 3.5 W of average output power for a 5 mW seed signal (coupled by usual fusion splicing through a thin end) corresponding to a 28 dB gain. The amplified pulses have duration of about 5 ps and energy of about 3.3 mu J that corresponding to over 0.5 MW peak power. The spectral width was 28 nm operating with center wavelength of 1057 nm. To the best of our knowledge it is the highest peak power obtained directly from the all-fiber amplifier..

A turnkey fiber laser source generating high-quality pulses with a spectral sech shape and Fourier transform-limited duration of order 100 fs widely tunable in the 1.6-2.65 μm range is presented. It is based on Raman soliton self-frequency shifting in the suspended-core microstructured TeO2-WO3-La2O3 glass fiber pumped by a hybrid Er/Tm fiber system. Detailed experimental and theoretical studies, which are in a very good agreement, of nonlinear pulse dynamics in the tellurite fiber with carefully measured and calculated parameters are reported. A quantitatively verified numerical model is used to show Raman soliton shift in the range well beyond 3 μm for increased pump energy.