Maxim Yu. Koptev

Towards Mid-Infrared Supercontinuum Generation With Germano-Silicate Fibers

A detailed study of supercontinuum (SC) generation in germano-silicate fibers with a femtosecond silica-based all-fiber laser system is performed. We report on more than octave spanning SC in the range 1-2.6 μm pumped at 1.6 μm as well as SC in the range 1.9-3 μm pumped at 2 μm. It is also shown theoretically that with optimal germano-silicate fiber parameters, SC extending beyond 3 μm can be produced effectively.

MW peak power diffraction limited monolithic Yb-doped tapered fiber amplifier

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 μm2 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 (M2 ~ 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.

Monolithic sub-MW peak power tapered ytterbium-doped fiber amplifier

ABSTRACT 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 µm (at the signal input end) to 50/430 µm (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° 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 (~30 µm) 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 µJ 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.. Keywords: Yb-doped tapered fiber, all-fiber megawatt system, low bend sensitive tapered fiber, ultrashort pulses amplification 1. INTRODUCTION The very rapid power scaling of both pulsed and cw Yb-doped fiber lasers dictates stringent requirements on the utilized fibers, mainly in terms of nonlinear effects threshold. Conventional single-mode Yb-doped fibers exhibit a relatively low threshold for nonlinear effects since the light is confined in a small core (6-10 µm in diameter) and propagates along long distances (above 10 m in some cases). The increasing of nonlinearity threshold is the urgent problem in the case of pulsed fiber systems, which have been demonstrated to reach power levels of several hundreds of kW and even approach MW power level. The most simple and obvious way to solve this problem is the enlargement of core diameter resulting in the enlarged mode filed diameter of the fundamental mode. In the same time, this approach has so me drawbacks: the fiber becomes a multimode, leading to degradation of output beam quality, and extremely bend-sensitive, resulting in requirement to keep the fiber straight, i.e. the system becomes cumbersome. The main goal of this work was to develop a novel approach based on utilizing of so-called tapered fibers that allows one to obtain large mode field areas and maintain an acceptable bend-loss sensitivity at the same time. The fiber parameters optimization and its using in the final amplification stage of picosecond chirped-pulse amplification system have been demonstrated. The obtained output peak power was record for all-fiber amplifying systems and approached by power level of microstructured fibers based systems.

Double-clad large mode area Er-doped fiber for high-energy and high-peak power amplifiers

The use of double-clad fibers for short pulses amplification requires high active ions concentration in order to keep the active fiber length short. In the case of Er-doped fibers an increase of concentration leads to a significant drop of efficiency due to Er ions clustering. We have demonstrated through numerical simulation that efficiency of amplifiers based on double-clad P2O5-Al2O3-SiO2 (PAS) Er-doped fibers decreases slower with Er-concentration growth if compared with standard Al2O3-SiO2 fibers. In this paper, we present single-mode large-mode-area heavily Er-doped double-clad fiber based on PAS glass matrix for short pulses amplification. The developed PAS fiber has a 36 μm singlemode core and a small signal cladding absorption of 3 dB/m at 980 nm leading to an optimal fiber length in range of 5-8 m depending on the central wavelength. At first, an all-fiber nanosecond MOPA at 1560 nm was built using our PAS fiber as the final amplifier. We obtained 28 W of average output power (efficiency of 25 % with respect to the launched pump power at 976) limited by amplified spontaneous emission. Pulse energy of 1.5 mJ was achieved at pump power level of ~120 W. We believe that it is the first demonstration of mJ-energy level single-mode nanosecond fiber system. Then, direct amplification of 100-fs source was performed using this fiber. We obtained 12 nJ pulse energy and 100 kW of peak power from the fiber which is close to the record value for Er-doped fiber amplifiers.

Sub-MW peak power diffraction-limited chirped-pulse monolithic Yb-doped tapered fiber amplifier

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.

Raman soliton generation in microstructured tellurite fiber pumped by hybrid Erbium/Thulium fiber laser system

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.

Tungstate-Tellurite Glass Microstructured Optical Fibers

Suspended core microstructured optical fibers were fabricated of high purity TeO2-WO3-La2O3 glass. The broadband emission with 1300 nm bandwidth was successfully generated in 0.8 m of fiber using 2 nJ femtosecond laser as a source.