Yuri Chamorovskii

Highly efficient 750 W tapered double-clad ytterbium fiber laser

The results of theoretical and experimental studies of active tapered double-clad fibers, intending the optimization of its imperative parameters--tapering ratio, longitudinal profile, core/cladding diameters ratio, are presented. Using a refined taper geometry we have demonstrated power scaling of a ytterbium fiber laser pumped by low-brightness, cost-effective laser diodes up to 750 W, with 80% efficiency.

600 W power scalable single transverse mode tapered double-clad fiber laser

Pump propagation and absorption in active tapered double-clad fiber has been analyzed based on a ray optics approach. Optimization of the longitudinal shape, absorption and angular distribution of the pump beam allowed for power scaling of a ytterbium fiber laser up to 600 W with high beam quality (M2<or=1.08) and a slope efficiency of 63%. It is shown that the influence of vignetting in a tapered fiber can be avoided, resulting in high overall efficiency, in good agreement with the presented model.

Actively Q-switched 1.6-mJ tapered double-clad ytterbium-doped fiber laser.

We have demonstrated an actively Q-switched tapered double-clad fiber laser capable of single-shot generation of 1.6-mJ, 64-ns pulses. The active medium based on tapered double-clad fiber is shown to exhibit a reduced level of amplified spontaneous emission which allows for high-energy pulse extraction at extremely low repetition rates.

Tapered fiber amplifier with high gain and output power

We present a high-power ytterbium fiber amplifier based on active tapered double-clad fiber (T-DCF) and capable of high single-pass gain. The T-DCF power amplifier seeded with a 320 mW narrow-band signal generates up to 110 W of average output power corresponding to more than 25 dB gain. The amplifier exhibits near-diffraction-limited beam quality (M2 = 1.06) at the highest output power, which was limited by the available pump power. With a broadband seed source, the amplifier produced a gain of nearly 40 dB obtained for low-signal limit of the seed. The high output power combined with high gain is achieved owing to amplified spontaneous emission (ASE) filtering and increased stimulated Brillouin scattering (SBS) threshold inherent to the axially non-uniform geometry. The amplifier operates efficiently with a wide range of input seed powers thus providing the basis for one-stage tapered amplifier which combines the functions of preamplifier and power amplifier and can be a competitive alternative to multi-stage design.

Principles and performance of tapered fiber lasers: from uniform to flared geometry

We have studied the recently demonstrated concept of fiber lasers based on active tapered double-clad fiber (T-DCF) in copropagating and counterpropagating configurations, both theoretically and experimentally, and compared the performance to fiber lasers based on conventional cylindrical fibers in end-pumped configurations. Specific properties of T-DCFs were considered theoretically using a rate-equation model developed for tapered fibers, and a detailed comparative study was carried out experimentally. Furthermore, we have studied mode coupling effects in long adiabatic tapers due to coiling and local bending. The results allow us to conclude that, with proper fiber design, the T-DCF technology offers a high-potential alternative for bright, cost-effective fiber devices.

Single-mode 212 W tapered fiber laser pumped by a low-brightness source

With a tapered double-clad all-glass ytterbium fiber as a gain medium, a maximum output power of over 200 W at 1079 nm and a slope efficiency of over 70% were demonstrated. The tapered double-clad fiber concept allows for using low-brightness diode bars and results in cost-effective and efficient high-power fiber lasers. The adiabatic conical fiber gain waveguide combines improved pump absorption owing to enhanced mode mixing in the pump cladding, low-noise single fundamental mode operation with M(2)< or =1.02, and strong potential for significant power scaling.

Optical amplifiers and lasers based on tapered fiber geometry for power and energy scaling with low signal distortion

We report theoretical and experimental study of tapered double-clad fibers (T-DCF) and consider various amplifiers and lasers using this fiber as a gain medium.

Theoretical and experimental comparison of different configurations of tapered fiber lasers

Recently, we have proposed an active tapered fiber as a medium for light generation and amplification. Using the active tapered double clad fiber (T-DCF) we have demonstrated a high-power CW fiber laser, amplifier and actively Q-switched high-energy fiber laser [1–3]. The model of light generation (amplification) and pump absorption in T-DCF has been developed earlier by exploiting the ray optics approach [1,3]. The ray optics model of a fiber laser with T-DCF has certain limitations. In presented work, we discuss a model of the T-DCF fiber laser based on rate equations, and a previously developed mode-based model of light propagation in a tapered fiber [4].

250-

We demonstrate supercontinuum generation in a photonic crystal fiber pumped with 50-ns pulses from a Q -switched tapered fiber laser. The continuum spans from 600 nm to beyond 1600 nm with pulse energy up to 250 μJ at the repetition rate of 1 kHz. To the best of our knowledge, this represents the highest pulse energy of a broadband supercontinuum demonstrated to date.

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The powerful picosecond master oscillator – power amplifier (MOPA) with double clad ytterbium doped tapered fiber as a buster amplifier has been demonstrated in the presented paper. The developed MOPA has 60ps pulses with 0.3mJ pulse energy and 5MW peak power.