Abstract
We present a birefringent Yb-doped tapered double-clad fiber with a record core diameter of 96 µm. An impressive gain of over 38 dB was demonstrated for linearly polarized CW and pulsed sources at a wavelength of 1040 nm. For the CW regime the output power was70 W. For a mode-locked fiber laser a pulse energy of 28 µJ with 292 kW peak power was reached at an average output power of 28 W for a 1 MHz repetition rate. The tapered double-clad fiber has a high value of polarization extinction ratio at 30 dB and is capable of delivering the linearly polarized diffraction-limited beam (M2 = 1.09).
Highlights
The technology of powerful fiber lasers has advanced rapidly over the last decade
In order to minimize the influence of these effects and increase the output pulse energy, special active fibers with a large effective-mode area are usually used in the last stage of the amplifiers
As follows from formula (3) and the results shown in Fig. 10, the size of the mode field diameter (MFD) is linearly dependent on the core diameter of the step-index fiber with aperture 0.1, and it can be approximated by the following linear dependence: MFD = 2.39 + 0.69D[μm]
Summary
The technology of powerful fiber lasers has advanced rapidly over the last decade. Highpower fiber lasers usually consist of a relatively low-power seed laser (master oscillator) and a concatenated chain of power amplifiers (so-called MOPA scheme). There are several types of active fibers with a large effective-mode area (LMA) described in the literature that have been developed for high-power scaling. These are wellknown LMA fibers with a low-aperture core [1], microstructured rod-type fiber [2], helical core [3] or 3C fibers [4], and tapered double-clad fibers [5]. In order to minimize the nonlinear effects and further increase the stored energy, it is important to use a T-DCF with the largest possible MFD, stable polarization and single-mode regime propagation of the amplified pulse. By implementing the anisotropic T-DCF as high power amplifier, we demonstrated experimentally the CW and pulsed picosecond MOPA with an average power of up to70W
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