Novel constant-cladding tapered-core ytterbium-doped fiber for high-power fiber laser oscillator

Abstract

Power scaling based on traditional ytterbium-doped fibers (YDFs) is limited by optical nonlinear effects and transverse mode instability (TMI) in high-power fiber lasers. Here, we propose a novel long tapered fiber with a constant cladding and tapered core (CCTC) along its axis direction. The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering (SRS) threshold and suppress higher-order mode resonance in the laser cavity. The CCTC YDF was fabricated successfully with a modified chemical vapor deposition (MCVD) method combined with solution doping technology, which has a cladding diameter of 400 μm and a varying core with a diameter of ~24 μm at both ends and ~31 μm in the middle. To test the performance of the CCTC fiber during high-power operation, an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally. As a result, a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%, although the TMI effect was observed at an output power of ~3.12 kW. The measured beam quality (M2 factor) was ~1.7, and no sign of the Raman component was observed in the spectrum. We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects, and further power scaling is promising by optimizing the structure of the YDF.

Functional Fibers and Functional Fiber-Based Components for High-Power Lasers

“…With the development of fiber preform preparation and mechanical polishing technology, the studies of tapered fibers has evolved to more degrees of freedom along the longitudinal dimension, which is driven by better pump absorption capacity and greater single-mode potential. A series of representative results at several-kilowatt-level have been reported with near single-mode outputs [76,[258][259][260][261][262][263][264][265][266][267][267][268][269][270][271][272][273][274][275][276][277][278][279][280]. Table 2 summarizes the recent progress of tapered fibers for HPFLs applications.…”

Study on laser performance of tapered ytterbium doped fiber in nanosecond pulse amplifier

“…Commercial 30/250 μm fibers could achieve a beam quality near the diffraction limitation, but could not achieve high average power and high pulse energy simultaneously 789 . With the longitudinal variation of core cladding structure, the ytterbium-doped tapered-double cladding fiber (T-DCF) could suppress SRS and beam quality deterioration, and then realized the laser output with high average power, high single-pulse energy and excellent beam quality, which provided a suitable method for improving the output performance of pulsed lasers 10 .…”

Transverse mode instability mitigation in a high-power confined-doped fiber amplifier with good beam quality through seed laser control

“…The TMI effect has now become one of the major limiting factors for the power scaling of high-brightness fiber lasers. In order to mitigate the TMI effect, various methods have been proposed, including but not limited to increasing the loss of high-order modes [6], shifting the pump or signal wavelength [7][8][9], employing the counter/bi-directional pumping scheme [10,11], increasing the ratio of cladding diameter to core diameter [12], exploiting specialty optical fiber design [13][14][15][16][17], etc. Among these solutions, adopting the specialty optical fibers, such as distributed mode filtering fiber [18], large-pitch fiber [19], tapered fiber [20], and confined-doped fiber [21], is an effective approach to solving the contradiction between the high output power and good beam quality.…”