Spectral Broadening Suppressed by a Gain-Enhanced Fiber in Polarization Maintaining High-Power Systems

Abstract

A gain-enhanced 10/125 µm polarizationmaintaining Yb-doped fiber (PMYDF), with the cladding absorption of 7.5 dB/m at 976nm, for narrow linewidth linearly polarized fiber oscillator or amplifiers is presented. By utilizing the gain-enhanced PMYDF in an all-fiber laser oscillator, an output power of 123 W is achieved with applying appropriate bending strategies and thermal management, corresponding to the slope efficiency of 86.7%. By applying the gain-enhanced PMYDF in seed, an increase of 34% in the longitudinal mode interval is effectively achieved compared to the commercial PMYDF, while the number of longitudinal modes is only 75%. According to the main oscillation power amplification (MOPA) system, the total amount of spectral broadening applying the seed with the gainenhanced PMYDF are only 67%, 64% and 54% of applying the seed with the commercial PMYDF, corresponding to co-pumping, bi-pumping and counter-pumping schemes, respectively.

3.2 kW, 0.22 nm narrow-linewidth MOPA configuration fiber laser with a homemade polarization-maintaining Yb-doped fiber

“…An all-fiber high-power narrow-linewidth linearly polarized MOPA was built up as shown in Figure 2, which has been described in our previous publication [5,32]. The system contains a PM-FOL seed and the main PM amplifier.…”

“…Different from the preparation of conventional Yb-doped fiber (YDF), the preparation of PMYDF needs to add two sets of processes: preform drilling and boron rod assembly. Subsequently, after achieving a well-prepared polarization maintaining (PM) preform, at temperatures of 1980 °C, the preform assembly was pulled into a 20/400 μm fiber with a circular cladding and coated with a low-index polymer [5].…”

“…High-power narrow-linewidth fiber lasers or amplifiers with linearly polarized have been a major area of interest within the field of gravitational wave detection (GWD), non-linear frequency conversion (NFC), spectral beam combining (SBC), coherent beam combining (CBC) [1][2][3][4][5][6], and ultrafast lasers [7][8][9][10][11][12], etc., Over the last decade, ytterbium (Yb)-doped master oscillator power amplifiers (MOPAs) with linearly polarized ones have made great progress, and the power scaling has reached the muti-kilowatt level [13][14][15]. However, a number of destructive non-linear phenomena, including stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and thermal mode instability (MI), can jeopardize the stability of the laser system because of the high intensity in the fiber core [6,[16][17][18].…”

“…However, few studies are reported on the fiber design solutions of MI in a linearly polarized fiber laser system due to its complexity of polarization-maintaining Yb-doped fiber (PMYDF) structure manufacturing. The traditional modified chemical vapor deposition (MCVD) technology combined with the solution doping process (SDP) is considered to be an easy and effective strategy to design the core NA of fiber and manufacture the excellent PMYDF [5,32]. The detailed experimental studies on the influence of core NA of the PMYDF have a significant impact on the further power scaling of a highpower linearly polarized fiber laser.…”

“…Taking the various strategies of seed sources into consideration, some typical approaches to realize high-power narrow-linewidth linearly polarized fiber amplifiers are to use phase-modulated singlefrequency laser (PMSFL) seeds [14,15], super-fluorescent (SF) seeds [33,34], random fiber laser (RFL) seeds [35,36], and fiber oscillator laser (FOL) seeds [5,13,32]. And the multi-stage pre-amplifier and main-amplifier schemes based on the PMSFL seeds, SF seeds, and RFL seeds make the entire system complex and expensive while the scheme based on the FOL seeds is straightforward and practical due to its one-stage amplification.…”