Paving way for fabrication of silica-based single -frequency seed laser: Ultrahighly Yb-doped optical fibers via sol-gel method combined with silica tube inner wall coating and fusion-tapering technique

•Sol-gel method combined with silica tube inner wall coating and fusion-tapering.•Overcomes rare-earth dissolution rate limit of silica fibers and splicing problem.•A ~ 1.03 μm laser with 70 dB-SNR is achieved.•Fiber core can extend to any heavily rare-earth-doped system.