Optical waveguide amplifiers are essential devices in integrated optical systems. Their gain bandwidths directly determine the operating wavelength of optical circuits. Due to the difficulty of developing wideband gain media, it has been a challenge to fabricate devices with broadband amplification capability, resulting in few reports on multi-band polymer waveguide amplifiers. Here, a polymer waveguide amplifier is demonstrated, which achieves loss compensation covering the whole (S+C)-band by using NaYF4:Tm,Yb@NaYF4@NaYF4:Er nanoparticles-doped SU-8 as the gain medium....