Approaching high gain in rare-earth-doped waveguide amplifiers: a technological review

With the advantages in integration, miniaturization and economical efficiency, the rare-earth doped waveguide amplifier (RDWA) is developed as an amplifier of new generation. Two feasible ways to optimize RDWA are to improve luminous efficiency of rare-earth doped in the material as well as to reduce the loss of the amplifier. This optimization of RDWA requires more applicable materials, high performance waveguide structure and ultra-low loss materials. This paper reviews glass-based, polymer-based, silicon-based and low-loss material based RDWA, and pictured the prospects of practical applications and possible development of RDWA.