On-Chip Waveguide Amplifiers for Multi-Band Optical Communications: A Review and Challenge

Erbium (Er)-doped fiber amplifier (EDFA) has achieved great success in modern optical communications for decades due to its outstanding gain performance in C-band. Nowadays, people are making efforts to make it monolithic integration due to the imperious demands from the advancement of high-performance and multi-function optoelectronic devices and chips. Except for the Er-doped waveguide amplifier, the other ion-doped on-chip waveguide amplifiers have also attracted much attention for multi-band optical communications, since they have own advantages in gain, bandwidth, selectivity of host materials, and integrability. Herein, we review the transmission characteristics of ion-doped on-chip waveguide amplifiers including gain and bandwidth, combining with the emission mechanisms and fabrication processes in applications of long-haul and short-reach optical communications. To facilitate the practical progress of the integrated waveguide amplifiers, from the perspective of gain medium, we also discuss the challenges and potential solutions for future technology roadmap. We expect that the bismuth (Bi)-doped waveguide amplifier would present impressive advantages in multi-band optical communications.