Based on the traditional EDFA optical design, Switchable EDFA achieves the gain adjustment in a very large range through the built-in two groups of switchable optical path. Compared with the 10~15dB gain adjustment range of conventional VGA, Switchable Gain EDFA achieves a gain adjustment range of more than 25dB, taking into account the excellent key optical performance such as NF and GF. This one model covers multiple VGA indicators, effectively simplifying customers' field deployment and inventory management.