填空题 （）is an auxiliary light source of EDFA. It causes the erbium icons of an erbium doped fiber to come from E1 to E3 quantum level.

多项选择题 对于OP保护，下面说法正确的是（）

填空题 For a DWDM system, the wavelength selection and frequency spacing comply with（），recommendation while that of a CWDM system comply with the requirements of （）。