Fotp236 - iec 61280 - 2 - 9 - fibre optic communication subsystem test procedures - part 2 - 6 : digital systems - optical signal - to - noise ratio measurement for dense wavelength - division multiplexed systems Fotp236 . iec 61280 - 2 - 9 .纤维光学通信子系统试验过程.第2 - 6部分:数字系统.密集波分多路复用系统的光学信噪比测量