With the exponential growth in bandwidth demand, WDM (Wavelength Division Multiplexed) technology has been widely used in fiber optic networks. Adding wavelengths in the same fiber effectively increases the bandwidth capacity of a fiber and thus avoid the need to install more fibers or increase the bit rate to higher level. For example, in the optical fiber of an FTTH/FTTP 1310/1490/1550 triplex service network, the 1490 nm wavelength is used for downstream voice and data signals, 1550 nm wavele