Patent ID: 8190024

Claim:
A module comprising: a first light source configured to emit a first light signal to one or more empty channels of an in-service Wavelength Division Multiplexing (“WDM”) system; a tunable second light source configured to emit a second light signal to the one or more empty channels to test the one or more empty channels; and a first switch module configured to: receive from the first light source and output to the one or more empty channels, the first light signal during a first time interval; and receive from the second light source and output to the one or more empty channels, the second light signal during a second time interval, the second time interval being a duration wherein a channel power monitoring function of the in-service WDM system is not triggered; and a testing output module configured to receive and analyze an output test signal, comprising: a splitter configured to receive and output the output test signal; a clock recovery module configured to receive the output test signal from the splitter and output a clock pulse indicative of a output time interval during which the output test signal is received; a second switch module configured to, in response to receiving the clock pulse from the clock recovery module: receive the output test signal from the splitter; and output the output test signal during the output time interval; and a signal analyzer configured to analyze the output test signal.