WDC Wavelength Dependent Coupler (or WDM Coupler)

The point of difference between WDC and WIC is that WDC regards wavelength as the basis of assigning input light to output channels but WIC stands on the ratio.

The picture shows the common component of three ports, among them regard the common end as the end of input from the light source, then the two output ports can have alternatives basing on different wavelengths. The main applications were traditional WDM, Wavelength Dependent Multiplexer component (1310/1550nm), and pumping power coupler of EDFA, Erbium Doping Fiber Amplifier (1480/1550nm or 980/1550nm), and so on.

So far as its applications is concerned, we maybe want to know how good it is to select the light of different wavelengths from light source at output ports. The parameter, Isolation, was useful to be defined:
Isolation = -10log(P2/P1) and should be greater than 20 to about 50dB.

Because the light is reversible, the WDC can be used for dividing waves for the light source (DeMux, the common end is regarded as the input end) or mixing waves (Mux, the common end is regarded as the output end) in a optical communication system.

Generally, its internal main structure is the thin film filter where regarded as the wavelength selector.