Compact full-band WDM wavelength division multiplexer

The invention discloses a compact full-wave-band WDM wavelength division multiplexer which can enable the reflection wavelength of a channel to work in a full-wave-band range, is additionally providedwith an upgrading port, and facilitates the subsequent upgrading and use of other wavelengths. The compact full-band WDM wavelength division multiplexer comprises a substrate assembly, wherein a supporting layer is arranged on the substrate assembly, multiple layers of wavelength division multiplexing assemblies are arranged on the substrate assembly, the wavelength division multiplexing assemblyat the bottommost layer is mounted on the bottom plate, the other layers of wavelength division multiplexing assemblies are arranged on the supporting layer, the wavelength division multiplexing assembly comprises a first collimator group, a second collimator group, a first filter disc group and a second filter disc group, the first filter disc group and the second filter disc group are positioned between the first collim