Compact coarse wavelength division multiplexers (CCWDM Mux) is the low insertion loss version of CWDM Mux. Compared with traditional CWDM technology, CCWDM technology adopts free-space optics platform which can significantly improve optical performance. Main advantages of CCWDM Mux are high wavelength accuracy and stability, low insertion loss, high isolation and low PDL(polarization dependent loss).