The spectral characteristics of all fiber Mach Zehnder interferometer structure are analyzed, and the all fiber dense wavelength division multiplexers (DWDM) with the smallest spacing channel of 0.45 nm are fabricated, using the equipment which we designed for fabricating coupler. The Fabricated DWDM operating wavelength in the range from 1530 to 1570 nm exhibits ultra low loss, polarization insensitivity, and good temperature and mechanism stability.