A new type fiber interferometer has been fabricated. It is a Mach-Zehnder Interferometer made of two 3×3 single-mode fiber couplers connected by 3 single-mode fibers. The lengths of these 3 single-mode fiber are L, L+ΔL, and L+2ΔL respectively. This interferometer acts as a 3 channel wavelength-division-multiplexer. The wavelength between two channels is dependent on ΔL only. The experimental sample tested offers 1.6 nm wavelength division spacing and 0.6 dB total insertion loss at 1.5 μm working wavelength.