Only one Mach-Zehnder interferometer is used in the proposed quantum bit distribution system where the two arms composing the Mach-Zehnder interferometer have been used as the transmission line. The loss of the photons due to absorption will decrease and the wavelets composing the photon are expected to transmit longer distance. The optical cable which contains many fiber belts which contain many fibers in parallel that is possible to make a Mach-Zehnder
interferometer with its two arms as long as possible. This transmission system uses only two couplers and physically ensures transmission security.