A data transmission system including subscriber units (5a, 5b) and a central office unit which are interconnected via optical fibers (3, 4a, 4b, 4c), the central office unit multiplexing a video signal with signals other than the video signal to deliver them to the multiple subscriber units, and each subscriber unit demultiplexing a received signal, characterised in that the data transmission system comprises in the subscriber unit: a wavelength division multiplexer/demultiplexer (41a, 41b) having a function of eliminating the particular wavelength signal associated with the video signal, wherein the elimination of the particular wavelength is achieved by one of: - a) the wavelength division multiplexer/demultiplexer (41 a, 41 b) comprises a reflecting layer for reflecting the particular wavelength signal at an input end surface of an optical fiber of the subscriber unit, or - b) the subscriber unit comprises an optical fiber with a core and a cladding that covers an external surface of the core, and that has multiple notches formed on the cladding to reflect the particular wavelength signal, adapted to transfer the input signal to the demultiplexing means of the subscriber unit (5a, 5b), as the wavelength division multiplexer/demultiplexer (41a, 4 1 b), or - c) wherein the wavelength division multiplexer/demultiplexer (41 a, 41 b) comprises an optical waveguide that is made of a polymer and absorbs a signal with a wavelength of 1650 nm, which is employed as the particular wavelength signal. a wavelength division multiplexer/demultiplexer (41a, 41b) having a function of eliminating the particular wavelength signal associated with the video signal, wherein the elimination of the particular wavelength is achieved by one of: - a) the wavelength division multiplexer/demultiplexer (41 a, 41 b) comprises a reflecting layer for reflecting the particular wavelength signal at an input end surface of an optical fiber of the subscriber unit, or - b) the subscriber unit comprises an optical fiber with a core and a cladding that covers an external surface of the core, and that has multiple notches formed on the cladding to reflect the particular wavelength signal, adapted to transfer the input signal to the demultiplexing means of the subscriber unit (5a, 5b), as the wavelength division multiplexer/demultiplexer (41a, 4 1 b), or - c) wherein the wavelength division multiplexer/demultiplexer (41 a, 41 b) comprises an optical waveguide that is made of a polymer and absorbs a signal with a wavelength of 1650 nm, which is employed as the particular wavelength signal. - a) the wavelength division multiplexer/demultiplexer (41 a, 41 b) comprises a reflecting layer for reflecting the particular wavelength signal at an input end surface of an optical fiber of the subscriber unit, or - b) the subscriber unit comprises an optical fiber with a core and a cladding that covers an external surface of the core, and that has multiple notches formed on the cladding to reflect the particular wavelength signal, adapted to transfer the input signal to the demultiplexing means of the subscriber unit (5a, 5b), as the wavelength division multiplexer/demultiplexer (41a, 4 1 b), or - c) wherein the wavelength division multiplexer/demultiplexer (41 a, 41 b) comprises an optical waveguide that is made of a polymer and absorbs a signal with a wavelength of 1650 nm, which is employed as the particular wavelength signal.