Principle of 7 × 5.71 Gbit/s on-off-keyed (OOK) over duty cycle division multiplexing (DCDM) technique is presented. The 40 Gbit/s DCDM signals are then recovered with a receiver operates at 5.71 GHz clock using seven sampling circuits. With seven-user DCDM we show that spectral width of return-to-zero signal can be reduced around 42.8 %. The 40 Gbit/s OOK using DCDM required an optical signal-to-noise ratio of around 31.6 dB and tolerate around 50 ps/nm of chromatic dispersion. In addition, performance of the system is compared against other multiplexing techniques and modulation formats.