Passive optical delivering network using conventional graded-index multi-mode fiber with mode division multiplexing and sub-carrier multiplexing

In today's passive optical network, each optical network unit receives not only the data that belongs to its user but also the data of other users. This makes the network vulnerable to sniffing even though encryption has been done. To solve this problem, optical channels from an optical line terminal are switched directly to different user locations in such a way that the optical network unit receives only the data that belongs to its user. This paper exploits a mode-forming technique in an optical network of multi-mode fiber (MMF) using a commercially viable fiber coupler to optically route only the desired channel to the desired destination. We have successfully implemented a 2 x 2 mode-forming network, and the total channel coefficients related to each user are estimated at their locations. The feasibility of the proposed technique has been confirmed using a conventional graded-index MMF. The total channel matrix coefficients of this network are obtained by processing the transmitted training sequence in their user locations. A pre-multiple-input-multiple-output equalizer is implemented at the transmitter. The channels are successfully transmitted to their destinations, clarifying wavelength independence while maintaining data security to some extent. Furthermore, the exchange of channel in the output port is also supported by this network.