Hello,
If you want to solve this problem without adding no new equipment in the network, there are generally 2 ways to solve it.
1. If the board for the interconnection is working with plug-able optical modules, you can replace the original modules into single-fiber bidirectional optical modules, so that one service only needs one fiber to work. However, one should use a module compatible with the equipment, and this type of module normally can't work with a span longer than 40km and can't reach 10Gbps speed.
2. If both long distance and high speed are required, we can use the smart line boards on OSN3500 to do the job. The smart line board can work on a 80km-span and on 40Gbps speed, such as the HSNS3 boad. This kind of board can transfer the SDH service or the ETH services, or both of them combined.