can you help me what's cisco gigabit module can run on FO multimode >1 km?
it is a limit due to a combination of speed modulation tecniques and attenuation.
It is not a choice of Cisco for its products.
you should deploy SM fiber in parallel with current MM fiber.
As a temporary fix you could think if you have more links FE over MM and to build a port-channel if you have free MM fiber already deployed.
Hope to help