Multimode Optical Signal Dropping

Hello Everybody,

Recently we upgraded our camera to a Sony SRG-A40 4K PTZ Camera because it supports 3G signal using 3G SDI extender. This great and all, but, upon switching to full 1080p 60hz the signal kept dropping resulting in a pixelated flashing screen. We are currently utilizing multi mode fiber. The distance between the points is around 600 meters which is close to the optical extender's signal limitation. Are there any optical signal  boosters so we do not require further investment in an 800 meter multimode extender kit?

Thank you,

Fredrick