A missing connection when using fibre optics can be due to a variety of reasons that should be systematically checked: Compatibility of transmitter and receiver: Check whether the transmitter and receiver support the same wavelengths and power ranges. Check the cabling: Check whether Rx and Tx are connected, whether the cables have been bent too much, are too long or damaged and therefore have too high an attenuation. Check the splice: Splice points can cause excessive attenuation due to contamination, blunt blades or lack of polish.