The transceiver converts the optical signal into the electrical signal needed by the device, and it also converts the signal from the device back to the fiber optic network.
High speed direct connection cables are used for direct connections between active devices (switches, servers, etc.) when data rates are 10G and above. The advantages are that the direct connection cables have an easy plug & play structure and they are more cost-effective than a solution combining fiber optic cables and optical transceivers. Also, they have lower power consumption compared to the transceivers.