What is the difference between the 8100xxA connector adapter and the 81000xI connector interface?
The 8100xxA series adapters are for use with optical heads. These adapt a fiber optic connector or bare fiber to an otherwise exposed detector active area. The optical heads have a different size than most of the other Keysight instrumentation.
The 81000xI series connector interfaces are for use with Keysight instrumentation that has a fiber optic ferrule accessible at the front panel, or exterior surface. For example, the 81000xI interfaces are used with source modules, sensor modules, and on some mainframe front panels.