I have distant memories of Smiths Industries flying a prototype optical fibre system in a BAC 1-11 (G-ASDJ ?) as a joint research venture with BAe and RAE; late 1970s.
My memory was that the fibre link was to be, or was part of a reduced stability control system.
The aircraft was aft cg loaded, further destabilised with lead wts moved aft during flight. This aspect of the tests complemented the RAE Bedford work on reduced stability in their BAC 1-11 (XX105) which used artificial destabilisation.