Abstract: A coupling between an optical fibre (1) and an opto-electronic device e.g. a semiconductor laser (2) is located within a hermetically sealed housing (3,6). The device is supported on a header (14) mounted on the front wall (3) of the housing, the lead (16) to the device passes through the housing wall via a glass-to-metal seal (17,19,20), and the fibre is soldered into a ferrule (10) which is inserted through a boss (4) on the front housing wall. After alignment of the fibre with the device, the ferrule is clamped in position by two parallel sets of screws (11(a), 11(b)) inserted through the boss, and is then soldered to the boss. The housing, header, ferrule and metal component(s) of the glass-to-metal seal are all formed of the same metal, preferably gold-plated copper, to avoid differential expansion.