Glass seals may be essential parts for fibre optic sensors, influencing their efficien cy, handling or reliabdlity. Housings for light emitting or light detecting elements with sealed in windows or lenses determine the light coupling to the fibres. The solder glass sealing technique is of increasing importance. Hermetic seals of fibres to metal tubes are also realised with solder glass. The technique is described and possibilities are mentioned to vary geometries and fibre end conditions.