Sealed fiber optic gyroscope assembly

A sealed fibre optic assembly for a fibre optic gyroscope which assembly comprises a fibre optic support ring carrying at least one loop of optic fibre, a hermetically sealed casing surrounding said support ring and comprising a base plate, a perimeter wall upstanding from the base plate and surrounding said support ring, a cover secured to the perimeter wall so as to close the casing on the side of the support ring remote from the base plate and electrically connecting circuitry comprising external electrical terminals and electrical connectors extending from said terminals through part of the casing in sealed engagement with the casing, to the interior of the casing, and optical circuitry coupled to said loop to direct light in opposite directions around said loop and to receive light from the loop, said optical circuitry comprising a light source, a light detector and phase detecting means, and being mounted on the base plate within said sealed casing, and electrically coupled to said electrical connectors in the interior of the casing, and said base plate comprising electrically insulating material and including buried electrical connectors extending below said perimeter wall interconnecting said optical circuitry with said external electrical terminals.