In one aspect the invention provides an optical circuit enclosure enclosing at least one optical circuit or optical circuit component; the enclosure comprises: a tray type container containing at least one optical circuit or optical circuit component; a tray type closure member closing the container; the closure member containing at least one further optical circuit component on an external side thereof for optically connecting the enclosed component to an external optical circuit; and sealing means providing a moisture resistant seal between the container and the closure member.