of the core glass in order to ensure the optical continuity said screen of high resolution and high luminous efficiency is used in display tubes such as night vision tubes x ray converter tubes slid scanning tubes cathode ray tubes used in oscilloscopy or in television application_number US 74762685 A description in order to define the invention let us consider in the assembly of display tubes to which the invention relates a particular example constituted by a picture intensifier tube for night vision such as is shown in fig1 said tube comprises an inlet window 40 traversed by the incident radiation 45 this through the intermediary of the photocathode 41 gives rise to a flow of electrons which is intensified by the microchannel plate 42 said densified flow of electrons will impact the screen having restored cavities 43 at the surface of the optical fibre output window 44 the input and output windows are maintained separated in a vacuum tight manner by means of a metallic washer 48 and an insulating ring 46 of a ceramic material through which ring means are led to apply electric potentials 47 for the microchannel plate the invention relates to the screen having restored cavities 43 to describe this let us first consider an optical fibre element according to the prior art as shown in fig2 said element is constituted by a core glass 10 a cladding glass 12 and grains of a luminescent material 14 filling the cavity said material under the.