FR2693559A1 - Hermetically sealed channel for optical fibre within metal tube - uses seal made by compression and heating of fusible glass powder within metal tube through which fibre passes - Google Patents

Abstract

The channel for the optical fibre (3), stripped of its insulation, is sealed inside a metal tube (14). The seal itself is situated in a machined valve (16) perpendicular to the axis of the tube and remote from its ends. The seal is created by the compression and heating of fusible glass powder at a temperature less than 600 degrees Celsius. ADVANTAGE - Secures the fibre within the sealed zone and minimises the level of rejects due to the fragility of the fibre within this zone.

Description

 The development of optoelectronics requires the production of housings comprising hermetic conductive crossings according to a technology known to those skilled in the art, but also the hermetic passage only through the wall of the optical fiber housing, which poses problems much more complex techniques.

 Figure 1 shows, in section, the way in which these passages are made: a ferro-nickel alloy tube 1 with an outside diameter of about 3 mm and an inside diameter of 200; im has at its end a hollow area Z funnel-shaped; the optical fiber 3 whose outer sheath 4 has been removed over the entire length penetrating into the housing 5 is introduced inside the tube 1; a paste 6 made of a volatile binder and a powder of a fusible glass at a relatively low temperature (less than 600 "C) is deposited in zone 2, around the fiber 3; this paste is then melted by means of the flame of a micro-torch, thus obtaining a hermetic seal.

 A second tube 7, sealed at 8 in an identical manner, holds the optical fiber and makes it possible to position its end exactly opposite the laser diode 9. This sealing 8, inside the housing, is not necessarily hermetic but must be made with a glass, since the presence of a resin capable of releasing organic vapors over time is to be prohibited throughout the housing.

 This relatively complex technology is difficult to implement. In addition, at the glass seals 6 and 8, the silica optical fiber is slightly attacked on the surface during the melting of the glass and, as it is not maintained beyond the tube 1, the assembly is very fragile . The fiber thus equipped with tubes 1 and 7 is then introduced into the tube 10 of the housing and the tubes 1 and 10 are welded together, hermetically, by laser or by any other suitable means, at their junction 11.

 All these operations are very delicate and the proportion of waste is high, resulting in an overall cost that is difficult to accept.

- The present invention consists of a particular arrangement of seals, which aims to keep the fiber in the sealing areas and to remove the numerous waste products due to the brittleness of the fiber in these areas.

 The original idea used here is not to make the seals at the end of the tubes, but by means of a factory light in the tube, perpendicular to its axis, quite far from the end.

In this way, the optical fiber, stripped of its sheath over about 30 mm from its end, is kept in a straight line on either side of the weakened zone and cannot break by bending. ,
Figure 2 shows the production of seals according to the present invention. The openings necessary for the seals are here cylindrical holes 12 and 13 passing right through the tubes 14 and 15, perpendicular to their axis. These holes have a diameter of the order of 1 mm. The seals are made using either a preform obtained from glass powder or a small fragment of a glass cane, or a small deposit of glass powder paste, 16 and 17.

 The glass chosen must simultaneously have a sufficiently low frank melting temperature (less than 600 "C) and a coefficient of thermal expansion between room temperature and the temperature of softening dilatometric lower or at most equal to that of the metal of the tubes 1 and 7.

 The glass can be melted either by the flame of a micro-torch, or by localized heating at high frequency, or by a loop heated by the Joule effect.

 The realization of hermetic passages of optical fibers in metal tubes according to the above principle and using one of the glass deposition methods and one of the recommended heating modes is relatively easy and allows very good manufacturing yields to be obtained. and reduced costs.

 The assembly of the assembly, optical fiber sealed in the tubes 14 and 15, is introduced into the housing 5 by the tube 10, the tube 14 being welded or brazed to the tube 10 by any suitable means.

 FIG. 3 shows the final embodiment obtained of the optical fiber in the housing.

Claims (7)

1- Hermetic passage of an optical fiber 3 stripped of its  sheath at its end in a metal tube 14, character  laughed at in that the hermetic seal is located in a  light 16 machined in the metal tube 14 perpendicular-  lie at its axis and at a distance from its ends. 2-- Passage - according to claim 1, characterized in that  The sceTTeesnt is made by means of a glass preform  obtained by compression and sintering of powder from a fu glass  susceptible to a temperature lower than 600 C.  3- Passage according to claim 1, characterized in that the  sealing is carried out by means of a fragment of a cane  a fusible glass at a temperature below 6000 C.  4- Passage according to claim 1, characterized in that the  sealing is carried out by means of a paste prepared from  powder from a fusible glass at a temperature below  600 C and a volatile binder.  5- Passage according to claim 1 in combination with one of  Claims 2 to 4, characterized in that the melting of the glass  is obtained by localized high frequency heating of the tube  metallic.  6- Passage according to claim 1 in combination with one of  claims 2 to 4, characterized in that the fusion of  glass is obtained by means of a heated metal loop  by-effect Joule.  7- Passage according to claim 2 in combination with one - of claims 2 to 4, characterized in that the fusion  glass is obtained by means of a microchalu flame  meau.