FR2504693A1 - FIBERGLASS CROSSOVER IN A METAL HOUSING - Google Patents

Abstract

THREADED FOR A FIBERGLASS 12 IN A METAL BOX 8, FOR WHICH THE FIBERGLASS IS FIXED WITH A VITRIFIED ENAMEL 13 AND A PRIMARY COVER 12 EXTENDS UNTIL THE VITRIFIED ENAMEL FROM THE PLACE OF WELDING TO REINFORCE THE RUPTURE PLACE LOCATED JUST ABOVE THE WELDING AREA.

Description

"Crossing for fiberglass in a metal case"
The invention relates to a fiberglass bushing in a metal case, in which an electro-optical element is housed, the glass fiber being fixed using a vitreous enamel in a hole in the case opposite the electro-optical element.

 Such a bushing for glass fibers is described in British patent application N 2 022 280. These bushings for glass fibers are of frequent use for the electrooptical components used in the optical (tele) communication system in which information in the form of light pulses is transmitted by photoconductive glass fibers from one place to another In general, said electro-optical components consist of a metal case in which an electro-optical element is mounted , like a laser, a semiconductor diode emitting light or detecting light.

For the lifespan of such electro-optical elements to be long, it is important that they can operate in a sealed enclosure isolated from the environment. Said enclosure is constituted by a metal case, which must however be provided with a bushing for the photoconductive glass fiber since the latter must be carried as close as possible (for example 100 μm) to the active surface of the semiconductor element to achieve a sufficiently high efficiency of the light transmission between the glass fiber and the active surface.

 The invention aims to provide an improved crossing for fiberglass in an airtight metal case.

 A bushing for glass fiber according to the invention is characterized in that the coefficient of expansion of the glass fiber is less than the coefficient of expansion of the enamel, the latter coefficient being in turn less than the coefficient of expansion of the metal shell and in that one end of the fiberglass fixed opposite the electro-optical element is stripped of its primary casing and fixed to the metal shell, the primary envelope of the glass fiber being inserted in vitreous enamel. In the fiber-glass bushing according to the invention, the place of welding is subjected to a radial pressure owing to the difference in coefficient of expansion of the various materials, which is advantageous, given the hermetic seal and the mechanical resistance of the bushing. In addition, the bushing for glass fiber according to the invention offers the advantage that the primary envelope protecting and reinforcing the glass fiber is inserted into the vitreous enamel of the fixing of the glass fiber. , so that a weak area of the fiberglass (especially the one just above the fixing location) is reinforced.

 The description below, with reference to the accompanying drawing, all given by way of non-limiting example, will make it clear how the invention can be implemented.

 In the single figure, the shoemaker 1 comprises a support 2, on which is fixed a photo-avalanche diode 3. The diode 3 is connected to two conductors 4 and 5, the conductor 4 of which is in contact via the sup port 2, and the conductor 5 via the connection wire 6. The conductor 5 is isolated from the support 2 using a mass of glass 7, which simultaneously secures the two conductors 4 and 5.

 A metal case 8 is fixed by welding by a flange 9 to a flange 10 of the support 2. The upper part of the case 8 has a hole II in which is fixed a glass light guide 12. At the location of the hole there is a vitrified enamel ring is placed around the glass lumiter guide 12. The vitrified enamel 13 is melted by high-frequency heating and attaches to the shoemaker 8 and the light guide 12. After the vitrified enamel 13 has cooled, the light guide 12 is fixed in the case 8 and an airtight passage for glass fibers is formed in the case 8.

 Preferably, a primary envelope (coating} 12 ′ of the photoconductive fiber 12 extends into the molten enamel 13. The primary coating 122 is quite often made of synthetic material and is thus removed from the end 14 of the fiber 12 , in order to allow good adhesion (metric) between the fiber 12 and the cap 8. The primary envelope 12 around the fiber 12 is a protective solid layer. Thus, it has proven advantageous for the primary envelope to extend into the enamel 13 so as to avoid the formation of a vulnerable spot on the fiber 12 (especially just above the spot of welding). ).

 To protect the fiber 12 and the place of welding (the vitreous enamel 13), a protective sleeve 15 is placed (using an adhesive) on the shoemaker 8 and has a hole 16 and a protective pipe 17. In the protective pipe 17 is fixed the secondary casing 18 of the glass fiber 12 by gluing or tightening the protective pipe 17 using pliers.

 The enclosure 19 around the fiberglass 12 (12 ', 18) and in the protective sleeve 15 can be filled with synthetic material (for example an epoxy resin) using the hole 16, so that the fiberglass 12 is fully submerged and protected.

 Finally, a cap 20 is slid over the protective sleeve 15 and the case 8 and fixed by welding to the edge 9 of the case 8. In the neck 21 of the cover 20 is fixed a second time using a constriction 22 ( using the pliers), the secondary envelope 18, so that the glass fiber 12 (and the vitreous enamel 13) are no longer subjected to traction and that the fixing using glue of the sleeve 15 on the case 8 is protected against the risk of detachment by impact.

 It should be noted that vitreous enamel is also known (sometimes called "welding glass"). Vitrified enamel has a lower melting point than that of fiberglass and can be applied in the form of a suspension of glass powder in a solution of nitrocellulose in amyl acetate, but also in the form of a ring of glass powder and a binder. The vitreous enamel is brought to around 440 ° C. (for example by high-frequency heating) so as to cause the glass powder to melt and to adhere to the glass fiber and to the metal shoemaker.

Claims (2)

1. Crossing for fiberglass in a metal case, in which an electrooptical element is housed, the fiberglass being fixed using a vitreous enamel in a hole in the case, opposite the electro element -optical, characterized in that the expansion coefficient of the glass fiber (12) is lower than that of the vitreous enamel (13), the expansion coefficient of which is in turn lower than that of the metal shoemaker (8) and in that one end (14) of the glass fiber fixed opposite the electro-optical element (3) is stripped of its primary envelope (12 ') and fixed to the metallized shoemaker, the primary shell of fiberglass extending into the vitreous enamel. 2. Bushing for fiberglass according to claim l, characterized in that. on the shoemaker (8) is fixed a protective sleeve (17) to which is formed a passage in which is fixed a secondary envelope (18) of the fiberglass (12), while the enclosure (19) delimited by the shoemaker and the protective sleeve is filled with a synthetic material.