JPH0667038A - Airtightly sealed structure of optical fiber introducing part - Google Patents

Abstract

PURPOSE:To relieve stress to an optical fiber and to prevent the deterio-ration of the characteristics of the optical fiber by reducing the contact area of a low m.p. glass for airtight sealing with the optical fiber. CONSTITUTION:An optical fiber 1 is allowed to pierce through a metal pipe 4 with a hole of a small diameter for injecting a low m.p. glass, glass pipes 6 used as positioning in common are inserted into the coated parts 2 at the both ends of the optical fiber 1 and the low m.p. glass powder 31 is filled from the small diameter hole of the metal pipe 4 in the state wher the optical fiber 1 is arranged so that the small diameter hole come to the inside of the end face. The metal pipe 4 is then heated with a high-frequency heater 7 to melt the low m.p. glass powder 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airtight structure for an optical fiber introducing section used in an optical device.

[0002]

2. Description of the Related Art Conventionally, an optical device in which optical components such as optical semiconductor elements and lenses / prisms are built in a package requires hermetic sealing in order to secure sufficient reliability. As an airtight method, the package alone has 10 ^-8 at
The seam welding method is generally used, which can secure the airtightness of about m · cc / sec. However, only the optical fiber introduction part of this optical device cannot secure high airtightness like seam welding from the resin material protecting the optical fiber,
A method of hermetically sealing an optical fiber by using a resin such as an adhesive has been used. In the airtight sealing method using such a resin, 10 ⁻⁴ to 10 ⁻⁶ atm · cc / se
Only the airtightness of about c was obtained, which was insufficient for ensuring the reliability of the optical semiconductor element.

As a conventional example of achieving a high airtightness in the optical fiber introduction portion, there is a method of directly depositing metal on the optical fiber and fixing it to the surrounding pipe or package with solder. This method can secure the airtightness equivalent to that of seam welding, but has the problem that the cost is high and the process is complicated because vapor deposition of metal on the optical fiber is indispensable.

In recent years, a method has been adopted in which an optical fiber is directly fixed to a metal pipe by melting low melting glass. FIG. 2 shows the structure of the hermetically sealed portion using this type of low melting point glass.

In this method, first, a part of the coating UV curable resin 22 coated on the optical fiber 21 is peeled off to expose the optical fiber 21. Then, the low melting point glass 23 is formed, for example, in the shape of a pipe-shaped tablet, and is inserted into the metal pipe 24 with the optical fiber 21 exposed through the through hole of the tablet. A ceramic pipe 25 for positioning is press-fitted at the tip of the metal pipe 24 to prevent the optical fiber 21 from being biased in one direction. The low melting point glass 23 is melted by heating from the outside of the metal pipe 24 and applying heat above a certain level to the low melting point glass 23 inside the metal pipe 24.

Since the optical fiber 21, the low melting point glass 23, and the metal pipe 24 have smaller thermal expansion coefficients in this order, when they are cooled from the heated state, they are sequentially compressed from the outside. For example, when SUS304 is used for the metal pipe 24, the thermal expansion coefficient is 5 × 10 −7, 60 × 10 −7, 180 × in the order of the optical fiber 21, the low melting point glass 23, and the metal pipe 24.
It will be 10-7. Due to this difference in the coefficient of thermal expansion, a strong compressive force is generated with respect to the optical fiber, and the optical fiber 21, the low melting point glass 23, and the metal pipe 24 are fixed in a completely adhered state.

[0007]

In this conventional structure,
Since the optical expansion coefficient of the optical fiber 21, the low melting point glass 23, and the metal pipe 24 has a large difference, when the low melting point glass 23 is melted and fixed, the optical fiber 21 is fixed with a considerable stress applied. . In the case of a polarization-maintaining fiber that transmits while preserving the polarization characteristics in the optical fiber 1, the polarization-maintaining characteristics deteriorate due to the stress on the optical fiber 21 when the low melting point glass 23 is fixed, and a sufficient extinction ratio is obtained. There is a problem that cannot be secured.

Further, in the conventional structure, the positioning ceramic pipe 25 is press-fitted into only one end of the metal pipe 24,
The other end is a free structure. Therefore, the take-out position of the outlet of the metal pipe 24 of the optical fiber 21 is deviated from the center, and uneven stress is further applied to the optical fiber 1.
There is a problem that the extinction ratio deteriorates.

[0009]

The airtight sealing structure of the optical fiber introducing portion according to the present invention is an optical fiber in which the coating of the central portion is removed to expose the core wire portion, and the core wire portion of the optical fiber is substantially centered. And a metal pipe having a hole formed at a position corresponding to substantially the center of the core wire, and inserted between the optical fiber and the metal pipe so as to face each other from both ends of the metal pipe. And a pair of glass pipes for positioning the optical fiber with respect to the metal pipe, and a low-melting glass filled with a hole in the metal pipe between the core of the optical fiber and the metal pipe. Has been done.

[0010]

An embodiment of the present invention will be described with reference to the drawings. 1A and 1B show the structure of the optical fiber introducing portion of the present embodiment. FIG. 1A is a sectional view in an assembling process, and FIG. 1B is a sectional view after completion.

In FIG. 1A, first, a part of the optical fiber 1 protected by the ultraviolet curable resin 2 is stripped of the ultraviolet curable resin 2 to expose the optical fiber 1. A metal pipe 4 and a glass pipe 6 also serving as a position are passed through the optical fiber 1. Then, the low-melting glass powder 31 is injected into the space between the end faces of the glass pipe 6 inserted into both ends of the metal pipe 4 through a small hole provided on the side surface of the metal pipe 4, and the high-frequency heater 7 locally heats the metal pipe 4. To do.

The low melting glass 3 inside the metal pipe 4 is heated and melted by this heat, so that the optical fiber 1 is moved to the metal pipe 4.
And is hermetically sealed. At the time of this melting, at least one of the glass pipes 6 is moved to bring the glass pipes 6 close to each other. At this time, all but the low-melting-point glass 3 which is the minimum necessary for hermetically sealing is made to flow out from the small diameter hole of the metal pipe 4. Thus, the hermetically sealed structure having the structure shown in FIG. 1B is completed.

[0013]

As described above, according to the present invention, when the metal pipe and the optical fiber are fixed by melting the low melting point glass, the contact area between the optical fiber and the low melting point glass is reduced, and the difference in the thermal expansion coefficient is applied to the optical fiber. The stress applied can be reduced, and the glass pipe for positioning the optical fiber can be brought close to it to protect it from external force applied to the optical fiber by fixing the low melting point glass. Therefore, there is an effect of preventing the characteristic deterioration of the optical fiber caused by the hermetically sealed structure.

[Brief description of drawings]

FIG. 1A of an airtight sealing structure according to an embodiment of the present invention.
It is sectional drawing in an assembly process, and sectional drawing after (b) completion.

FIG. 2 is a cross-sectional view of a conventional hermetically sealed structure.

[Explanation of symbols]

 1 optical fiber 2 protective coating (ultraviolet curable resin) 3 low melting glass 31 low melting glass powder 4 metal pipe 5 ceramic pipe 6 glass pipe 7 high frequency heating machine

Claims (3)

[Claims] 1. An optical fiber having a core portion exposed by removing a coating on a central portion, and a position corresponding to the center of the core wire which penetrates into the inner space so that the core portion of the optical fiber is located substantially in the center. And a pair of glasses for inserting the optical fiber between the optical fiber and the metal pipe so as to be opposed to each other from both ends of the metal pipe for positioning the optical fiber with respect to the metal pipe. An airtight sealing structure for an optical fiber introducing part, comprising a pipe and a low melting point glass filled between the core of the optical fiber and the metal pipe by a hole of the metal pipe. 2. The hermetically sealed structure for an optical fiber introducing portion according to claim 1, wherein the glass pipe has a melting point higher than that of the low melting point glass. 3. The low melting point glass is prepared by injecting powdery low melting point glass through a hole of the metal pipe into a gap formed between the core wire portion of the optical fiber and the metal pipe. The airtight sealing structure for an optical fiber introducing portion according to claim 1 or 2, wherein the low melting point glass in a powder form is melted and filled by heating to a low temperature.