Airtight seal structure of low melting point glass to be used in optical fiber guiding portion of optical device and method of airtight seal using low melting point glass

An airtight seal structure of an optical fiber leading portion of an optical device, comprising:

• an optical fiber;
• a pipe member having a through-hole for receiving said optical fiber inserted thereinto, for connecting an interior of said optical fiber leading portion to an exterior of said optical fiber leading portion;
• at least one glass pipe having a through-hole for receiving said optical fiber inserted thereinto and an outer diameter larger than an inner diameter of said pipe member, said glass pipe being in contact with at least an end face of said pipe member;
• and
• a low melting point glass material disposed within an annular space defined by an inner wall of said pipe member and said optical fiber and filling said space when melted by heating to thereby airtightly seal said interior of said optical fiber leading portion against said exterior of said optical fiber leading portion within said pipe member.

An airtight seal structure of an optical fiber leading portion of an optical device, comprising:

• an optical fiber having a thermally sensitive protective layer thereon;
• a pipe member having a through-hole for receiving said optical fiber inserted thereinto, for connecting an interior of said optical fiber leading portion to an exterior of said optical fiber leading portion;
• two glass pipes, each having a through-hole for receiving said optical fiber inserted thereinto and inserted into said pipe member;
• and
• a low melting point glass material disposed within said pipe member between said two glass pipes and filling a space defined by an inner wall of said pipe member and said optical fiber when melted by heating to thereby airtightly seal said interior of said optical fiber leading portion within said pipe member;
• wherein said two glass pipes each abut one end of said space defined by said low melting point glass material, so that, upon heating and melting of said low melting point glass material, said two glass pipes may be pushed toward each other to expel any gas that may be formed and to urge molten low melting point glass into intimate contact with neighboring parts to form said airtight seal structure;
• and
• wherein said pipe member is of a minimal length required for retaining said low melting point glass material, and wherein said thermally sensitive protective layer is removed from said optical fiber in the region of said heating to prevent said thermally sensitive protective layer from being damaged upon heating and melting of said low melting point glass material.

An airtight seal structure of an optical fiber leading portion of an optical device, comprising:

• an optical fiber having a thermally sensitive protective layer thereon;
• a metal pipe member having a through-hole for receiving said optical fiber inserted thereinto, for connecting an interior of said optical fiber leading portion to an exterior of said optical fiber leading portion;
• at least one glass pipe having a through-hole for receiving said optical fiber inserted thereinto and inserted into said metal pipe member;
• a low melting point glass material disposed within said metal pipe member in the vicinity of an end face of said glass pipe and filling a space defined by an inner wall of said metal pipe member and said optical fiber when melted by heating to thereby airtightly seal said interior of said optical fiber leading portion against said exterior of said optical fiber leading portion within said metal pipe member;
• and
• a casing having a hole on a surface thereof for receiving said metal pipe member, said hole having a diameter slightly larger than the outer diameter of said metal pipe member to facilitate subsequent attachment of said pipe member to said casing by welding;
• wherein said metal pipe member is of a minimal length required for retaining said low melting point glass material, and wherein said thermally sensitive protective layer is removed from said optical fiber in the region of said heating to prevent said thermally sensitive protective layer from being damaged upon heating and melting of said low melting point glass material.

A method of airtightly sealing an optical fiber leading portion of an optical device, comprising the steps of:

• inserting an optical fiber having a length covered substantially by a thermally sensitive protective layer into a first glass pipe and inserting said first glass pipe into a pipe member;
• mounting a tablet of low melting point glass material on said optical fiber in said pipe member;
• fitting a second glass pipe on said optical fiber from the side thereof on which said tablet is mounted and inserting said second glass pipe into said pipe member;
• heating an outer periphery of said pipe member to melt said tablet of low melting point glass material;
• exerting inward pressure to outer end faces of said first and second glass pipes;
• and
• cooling said pipe member;
• wherein said pipe member is of a minimal length required for retaining said low melting point glass material, and wherein said thermally sensitive protective layer is removed from said optical fiber in the region of said heating to prevent said thermally sensitive protective layer from being damaged upon heating and melting of said low melting point glass material.