Rare earth element-doped multiple-core optical fiber and method for fabricating the same

A rare earth element-doped multiple-core optical fiber, comprising:

• a plurality of cores each having a refractive index of n.sub.w doped with at least one rare earth element and Al therein;
• a plurality of intermediate cladding layers each having a refractive index of n.sub.l (n.sub.l <n.sub.w) doped with at least one rare earth element, and covering said plurality of cores;
• a plurality of primary cladding layers each having a refractive index of n.sub.p (n.sub.p .ltoreq.n.sub.l and n.sub.p <n.sub.w) containing no rare earth element dopant, and covering said plurality of intermediate cladding layers;
• and
• an outer cladding layer having a refractive index of n.sub.c (n.sub.w >n.sub.c n.sub.l .ltoreq.n.sub.c and n.sub.p .ltoreq.n.sub.c), and covering said plurality of cores covered with said plurality of intermediate and primary cladding layers;
• wherein said plurality of cores are positioned substantially on a central axis of said outer cladding layer, and separated with a predetermined spacing by said plurality of intermediate cladding layers.

A method for fabricating a rare earth element-doped multiple-core optical fiber, comprising the steps of:

• fabricating a plurality of soot glass rods, each of which is provided with a core having a refractive index of n.sub.w and containing Al, and a primary cladding layer having a refractive index of n.sub.p (n.sub.p <n.sub.w) and covering directly said core;
• immersing said plurality of soot glass rods in an rare earth element compound solution;
• picking up said plurality of soot glass rods from said solution, and drying and consolidating them to provide a plurality of rare earth element and Al co-doped transparent glass rods;
• inserting said plurality of co-doped transparent glass rods into a quartz tube;
• heating and collapsing said quartz tube thus inserted with said plurality of co-doped transparent glass rods to fabricate an optical fiber preform rod;
• and
• heating and drawing said optical fiber preform to provide an rare earth element-doped multiple-core optical fiber.

A method for fabricating a rare earth element-doped multiple-core optical fiber, comprising the steps of:

• fabricating a plurality of soot glass rods for cores each having a refractive index of n.sub.w and containing Al;
• producing primary cladding layers, having a refractive index of n.sub.p (n.sub.p <n.sub.w), of soot glass thin layers around each of said soot glass rods;
• immersing said soot glass rods with said soot glass thin layers in an rare earth element-compound solution;
• picking up said soot glass rods from said solution, and drying and consolidating them to provide a plurality of co-doped rare earth element-Al co-doped transparent glass rods;
• inserting said plurality of co-doped transparent glass rods into a quartz tube;
• heating and collapsing said quartz tube thus inserted with said plurality of co-doped rare earth element-Al co-doped transparent glass rode to fabricate an optical fiber preform rod;
• and
• heating and drawing said optical fiber preform rod to provide an rare earth element-doped multiple-core optical fiber.

A method for fabricating a rare earth element-doped multiple-core optical fiber, comprising the steps of:

• fabricating a plurality of soot glass rods, each of which is provided with a core having a refractive index of n.sub.w and containing Al, and an intermediate cladding layer having a refractive index of n.sub.l (n.sub.l <n.sub.w) and covering directly said core;
• immersing said plurality of soot glass rods in a rare earth element-compound solution;
• picking up said plurality of soot glass rods from said solution, drying and consolidating them to provide a plurality of rare earth element and Al co-doped transparent glass rods;
• covering each of said co-doped transparent glass rods by a primary cladding layer having a refractive index of n.sub.p (n.sub.p .ltoreq.n.sub.l and n.sub.p <n.sub.w);
• inserting said plurality of co-doped transparent glass rods with said intermediate cladding layers and said primary cladding layers into a quartz tube;
• heating and collapsing said quartz tube to fabricate an optical fiber preform rod;
• and
• heating and drawing said optical fiber preform rod to provide an rare earth element-doped multiple-core optical fiber.

A method for fabricating a rare earth element-doped multiple-core optical fiber, comprising the steps of:

• fabricating a plurality of soot glass rods for cores having a refractive index of n.sub.w and containing Al;
• producing a plurality of intermediate cladding layers, having a refractive index of n.sub.l (.sub.n.sub.l <n.sub.w), of soot glass than layers around each of said soot glass rods;
• immersing said plurality of soot glass rods with said soot glass thin layers in a rare earth element-compound solution;
• picking up said plurality of soot glass rods from said solution, drying and consolidating them to provide rare earth element and Al co-doped transparent glass rods;
• covering each of said plurality of glass rods by a primary cladding layer having a refractive index of n.sub.p (n.sub.p .ltoreq.n.sub.l and n.sub.p <n.sub.w);
• inserting said plurality of rods with said intermediate cladding layers and said primary cladding layers into a quartz tube;
• heating and collapsing said quartz tube to fabricate an optical fiber preform rod;
• and
• heating and drawing said optical fiber preform rod to provide an rare earth element-doped multiple-core optical fiber.