Optical fiber amplifier

Claim 2

An optical fiber amplifier adapted to directly amplify signal light, comprising: a rare-earth element doped fiber doped with a rare-earth element; means for introducing signal light into said doped fiber; a light source for emitting pumping light; means for introducing the pumping light into said doped fiber; and means for causing the pumping light from said light source to pass a plurality of times in said doped fiber.

Claim 3

An optical fiber amplifier adapted to directly amplify signal light, comprising: a signal light transmission line including a rare-earth element doped fiber doped with a rare-earth element; a light source for emitting pumping light; a first optical multiplexer/demultiplexer interposed in said signal light transmission line and having an end connected to said light source; and pumping light reflecting means for returning pumping light which has been introduced into said doped fiber by way of said first optical multiplexer/­demultiplexer and has passed through part or all of said doped fiber again into said doped fiber.

Claim 4

An optical fiber amplifier adapted to directly amplify signal light, comprising: a signal light transmission line including a rare-earth element doped fiber doped with a rare-earth element; a light source for emitting pumping light; a first optical multiplexer/demultiplexer interposed in said signal light transmission line and having an end connected to said light source; and pumping light reflecting means for returning pumping light which has been introduced into said doped fiber by way of said first optical multiplexer/­demultiplexer and has passed through part or all of said doped fiber again into said doped fiber.

Claim 5

An optical fiber amplifier according to claim 2, wherein said pumping light reflecting means is a reflecting film interposed in said signal light transmission line for transmitting signal light therethrough but reflecting pumping light.

Claim 6

An optical fiber amplifier according to claim 2, further comprising a second optical multiplexer/­demultiplexer interposed in said signal light transmission line on the opposite side of said first optical multiplexer/demultiplexer with respect to said doped fiber for separating signal light and pumping light from each other, said pumping light reflecting means being provided on the pumping light emerging side of said second optical multiplexer/demultiplexer.

Claim 7

An optical fiber amplifier according to claim 4, wherein said pumping light reflecting means is a reflecting film which reflects at least pumping light.

Claim 8

An optical fiber amplifier according to claim 2, wherein said first optical multiplexer/demultiplexer is an optical multiplexer/demultiplexer of the fusion joined fiber type in which said doped fiber, an output fiber and a fiber connected with said light source are fused and joined together.

Claim 9

An optical fiber amplifier adapted to directly amplify signal light, comprising: a signal light transmission line including a rare-earth element doped fiber doped with a rare-earth element; a light source for emitting pumping light; a first optical multiplexer/demultiplexer interposed in said signal light transmission line; a second optical multiplexer/demultiplexer interposed in said signal light transmission line for cooperating with said first optical multiplexer/­demultiplexer to sandwich said doped fiber therebetween; a connecting fiber for connecting said first and second optical multiplexer/demultiplexers to each other to form a fiber loop including said doped fiber; and means for connecting said light source to said fiber loop.

Claim 10

An optical fiber amplifier adapted to directly amplify signal light, comprising: a signal light transmission line including a rare-earth element doped fiber doped with a rare-earth element; a light source for emitting pumping light; a first optical multiplexer/demultiplexer interposed in said signal light transmission line; a second optical multiplexer/demultiplexer interposed in said signal light transmission line for cooperating with said first optical multiplexer/­demultiplexer to sandwich said doped fiber therebetween; a connecting fiber for connecting said first and second optical multiplexer/demultiplexers to each other to form a fiber loop including said doped fiber; and means for connecting said light source to said fiber loop.

Claim 11

An optical fiber amplifier according to claim 7, wherein each of said first and second optical multiplexer/demultiplexers is an optical multiplexer/­demultiplexer of the fusion joined fiber type.

Claim 12

An optical fiber amplifier adapted to directly amplify signal light, comprising: a first signal light transmission line including a first rare-earth element doped fiber doped with a rare-earth element; a second signal light transmission line including a second rare-earth element doped fiber doped with a rare-earth element; a light source for emitting pumping light; a first optical multiplexer/demultiplexer interposed in said first signal light transmission line; a second optical multiplexer/demultiplexer interposed in said first signal light transmission line for cooperating with said first optical multiplexer/­demultiplexer to sandwich said first doped fiber therebetween; a third optical multiplexer/demultiplexer interposed in said second signal light transmission line; a fourth optical multiplexer/demultiplexer interposed in said second signal light transmission line for cooperating with said third optical multiplexer/­demultiplexer to sandwich said second doped fiber therebetween; a first connecting fiber for connecting said second and third optical multiplexer/demultiplexers to each other; a second connecting fiber for connecting said first and fourth optical multiplexer/demultiplexers to each other to form a fiber loop including said first and second doped fibers; and means for connecting said light source to said fiber loop.

Claim 13

An optical fiber amplifier adapted to directly amplify signal light, comprising: a first signal light transmission line including a first rare-earth element doped fiber doped with a rare-earth element; a second signal light transmission line including a second rare-earth element doped fiber doped with a rare-earth element; a light source for emitting pumping light; a first optical multiplexer/demultiplexer interposed in said first signal light transmission line; a second optical multiplexer/demultiplexer interposed in said first signal light transmission line for cooperating with said first optical multiplexer/­demultiplexer to sandwich said first doped fiber therebetween; a third optical multiplexer/demultiplexer interposed in said second signal light transmission line; a fourth optical multiplexer/demultiplexer interposed in said second signal light transmission line for cooperating with said third optical multiplexer/­demultiplexer to sandwich said second doped fiber therebetween; a first connecting fiber for connecting said second and third optical multiplexer/demultiplexers to each other; a second connecting fiber for connecting said first and fourth optical multiplexer/demultiplexers to each other to form a fiber loop including said first and second doped fibers; and means for connecting said light source to said fiber loop.

Claim 14

An optical fiber amplifier according to claim 9, wherein each of said first to fourth optical multiplexer/demultiplexers is an optical multiplexer/­demultiplexer of the fusion joined fiber type.

Claim 15

An optical fiber amplifier adapted to directly amplify signal light, comprising: a plurality of signal transmission lines each including a rare-earth element doped fiber doped with a rare-earth element; a plurality of connecting fibers for individually connecting adjacent ones of said signal light transmission lines to each other to form a fiber loop including the doped fibers; a plurality of optical multiplexer/­demultiplexers individually provided at connecting points between said signal light transmission lines and said connecting fibers for passing signal light therethrough but causing pumping light to circulate in said fiber loop; a light source for emitting pumping light; and means for connecting said light source to said fiber loop.

Claim 16

An optical fiber amplifier adapted to directly amplify signal light, comprising: a plurality of signal transmission lines each including a rare-earth element doped fiber doped with a rare-earth element; a plurality of connecting fibers for individually connecting adjacent ones of said signal light transmission lines to each other to form a fiber loop including the doped fibers; a plurality of optical multiplexer/­demultiplexers individually provided at connecting points between said signal light transmission lines and said connecting fibers for passing signal light therethrough but causing pumping light to circulate in said fiber loop; a light source for emitting pumping light; and means for connecting said light source to said fiber loop.

Claim 17

An optical fiber amplifier according to claim 11, wherein each of said plurality of optical multiplexer/­demultiplexers is an optical multlplexer/demultiplexer of the fusion joined fiber type.