Multi-port coupler, optical amplifier, and fiber laser

1. A multi-port coupler for coupling a pumping light source to a cladding pump fiber for optical amplification, comprising:

a central signal fiber and a plurality of pumping fibers arranged around the central signal fiber, the central signal fiber and the plurality of pumping fibers being unified and a front side is reduced in diameter,

wherein an emitted light confining waveguide part is provided around a core of the signal fiber located at the center, and

the emitted light confining waveguide part whose outer diameter is larger than that of the core has a higher refractive index than a cladding and a lower refractive index than the core and the emitted light confining waveguide part is formed continuously from a splicing point of the cladding pump fiber to a coupler front end branched into multiple fibers.

2. The multi-port coupler of claim 1 , wherein the emitted light confining waveguide part is provided in a concentric circle shape around the core of the signal fiber.

3. The multi-port coupler of claim 1 , wherein the emitted light confining waveguide part is provided in a polygonal shape around the core of the signal fiber.

4. A multi-port coupler for coupling a pumping light source to a cladding pump fiber for optical amplification, comprising:

a central signal fiber and a plurality of pumping fibers arranged around the central signal fiber, the central signal fiber and the plurality of pumping fibers being unified using a capillary, the capillary being connected to a rear end of a bridge fiber along with the signal fiber and the pumping fibers, a front side of the bridge fiber being reduced in diameter,

wherein an emitted light confining waveguide part is provided around a core of the bridge fiber,

the emitted light confining waveguide part, whose outer diameter is larger than that of the core and smaller than that of a cladding of the signal fiber, has a higher refractive index than a cladding of the bridge fiber and a lower refractive index than the core, and

the capillary whose refractive index is lower than that of a cladding of the signal fiber, the capillary having an effect of confining emitted light in the signal fiber.

5. The multi-port coupler of claim 4 , wherein the emitted light confining waveguide part is provided in a concentric circle shape around the core of the bridge fiber.

6. The multi-port coupler of claim 4 , wherein the emitted light confining waveguide part includes a section of a polygonal shape around the core of the bridge fiber.

7. A multi-port coupler for coupling a pumping light source to a cladding pump fiber for optical amplification, comprising:

a central signal fiber and a plurality of pumping fibers arranged around the central signal fiber, the central signal fiber and the plurality of pumping fibers being unified using a capillary, the capillary being connected to a rear end of a bridge fiber along with the signal fiber and the pumping fibers, a front side of the bridge fiber being reduced in diameter,

wherein an emitted light confining waveguide part is provided around a core of the bridge fiber, the emitted light confining waveguide part whose outer diameter is larger than that of the core has a higher refractive index than a cladding and a lower refractive index than the core,

the capillary whose refractive index is equal to that of a cladding of the signal fiber, and

an pumping fiber cladding whose refractive index is lower than that of the capillary, the pumping fiber cladding having an effect of confining emitted light in the signal fiber and the capillary.

8. The multi-port coupler of claim 7 , wherein the emitted light confining waveguide part is provided in a concentric circle shape around the core of the bridge fiber.

9. The multi-port coupler of claim 7 , wherein the emitted light confining waveguide part includes a section of a polygonal shape around the core of the bridge fiber.

10. The multi-port coupler of claim 1 , wherein the outer diameter of the emitted light confining waveguide part is smaller than that of the signal fiber connected to the multi-port coupler.

11. A multi-port coupler, for coupling a pumping light source to a cladding pump fiber for optical amplification, comprising:

a central signal fiber and a plurality of pumping fibers arranged around the central signal fiber, the central signal fiber and the plurality of pumping fibers being unified and a front side is reduced in diameter,

wherein an emitted light confining waveguide part is provided around a core of the signal fiber located at the center,

the emitted light confining waveguide part, whose outer diameter is larger than that of the core, has a higher refractive index than a cladding and a lower refractive index than the core, and the emitted light confining waveguide part is formed continuously from a splicing point of the cladding pump fiber to a coupler front end branched into multiple fibers, and

an emitted light attenuation part is provided in which the signal fiber is extended for an appropriate distance and rolled.

12. An optical amplifier, comprising:

the multi-port coupler of claim 1 ;

a cladding pump fiber for optical amplification; and

an pumping light source.

13. A fiber laser, comprising:

the multi-port coupler of claim 1 ;

a cladding pump fiber for optical amplification; and

an pumping light source.