Optical fiber amplifier that can attain sufficient gain shift effect, small noise property and high operation efficiency at the same time even in two-wavelength excitation Tm dopant optical fiber amplifier, and optical amplifier having the same

Abstract

A laser amplifier includes a gain medium of a glass fiber, a first exciting light source, a second exciting light source, and another first exciting light source. The gain medium of the glass fiber includes rare earth dopant in a host medium. Ions of the rare earth dopant has an energy level structure including a ground level and a pair of laser upper level and laser lower levels between which a stimulated transition is to be produced after production of a population inversion between the pair of laser upper and laser lower levels. The pair of laser upper and laser lower levels being higher than the ground level. The first exciting light source is coupled to the input side of the glass fiber for introducing first exciting light to the glass fiber to produce the population inversion. The second exciting light source is coupled to the input side of the glass fiber for introducing second exciting light source to the glass fiber to raise ions of the rare earth dopant from the ground level to the laser lower level. The second exciting light has a wavelength band different from a wavelength band of the first exciting light. The other first exciting light source is coupled to the output side of the glass fiber for introducing the first exciting light to the glass fiber. A two-way excitation is performed on the glass fiber

What is claimed is:  
     
         1 . A laser amplifier comprising: 
 a gain medium of a plurality of stages of a plurality of glass fibers coupled to each other in series, each of said plurality of glass fibers including rare earth dopant in a host medium, and ions of said rare earth dopant having an energy level structure including a ground level and a pair of laser upper level and laser lower levels between which a stimulated transition is to be produced after production of a population inversion between said pair of laser upper and laser lower levels, said pair of laser upper and laser lower levels being higher than said ground level;    a first exciting light source coupled to the input side of said glass fiber of a specific stage other than at least a final stage of said plurality of stages for introducing first exciting light to said glass fiber of said specific stage to produce said population inversion;    a second exciting light source coupled to the input side of said glass fiber of said specific stage for introducing second exciting light source to said glass fiber to raise ions of said rare earth dopant from said ground level to said laser lower level, said second exciting light having a wavelength band different from a wavelength band of said first exciting light;    a third exciting light source coupled to the input side of said glass fiber of said final stage for introducing said first exciting light to said glass fiber of said final stage to produce said population inversion;    a fourth exciting light source coupled to the input side of said glass fiber of said final stage for introducing said second exciting light source to said glass fiber of said final stage; and    another third exciting light source coupled to the output side of said glass fiber of said final stage for introducing said first exciting light to said-glass fiber of said final stage, and    wherein a two-way excitation is performed on said glass fiber of said final stage.    
     
     
         2 . The laser amplifier according to  claim 1 , further comprising: 
 an optical isolator provided between said specific stage and said final stage, wherein said optical isolator protects ASE (Amplified Spontaneous Emission) generated in said final stage from getting into said specific stage.    
     
     
         3 . The laser amplifier according to  claim 1 , wherein said two-way excitation is performed on said glass fiber of said final stage without providing another fourth exciting light source coupled to the output side of said glass fiber of said final stage for introducing said second exciting light to said glass fiber of said final stage.  
     
     
         4 . The laser amplifier according to  claim 1 , wherein said rare earth dopant is selected from a group consisting of thulium(Tm), holmium(Ho), erbium(Er) and praseodymium(Pr).  
     
     
         5 . The laser amplifier according to  claim 1 , wherein the ions of said rare earth dopant are thulium ions (Tm 3+ ).  
     
     
         6 . The laser amplifier according to  claim 1 , wherein said first exciting light source produces light having a wavelength band ranging from 1.04 μm to 1.07 μm, and said second exciting light source produces light having a wavelength band ranging from 1.53 μm to 1.90 μm.  
     
     
         7 . The laser amplifier according to  claim 1  wherein said glass fiber is a fluoride-based glass fiber including rare earth dopant in a host medium.  
     
     
         8 . The laser amplifier according to  claim 1 , wherein said host medium is fluorozirconiumate glass.  
     
     
         9 . A laser amplifier apparatus, comprising: 
 a first laser amplifier; and    a second laser amplifier coupled to said first laser amplifier in series or parallel, and    wherein at least one of said first and second laser amplifiers includes: 
 a first exciting light source coupled to the input side of said glass fiber for introducing first exciting light to said glass fiber to produce said population inversion;  
 a second exciting light source coupled to the input side of said glass fiber for introducing second exciting light source to said glass fiber to raise ions of said rare earth dopant from said ground level to said laser lower level, said second exciting light having a wavelength band different from a wavelength band of said first exciting light; and  
 another first exciting light source coupled to the output side of said glass fiber for introducing said first exciting light to said glass fiber, and  
   wherein a two-way excitation is performed on said glass fiber.