Patent ID: 6914915

Claim:
A laser amplifier comprising: a single gain medium of a glass fiber including rare earth dopant in a host medium, 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 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 a second exciting light 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 another first exciting light to said glass fiber, and wherein a two-way excitation is performed on said glass fiber, and without providing another second exciting light source coupled to the output side of said glass fiber for introducing said second exciting light to said glass fiber.