Patent ID: 8509580

Claim:
An optical amplifier comprising: a first optical fiber through which seed light and excitation light propagate, the first optical fiber including a core and a clad surrounding an outer circumference of the core such that the seed light propagates through the core and the excitation light propagates through the clad; a first lens to which the seed light and the excitation light output from the core and the clad of the first optical fiber are input and which increases diameters of the seed light and the excitation light; a glass rod which is doped with rare earth elements to be excited by the excitation light, to which the seed light and the excitation light output from the first lens are input, and which amplifies and outputs the seed light as output light; a second lens to which at least the output light output from the glass rod is input and which decreases a diameter of the output light; and a second optical fiber to which the output light output from the second lens is input and through which the output light propagates, wherein, inside the glass rod, the excitation light has a larger diameter than the seed light over the entire length of the glass rod.