Optical amplifier

The embodiment of the invention provides an optical amplifier. The optical amplifier comprises a pump light source assembly, an input optical fiber collimator, an input optical isolator core part, a cylindrical glass body used for achieving optical signal amplification, an output optical isolator core part and an output optical fiber collimator. The cylindrical glass body comprises a gain core area doped with rare earth ions, the pump light source assembly outputs pump light capable of exciting the rare earth ions in the gain core area to the cylindrical glass body, signal light enters the gain core area in the axial direction of the cylindrical glass body, and the diameter of the gain core area is larger than or equal to 30 micrometers. According to the optical amplifier in the embodiment, the diameter of the gain core area in the cylindrical glass body is greater than that of the core area of a rare earth optical fiber with the same concentration; under the condition that the total amount of the rare earth