Patent ID: 8576480

Claim:
An optical amplifier comprising: a waveguide path configured to transmit an optical signal; an optical amplification unit formed on the waveguide path and configured to amplify the optical signal by an excitation light; an irradiation unit configured to irradiate the excitation light to the optical amplification unit; an optical detection unit configured to detect a light and generate an electric signal which corresponds to the detected light; a branching unit configured to branch an evanescent light being the optical signal outputted from the optical amplification unit to the waveguide path and leaked outside the waveguide path, and focus the evanescent light on the optical detection unit; a wavelength detection unit configured to detect a wavelength multiplicity of the optical signal based on the evanescent light detected by the optical detection unit; and a light amount adjustment unit configured to adjust a light amount of the excitation light irradiated by the irradiation unit based on the wavelength multiplicity.