Patent ID: 6870667

Claim:
An optical amplifier comprising: an erbium-doped optical fiber; an excitation light source device having a semiconductor laser element that generates an excitation beam and a housing that accommodates said semiconductor laser element; and an optical multiplexer having a first input optically coupled with said excitation light source device, a second input for receiving a signal beam and an output for supplying said excitation beam and signal beam to said erbium-doped optical fiber; wherein said semiconductor laser element comprises: a first cladding layer that includes a chemical compound semiconductor of first conductivity type; a second cladding layer that includes a chemical compound semiconductor of second conductivity type; and an active layer including a chemical compound semiconductor, provided between said first cladding layer and said second cladding layer and constituted such that the oscillation wavelength of said semiconductor laser element at 20° C. is less than 1470 nm but not less than 1440 nm.