PROBLEM TO BE SOLVED: To provide an optical amplifier capable of reducing ASE light containing the light of unnecessary wavelength, while attaining a sufficient light output intensity at a required wavelength.SOLUTION: In an optical amplifier having a laminate including two electrode layers 203, 204, an active layer 205 provided therebetween, and a waveguide for guiding light in the in-plane direction of the active layer, where incident light to the laminate is emitted, while being amplified, from the end face side 202 of the laminate in the in-plane direction via the waveguide, at least one of two electrode layers has an electrode group including more than one electrodes provided separately in the waveguiding direction of the waveguide, and changes amplification factor according to the wavelength of the incident light, by injecting a current independently into multiple different regions in the active layer by using more than one electrode.SELECTED DRAWING: Figure 2【課題】必要な波長において十分な光出力強度を得つつ、不必要な波長の光を含むＡＳＥ光を低減可能な光増幅器を提供する。【解決手段】２つの電極層２０３、２０４と、それらの間に設けられた活性層２０５と、活性層の面内方向に光が導波される導波路とを含む積層体を有し、積層体への入射光が導波路を経て積層体の面内方向の端面側２０２から増幅されて射出される光増幅器であって、２つの電極層の少なくともいずれか一方は導波路の導波方向に分離されて設けられた２つ以上の電極を含む電極群を有し、２つ以上の電極を用いて活性層における複数の異なる領域に独立に電流を注入することで、入射光の波長に応じて増幅率を変化させる光増幅器。【選択図】図２
