A　new　device　of　two　parallel　distributed　feedback　(　DFB)　laser　integrated　monolithically　with　Y-branch　waveguide　coupler　was　fabricated　by　means　of　quantum　well　intermixing.　Optical　microwave　signal　was　generated　in　the　Y-branch　waveguide　coupler　through　frequency　beating　of　the　two　laser　modes　coming　from　two　DFB　lasers　in　parallel,　which　had　a　small　difference　in　frequency.　Continuous　rapidly　tunable　optical　microwave　signals　from　13　GHz　to　42　GHz　were　realized　by　adjusting　independently　the　driving　currents　injected　into　the　two　DFB　lasers.