| 摘要 |
PURPOSE:To obtain low noise characteristics in a wide range of backward light quantity, by a method the light waveguide layer of a trench part is made thick as compared with the side part of the trench, only in the vicinity of one side terminal surface of a resonator, and the thickness of the light waveguide layer is made uniform in the other parts. CONSTITUTION:On a substrate 1 on which a trench is formed, the following are stacked in order; a clad lay 2 of first conductivity type, a light waveguide layer 3 of first conductivity type whose reflectivity is larger than the clad layer 2, an active layer 4 and a clad layer 5 of second conductivity type. The light waveguide layer 3 of the trench part is made thick as compared with the side part of the trench, only in the vicinity of one side terminal surface of a resonator, and its thickness in the other parts is made uniform. In other words, the light waveguide layer 3 is flat in the inside of the resonator, and the active layer 4 and a substrate 1 are comparatively separated in the side part of the trench, so that the difference of reflectivity is very small. Therefore, the coherency of a laser light is decreased, the sensitivity for a backward light is reduced, and low noise characteristics is obtained in a wide range of backward light quantity.
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