Semiconductor laser and method for manufacturing the same

A semiconductor laser comprising:

• an active layer having a light-emitting region of striped structure;
• an upper cladding layer formed on said active layer;
• a lower cladding layer formed under said active layer, said active layer being interposed between said upper and lower cladding layers;
• facets formed on both ends of a stripe of said light-emitting region in which a part of light emitted is radiated, remaining light is reflected and amplified;
• and
• a means for having a minimum value of a coherence in a range between 2 mW and 7 mW of output of a light radiated from one of said facets which is a light output power, and for preventing a phenomenon in which said output power is reduced in a range at most 25 mW in accordance with an increase of said current, varied by a variation of a current applied to said active layer, wherein said means includes a current blocking layer having a striped groove, said upper cladding layer includes first and second upper cladding layers, said current blocking layer formed between said first and second upper cladding layers, said first upper cladding layer being provided on one side of said active layer, a difference of a refractive index in a lateral direction of said active layer, said first upper cladding layer, and said current blocking layer being ranged between 4.2.times.10.sup.-3 and 5.times.10.sup.-3, said difference of refractive index being calculated from each refractive index and each thickness of said active layer, said first upper cladding layer and said current blocking layer.