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Disclosed is a distributed feedback semiconductor laser diode device capable of operating at a high output ratio of forward/backward optical power while ensuring satisfactory stability of single-mode oscillation. The distributed feedback semiconductor laser diode device is configured to include a di

Disclosed is a distributed feedback semiconductor laser diode device capable of operating at a high output ratio of forward/backward optical power while ensuring satisfactory stability of single-mode oscillation. The distributed feedback semiconductor laser diode device is configured to include a diffraction grating formed in an optical waveguide thereof. In a partial region of the optical waveguide, there is formed an alternately repetitive pattern of a grating part possessing a distributive refractivity characteristic and a no-grating space part possessing a uniform refractivity characteristic. The no-grating space part possessing a uniform refractivity characteristic has an optical path length that is half an integral multiple of a wavelength of laser oscillation, and the grating part possessing a distributive refractivity characteristic includes at least five grating periods.

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1. A distributed feedback semiconductor laser diode device including a diffraction grating formed in an optical waveguide thereof, the optical waveguide comprising: a plurality of grating parts each possessing a distributive refractivity characteristic; anda plurality of no-grating space parts each

1. A distributed feedback semiconductor laser diode device including a diffraction grating formed in an optical waveguide thereof, the optical waveguide comprising: a plurality of grating parts each possessing a distributive refractivity characteristic; anda plurality of no-grating space parts each possessing a uniform refractivity characteristic;wherein an alternately repetitive pattern of the grating parts each possessing a distributive refractivity characteristic and the no-grating space parts each possessing a uniform refractivity characteristic is formed to provide a coarse grating lithographic region,wherein the grating parts each possessing a distributive refractivity characteristic each includes at least a predetermined number of grating periods, andwherein the no-grating space parts each possessing a uniform refractivity characteristic each has an optical path length that is half an integral multiple of a wavelength of laser oscillation,wherein, in the optical waveguide, the coarse grating lithographic region is extended from the device front end position across the phase shift part located in the vicinity of the center of the optical waveguide, and a continuous grating lithographic region without partial missing of grating lines is extended from the end position of the coarse grating lithographic region to the device rear end position. 2. The distributed feedback semiconductor laser diode device according to claim 1, wherein the grating parts each possessing a distributive refractivity characteristic each includes at least five grating periods. 3. The distributed feedback semiconductor laser diode device according to claim 1, wherein a phase shift part is disposed at a predetermined position in a region where the grating parts are formal in the optical waveguide. 4. The distributed feedback semiconductor laser diode device according to claim 1, wherein one of the no-grating space parts possessing a uniform refractivity characteristic has an optical path length corresponding to half an integral multiple of a grating period of the grating part. 5. The distributed feedback semiconductor laser diode device according to claim 1, wherein the coarse grating lithographic region is provided on the device front side in the optical waveguide. 6. The distributed feedback semiconductor laser diode device according to claim 3, wherein the coarse grating lithographic region is provided in the vicinity of the phase shift part in the optical waveguide. 7. The distributed feedback semiconductor laser diode device according to claim 1, wherein a phase shift part is disposed in the coarse grating lithographic region in the optical waveguide, andwherein the continuous grating lithographic region without partial missing of grating lines is provided on each of the device front side and the device rear side in the optical waveguide. 8. The distributed feedback semiconductor laser diode device according to claim 3, wherein, instead of the phase shift part, there is provided a region that possesses a uniform refractivity characteristic and has an optical path length corresponding to half an integral multiple of a grating period of the grating part. 9. The distributed feedback semiconductor laser diode device according to claim 1, wherein the no-grating space part possessing a uniform refractivity characteristic has an optical path length represented as “an integral multiple of a grating periodic length of the grating part multiplied by a correction value of refractive index”.