Semiconductor laser diode device and method of fabrication thereof

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;
• and
• a 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, and
• wherein 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.