| 摘要 |
PURPOSE:To obtain a semiconductor laser at a stable longitudinal single mode with excellent productivity and with high yield even on modulation at high speed by forming an antiphase corrugation region having a refractive index smaller than an active layer and larger than a waveguide layer between a clad layer and the waveguide layer. CONSTITUTION:The phase of a effective refractive index is displaced at 180 deg. on antiphase corrugations through the phase of the shape of corrugations is the same on the right and left of A-A. In a distributed feedback type semiconductor laser having such effective refractive index distribution, phase is displaced at 90 deg. when laser beams S1 proceeding to the right side from M-M are reflected from a distribution reflector and return in laser beams S1 in a Bragg wavelength determined by a period W and the effective refractive index n0. Likewise, phase is also displaced at 90 deg. in laser oscillation beams S2 proceeding to the left side from A-A. Since A-A and M-M are at W/2 distance at the distance corresponds to the phase of 180 deg., phase is displaced at 360 deg., thus satisfying the conditions of oscillation. Accordingly, the laser is oscillated at a single longitudinal mode at a minimum threshold current value in the same manner as a conventional 1/4 wavelength shift DFB laser. |
