| 摘要 |
PURPOSE:To obtain an optical external modulating element whose integration to a semiconductor laser can be executed, by providing a diffraction grating provided with a desired inclination, and also varying a refractive index of a waveguide area in which the diffraction grating is formed. CONSTITUTION:An optical external modulator is provided along a waveguide, and a diffraction grating is formed diagonally at an angle of theta against the advancing direction of an incident light. When a period of the diffraction grating, and a refractive index of the waveguide of the diffraction grating part are denoted as LAMBDA and n1, respectively, the incident light of a Bragg wavelength lambda1 for satisfying lambda1=2n1LAMBDAcostheta is radiated in the direction of 2theta against the advancing direction of the incident light. When theta is set to about 45 deg., the radiated direction of the reflected light becomes nearly vertical to the waveguide, and it is not wave-guided any longer, and not outputted as a transmitting light. That is to say, as for the prescribed incident light lambda1, its reflection can be switched to the transmission by varying the refractive index so that the wavelength whose transmissivity being in the vicinity of the Bragg wavelength becomes maximum coincides with the Bragg wavelength lambda1 of before the refractive index is varied.
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