| 摘要 |
PURPOSE:To provide an optical directional coupler which reduces the insertion loss by considerably reducing the scattering loss of signal light in an expanded waveguide part in comparison with a conventional device. CONSTITUTION:An optical directional coupler 15 is provided with coupling waveguide parts 16 formed on a substrate, expanded waveguide parts 17 and 18 connected to both sides of these coupling waveguide parts 16, input waveguide parts 19 which are connected to one expanded waveguide parts 17 and to which signal light is led, and output waveguide parts 20 which are connected to the other expanded waveguide parts 18 and send out signal light, and plural linear waveguides are connected to form expanded waveguide parts, and the length of each of these linear waveguide is set to lambda.(2k+1)/(n2-n2) where lambda, (k), n1, and n2 are the wavelength of signal light, an integer larger than 0, the refractive index of the core constituting the waveguide, and that of the clad around the core respectively. |
