a vertical upward direction said third dielectric cylinder is adopted as a semi circular cylinder and the radius of the semi circular dielectric compensation scattering cylinder with high refractive index at the lower right corner is 0 33986a the displacements of said semi circular dielectric compensation scattering cylinder in the x direction and in the z direction measured from the original benchmark point are respectively 0 80645a and 0 94086a the rotation angle is 131 5 degrees the position of an optical source measured from the coordinate origin in the x direction and in the z direction is u2212 4 94a 0 and the initial phase of incident light the optical source is 249 88 degrees the material of the background dielectric with high refractive index is silicon si and the refractive index of si is 3 4 and the background dielectric with low refractive index is air the structure size of the right angle waveguide is 15a 15a and a return loss spectrum and an insertion loss spectrum of the right angle waveguide formed in the the phc are then obtained and shown in fig3 at the normalized frequency of 0 3975 u03c9a 2 u03c0c the maximum return loss and the minimum insertion loss of the right angle waveguide formed in the phc are 41 91 db and 0 0021 db the lattice constant a of said square lattice phc is 0 5208 u03bcm so that the optimal normalized wavelength is 1 55 u03bcm said first dielectric cylinders with high refractive index are adopted as.