Control of polarization deviation at two separate wavelength by using all dielectric thin film materials

Two separate wavelength 1315 nm and 1550 nm were most widely used in near-infrared spectrum region. Based on a four-layer structure and a symmetry structure, a initial thin film stack system was constructed. Then it was optimized alternately by simplex and conjugate graduate algorithm, a beam splitter with splitting ratio R:T = 50:50 at this two wavelength was gained. The design result showed that the difference between reflectivity of P and S light around wavlength range 1300⿿1330 nm and 1535⿿1565 nm at incident angle 40°⿿50° was all below 2%. That indicated our design controlled the polarization deviation well at two separate wavelength with a reasonable range for both wavelength and incident angle.