Interference filters in optically written display based on up-conversion of near infrared light

The display based on up-conversion of near infrared light is a novel display. To improve the screen luminance and avoid leakage of infrared light, two multilayer interference filters are designed on the screen of the display. One is called the LP filter, having low transmittance for visible light between 400 and 800 nm, and high transmittance for infrared light between 800 and 1000 nm; the other is called the SP filter with opposite characteristics to those of the LP filter. Layer-symmetric films are used to design the filters and the conjugate gradient method is used to optimise the design. The LP and SP filters obtained have good characteristics within the whole wavelength bandwidth between 400 and 1000 nm and the incident angle range 0-20°. The manufacturing tolerances on film thickness and refractive index are reasonably large.