Design of large acceptance angle polarizing beam splitter for laser-based displays

Abstract

The performance of broadband polarizing beam splitters (PBSs) is sensitive to the incident angle. By taking account of the spectrum of the laser source and using the needle optimization method, a large acceptance angle PBS for laser-based displays is designed. The average degrees of polarization in transmission and reflection can reach 0.989 and 0.980 for an acceptance angle of 13.6° in air using two materials, while better results of 0.993 and 0.989 for an acceptance angle of 14.8°i n air are attained when three common materials are used. Both designs consist of 40 layers.Recently, developments in compact and efficient visible lasers are expected to give momentum to the development of laser-based displays for the consumer market [1][2][3][4] . Polarizing beam splitters (PBSs) play an important role in display systems for the modulation of polarized light. The PBS has strong angular dependency, which decreases the contrast for low fnumber illumination [5] .Li [6] proposed a method for the design of broadband and wide angle PBS, and the Brewster angle condition was still necessary. After that Li [7] designed a new PBS with a wide acceptance angle and high extinction, but the PBS is hard to be fabricated. Mouchart [8] and Baumeister [9] designed a large acceptance angle PBSs for a single laser wavelength. In this letter, the spectrum of the monochromatic light source is taken into account for the design, and a more powerful optimization technology is introduced into the design process. A PBS operating in a large angular field for RGB lasers is designed. Two materials satisfying Brewster angle condition are enough to achieve the purpose, and three common materials which don't satisfy the Brewster angle condition can obtain a better result. These PBSs are more suitable for laser-based displays.A typical device of MacNeille PBS [10] consists of multilayer of two different coating materials embedded between two prisms. The two diagonal faces are cemented together, and the light is incident upon the hypotenuse. It is known that for oblique incidence, calculations of a multilayer optical film, p-polarized waves and s-polarized waves can be treated quite independently. A tilted optical admittance should be involved instead of that for normal incidence: