Jiaying Ma

3M PBS for high-performance LCOS optical engine

A new 3M Polarizing Beamsplitter (PBS) enables high performance optical engines for Liquid Crystal on Silicon (LCOS) projectors. It overcomes the limitations of previous LCOS optical engines that have insufficient light efficiency, contrast, and dark state uniformity. These limitations are the direct result of the performance of existing MacNeille PBSs: poor transmission of p-polarized light (Tp) and reduced contrast at modest beam angles and wavelength sensitivity. 3M has addressed these problems by creating a plastic polarizing film made of alternating layers of different plastics with the refractive indices tailored so that they match in one direction but not in the other. In the unmatched direction, a quarter-wave stack is formed that is highly reflective, while the matched direction appears as a transparent slab of plastic. This film is laminated between glass prisms to form a PBS with none of the problems associated with MacNeille PBS’s. For an F/2 beam, Tp exceeds 92% across the visible and photopic contrast exceeds 2000:1. High contrast is achievable in an optical engine without the use of a post-polarizer, avoiding this 15% loss that is necessary with a MacNeille PBS. Finally, the input light need not be highly polarized, allowing the engineer additional design freedom.