Design and optimization of compact LCoS projection optics using a freeform PBS prism

Area of Science:

• Optics and Photonics
• Display Technology
• Augmented Reality Systems

Background:

• Miniaturization of waveguide-based projection engines is crucial for augmented reality (AR) and wearable displays.
• Liquid Crystal on Silicon (LCoS) is a mature technology but faces challenges in system volume reduction due to complex illumination and imaging subsystems.

Purpose of the Study:

• To develop a miniaturized projection engine for AR displays.
• To overcome the limitations of conventional polarizing beam splitter (PBS) prisms in LCoS systems.
• To achieve a compact optical configuration through quantitative étendue analysis and novel prism design.

Main Methods:

• Quantitative étendue analysis based on the Köhler illumination scheme.
• Design and implementation of a freeform PBS prism with multiple optically active surfaces.
• Stepwise optimization of projection optics and stray light analysis.

Main Results:

• A novel freeform PBS prism was proposed to replace conventional PBS prisms.
• A compact initial optical configuration was constructed guided by étendue analysis.
• The resulting projection engine achieved a total volume of 1.37 cm³, a 32° field of view, and a 4 mm exit pupil diameter.

Conclusions:

• The developed projection engine demonstrates significant potential for integration into compact waveguide-based AR displays.
• The freeform PBS prism design is key to achieving miniaturization in LCoS-based AR systems.
• This work advances the development of smaller, high-performance optical systems for AR applications.