SPLAY

Optical Design of a Compact Projector Lens for a Portable Display

Project Vision

The desired product is a portable display consisting of a collapsible screen and a compact projector with a very short focal length. The project goal is to reduce the focal length of the current projector design by half while maintaining all other performance and packaging requirements. This will allow the footprint of the extended portable display to be reduced which will increase working space for customers.

Other potential areas of improvement include increasing the resolution on the display screen and designing a larger screen with uniform illumination. However, these improvements are not within the scope of the senior design project.

Design Process

The starting point was essential to design a high field-of-view, low-distortion lens. Retrofocus, fisheye, and similar projection lens patents are some of the starting points analyzed. The most successful starting point was a standard Double Gauss lens with a low F/#, moderate field-of-view, and low distortion. Distortion was held at a low percentage throughout optimization, while the field-of-view was slowly increased.

The final design consists of mostly glass elements with two plastic aspheric elements as the second and third elements for aberration correction in the small packaging size. A significant challenge for this design was including 20 mm image clearance for the RTIR prism and DMD actuator. The design is telecentric within 1 degree.

Evaluation

The final lens has greater than 25% contrast nominal MTF performance at the 92 lp/mm Nyquist frequency.

The image simulation below demonstrates how these more abstract specifications translate to the screen. This image simulation gives an idea of the brightness at the edges of the screen, the distortion, and the resolution of the screen of the Splay product.

Conclusion

A F/1.52, 120-degree full field-of-view projection lens was designed for a portable display product from Arovia Inc. From the current Splay design, the throw ratio was reduced by 25%, shortening the distance from the first lens to the screen by 15%. Manufacturability and environmental analysis was performed with precision drop-in tolerances from Optimax to ensure desired performance across the functional temperature range.

Acknowledgments

We want to thank the Institute of Optics and Professor Knox for the resources and inspirations of this Senior Capstone project, Alex Wesley and George Zhu for presenting this design challenge, and Jake Sacks for his optical design wisdom and support throughout this project.