Reflexite to Increase Film Fresnel Size

Reflexite to Increase Film Fresnel Size

11.18.2002

One of the major problems with rear-projection systems is the ghosting of images on the screen, but Reflexite (Rochester, NY) (www.reflexite.com) has come up with an ultra-thin Fresnel screen design that can eliminate this. Currently, it is selling products to support screen sizes up to 43 inches, but soon will offer screens up to 59 inches in diagonal.

Reflexite operates as a subsidiary under Fresnel Optics, Inc. Overall, the company has core technologies in microreplication, polymer processing and optical engineering. The Display Optics Business is responsible for rear-projection screen components and backlighting films.

Reflexite identifies two major sources of ghosting in a rear-projection system. The first is caused by variations in the thickness of the Fresnel lens itself. This is the result of optical path length differences and multiple reflections, which vary with the thickness of the lens.

Near the center of the Fresnel, the lens is thinner, but toward the edges it is much thicker, thus leading to ghosting. The result is ghosting that is radially distributed and more prevalent at the edges of the screen.

Ghosting factor number two results from the geometry of the fold mirror with respect to the Fresnel lens. Since some light is back reflected from the Fresnel, it will hit the fold mirror and be reflected again. Physically, the top of the fold mirror is closer to the Fresnel than the bottom. The interaction of these reflected waves leads to ghosting, but it is more prevalent at the top of the screen because of the close proximity of the fold mirror and the Fresnel lens.

To address these ghosting problems, Reflexite was awarded a $4.98M contract from USDC (San Jose, CA) (www.usdc.org), which required a 50-50 cost sharing for the development effort. The program was initially targeted at rear-projection monitors and was successful. As a result, Reflexite is currently shipping the no-ghost screens to an undisclosed military customer, where there was a keen need to eliminate ghosting that can effect the readability of text on the display screen. But there is a similar need in the commercial TV industry, so the technology is now being expanded to serve that market.

The solution that Reflexite came up with for the radial ghosting problems was to develop a much thinner Fresnel lens design. To solve ghosting problem number two, Reflexite Display Optics president Joe Lupone says they added a film that has a moth eye structure.

"Moth eye is a sub-wavelength microstructure that is molded or cast onto the plano [SM1] surface of the Fresnel. It significantly reduces the magnitude of the reflection, thus making it invisible to the viewer and eliminating ghosting," explained Lupone.

To manufacture the ghost-free screens, Reflexite has developed a cast process whereby the Fresnel lens design is fabricated in a round drum tool. A thin polymer sheet is passed under the rotating drum to create an impression of the thin Fresnel in a roll-to-roll process. This thin Fresnel can then be bonded to other screen components like diffusers and lenticulars, which are offered by a variety of companies.

Reflexite plans to expand applications for the lens into the commercial TV arena. Typically, it does all of the tooling and manufacturing for commercial customers, but the customer would own the particular Fresnel lens design. Apparently, Reflexite is already working with a customer on this but cannot disclose the name yet.

Reflexite, Joe Lupone, 716-647-1140, joe.lupone@reflexite.com

Excerpted from the Projection Supply Chain Report--Autumn 2002