Sunday, April 20th, 2014

Polymer technology for photonics – SID 2011


 May 17, 2011, Society for Information Display, Los Angeles—Yashiro Koike, professor at Keio University in Japan espoused on the possibilities for overwhelmingly realistic face-to-face communications based on polymer technologies. The need for greater bandwidth requires ongoing research into polymers.

Currently, computer users interact with their machines through displays and keyboards. The technology is available to create tools to make people happy, by increasing the available bit rates for communications. In fact, extremely high bit rates are required to realize people size displays. A telepresence conference is completely different when the people on the other side are life-size rather than small images on a screen.

As a result of these requirements, research continues to improve the capabilities of polymers to handle high bit rate indications. At dimensions above 1 nm, particles cause scattering in the plane waves. In a millimeter range get full reflections, the nanometer range get scattering which can range from many factors in the fibers including graded index granularity, index mismatch, and many others. But at the nanometer range polarizing effects can result in zero birefringence, so a wavelength can be chosen either for absorption or emission.

Pundits expect data bit rates to increase by a factor of 400 to keep with the demand for new services and capabilities. To meet this demand requires many miles of high-flexibility polymer optical fiber to meet both the cost and performance parameters. Some of these capabilities were recently demonstrated at the Fukushima nuclear power plant in Japan where inspection robots were connected through plastic optical fiber for the high resolution imaging and motion control functions.

Polymer fibers have a long development history. Initial efforts were directed to reducing attenuation from 1000 db/km to less than 20 db/km. the DeBye theory posited that scattering loss is a function of correlation length. It's possible to use high scatter materials for optical transmission and polymers can even be used for back haul operations. The first practical solution used a graded index, highly doped polymer to control group delay and scattering losses.

The birefringence properties of polymers added to a transverse mix of polymers and then stressed to create a photo-elastic material with interesting characteristics. The faster waves take a sinusoidal path through the graded index materials while the slower waves go through a shorter saw-tooth path in the central core and both types of waves end up at the far end at the same time. In this way, the graded polymer fibers can supplant the single-or multi-mode glass fibers.

In a different application, high birefringence polymers can be used in the optics for LED backlighting. In fact, by changing the backlight from LEDs to laser diodes, the LCD screens can be simplified because the lasers can be polarized, eliminating one polarizer in the LCD stack. This layer elimination doubles the amount of light available enabling either much brighter screens or reductions in backlight power by half.

The elimination of the retarder film can be coupled with a highly scattering optical transmission (HSOT) material to provide collimated light. Integrating the reflection sheet and the prism sheet provides greater evenness and minimizes Mura problems. The LCD backlight assembly now can be made entirely from polymers and adhesives. The HSOT diffuser eliminates color degradation and Mie scattering in the LCD panel.

The scattering efficiency of the materials is a function of particle diameter. For particles of 2 microns, blue scatters more than red. For particles of 8 microns, red scatters more than blue. Tests with their materials show a color shift at a 60 degree viewing angle is less than the shifts from plasma and OLED materials.

Summing all of these changes in LCDs results in the following: laser backlights reduce power by 50 percent, Mura birefringence is eliminated, color degradation is eliminated and the best feature is that costs drop dramatically. The costs drop due to the reduction in films and the ability to extrude the materials into final shapes rather than casting the materials. This process also eliminates the use of solvents, so it is "greener" than other processes.

The ways to use the combination of polymer high-speed graded optical fiber and high efficiency LCD screen are highly varied. A 4k 3-D screen that is 150 inches diagonal provides a window to the world. This very large screen could be only 1 cm thick and would make telepresence seem like the other person is in the same room as you. Other applications are possible in telemedicine, where the high resolution, 3-D images could be as clear as real life, enabling high quality diagnosis from real-life images.

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