Polarization

With the rapid growth of the optical communications industry, there is an increasing emphasis on developing better and more advanced optical devices. An optical attenuator devices which reduce the power level of an optical signal falls into this category.

Traditional techniques used for variable optical attenuation like electro-chromic technology, liquid crystal technology and circular polarizers are often uneconomical, environmentally susceptible or limited in their applications due to mechanical shape constraints.

Researchers Franz Pertl and Joshua Gross are researching, developing, and testing a novel optical attenuator design that not only overcomes these problems but also holds promise for numerous applications. This design relies on a patented technology, which is under development by CIRA, and allows uniform gradual dimming of an optical element through two special polarizers that can linearly translate with respect to one another, unlike conventional polarizers that require rotation with respect to one another. By controlling the distance of translation between the polarizers, the desired amount of optical attenuation can be achieved.

A light wave is an electromagnetic wave whose fields vibrate in numerous planes. If the fields are vibrating in random planes, the light is referred to as unpolarized light. Thermally created light emitted by the sun, by a lamp in the classroom, or by a candle flame are some examples of unpolarized light. It is possible to transform unpolarized light into polarized light . Polarized light waves are light waves in which the vibrations occur in a single plane, ellipse or circle. The process of transforming unpolarized light into polarized light is known as polarization and polarizers are filtering devices used for this purpose.

The optical attenuator under development consists of two specially constructed polarizers on which a special spatial polarization pattern is designed. This pattern varies the polarization-axis as a function of position. The polarization axis extends across the length of the filter and only allows vibrations of the electromagnetic wave that are parallel to the axis to pass through. Vibrations which are perpendicular to the polarization axis are blocked by the filter.

When the two polarizers are perfectly aligned, maximum amount of light is transmitted, much like a rope that can vibrate between two picket fences that are perfectly aligned. When one polarizer slides linearly with respect to the other, depending on the translation distance, the polarization field becomes crossed and attenuation increases to a maximum point. Translation beyond the maximum attenuation will result in the two overlaid filters passing more light again.

A major advantage of this technology is that it requires only a small customizable linear translation to achieve attenuation or transmission. The research challenge in the months ahead is to find the best manufacturing technique to make each of the devices and match it with an application. The research group is also engaged in finding industrial partners for this project.