What is Autocloning?

The corrugated multilayer film is the basic structure of the Autocloned photonic crystal. It is fabricated by sputterring onto a preprepared substrate with a corrugated surface. This corrugated shape is the source of the unique optical properties which cannot be obtained by conventional multilayer films. During the process of deposition the shape of subsequent layers gradually becomes smooth and the sharp discontinuities of the substrate disappear because of the sputtering deposition process. This deposition technology is known as the Autocloning Technology.

The triangular corrugation tends to be rounded by the process of deposition. When this is allowed to progress the surface ultimately becomes smooth. To counterbalance this smoothing the surface is etched, as the etching rate of a diagonal surface of 45 degrees is highest, the surface modulation stablizes at 45 degrees. It is possible to accumulate, by combining the effects of deposition and etching, hundreds of layers maintaining the same triangular wave shape.

Our company has covering patents concerning the design, fabrication, and applications of photonic crystal fabricated by the autocloning method. At the time of writing the number of domestic and foreign patent applications is 71.

Functionality

An autocloned photonic crystal with a three dimensional periodic structure, can be fabricated as a 1D periodic structure in the direction of deposition, deposited on a 2D patterned substrate. However, it is very difficult to obtain the unique optical characteristics obtained by a three dimensional periodic structure consistently. To fabricate such a unique structure consistently, we have developed an element that consists chiefly of a unit cell that is a 2D structure.
An autocloned photonic crystal of two dimensions functions as an anisotropic optical multilayer film, and can achieve familiar functions such as that of a polarizer or wave-plate. There are three degrees of freedom during design; the choice of the optical materials used, the depth of the pattern of the substrate, the thickness of the films (pitch of the structure) by appropriate choice of which a polarizer or wave-plate can be fabricated. Moreover, it is possible to improve the extinction ratio of the polarizer by for instance increasing the number of layers deposited. Accurate control of the retardance of a wave-plate is possible by fine-tuning of the film thickness. In principal any material suited to sputtering deposition can be freely chosen. Typical substrate materials are quartz, optical glasses, and Si.

Because the final layer to be deposited on the photonic crystal results in a flat surface, Autocloned photonic crystals can be handled (cleaned) in the same way as conventional multilayer films.

The features of autocloned photonic crystals

The most significant advantage of autocloned photonic crystal is the ability to fabricate a photonic crystal with a large number of elements on a substrate with arbitrary patterning in a single deposition process. Therefore, if the substrate were produced at low cost, perhaps by nano-imprinting technology, it would be possible to manufacture photonic crystals in large quantities using the same processes already established for conventional optical multilayer films. It is already possible to support mega-pixel devices by producing photonic crystals with elements in a one to one correspondence with the device.

Autocloned elements can be fabricated on a substrate with curved patterning. Novel optical elements that were not possible using conventional technology, such as polarizers and wave-plates with transmission axis azimuths that vary gradually along a curve can easily be fabricated. New optical elements have been invented based on such autocloned photonic crystals.