Direct Photo Fabrication of Micro Optical Elements

The emergence and rapid growth of the microelectronic technology combined with the optical technology need to couple and control light in and out of optical waveguides, together with concomitant drive for the miniaturization of components. A new area of optics termed "micro-optics" means optical elements of dimension of a millimeter or smaller [1, 7] . Mainly, this has implied lenses, or elements that act as lenses, as well as structures that redirect, polarize, and otherwise alter some state or direction of light. These would include elements like lenses, mirrors, gratings, and polarizers etc. made in micrometer scale. Also, optical waveguide structures can be considered in the broader classification under the name of "integrated optics" [3, 5]. These micro-optical elements are achieved by surface relief or refractive index modulation whose periods would be in the micrometer scale or of a submicron size comparable to the optical wavelength. The micro-optical structures are usually fabricated using multi-step processes including the photoresist and the etching processes based on the microelectronic fabrication technology. On the other hand, the direct photo-fabrication technology, in which the micro-optical structures are inscribed on the photosensitive materials just by selective light illumination, can remove the photoresist and the etching processes to simplify the fabrication of the micro-optical components. The elimination of the developmental step results in improved surface quality of the fabricated elements. Different selective light illumination technologies can be employed for the direct photo-fabrication. The simplest method is to use a photomask which gives the selective light-wave amplitude. However, with photomask illumination it is difficult to create submicron size patterns due to the limitation of the wavelength of light and resolution of the photosensitive materials. The phase-mask illumination producing light interference using a laser on the photosensitive materials can pattern submicron size relief or modulation. Also, the holographic interference using two or more laser beams, is the most useful method to pattern submicron size features in a large scale but is limited to imprint only periodic structures. Finally, the direct laser writing (DLW) has been applied for fabrication of various micrometer scale micro-optical structures. The DLW is a convenient method owing to its mask-free and non-contact features but is time consuming. For submicron size patterns, the electron beam writing can be used instead of using a laser. Direct photo-fabrication of micro-optical components such as gratings, optical waveguides, and microlenses on the photosensitive hybrimers has been reported using different fabrication technologies, as listed in Table 13.1. In this section, these will be introduced to prove the potential applicability of the photosensitive hybrimers.

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