Fabrication of Micro-Optical Devices by Holographic Interference of High Photosensitive Inorganic-Organic Hybrid Materia
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Fabrication of Micro-Optical Devices by Holographic Interference of High Photosensitive Inorganic-Organic Hybrid Materials (Photo-HYBIRMER)
Dong Jun Kang, Jin-Ki Kim and Byeong-Soo Bae Laboratory of Optical Materials and Coating (LOMC), Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea ABSTRACT Sol-gel derived photosensitive inorganic-organic hybrid materials (Photo-HYBRIMER) containing a large quantity of photoactive molecules exhibit the large changes in both refractive index (over 10-2) and volume (over 30%) on UV exposure. The materials could be used for direct fabrication of micro-optical devices using holographic interference. With the change of the beam number for holographic interference (1-beam, 2-beam, 3-beam and 4-beam interference), various typed micro-optical devices (Fresnel-type lens, 1D- and 2D-typed diffraction gratings) could be easily fabricated. Importantly, the fabricated micro-optical devices exhibited the very homogeneous surface structures and good optical performance.
INTORDUCTION Micro-optical devices are the important component for beam dispersion and conversion, optical signal processing and modulation in compact and complicated optical data storage systems and optical integrated circuits [1-3]. Thus, the study of fabricating micro-optical devices has been intensively performed using a variety of methods, including a photo-mask, beam lithography, etching techniques, holographic interference. Contact imprinting using a photo-mask is not suitable for the fabrication of devices with a submicrometer period due to the diffraction limit between the mask and the samples. The beam lithography, which includes the etching process, is rather complex and needs several steps to reveal the precise surface structure. These disadvantages of a photo-mask and lithographic techniques cause limitations to easy fabrication and obtaining higher performance of micro-optical devices. However, the holography can produce fine and precise patterns easily. Thus, the holographic interference has great potential for the direct fabrication of micro-optical devices with good performance. The materials as well as the fabrication processes are crucial factors in fabricating the microoptical devices with good performance. In order to achieve higher performance in optical devices,
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materials must have high photosensitivity, meaning a large refractive index, and undergo a volume change upon light irradiation, because the direct photo-fabrication and the performance of an element depend on the photosensitivity of the materials used. In recent years, sol-gel hybrid materials (HYBRIMERs) [4-6] and photosensitive polymers [7,8] have been used as potential materials for fabricating highly efficient micro-optical elements. In particular, the photosensitive hybrid materials (Photo-HYBRIMERs) doped with large amounts of photoactive molecules were found to exhibit larger refractive index and volume change on UV exposure [9-11]. Th
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