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Title: Design and fabrication of multi-step polymer optical power splitter using micro-embossing technique
Other Titles: Ying yong wei ya mo ji shu zhi duo jie ti jie gou ju he wu guang gong lü fen shu qi yan zhi
Authors: Huang, Zhe ( 黃喆)
Department: Department of Electronic Engineering
Degree: Master of Philosophy
Issue Date: 2010
Publisher: City University of Hong Kong
Subjects: Optical communications -- Equipment and supplies.
Optoelectronic devices -- Design and construction.
Notes: CityU Call Number: TK5103.59 .H84 2010
xxiii, 145 leaves : ill. (some col.) 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2010.
Includes bibliographical references.
Type: thesis
Abstract: Passive optical network (PON) is a cost-effective and efficient point-to-multi-point access network technology for fiber-to-the-home (FTTH). In such a network, the optical power splitters are the key components for splitting and combining optical signals between the optical line terminal (OLT) and multiple optical network units (ONUs) / optical network terminals (ONTs). The key characteristics of a splitter of PON application include wavelength/polarization-independent and low loss. In addition, it is also desirable to be compact for constructing high splitting ratio power splitter. Although there are a number of splitters designs have been published by other researchers, they are either wavelength dependent or not compact enough, and demands more complicated fabrication processes. Polymeric optical waveguide devices have recently attracted significant attention since polymer materials offer superior features, such as low cost for mass production using embossing technique or UV writing, rapid processing, small birefringence, and large thermo-optic coefficient. The typical hot embossing or UV embossing techniques are the most promising fabrication techniques for thermo-plastic or UV-curable polymer based optical waveguide devices. The fabrication costs of the embossed devices are hardly affected by the complexity of the design. Therefore the objectives of this study are to design a multi-step Y-junction based ultra-compact optical power splitter, and then investigating the materials and process parameters in the fabrication using embossing technique. As the first step of this project, a low loss, ultra-compact optical splitter based on multi-step structure is designed without the introduction of a third material. The proposed multi-step optical power splitter is implemented with only two polymer materials for core, cladding, and therefore compatible to low cost micro-embossing process. The branching angle of the multi-step power splitter is 24 times as large as the conventional Y-junction splitter. The total excess loss for both TE and TM polarizations is within 0.7 dB and wavelength dependent loss is around 0.3 dB, PDL is less than 0.05 dB over the operating wavelength between 1.26 and 1.63 μm. Second, embossing fabrication method is chosen over photolithography method, since it facilitates more convenient mass reproduction of the 3D structural multi-step splitter. During the whole embossing fabrication, an initial master with the same geometry of the design is necessary to fabricate first. We propose a novel method to fabricate the multi-step structural master using multiple metals assisted multiphotolithography without the necessary to use e-beam facility. A polydimethylsiloxane (PDMS) mold is then cast with the fabricated master. Finally, the multi-step splitter is replicated using the PDMS mold. In this thesis, the particular issues encountered in whole embossing, such as volume of UV curable polymer, and applied pressure, etc., are presented and discussed. Potential solutions to the corresponding key issues are also provided. The studies presented in the thesis are expected to be useful as a guide for the design and mass production of low cost, ultra-compact polymeric optical waveguide devices.
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