| Research Abstract |
Narrow band wavelength demultiplexers and filters are indispensable for the next generation of optical communication system using dense wavelength multiplexing. However, there has been aproblem that the central wavelength varies against the temperature change of environment. Inthis study, we aimed at realizing the temperature independent narrow band optical filter, and developed an athermal waveguide of which optical pathlength is independent of temperature.
In the last fiscal year, we developed a numerical tool to calcultate the temperature coefficient of optical path-length of waveguides using finite element method, and designed a three dimensional athermal waveguide by using this tool. As a result, the temperature coefficient of optical path-length was successfully reduced to 2% of conventional waveguide at the wavelength of 0.633mum. However, to apply this athermal waveguide to actual wavelength filter for optical communication, it has been needed to develope an athermal waveguide at the wavelength of 1.3 or 1.55mum.
Therefore, in this fiscal year, we first measured the temperature coefficient of refractive indeces of NA45 glass, SiO_2, and poly-Methylmethacrylate for their films at the wavelength of 1.3mum using Mach-Zehnder interferometer. Next, a ridge-loaded three-dimensional athermal waveguide was designed from these data, and fabricated using RF sputtering and spin coating. As a result, the temperature dependence of optical pathlength at the wavelenth of 1.3mum was successfully reduced to 9.6x10^<-9> [1/K] , which corresponds to 0.1% of that of conventional waveguide, and thus we confirmed the realization of athermal waveguide at infrared wavelength region.
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