Study of Athermal Waveguides for Temperature Independent Lightwave Circuit

窄带波长解复用器和滤波器是下一代密集波长复用光通信系统不可缺少的器件。然而，中心波长随环境温度变化而变化的问题一直存在。在本研究中，我们以实现与温度无关的窄带滤光片为目标，开发了一种光程与温度无关的非热波导。在上一财年，我们开发了一个用有限元法计算波导光程长度温度系数的数值工具，并利用该工具设计了一个三维非热波导。结果表明，在0.633mum波长处，光程长度温度系数降至传统波导的2%。然而，要将这种非热波导应用于光通信的实际波长滤波器，需要开发波长为1.3或1.55 μ m的非热波导。因此，在本财年，我们首次使用Mach-Zehnder干涉仪测量了NA45玻璃、SiO_2和聚甲基丙烯酸甲酯薄膜在1.3 um波长处的折射率温度系数。然后，根据这些数据设计了脊载三维非热波导，并采用射频溅射和自旋镀膜制备了三维非热波导。结果表明，在1.3 μ m波长处，光程长度的温度依赖性成功降低到9.6x10^<-9> [1/K]，相当于传统波导的0.1%，从而证实了红外波长区域非热波导的实现。

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.