Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon,Hong Kong, China.
Opt Lett. 2010 Feb 15;35(4):484-6. doi: 10.1364/OL.35.000484.
We fabricate a long-period grating band-rejection filter with a lithium niobate (LiNbO(3)) channel waveguide, where the grating is formed on the waveguide surface by plasma reactive ion etching. The filter shows three distinct thermal tuning regimes. Below approximately 55 degrees C, the center wavelength of the rejection band decreases linearly with an increase in the temperature at a high sensitivity (-1.4 nm/ degrees C). The temperature sensitivity drops abruptly to a negligible value at approximately 55 degrees C and stays low up to approximately 70 degrees C, above which it jumps abruptly to a large positive value (1.6 nm/ degrees C). We attribute these peculiar tuning characteristics to the formation of different crystal phases in the core and cladding areas of the LiNbO(3) waveguide and the abrupt transitions of the thermo-optic coefficients of some crystal phases. The grating could be developed into various kinds of integrated-optic filters and switches for application in optical signal processing.
我们制作了一种具有铌酸锂（LiNbO(3)）通道波导的长周期光栅带阻滤波器，其中光栅通过等离子体反应离子刻蚀形成在波导表面上。该滤波器显示出三个明显的热调谐区域。在大约 55°C 以下，阻带的中心波长随温度升高以高灵敏度线性减小（-1.4nm/°C）。在大约 55°C 左右，温度灵敏度突然急剧下降到可忽略的值，并保持在较低水平，直到大约 70°C 左右，超过该温度后，它突然急剧上升到一个较大的正值（1.6nm/°C）。我们将这些特殊的调谐特性归因于 LiNbO(3)波导的芯区和包层区中不同晶体相的形成，以及某些晶体相的热光系数的突然跃迁。该光栅可开发成各种集成光学滤波器和开关，用于光信号处理。
