Sugaya Toshio, Kawano Yukio
Department of Electrical and Electronic Engineering, School of Engineering, Tokyo Institute of Technology, Tokyo 1528552, Japan.
Laboratory for Future Interdisciplinary Research of Science and Technology, Tokyo Institute of Technology, Tokyo 1528552, Japan.
Sensors (Basel). 2021 Feb 18;21(4):1419. doi: 10.3390/s21041419.
Terahertz waves are located in the frequency band between radio waves and light, and they are being considered for various applications as a light source. Generally, the use of light requires focusing; however, when a terahertz wave is irradiated onto a small detector or a small measurement sample, its wavelength, which is much longer than that of visible light, causes problems. The diffraction limit may make it impossible to focus the terahertz light down to the desired range by using common lenses. The Bull's Eye structure, which is a plasmonic structure, is a promising tool for focusing the terahertz light beyond the diffraction limit and into the sub-wavelength region. By utilizing the surface plasmon propagation, the electric field intensity and transmission coefficient can be enhanced. In this study, we improved the electric field intensity and light focusing in a small region by adapting the solid immersion method (SIM) from our previous study, which had a frequency-tunable nonconcentric Bull's Eye structure. Through electromagnetic field analysis, the electric field intensity was confirmed to be approximately 20 times higher than that of the case without the SIM, and the transmission measurements confirmed that the transmission through an aperture had a gap of 1/20 that of the wavelength. This fabricated device can be used in imaging and sensing applications because of the close contact between the transmission aperture and the measurement sample.
太赫兹波位于无线电波和光波之间的频段，作为一种光源，正被考虑用于各种应用。一般来说，使用光需要聚焦；然而，当太赫兹波照射到小探测器或小测量样本上时，其波长比可见光长得多，会引发问题。衍射极限可能使得无法通过使用普通透镜将太赫兹光聚焦到所需范围。作为一种等离子体结构的靶眼结构，是将太赫兹光聚焦到衍射极限之外并进入亚波长区域的一种有前景的工具。通过利用表面等离子体传播，可以增强电场强度和传输系数。在本研究中，我们通过采用我们之前研究中的固体浸没方法（SIM），改进了小区域内的电场强度和光聚焦，该方法具有频率可调的非同心靶眼结构。通过电磁场分析，证实电场强度比没有SIM的情况高出约20倍，传输测量证实通过孔径的传输具有波长的1/20的差距。由于传输孔径与测量样本之间紧密接触，这种制造的器件可用于成像和传感应用。
