复合金属光栅模式分离与高性能气体传感器应用

Split modes of composite metal grating and its application for high performance gas sensor

为实现近红外波段表面等离子体共振(SPR)模式的分裂和移动,同时提高光栅基SPR传感器的品质因数,提出了一种由双金属光栅构成的新型复合结构光栅,并研究了其气体传感特性.运用有限时域差分算法对该结构进行了数值模拟,发现由复合金属光栅激发的SPR出现模式分裂的现象.通过增大双金属光栅阵列间的相对位移改变原结构的对称性,导致复合金属光栅分裂的SPR模式朝相反方向移动.当相对位移量进一步增大到双光栅合并成新的单一光栅时,随光栅结构对称性的恢复,分裂的两共振模式最后又重新合并为一个模式.如果待测物的折射率为1.01 na 1.05,当相对位移量为0时,基于复合光栅结构气体传感器的折射率灵敏度为1207.5 nm/RIU,且品质因数达到1290.7;当相对位移量为100 nm时,与双共振模式对应的折射率灵敏度分别为1205.0 nm/RIU和1210.0 nm/RIU,品质因数分别为1295.4和762.3.因此,复合光栅SPR传感器具有超高品质因数的性能,使得它在生物化学传感领域中有巨大的应用潜力.

To achieve the surface plasmon resonance （SPR） mode splitting in infrared wavelength band, and to improve the figure-of-merit （FOM） of grating based SPR sensor, in this article we present a new composite grating structure, which consists of double metal gratings, and study the gas sensing performance. Split modes of SPR in composite metal grating are observed by using the finite difference time domain method. The original structure symmetry is broken and changed with increasing relative displacement between the double gratings, as a result, the resonant modes move to opposite directions. Calculated electric field distribution of the two separate resonant modes displays two different degrees of coupling effect between the double gratings. When the relative displacement is further increased till the double gratings are connected to form a new symmetrical single grating, the separate resonant modes will merge into another single resonant mode. If the refractive index of analyte （na） is in a range 1.01 ≤ na ≤ 1.05 and the relative displacement of double gratings is zero, the wavelength sensitivity based on composite metal grating gas sensor reaches 1207.5 nm/RIU （per refractive index of unit） and the FOM is obtained to be 1290.7, while the relative displacement of the double gratings is 100 nm, for the double split modes the wavelength sensitivities are 1205.0 nm/RIU and 1210.0 nm/RIU, respectively, and the corresponding FOMs are 1295.4 and 762.3. Therefore, the high FOM of the composite grating based on SPR sensor possesses great potential applications in biochemical sensing.