All-optical sensors have attracted much attention in biological/ medical research, chemical safety, and environmental monitoring. The optical sensors principle of operation relies on variations of optical characters when properties of the surrounding media change [1, 2], a key performance indicator of the sensors is the ability to detect the small change of refractive index (RI). For resonant sensors, this ability is expressed in terms of quality (Q) factor and sensitivity (S) [3].

In this work we propose a novel refractive index optical sensor based on 2D photonic crystal filter structure. Whereas, the refractive index sensing is realized by introducing a resonant cavity in the photonic crystal structure. In order to acquire the high sensitivity and transmission and increase quality factor of this sensor, the geometric structure is modified. We begin our consideration by the study of an optical filter that is initially based on two waveguides sections (W1) and one linear cavity. By the increase of holes number between the cavity and the waveguide structure, and changed the holes sizes that are located at the cavity ends and the position of the fourth adjacent cavity holes, we demonstrate that the quality factor and the transmission efficiency gradually evaluates. Then, we infiltrated the holes nearby the resonant cavity being functionalized. We vary the number of holes (N= 10, 16, 26, 34, 40 holes) to study the mass sensitivity (Δλ/N) of the device as a function of the number of functionalized holes. In our sensor design we determine that the functionalized hole number is N=26. After that we filled the functionalized holes with a change in refractive index from n=1.33 to 1.338 with an interval Δn=0.002. The sensitivity can achieve 300 nm/RIU. All analyses are based on the finite difference time domain method (FDTD).

References

[1]    O. Levi, M. Lee, J. Zhang, V. Lousse, S. Brueck, S. Fan, and J. Harris, Proc SPIE 6447, 64470P, 2007.

[2]    M. Adams, G. DeRose, M. Loncar, and A. Scherer, J. Vac. Sci. Technol., B 23(6), 3168–3173, 2005.

[3]    Yanan Zhang, Yong Zhao, Haifeng Hu, Miniature photonic crystal cavity sensor for simultaneous measurement of liquid concentration andtemperature, Sens. Actuators B-Chem. 216, pp. 563–571, 2015.