Cancer detection by photonic crystal optical biosensors: Effect of hexagonal micro ring resonator design

In this paper, an efficient hexagonal micro-ring resonator is proposed to improve the cancer biosensor performance. The sensor is based on a two-dimensional photonic crystal lattice with a horizontal waveguide. Finite-difference time-domain method is used to calculate the response of the sensor. The simulations show that by using the optimum hexagonal micro-ring resonator, the sensor performance parameters such as full width half maximum, absorption/transmittance, quality factor & sensitivity have been improved. Various parameters are involved in the design of a micro-ring resonator, which include; the coupling area length, the side length, the inner and outer radius of the micro-ring resonator and the waveguide gap width. This study not only unveils the obscure effect of some kind of symmetries in the design of micro-ring resonators on the final device performance, but also brings important perspectives to designing micro-ring resonators for cancer sensing applications. It is found that when the length of the coupling area is equal to the width of the waveguide gap and when the lengths of the sides create the most possible symmetry in the hexagonal micro-ring resonator structure, the sensor exhibits superior performance. The best design is when the maximum possible symmetry occurs in the design of micro-ring resonators. In this research, at least 32 different hexagonal micro-ring resonators have been designed and examined from the largest to the smallest possible cases. Finally, by selecting the optimal hexagonal micro-ring resonator and using it in the proposed optical biosensor, five different types of cancer cells have been detected. Using the optimized hexagonal micro-ring resonator in the structure of optical biosensor for cancer detection has resulted in obtaining promising results in terms of quality factor, figure of merit and sensitivity with respective values of 4782, 2113 1/RIU, and 661 nm/RIU. The results obtained from the simulation of the proposed optical biosensor using the optimized micro-ring resonator show significant improvements compared to other structures in this field.