Refractive Index Sensor Design Based On Tamm Plasmon Polaritons

Tamm plasmon polaritons（TPPs）are a new type of surface electromagnetic wave localization modes,which are mainly found at the metal-distributed Bragg Reflection（DBR）interface and in photonic crystal heterojunctions.The intensity of the electromagnetic field of TPPs reaches its maximum at the interface and decreases the farther away from the interface.Compared with conventional surface plasmon polaritons（SPPs）,TPPs can be excited by TM polarization or TE polarization without the need for specific incidence angles and wave-loss matching devices;moreover,TPPs have higher field localization and lower losses,etc.Based on the above-mentioned properties,TPPs have promising applications in the field of micro-and nano-scale refractive index sensor design.In this paper,a transmissive index sensor structure is designed based on the transmission enhancement effect of TPPs in this context.The generation principle of TPPs in metal-DBR structure is studied,and the field intensity distribution and spectral line diagram are analyzed.And the characteristics of the TPPs excited in the metal-DBR structure are analyzed from several angles,and the effects of the two polarization states of electromagnetic waves,the thickness of the metal layer,the number of DBR periods,and the angle of incidence on them are studied.Meanwhile,the transmission enhancement effect（EOT）of the metal grating-DBR structure is studied based on the optical anomalous transmission phenomenon of the metal period array,and the effects of the metal grating height,slit width and grating period width on transmittance were analyzed.The results show that the coupling of TPPs excited at the metal-DBR interface with SPPs inside the metal slit can significantly enhance the transmittance of the structure,and this study has a wide range of applications in the fields of optical sensing,optical filters,optical switching.A refractive index sensor with a three-layer composite structure of metal grating,metal film and DBR is designed.The electromagnetic wave is incident from one side of the DBR and excites TPPs at the intersection with the metal on the other side,while the TPPs penetrate the metal film into the grating slit to excite SPPs and their Farby-Perot（F-P）resonances.The effect of the thickness of the metal film on the wavelength of the center of the transmission peak and the peak transmittance produced by this structure was quantitatively analyzed using the finite element method（FEM）.Simulation results show that the excitation efficiency of the TPPs can be effectively improved by introducing the metal film between the metal grating and the DBR,thus increasing the field strength of the SPPs mode and the amplitude of the transmission peak in the grating gap.The sensing performance indexes of the 3rd-5th order F-P resonant mode transmission peaks in the grating slit were analyzed by changing the duty cycle and the height of the metal grating.The results show that the sensitivity of the transmission peaks of each order of resonant mode increases significantly with decreasing duty cycle.At a duty cycle of 60%and a metal grating height of 1200 nm,the sensitivities of the 4th and 5th order resonant modes are 171.2 nm/RIU and 178.35 nm/RIU,respectively,and the FOM values are higher than 8.1 RIU^-1 and 10.74 RIU^-1,respectively.The full range of refractive index can be linearly detected from 1.0 to 2.27.The results of this study provide an effective design idea for refractive index sensors based on TPPs.