A Wavelength Demultiplexer With High Performance Based On Surface Plasmon Polaritons

Surface plasmon polaritons(SPPs)are transverse electromagnetic waves which propagating at metal-dielectric interface,can form strong local field intensity.Because interaction between the free electrons in metals and photons,SPPs can overcome the diffraction limit and have significant local field enhancement effects.By using these characteristics of surface plasmons,it is possible to manipulate optical wave at sub-wavelength scales.Therefore,SPPs have become one of the hot spots in nanophotonics and providing important solutions for high-density optical circuits and chips.At the same time,SPPs have important applications in the fields of optical switches,optical antennas,biological detection,and solar cells.In this paper,several symmetric cavity filters are proposed based on metal-medium-metal(MIM)waveguides and plasmonic resonators.We optimized the filter and a high performance wavelength demultiplexer with high isolation and low insertion loss is designed.The finite element method(FEM)is utilized in numerical simulation to study the transmission characteristics of device.The main work and conclusions are as follows:A symmetric dual groove resonator filter based on SPPs is proposed.The structure consists of three parts: input waveguide,output waveguide and two symmetrical groove resonators.Compared with single side-coupled resonator,it is found that symmetric dual resonator has better transmission,and the transmittance increases from 0.672 to 0.811.We discuss the reasons for transmission enhancement based on the temporal coupled mode theory.Because of the low spatial symmetry of the groove structure,the cavity quality factor is 11.The quality factor of symmetric dual groove resonator filter is low,so we design a symmetric dual disk and ring resonator filter.Compared with symmetric dual groove resonator filter,the symmetric disk resonator structure has higher spatial symmetry and high quality factor with 38,which is more suitable for narrowband filtering.The symmetric ring resonator filter has two resonance modes in the waveband of 800~1800nm,it shows the characteristics of multi-wavelength filtering as the ring center radius increases.Based on the above research of symmetric cavity filter,two-channel and three-channel wavelength demultiplexers based on symmetric disk and groove resonator are designed respectively.The structure is numerically simulated by COMSOL software and the transmission spectrum is analyzed.It was found that the wavelength of each channel can be adjusted by changing the geometric parameters and refractive index of the cavity.Meanwhile,in order to avoid the crosstalk between the channel and the change of mode after combined filters,it is necessary to optimize the structure parameters.The transmission of the 1310/1550 nm dual-channel wavelength demultiplexer based on the symmetric cavity reaches about 70%.The wavelength demultiplexer based on the symmetric disk resonator has a higher isolation(54.7dB)because of high quality factor.As for symmetric groove wavelength demultiplexer,because the loss of SPPs in propagation is less,so the insertion loss is smaller(close to 1dB),which is more suitable for large scale-integrated photonic circuit.In the end,we proposed three-channel wavelength demultiplexer at the wavelengths of 1310 nm,1490nm,1550 nm and both of them can realize the function of wavelength division multiplexing.