A novel nanometeric plasmonic filter in a tooth-shaped metal-insulator-metal waveguide is proposed and demonstrated numerically. An analytic model based on the scattering matrix method is given. The result reveals that the single tooth-shaped filter has a wavelength-filtering characteristic and an ultracompact size in the length of a few hundred nanometers, compared to gratinglike surface plasmon polariton (SPP) filters. Both analytic and simulation results show that the wavelength of the trough of the transmission has linear and nonlinear relationships with the tooth depth and the tooth width, respectively. The waveguide filter could be utilized to develop ultracompact photonic filters for high integration.

A novel subwavelength surface plasmon polaritons optical filter based on an incompletely directional coupler is proposed and numerically simulated by using the finite difference time domain method with perfectly matched layer absorbing boundary condition. An analytical solution for the resonant condition of the structure is derived by means of the cavity theory. Both analytical and simulative results reveal that the resonant wavelengths are proportional to the length of the slit segment, inversely proportional to the antinode number of a standing wave in the segment, and are related to the slit width and the gap between the two slits. The analytical solution being consistent with the numerical simulation verifies the feasibility of the concept of the new filter structure.

Characteristics of a multiple-teeth-shaped plasmonic filter are analyzed. As an extension of this structure, an asymmetrical multiple-teeth-shaped structure is proposed and numerically simulated by using the finite difference time domain method with perfectly matched layer absorbing boundary condition. It is found that the asymmetrical structure can realize the function of a narrow-passband filter. The central wavelength of the passband linearly increases with the simultaneous increasing of d ₁ and d ₂.

A structure based on plasmonic nano-capillary resonators for optical wavelengths demultiplexing is proposed and numerically investigated. The structure consists of main/bus waveguide connected with series of nano-capillary resonators, each of which tuned at different wavelength transmission band. A model based on resonator theory is given to design the working wavelength of the structure. Both analytical and simulation results reveal that the demultiplexing wavelength of each channel has linear and nonlinear relationships with length and width of the nano-capillary structure.

Tooth-shaped and multiple-teeth-shaped plasmonic filters in the metal–insulator–metal (MIM) waveguides are demonstrated numerically. By introducing a three-port waveguide splitter, a modified model based on multiple-beam interference and the scattering matrix method is given. The transmittance spectra as a function of teeth width, depth, period, and period number are addressed, respectively. The results show that the new structure not only performs the filtering function as well as MIM gratinglike structures, but that it is also of submicrometer size for ultrahigh integration and relatively easy fabrication.

A simple fiber sensor for magnetic field measurement based on nanoparticle ${\mathrm{Fe}}_3{\mathrm{O}}_4$ magnetic fluid and relative Fresnel reflection is presented. The sensor includes only a light source, three couplers, two photodetectors, and two fiber sensing ends. Magnetic fields at different concentrations of magnetic fluid are measured. Magnetic fluid with high concentration can be used for the measurement of weak magnetic fields, while low concentration fluid is used for the measurement of strong magnetic fields. The temperature dependence of the sensor is also addressed.