In this paper, multiple Fano resonances preferred in the refractive index sensing area are achieved based on sub-wavelength metal-insulator-metal (MIM) waveguides. Two slot cavities, which are placed between or above the MIM waveguides, can support the bright modes or the dark modes, respectively. Owing to the mode interferences, dual Fano resonances with obvious asymmetrical spectral responses are achieved. High sensitivity and high figure of merit are investigated by using the finite-difference time-domain (FDTD) method. In view of the development of chip-scale integrated photonics, two extra slot cavities are successively added to the structure, and consequently, three and four ultra-sharp Fano peaks with considerable performances are obtained, respectively. It is believed that this proposed structure can find important applications in the on-chip optical sensing and optical communication areas.

In this paper, multiple Fano resonances based on semi-ring-rectangular composite cavity (SRRCC) structure are numerically investigated and explained by FDTD method and MICMT method. High refractive-index sensitivities and high figure of merits (FOMs) are obtained in SRRCC system, and thus it may be preferred in the chip-scale optical sensing area. Besides, the phase response and the delay time within the Fano resonant windows are also investigated. Additionally, two more Fano resonances with high sensitivities and FOMs emerge through adding a new semi-ring cavity. These structures show widely applications in the sensing area and promote development of on-chip integrated photonics.

Plasmon-induced transparency (PIT) is theoretically explored for a graphene metamaterial using finite-difference time-domain numerical simulations and coupled-mode-theory theoretical analysis. In this work, the proposed structure consists of one rectangular cavity and three strips to generate the PIT phenomenon. The PIT window can be regulated dynamically by adjusting the Fermi level of the graphene. Importantly, the modulation depth of the amplitude can reach 90.4%. The refractive index sensitivity of the PIT window is also investigated, and the simulation results show that a sensitivity of 1.335 THz RIU⁻¹ is achieved. Additionally, when the polarization angle of the incident light is changed gradually from 0° to 90°, the performance of the structure is greatly affected. Finally, the proposed structure is particularly enlightening for the design of dynamically tuned terahertz devices.

This Letter presents a non-local means filter based on the Pearson correlation coefficient and Butterworth high-pass filter. In the method, the new gray value of the denoising pixel is equal to the weighted sum of the surrounding pixel values. We use the Pearson correlation coefficient between the pixels to calculate the weight of the surrounding pixels to the denoising pixel, then use Butterworth high-pass filter to optimize. Experimental results show that the method effectively reduces the speckle noise of digital holography and the image details are also very rich. At the same time, its performance is still better when compared with methods such as BM3D.

A novel chip-scale metal-dielectric-metal (MDM) refractive-index sensor is proposed and investigated in this paper by using finite-difference time-domain (FDTD) method and multimode interference coupled-mode theory (MICMT), respectively. A slot cavity with an embedded tooth-shape cavity and a side-coupled semi-ring cavity are inserted between the input and output MDM waveguides. According to the simulation results, dual ultra-sharp and asymmetrical Fano peaks emerge in transmission spectrum with high performances. Besides, the transmission responses for the primary parameters of this structure are also investigated. To focus on developing integrated photonic devices, the original structure is successfully expanded by two additional semi-ring cavities through an innovative coupling approach, generating up to eight Fano peaks with outstanding characteristics. It is believed that this novel MDM structure will be a guideline for designing the chip-scale plasmonic devices.