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Abstract: A novel two-dimensional nanoscale structure for sensing which consists of a metal–insulator–metal (MIM) waveguide with a defect, is designed and numerically simulated by using the finite element method (FEM). Both of the refractive index sensing characteristics and the temperature sensing characteristics of the structure are analyzed systematically by investigating the transmission spectrum. The numerically simulated results show that the dip positions of the transmission spectrum have linear relationships with the refractive index of the material under sensing and the ambient temperature, respectively. Based on the relationships, the refractive index of the material under sensing or the ambient temperature can be obtained from the dip wavelength shift detection. When the width and the height of the defect are set to be 50nm, 300nm, respectively, the refractive index sensitivity can be obtained as high as 1736nmRIU−1 and the temperature sensitivity is about 0.51nm/°C with a FOM of 9.79. This work has a certain significance for designing nanoscale refractive index sensors and temperature sensors. [Copyright &y& Elsevier]

In this paper, we present a general design scheme for waveguide-integrated demultiplexing devices based on intelligent topology search method combining density model and gradient-based method of moving asymptotes. 2D finite element method is adopted to simulate and evaluate the performance of demultiplexers with quasi-3D configuration by setting equivalent refractive index of silicon. The obtained pixelated digital metamaterials individually fulfill functionalities including 1550nm/1310nm and 1500nm/1600nm wavelength demultiplexing, TE0/TE1 mode demultiplexing at 1550 nm, and TE0/TM0 polarization demultiplexing at 1550 nm. The footprint of the functional region is as small as 1.55 μm × 1.55 μm. To validate our designs with SOI configuration, 3D models are simulated by finite difference time domain. Comparable and satisfactory performances of the target functionalities are demonstrated. For all four demultiplexers, the worst transmission efficiency is 44.5% of TE0 in polarization demultiplexing, the worst contrast ratio is 14.1 dB of TE1 in mode demultiplexing and the worst crosstalk is −15.1 dB of TE0 in mode demultiplexing. Within an ultra-compact footprint, this design scheme can efficiently enable the device to separate or route photons based on specific dimension, such as wavelength, mode and polarization. • Digital metamaterials are designed for wavelength, mode and polarization demultiplexing. • The inverse design scheme combines DM and MMA method, which needs only 200 iterations to search for a design. • The functional region of the demultiplexer occupies only λ2. • The performances of the four ultra-compact demultiplexers are comparable and satisfactory. [ABSTRACT FROM AUTHOR]