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Waveguide-integrated reconfigurable nanophotonic devices are of importance for on-chip all-optical connection and flexible photonic circuits. In this paper, we propose inversely designed reconfigurable TE0-to-TE1 and TE0-to-TE2 mode converters based on digital metamaterials consisting of nanoscale silicon and non-loss phase change material Sb 2 Se 3 pixels. The design strategy combines finite element method, density method and method of moving asymptotes. Only 73 and 56 optimization iterations are taken to obtain the optimal digital metamaterials for targeted mode conversions. The footprints of ultra-compact functional regions are 0.92 and 1.04 square center wavelengths, respectively. TE0-to-TE1 and TE0-to-TE2 mode conversions with high transmission efficiency and output mode purity are realized with crystalline Sb 2 Se 3 , while TE0 mode directly pass through with amorphous Sb 2 Se 3. Meanwhile, by cascading these two mode converters, TE1-to-TE2 mode conversion is achieved as well. Moreover, the robustness of these designs is demonstrated by introducing random wrong pixels. • Reconfigurable mode order converters are inversely designed with pixelated Sb 2 Se 3 phase change material. • Highly efficient inverse design scheme combines finite element method, density model and method of moving asymptotes. • Footprints of functional regions are as compact as 0.92 and 1.04 square center wavelengths. • Performances of the reconfigurable mode converters are comparable and satisfactory. [ABSTRACT FROM AUTHOR]

The waveguide-integrated reconfigurable power splitting is of great importance for on-chip all-optical connection. Based on the combination of silicon and Sb-based phase change materials (PCMs), a series of ultra-compact reconfigurable power splitters is topologically designed. The footprints of the functional regions are kept less than 1.0λ2. The power splitting ratio between the output channels can be reconfigured through the amorphous and crystalline switching of Sb-based PCMs. We demonstrate Sb 2 Se 3 -based and Sb 2 S 3 -based digital metamaterials for the reconfiguration between power splitting ratio of 5:5 and power splitting ratios of 5:5, 6:4, 7:3, 8:2 and 9:1. The three-dimensional FDTD simulations show that the targeted power splitting ratio can be achieved with acceptable precision. Moreover, the robustness of design is validated by introducing pixel errors. • Reconfigurable power splitter is topologically designed with pixelated Sb-based phase change materials. • The reconfiguration between splitting ratio 5:5 and splitting ratios 5:5, 6:4, 7:3, 8:2 and 9:1 are achieved. • The topology design scheme combines finite element method, density model and MMA. • The footprint of the functional region is less than λ2. [ABSTRACT FROM AUTHOR]

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]