# Compact SOI Dual-Mode (De)multiplexer Based on the Level Set Method
## 3 Results
### Experiment  
The device was fabricated on SOI wafer with electron beam lithography and etching at Applied Nanotool. Figure 9a shows the setup of the experimental apparatus. We used the broadband continuous light from the amplified spontaneous emission (ASE) as the input source and polarized it into linearly polarized light by a polarizer. Then, we coupled the light into and out of the chip by grating couplers and measured the output spectrum of the device by an optical spectrum analyzer (OSA). As shown in Figure 9b, the micrograph of the fabricated structures, we measured the IL and CT by forming (de)MUX into pairs. In addition to measuring the original structures, we additionally measured the performance of the device with the fabrication deviation of \(\pm 40\) nm. Figure 9c illustrates the microstructure under electron microscopy, revealing a single connected structure for the designed architecture. The absence of holes and gaps within the device contributed to the simplicity and stability in the manufacturing process, while it also played a role in improving device performance, which is discussed further. Figure 8: (**a**) The ILs and CTs vs. deviation; whether the device was zoomed in or zoomed out depended on the value of \(\Delta\)deviation greater or less than \(0\). (**b**) The ILs and CTs vs. thickness. Figure 10 shows the transmission spectra for the structures shown in Figure 9, where Device P40 represents a dilated structure with a positive deviation of 40 nm compared with the original ones (Device O40), while Device M40 represents an eroded structure with a negative deviation of \(-40\) nm. Figure 10: Experiment results of the effect of fabrication deviation on ILs of TE\({}_{0}\)**(a)** and TE\({}_{1}\)**(b)** as well as the CTs of TE\({}_{0}\)**(c)** and TE\({}_{1}\)**(d)**. The value of the deviation is [40 nm, 0 nm, \(-40\) nm], represented in the figure as Device P40, O40, and M40, respectively. The ripple curve is attributed to the resonance formed by the reflection between two grating couplers, while the solid traces represent the smooth fit to the corresponding ripple curve. Figure 9: Micrograph of devices that contain dual-mode demultiplexers in the testing experiment. (**a**) The configuration of the experimental apparatus. (**b**) The structures from top to bottom are the waveguide where grating couplers are at the both ends, the waveguides with both sides using dual-mode (de)MUX with the original width, 40 nm inward contraction, and 40 nm external expansion, denoted as Device O40, Device M40, and Device P40, respectively. (**c**) The structure of our device under the scanning of the electron microscopy. Figure 10a,b display the insertion losses for TE\({}_{0}\) and TE\({}_{1}\) modes, respectively, and Figure 10c,d shows the CTs of the two modes. For the O40 structure, the average ILs of TE\({}_{0}\) and TE\({}_{1}\) in the wavelength range of 1530 nm to 1570 nm were 0.39 dB and 0.24 dB, respectively, with maximum IL values of 0.89 dB for TE\({}_{0}\) and 0.44 dB for TE\({}_{1}\). For the deviation of \(\pm\)40 nm, compared with the simulation results, with the IL degradation by 0.36 (0.11) dB for TE\({}_{0}\) (TE\({}_{1}\)), the values of ILs were 0.72 dB for TE0 mode and 0.60 dB for TE\({}_{1}\) mode. In the range of 1530 nm to 1570 nm, the losses for TE\({}_{0}\) and TE\({}_{1}\) mode were less than 0.93 dB and 1.5 dB, respectively. The transmission from the TE\({}_{0}\) mode to output 2 port and the transmission from the TE\({}_{1}\) mode were less than \(-\)13 dB, \(-\)24 dB, and \(-\)17 dB, corresponding to P40, O40, and M40, respectively. The measured IL in the experimental data was higher than the simulated data due to the introduced random errors in the electron beam lithography (EBL) and etching steps in the fabrication process, while the misalignment of the grating coupler during the experimental measurement process can lead to slight inconsistency between the experimental and simulated results.