# Holographic Silicon Metasurfaces for Total Angular Momentum Demultiplexing Applications in Telecom
## 2 Materials and Methods
### Optical Characterization Setup  
The experimental setup for the optical analysis of the fabricated samples is depicted in Figure 6. The performance of the metasurfaces has been analyzed with input optical beams endowed with integer orbital angular momentum, generated by uploading the proper phase patterns on a LCoS spatial light modulator (SLM) (X13267-08, Hamamatsu, Shizuoka, Japan) with amplitude/phase modulation [43]. An aspheric lens with focal length \(f_{\mathrm{F}}\) = 7.5 mm (A375 TM-C, Thorlabs, Newton, NJ, USA) was used to collimate the output of a DFB laser (\(\lambda\) = 1310 nm) emerging at the end of a single mode fiber. Then the output beam was linearly polarized and expanded with a first telescope (\(f_{1}\) = 3.5 cm, \(f_{2}\) = 10.0 cm) before illuminating the display of the SLM. A beam-splitter (50:50) was inserted after the telescope in order to produce a second coherent Gaussian beam for interferometric analysis. A second telescope (\(f_{3}\) = 20.0 cm,\(f_{4}\) = 12.5 cm) with an aperture in the Fourier plane was used to isolate and image the first-order encoded mode onto the sorter. A second beam-splitter (50:50) was used to split the beam and check the input beam profile with a first camera (WiDy SWIR 640U-S, NIT, Verrieres-le-Buisson, France). A Mach-Zehnder interferometric bench was added, as shown in Figure 6, in order to analyze the phase pattern of the modes generated with the SLM. Afterwards, the OAM beam illuminated the silicon sample, mounted on a 6-axis kinematic mount with micrometer drives (K6 XS, Thorlabs, Newton, NJ, USA). Finally, a second camera (WiDy SWIR 640U-S, NIT, Verrieres-le-Buisson, France) was used to collect the far field at the back-focal plane of a lens with focal length \(f_{5}\) = 7.5 cm. A sequence of linear polarizer (LPIREA100-C, Thorlabs, Newton, NJ, USA) and quarter-wave plate (WPQ10M-1310, Thorlabs, Newton, NJ, USA) was placed before and after the sorter, in reverse order, to control and select the circular polarization state of the input and output beams.  
Figure 6: Experimental setup used for the optical analysis of the fabricated Pancharatnam–Berry optical elements (PBOE). The output of the DFB laser (\(\lambda\) = 1310 nm) is collimated after a single mode fiber (SMF) using an aspheric lens (focal length \(f_{\mathrm{F}}\) = 7.5 mm), linearly polarized (P\({}_{1}\)) and magnified with a first telescope (\(f_{1}\) = 3.5 cm,\(f_{2}\) = 10.0 cm). The first order of the spatial light modulator (SLM) used for OAM-beam generation is filtered (D) and resized (\(f_{3}\) = 20.0 cm,\(f_{4}\) = 12.5 cm) before impinging on the demultiplexer. A beam splitter (BS) is exploited both to check the input beam and collect the output intensity at the back-focal plane of a fifth lens (\(f_{5}\) = 7.5 cm). A sequence of quarter-wave plates (Q) and linear polarizers (P) is placed before (P\({}_{2}\), Q\({}_{1}\)) and after (Q\({}_{2}\), P\({}_{3}\)) the sorter, in reverse order, in order to control and select the desired circular polarization. A Mach–Zehnder interferometric setup is used to analyze the spiralgram of the input optical vortices and infer the carried OAM value and sign.