## 2 Experimental Setup  
In our HDSS, we used a convergent processor architecture for the object beam. This setup is also known as VanderLugt correlator [24]. This alternative provided us some flexibility. It allowed a wider freedom when selecting lenses to be used, because it is not necessary that the focal lengths match, as is the case in the classical 4-f system. Furthermore, the areal density on the recording material can be varied without the need to change the lenses, as explained in [25].  
In Figure 1, we show the complete experimental setup. The object beam follows the path formed by lenses L2 to L5. Along the same optical axis, we have lens L8 to form the image of the data page onto the CCD camera plane. Path formed by lenses L6 and L7 is the reference beam. In our discussion about limitations, we only refer to the object beam combined with lens L8.  
In the object beam, we introduced the data page by means of the PA-LCoS. The display was placed after the L3 lens. We used a divergent lens L2, so that the combination of L2 and L3 enables to modify the convergence angle of the beam onto the LCoS. The beam impinges onto the PA-LCoS while it is converging. The Fourier transform forms at the convergence plane, where we placed a Nyquist filter to control the Fourier Transform orders that we store. Lenses L4 and L5 form a relay system to image the Nyquist filter plane, which contains our information, onto the recording plane. In the present work, we did not use the filtering option by the Nyquist filter, since our focus was the study of the anamorphic and optical limitations of our system.  
The PA-LCoS used in this work is a commercially available PA-LCoS microdisplay, model PLUTO distributed by the company HOLOEYE. It is filled with a nematic liquid crystal, with 1920 \(\times\) 1080 pixels and 0.7\" diagonal. The fill factor is 87% and its pixel pitch is 8.0 \(\upmu\)m. It is important to remark the pixel pitch, because it defines the information bit size for different resolutions. The incident angle to separate impinging and reflecting object beam is 11.5\", and it is fixed during all the experiment.  
We used different numbers of pixels in the PA-LCoS to form a bit of information. These bit sizes were: 8 \(\times\) 8, 4 \(\times\) 4, 3 \(\times\) 3, and 2 \(\times\) 2 pixels. This means that, for every bit of information, we used, respectively, 64, 16, 9 and 4 pixels in the PLUTO device. Thus, they have, respectively, a 64 \(\upmu\)m, 32 \(\upmu\)m, 24 \(\upmu\)m, and 16 \(\upmu\)m length in each side for the square that forms the information bit. In this work, we aggregated the bits in the shape of linear stripes, arranged in a vertical or horizontal orientation, because we wanted to test if the reduction in the performance of the HDSS system is related to an anamorphic effect in the PA-LCoS. In this context, the bit size defines the minimum stripe width.  
Figure 1: Diagram of the experimental setup using convergent processor.  
In the data analysis, for statistical reasons, we considered individual bits of information, instead of individual stripes, to calculate the Bit Error Rate: in this way, we ensured that we have enough information to statistically analyze the image. We addressed LCoS data pages with 512 \(\times\) 512 pixels. If we would consider stripes as a block of information, we would only have 64 information blocks for 8 \(\times\) 8 pix. size, 128 for 4 \(\times\) 4, etc. Considering individual bits, we have 4096 bits of information for 8 \(\times\) 8 pix. size, 16,384 for 4 \(\times\) 4, etc.  
To retrieve information, we used a CCD camera. We used the PCO.1600 model from PCO.imaging company. This is a high dynamic 14-bit cooled CCD camera with a resolution of 1600 \(\times\) 1200 pixels, and a pixel size of 7.4 \(\times\) 7.4 \(\upmu\)m\({}^{2}\). The magnification of the PA-LCoS plane onto the camera plane is about a factor of two. Therefore, there is no limitation from the CCD camera since the image built on the CCD plane is oversampled.