## 3 Materials and Methods
### Phase Modulation and Time Reversal  
The time reversal process is shown in Figure 2b. After placing the bezel shown in Figure 2b, we adjust the intensity of the reference light and finally load the speckle conjugate phase on the SLM. The reference light was phase-modulated by the SLM to form a light wave conjugated with the original speckle phase, that is, conjugate compensation for the scattered light to form a time-reversed light wave, which reversely passed through the diffuser and then was detected by a CCD (charge coupled device) camera.  
The DOPC system shown in Figure 2 consists of a SLM (Holoeye, PLUTO-VIS-016, resolution 1920 pixels \(\times\) 1080 pixels, pixel size 8 \(\upmu\)m \(\times\) 8 \(\upmu\)m), a beam splitter, a CMOS camera (PCO.EDGE 3.1, resolution 2048 pixels \(\times\) 1536 pixels, pixel size 6.5 \(\upmu\)m \(\times\) 6.5 \(\upmu\)m), and a lens (Lens 3, f = 100 mm). The SLM is mounted on a six-degrees-of-freedom combination mount. Since the pixel size of the SLM and CMOS camera do not match, it is necessary to adjust the Lens 3 so that the SLM and CMOS camera sensor planes are mutually imaged [17], to ensure the SLM and COMS camera pixels are aligned one by one; thus the camera can accurately extract the interference patterns on the SLM. According to the theoretical calculations, the object image relationship of the convex lens satisfies \(\mathrm{u_{o}}+\mathrm{v_{i}}=\mathrm{f}(\mathrm{M}+1)^{2}/\mathrm{M}\) (\(\mathrm{u_{o}}\): object distance, \(\mathrm{v_{i}}\): image distance, f: focal length, M: magnification). We determined the target magnification is 0.8125 (M = 6.5/8) from the pixel size of the SLM and CMOS camera. In the experiment, the Lens 3 focal length is 100 mm, so the spatial distance between the CMOS camera and SLM needs to be adjusted to approximately 404 mm.  
The pixel matching process of the SLM and CMOS camera is divided into two steps: coarse adjustment and fine adjustment. We removed the Lens 3 in front of the CMOS camera during coarse adjustment and adjusted the position of the SLM, CMOS camera, and beam splitter 4 to place the light not only at the center of the SLM and CMOS camera, but also incident vertically. We loaded a phase pattern with a specific pattern on the SLM and adjusted its imaging focal length. When a clear pattern is presented on a CMOS camera, this focal length is the spatial straight-line distance from the SLM to CMOS camera. We adjusted the position of the SLM and CMOS camera to ensure that the two devices were center-aligned horizontally. Before fine adjustment, we placed Lens 3 in front of the CMOS camera and adjusted its spatial position to ensure that its focus was at the center of the CMOS camera. We then loaded the grid image on the SLM and adjusted the distance between Lens 3 and the CMOS camera to make a clear image on the latter. We observed the magnification corresponding to the grid, if M > 0.8125, it is necessary to increase the spatial distance between the CMOS camera and SLM, as well as adjust the position of Lens 3 again to ensure the CMOS camera presents a clear image. We repeated the operation several times to guarantee magnification in the condition that the imaging is clear. After the above-two steps, the pixel matching process for the SLM and CMOS camera was completed.  
In the experiment, the phase conjugate reduction performance of the off-axis holographic DOPC system without the scattering sheet was tested, and then the scattering sheet was placed to verify its ability to focus through the scattering medium.