## 2 Experimental Setup
### Principle of Numerical Correction Method for Perfect Circularly Polarized Light
The system configuration uses a polarization sensitive two-channel detection unit, where \(k\) assumes values 1 and 2. The modulus of the complex degree of coherence between the sample and reference arms, ranging from 0 to 1, is represented by \(\left|\gamma\left(z-z_{0}\right)\right|.\)  
Considering the use of the Hilbert transform to handle the above-mentioned interference signal \(I_{k}(z)\), we have the following [30]:  
\[I_{k}(z)+i\cdot H\{I_{k}(z)\}=A_{k}(z)\cdot\exp[i\cdot\delta_{k}(z)] \tag{10}\]  
In the demodulation of birefringence information from the sample, it is assumed that the incident light is perfectly circularly polarized. In practical measurements, any deviation from perfect circular polarization is considered polarization information from the sample. A QWP can be used to convert linearly polarized light to circularly polarized light. This requires an angle of 45\({}^{\circ}\) between the fast and slow axis directions of the wave plate and the polarization direction of the linearly polarized light. When this angle deviates by 45\({}^{\circ}\), linearly polarized light passes through the QWP and becomes elliptically polarized light. In order to verify that the deviation of circularly polarized light will affect the imaging effect, the imaging was carried out by controlling circularly polarized light as the variable. As shown in Figure 3, when the angle reading of the QWP in the PSOCT system built in this study was 120\({}^{\circ}\), the incident light was closest to perfect circularly polarized light. Depth profiles present depth information in an A-line with depth as the horizontal coordinate and intensity as the vertical coordinate. One of them is used here as an illustration to compare its SNR before and after calibration. A higher SNR generally means that the signal is stronger relative to the noise, thus demonstrating the increased imaging sensitivity. The samples were thinly sliced chicken breasts. According to the imaging and depth profile information, the reflected light collected was mainly concentrated near the depth of 200, and the depth of more than 500 is noise. Therefore, it is necessary to calibrate the circularly polarized light to ensure accurate measurements. To address this issue, a simple numerical method for correcting the magnitudes of s-polarized and p-polarized light from two detectors is proposed. As shown in Figure 4a, to obtain circularly polarized light, a numerical correction was applied to the field map. The inverse Fourier transform of the fringes generated the complex field and expressed vectors \(I_{A}\) and \(I_{B}\) in the complex plane. \(I_{A}\) and \(I_{B}\) are orthogonal to each other and have the same  
Figure 3: Depth profiles of a single reflector with different angles of the QWP. (**a**) The angle of the QWP is 105\({}^{\circ}\); (**b**) The angle of the QWP is 120\({}^{\circ}\); (**c**) The angle of the QWP is 135\({}^{\circ}\). order of magnitude when the incident light is circularly polarized. In order to satisfy all requirements, \(I_{A}\) and \(I_{B}\) must be reconstructed before quadrature assembling. First, \(I_{A}\) and \(I_{B}\) are normalized by dividing each by its own absolute value, leading to vectors \(I_{A}\) and \(I_{B}\), both with a magnitude of 1. The new vectors \(I^{\prime}_{A}\) and \(I^{\prime}_{B}\) are obtained using the following:  
\[I^{\prime}_{A} =I_{A}+I_{B} \tag{11}\] \[I^{\prime}_{B} =I_{A}-I_{B} \tag{12}\]  
These newly constructed vectors \(I^{\prime}_{A}\) and \(I^{\prime}_{B}\) clearly meet the criteria of orthogonality and equality and serve as the correction field vectors. The imaging of perfect circularly polarized light is obtained using the newly constructed vectors \(I^{\prime}_{A}\) and \(I^{\prime}_{B}\) as the complex field of the interference fringes acquired.