## 3 Experiments and Discussions
### System Parameters  
In the experiments, we developed a homemade full-range SD-OCT system including a homemade spectrometer. Here are some parameters of the components used by the system: the center wavelength  
Figure 5: The effect of light source bandwidth on complex conjugate artifacts (CCA) suppression. Figure 6: The effect of phase-shifting error on CCA suppression. \(\lambda_{0}\) of SLD was 850 nm and the bandwidth \(\Delta\lambda\) was 75 nm, the focal length \(f_{Obj}\) of object lens was 75 mm, the spot diameter \(d\) of parallel light was 6 mm, cylindrical lens with a focal length of 75 mm, collection lens with a focal length of 75 mm, and the SNR (Signal-to-Noise Ratio) of the system was 60 dB. The camera detector (Ximea, Munster, Germany) had maximum FPS (frames per second) of 30, for the camera, a minimum resolution of 4244 \(\times\) 200 pixels. However, we only used 4244 \(\times\) 21 pixels in the experiment; we got the average of the 21 lines of signals as interference signal in order to improve the imaging quality. The reason is that the SNR is the best when 21 lines are used for the average, as can be seen from Figure 7 which shows the SNR for different line numbers when we measured the ex vivo rat eyeball. In the calibration procedure, the interferometric signal whose optical path is 1005 \(\upmu\)m, was used to calibrate the wavelength axis. The reason for choosing the optical path difference is that the density of interference fringes is more suitable for finding the variation of the wavelength. A single-frequency laser (Thorlabs CPS850) with a wavelength of 850 nm was employed to determine the pixel location for the corresponding 850 nm wavelength. Subsequently, the wavelength \(\lambda_{1}=\lambda_{0}\times|d_{1}-d_{2}|/\left(|d_{1}-d_{2}|+\lambda_{0} \times|T_{1}-T_{1}^{\prime}|\right)\) of the first pixel of the camera and the one of the last pixel \(\lambda_{2}=\lambda_{0}\times|d_{1}-d_{2}|/(|d_{1}-d_{2}|-\lambda_{0}\times|T_ {2}-T_{2}^{\prime}|)\) can be calculated [17], where \(\lambda_{0}=850\) nm; \(d_{1}\) is the location of the reference arm when the period number of interference fringes between the first pixel and the pixel for 850 nm is \(T_{1}\) whilst the one between the last pixel and the pixel for 850 nm is \(T_{2}^{\prime}\). With the variation of wavelength and the wavelength of the first pixel and last pixel, the wavelength axis can be calibrated as shown in Figure 8. The wavelength can be used in Equation (7) to calculate the corrected phase shifts which can be substituted to Equations (9) and (10) to calculate intensity and phase of interference signals. It is noted here that the wavelength-calibration error is \(\pm\)0.15 nm using the calibration method. The maximum phase shift error caused by the wavelength-calibration error using Equation (7) is \(\frac{90\times 2\times\pi/895}{2\times\pi/850}-\frac{90\times 2\times\pi/894 85}{2\times\pi/849.85}=0.00076^{\circ}\). This value is so small that the influence of wavelength-calibration error can be ignored. Figure 8: The relation of the wavelengths and the pixels of the spectral domain optical coherence tomography (SD-OCT) system. Figure 7: The SNR (Signal-to-Noise Ratio) for different line numbers for averaged interference signal. The system's axial resolution could be obtained from the point spread function (PSF). Figure 9 is the PSF of the system at a light path difference of 1005 \(\upmu\)m. The dashed line is obtained by FFT of the original interference signal. The solid line is the FFT of the interference signal after the wavelength calibrations. From Figure 9, we could find the effect of wavelength calibration on the system's PSF. By the definition, the full width half maximum (FWHM) of PSF is the system axial resolution.