多面转镜激光器扫频光学相干层析成像系统的全光谱重采样方法

在多面转镜激光器扫频光学相干层析成像系统中,激光器存在着输出光谱错位与扫频范围波动的问题.目前的重采样方法中,普遍利用互相关运算校正光谱错位,并进行大范围的截取,保证扫频范围的一致性,但这会导致成像信噪比与分辨率的降低.本文用马赫-曾德尔干涉仪(MZI)采集到的干涉信号对扫频范围波动的问题进行了详细的测量与分析,其中干涉信号的解缠相位曲线的非随机性和平行性,表明该类激光器输出光谱的波长分布具备一致性.在此基础上,提出了一种用最长扫频范围的MZI干涉信号,对样品干涉信号进行时域光谱对齐、然后进行一对多插值的重采样方法.实验与分析表明,该方法利用了所有的光谱信号,保证了样品干涉信号的能量利用率,能有效提高图像的信噪比与分辨率.

A full spectrum resamping method in polygon tunable laser-based swept-source optical coherence tomography

Swept-source optical coherence tomography (SS-OCT) has high sensitivity and signalnoise ratio compare with time-domain optical coherence tomography and spectral-domain optical coherence tomography. Therefore, SS-OCT is the form of Fourier domain optical coherence tomography predominantly used in experimental research and biomedical image. However, polygon tunable laser-based SS-OCT suffers sweep range fluctuation and spectral misplacement. Under certain circumstances, in the current resampling methods cross-correlation is widely used to align spectrum misplacement, and truncate A-lines in order to ensure the consistency of frequency-scanning range, which, however, degrades the image SNR and resolution. We use the Mach-Zehnder interference (MZI) signal to quantify and analyze this problem in two typical polygon tunable lasers. The periodical change of sweep range and spectrum misplacement show the instability derived from polygon mirror. The parallelism among unwrapped phase curves indicates that polygon tunable laser output spectra have consistent wavelength distributions, and thus it is suited to implement cross-correlation between MZI signals in time domain, and an unwrapped phase curve can represent the wavelength distribution of all A-lines.According to the above conclusions, we demonstrate a resampling method in which the zero-padding interpolation and cross-correlation are used to align A-lines in time domain and eliminate the residual phase noise caused by integer shift. Then the unwrapped phase curve that has a largest sweep range is used to resample all the aligned A-lines, and the interference signals can be fully utilized. The experiments for signal truncation and Pomelo fruit flesh indicate that the proposed method can improve image SNR but does not make the intensity image dislocated. The phase noise (3.9 mrad for a 49 dB SNR) from static mirror is close to theory limit after resampling, thus showing good phase stability and resampling precision. The proposed resampling method also needs less computational work than one-to-one resampling method because it only fits unwrapped phase curve and calculates interpolation coefficient once.