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

Abstract

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.