Flexible fiber-optic based imaging probes have significantly broadened the clinical application scope of optical coherence tomography (OCT), enabling high-resolution imaging of several regions in human body. The movement of flexible catheter causes the asymmetries of fiber geometry and stress, resulting in the presence of fiber birefringence. Scanning and flexing of the OCT probes results in variations in the polarization states of light from the sample arm. When the polarization states of light from the sample are misaligned with those of the reference arm, the interference fringes would fade out, leading to intensity variations and SNR degradation in OCT images.
From the statistical view, we characterized the intensity fluctuation and average signal-to-noise ratio (SNR) loss induced by the fringe fading of the sample arm polarization randomization. By taking advantage of an interesting observation, that the output polarization states of round-trip sample arm SMF are not uniformly distributed on the Poincare sphere, an optimum polarization state of reference arm can be found for the Michelson-type OCT configuration. From our analysis, we also suggested that the light source with low degree of polarization such as super-continuum source, or light source with long fiber, should be carefully managed to achieve the optimal SNR. We demonstrated our optimal polarization management, using two additional polarizers, could statistically provide 3.5 dB increase in system sensitivity.
Nanshuo Wang, Xinyu Liu, Qiaozhou Xiong, and Linbo Liu, "Polarization management to mitigate misalignment induced fringe fading in fiber-based optical coherence tomography (Conference Presentation)," Proc. SPIE 10488, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII, 1048806 (Presented at SPIE BiOS: January 27, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287645.5751456474001.
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