Abstract
Within the last decades, several studies have been published that prove the benefit of polarisation sensitive optical coherence (psOCT) tomography for the field of biomedical diagnostics. However, polarisation sensitive imaging typically requires careful control of the polarisation state of the input illumination, which leads to bulky and delicate systems. While psOCT provides quantitative information, it is mostly sufficient to analyse the images qualitatively in the field of biomedical diagnostics. Therefore, a reduced form of this technique, cross-polarised optical coherence tomography (cpOCT), moves into the focus of interest that serves to visualise the birefringence properties of a sample. Despite the low requirements for the illumination’s polarisation, most of the proposed systems still include complex illumination control mechanisms. Here, we propose a common path probe based endoscopic system with an lateral resolution of 30 µm and a sensitivity of 103 dB comprising a commercially available swept-source OCT system and a free-space module which does not require any polarisation controlling elements. A Faraday mirror substitutes the complex polarisation control apparatus. We demonstrate the independence of the approach from the polarisation state of the light source by monitoring the illumination power in the orthogonal channels while varying the source polarisation. Furthermore, we validate the ability of the system to reveal the birefringence properties of different samples, starting from a quarter-wave plate, since its properties are fully characterised. Additionally, we present imaging results from several tissues to demonstrate its feasibility for the field of biomedical diagnostics.
Highlights
Since its development in 1991 [1], optical coherence tomography (OCT) found multiple applications in the field of biomedical diagnostics
Within the last decades, several studies have been published that prove the benefit of polarisation sensitive optical coherence tomography for the field of biomedical diagnostics
We demonstrate the independence of the approach from the polarisation state of the light source by monitoring the illumination power in the orthogonal channels while varying the source polarisation
Summary
Since its development in 1991 [1], optical coherence tomography (OCT) found multiple applications in the field of biomedical diagnostics. It is oftentimes sufficient if the images show phase induced effects qualitatively, in particular the birefringence properties of the sample Another class of psOCT devices called cross-polarised OCT (cpOCT) gained importance. In simplest CPP, the reflecting surface on tip of a bare single-mode fibre (SMF) serves as interference plane [32] These probes come with a fixed working distance and reference illumination power. The system still shows some fluctuations in the sample power during the measurement [35] Another option to create an input-polarisation independent approach is to implement a Faraday mirror which introduces a delay of 90◦ between the vertical components of the input light making it orthogonal. We display an even simpler system combining the free space module with the commercially available ssOCT engine and the monolithic CPP such that the co-polarised and the cross-polarised images are acquired simultaneously using a depth encoded scheme
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