Optical design and simulation of a cervical scanning probe for polarization-sensitive optical coherence tomography using Ansys Zemax OpticStudio

The leading global cause of death in children under the age of five is due to complications arising from preterm birth (PTB). Although it is not fully understood why PTB can happen spontaneously, it is known that the cervix’s collagen rich extracellular matrix remodels prior to both term and preterm labor. In vitro polarization-sensitive optical coherence tomography (PS-OCT) has successfully imaged the distribution and 3D alignment of collagen in the cervix, as well as determined birefringence and measured cervical tissue depolarization in healthy tissue samples. The present investigation aims to expand on this research, by implementing in silico design, optimization, and simulation techniques for a PS-OCT probe to be used for human in vivo cervical scanning. The design considers patient comfort and clinical access as key parameters; ensuring the components are suitable for a colposcope-like probe and commercially available for quick and cost-effective manufacturing. To achieve these aims, the design benefits from using as few components as possible and limiting optical surface reflections. In this paper we demonstrate that with the use of a cemented gradient index (GRIN) relay system, a field of view (FOV) of up to 6 mm can be achieved, with a back-coupling efficiency of over 73%, on-axis and at up to a 2° scanning angle. Although Huygens point spread function (PSF) lateral resolution reached 81 μm, this paper demonstrates that manual adjustment and optimization of the components can increase this resolution to 12 μm, although at the expense of FOV width reduction. The simulated probe design was verified in preliminary experiments using an in-house built fiber-based OCT engine where high-quality OCT images with wide FOV were obtained from various samples, including healthy human skin.