Ultrathin lensed fiber based anastigmatic needle probe for endoscopic swept source optical coherence tomography

Abstract

We present an anastigmatic all-fiber needle probe utilizing a fiber ball lens for endoscopic swept source optical coherence tomography (OCT). In order to avoid the astigmatism caused by the cylindrical profile of the imaging fiber or the outer protective tube, the lensed fiber probe is directly packaged into a 26-gauge hypodermic needle with a side opening optical window. A total internal reflection surface is fabricated on the tip of the no-core fiber (NCF) to deflect the beam with the lowest power loss. The working distance and the focused spot size of the probe can be optimized by adjusting the length of the NCF and the curvature radius of the fiber ball lens independently. The working distance of the assembled probe is experimentally measured to be 0.62 mm. The focused spot size is measured to be 18.72 μm and 19.03 μm in the x and y direction, respectively, i.e. the astigmatism ratio is 1.016. The needle probe is incorporated into a fiber-based endoscopic swept source OCT system with the insertion loss of 0.25 dB. The imaging performance of the proposed probe is validated by the linear and circumferential imaging of the biological tissue.