  A fundamental challenge in endoscopy is how to fabricate a small fiber-optic
probe that can achieve comparable function to probes with large, complicated
optics (e.g., high resolution and extended depth of focus). To achieve high
resolution over an extended depth of focus (DOF), the application of
needle-like beams has been proposed. However, existing methods using
miniaturized needle beam designs fail to adequately correct astigmatism and
other monochromatic aberrations, limiting the resolution of at least one axis.
Here, we describe a novel approach to realize freeform beam-shaping endoscopic
probes via two-photon direct laser writing, also known as micro 3D-printing. We
present a design achieving approximately 8-micron resolution with a DOF of >0.8
mm at a central wavelength of 1310 nm. The probe has a diameter of 0.25 mm
(without the catheter sheaths) and is fabricated using a single printing step
directly on the optical fiber. We demonstrate our device in intravascular
imaging of living atherosclerotic pigs at multiple time points, as well as
human arteries with plaques ex vivo. This is the first step to enable
beam-tailoring endoscopic probes which achieve diffraction-limited resolution
over a large DOF.
