Micro-Optics Review: The 3D Printed Fiber Endoscope Addressing Chromatic Aberration

The central claim of this study is that multiphoton lithography can successfully integrate complex, freeform lens elements onto a single optical fibre tip to produce high-fidelity images. Historically, the fabrication of a microsized full-colour endoscope has been an exercise in frustration. Engineers have long struggled to shrink optical components without introducing significant distortions, particularly when attempting to align the focal points of red, green, and blue light within a diameter smaller than a strand of hair.

To understand the leap claimed here, one must contrast traditional micro-manufacturing with the method used in this study. Standard fabrication often relies on grinding or moulding, techniques which are inherently limited by physical tool access and material stress. These older methods struggle to create 'freeform' surfaces—complex, non-symmetrical curvatures required to correct optical errors at the micron scale. Consequently, images often suffer from spherical and chromatic aberrations. In contrast, the Two-Photon Polymerisation (TPP) employed here functions like a microscopic 3D printer, curing liquid resin only at the precise focal point of a laser. This allows for the construction of multi-element lens stacks with geometries that traditional grinding simply cannot replicate, theoretically allowing for the precise manipulation of light paths that was previously impossible in such a small form factor.

Performance of the 3D printed fiber endoscope

The resulting 3D printed fiber endoscope was subjected to rigorous imaging tests to validate these design choices. The team measured a field of view (FOV) of 60° and a resolution of 7.13 line pairs per millimetre (lp/mm). While the paper asserts this constitutes 'good optical performance,' the definition of 'good' is relative. In a clinical setting, 7.13 lp/mm is competent for general navigation, but it may lack the extreme sharpness required for differential diagnosis of cellular pathologies without further magnification.

The study suggests that the integration of the microlens directly onto the imaging fibre tip effectively preserves image details across full-colour spectrums. However, the data presented is primarily optical characterisation. While the correction of aberrations is technically impressive, the durability of a polymer lens printed on a fibre tip during actual clinical insertion remains an open question. The physics holds up, but the mechanical resilience in a hostile biological environment is yet to be proven.