Endoscopic lens minimally invasive imaging core ultra-fine diameter large depth of field illumination optical element

The endoscopic lens is the imaging core of rigid/fiber optic endoscopes, typically composed of a Hopkins rod lens group, objective lens, rod lens, eyepiece, and protective glass. It employs an alternating arrangement of solid glass rods and air gaps, reducing interfaces to 4–6, increasing light transmission efficiency by 80%, with a field of view of 90°, a depth of field of 3–50mm, and significantly superior brightness and contrast compared to traditional fiber optic bundles. The front objective lens often uses a "negative-positive" retrofocus structure, combined with doublet lenses to correct spherical and chromatic aberrations, and incorporates an image-space telecentric optical path to ensure off-axis light beams enter the image transmission bundle vertically, preventing edge darkening. The latest designs achieve MTF ≥0.8 in both visible and near-infrared dual bands, distortion <31%, energy concentration >89%, and can match fiber optic bundles with a diameter of 1.6mm and single fiber size of 16µm, enabling an 80° wide field of view and 1.3mm ultra-short focal length. To meet minimally invasive requirements, lens diameters have been reduced to 0.3mm, with surfaces coated with DLC or hydrophobic films for scratch and liquid adhesion resistance; metasurface versions further reduce thickness to the wavelength level, using sub-millimeter apertures to focus RGB lasers, providing 150° wide-angle and three-color fluorescence imaging for capsule endoscopes and angioscopes. Future trends point toward wafer-level aspheric lenses, metasurface arrays, and tunable liquid lenses.