An Auto-Focusing System for Endoscopic Laser Surgery based on a Hydraulic MEMS Varifocal Mirror

Endoscopic laser surgery is a minimally invasive procedure in which a fiber laser tool is used to perform precise incisions in soft tissue. Although the precision of such incisions depends on the proper focusing of the laser, endoscopic laser tools use no optics at all, due to the limited space in the endoscopic system. Instead, they rely on placing the tip of the fiber in direct contact with the tissue, which often leads to tissue carbonization. To solve this problem, we developed a compact auto-focusing system based on a MEMS varifocal mirror. The proposed system is able to ensure the focusing of the laser by controlling the deflection of the varifocal mirror using hydraulic actuation. Validation experiments showed that the system is able to keep the variation of the laser spot diameter under 3% for a distance range between 12.15 and 52.15 mm.