An integrated approach to design and fabrication of a miniature endoscope using freeform optics

Endoscopes are important medical optical devices widely used in minimally invasive surgery. However, manufacturing issues such as tight packaging constraints and tolerance requirements hinder their development. These problems often result in high manufacturing cost or poor image quality. To cope with these issues, in this research, a novel endoscope utilizing an off-axis freeform optics is developed by using an integrated ultraprecision diamond machining process. The major optical components of this endoscope include a prism with two reflective surfaces and a freeform entrance surface. In addition, a doublet and a field lens were added to complete the system design. To validate the feasibility of the endoscope design, single-point diamond turning and rastering processes were utilized to machine the required components. After the lenses were machined, the geometry of the lenses was measured using a white light optical profilometer. The results show that their profiles have a manufacture error of ±2 μm along the optical axis. Lastly, the prototype was assembled and tested to evaluate its imaging performance, including measurement of its modulation transfer function.