Design, manufacturing, and opto-mechanical considerations for multimodal micro-endoscope featuring optical coherence microscopy, multiphoton microscopy, and visible navigation

Complex endoscopes which utilize optics with less than 1.5 mm diameter have an elevated risk of failure. Therefore, to ensure functionality and minimize risk proper design, optomechanical analysis and modelling must be performed while taking into consideration current manufacturing capabilities. Our endoscope is designed to perform Optical Coherence and Multiphoton Microscopy (OCM and MPM) which are powerful endoscopic imaging techniques used to characterize tissue. Separately each imaging technique has limitations when used by itself; however, this design combines these two modalities into a single optical system to work in synergy achieving both high sensitivity and specificity for diagnosis at the point of care. The optical design features two optical paths with different numerical apertures (NA) through a single lens system with a scanning optical fiber. The dual path is achieved using dichroic coatings embedded in a triplet that functions in a telescope like fashion. A high NA ~0.44 path is designed to perform OCM and MPM while a low NA ~.18 path is designed for the visible spectrum to allow navigation of the endoscope to areas of interest. We present the optical design of the endoscope, optomechanical considerations, manufacturability, stress and temperature effects. All these factors may be a source of problems in such small optics utilizing rare materials such as ZnS MS lenses. While very tight tolerances were the driving factor for the manufacturability of this system, temperature and stress must also be evaluated to obtain a better idea of the durability of the endoscope at the point of care. While it is challenging to evaluate the real performance of multimodality endoscopes, the models ensure that the system is designed for the expected imaging techniques, providing acceptable imaging across the entire field of view. Finally, we will give insight on what lessons were learned during the design, analysis, lens manufacturing, and assembling processes of the endoscope to provide a baseline of parameters to take into consideration when designing such complex small optical systems.