Endoscope window assembly designs and methods of assembling sub-millimeter imaging endoscopes are disclosed. An endoscope apparatus comprises an elongated cylindrical probe having rotating illumination optics in the middle and at least one detection fiber and a spectrometer connected to the detection fiber and a light source connected to the illumination optics and a processor for imaging. An optically transparent window is attached to the cylindrical probe at the distal end thereof, the window seals the rotating illumination optics inside the cylindrical probe, and the at least one detection fiber is located on the outer surface of the cylindrical probe. The present disclosure provides various embodiments of a window component that covers only the illumination component of the optical probe. Endoscope embodiments where the window component covers only the illumination component eliminate or significantly reduce exposure of detection fibers to reflected illumination light without blocking a light collection optical path.
