An apparatus includes an optical element, a GRIN lens, and a detector. The optical element has a first optical aperture. The GRIN lens has first and second ends. The first end of the GRIN lens is positioned to receive light from the first optical aperture. The detector is configured to measure values...http://www.google.es/patents/US7336988?utm_source=gb-gplus-sharePatente US7336988 - Multi-photon endoscopy
