Multimode optical fiber, endoscopic system and method for examining a sample

A method for examining a sample using an endoscopic system which comprises a coherent light source, a photodetector, and a multimode optical fiber with an optical axis and having a single fiber core surrounded by a cladding, the multimode optical fiber comprising:

• a proximal end configured to be connected to the endoscopic system;
• and
• a distal end configured to be inserted into the sample,
• wherein the distal end has a light transmission surface which extends essentially parallel to the optical axis, and is designed to transmit light radially to the optical axis, wherein the light transmission surface is (i) at least one of an approximately flat surface, a spherical segment surface or a paraboloid segment surface, and (ii) an interface of the fiber core,
• wherein the distal end has a light reflection surface which approximately runs such that (i) the optical axis at the distal end, a normal to the light transmission surface and a normal to the light reflection surface lie approximately in one plane, and (ii) an angle between the light-reflecting surface and the optical axis is between 30° and 60°,
• wherein the coherent light source is arranged to introduce the light into the proximal end of the multimode optical fiber, and the photodetector is arranged to detect a multimode light emerging from the proximal end emitted by the optical fiber, and
• wherein the method comprises illuminating a large number of object points in the sample using the coherent light source through the multimode optical fiber, such that light is reflected from the object points through the multimode optical fiber and detected using the photodetector.