Coupling Of Scattering Light From Large Object Into Single-mode Fiber

The technology of coupling the spatial light into the fiber has been widely used in many devices of both military and civilian. While most of these applications are used in the condition that the beam received by the coupling system is approximate parallel beam because of the extra long distance of the light source and the coupling system, for example, the receiving system of free space optical communication. And in some other cases, the light source is close to the fiber, for example, the endoscope in medical imaging system.However if the target tested is large object, the light irradiated the target will be reflected from almost all directions. And in this case, the way that how to couple scattering light from large object into single-mode fiber is urgent needed but barely researched, and this technology will be well applied in many fields up to now.In this paper, we compare several methods of direct coupling, single lens coupling (ball lens, aspheric lens, cylindrical lens, GRIN lens, tapered fiber included) and lenses coupling, and analyze the different responses of some direct coupling methods and single lens coupling method when the light source is point light source and scattering light source respectively. Then several methods that may couple scattering light from large object into single mode fiber efficiently are analyzed in detail in this paper. It is verified in this paper that some kinds of coupling methods, especially single coupling method, are not suitable to couple scattering light from large object to single-mode fiber.The coupling efficiency and the receiving view field which are two parameters of receiving device. In order to couple scattering spatial light into a single mode fiber, we discuss some factors that may influence the single mode coupling efficiency based on the two parameters. The efficiency of some lens coupling methods in the condition of completely collimation of the whole coupling system and the receiving view field when a certain degree of the coupling efficiency loss is satisfied are compared separately by theoretical analysis and ZEMAX simulation. We use a moving point light source in radial direction to simulate the scattering light source from a large object. At last, the main simulation results of these coupling methods are verified by experimental.