Optical modeling of an ultrathin scanning fiber endoscope, a preliminary study of confocal versus non-confocal detection

An optical model of an ultrathin scanning fiber endoscope was constructed using a non-sequential ray tracing program and used to study the relationship between fiber deflection and collection efficiency from tissue. The problem of low collection efficiency of confocal detection through the scanned single-mode optical fiber was compared to nonconfocal cladding detection. Collection efficiency is 40x greater in the nonconfocal versus the confocal geometry due to the majority of rays incident on the core being outside the numerical aperture. Across scan angles of 0 to 30 degrees, collection efficiency decreases from 14.4% to 6.3% for the nonconfocal design compared to 0.34% to 0.10% for the confocal design. Nonconfocality provides higher and more uniform collection efficiencies at larger scan angles while sacrificing the confocal spatial filter. (c) 2005 Optical Society of America.