the optical switch 502 which pivots about the shaft 504 to produce an oscillating vertical motion at the end of the movable arm determined by the rotary position of the filter wheel 506 each source fiber is imaged in turn onto a single delivery fiber 508 by the lens set 510 the delivery fiber carries the light from each source fiber in turn to the distal tip of the forward looking probe the optical switching of the source fiber light into the delivery fiber is thus accomplished mechanically and is locked in phase with the filter wheel fig8 b shows an enlarged view of the end of the movable arm or fiber coupler 502 and the ferrule 512 holding the source fibers in their proper positions the three fibers are aligned into a single column by close packing them with dummy fibers 514 and bonding them in place after bonding the source fiber ends are polished so that their light can be launched into free space towards the imaging lens set 510 the ferrule is rotated before being locked into place with respect to the movable arm so that the three source fibers are aligned along the axis of motion of the movable arm.