According to at least one embodiment of the present disclosure, there is provided an apparatus comprising: a first optical fiber in communication with a light source; a second optical fiber in communication with an imaging probe; and a fiber optic rotary joint (FORJ) where a distal end of the first optical fiber and a proximal end of the second optical fiber are positioned coaxially with a gap between the fibers' end faces. The FORJ is adapted to transmit light between the fibers' end faces, and to rotate at least one of first and second optical fibers relative to the other. An actuator is configured to axially translate at least one of the first and second optical fibers relative to the other in a reciprocal motion. A light intensity sensor is adapted to measure light intensity changes due to optical interference between light reflected from the fibers' end faces. And, a control system is configured to receive light intensity measurements from the sensor and to use the light intensity measurements to control the reciprocal motion of the linear actuator to maintain the length of the gap between fibers' end faces substantially constant.