Optical path length fine tuning structure and application structure thereof

The present invention relates to the laser and optical fiber communication field, and discloses an optical path length fine tuning structure and an application structure thereof. The fine tuning structure comprises an optical path separating mechanism used for separating the incident light and reflected light, a condensation element and a micro-electro-mechanical system (MEMS) planar mirror which are arranged orderly along an incident optical path. A reflection plane of the MEMS planar mirror is vertical with an optical axis of the optical path length fine tuning structure, and can be moved along the direction of the optical axis. The incident light beam is focused on the parallelly moved MEMS planar mirror via a focusing lens, and the reflected light is collimated by the focusing lens and then is spatially separated from the incident light via the optical path separating mechanism. The micromotion of the MEMS planar mirror does not change the direction of the reflected light, but changes the optical path len