Fiber-optic interferometer for measuring low velocity of diffusely reflecting surface

All‐fiber multipoint VISAR

“…Additionally, the two channel signals have a relation of reverse phase, which is indicated by the Eqs. (2) and (3). These matches show that the prototype all-fiber two-point VISAR can response to the movements of two points, respectively.…”

“…A -delay can be produced between beams when they arrive at the targets through the direct arm and the delay arm. Compared with previous all-fiber VISAR [3,4], the configuration introduces a collimator C II and T-delay fiber (called TDM fiber due to its function) into the system to create a probing port for the T II.…”

“…They are described as Beams of T I: Beams (1) and (2), counter propagating the common path, can interfere at coupler II. The symmetry ensures that all-fiber multipoint VISAR can use a short coherence length source [3,4], such as an SLD. Also, beams (3) and (4), as well as beams (1) and (2), can interfere at coupler II due to the movement of the T II.…”

“…As we know [1,3], for T I the number of fringes counted by VISAR is related to the velocity of T I by…”

“…Based on the traditional VISAR, a multipoint VISAR [2] was proposed to measure velocity histories of two to six points, where the same disadvantages in single-point VISAR also exist. In the 1990s, a new VISAR called all-fiber VISAR (AFVISAR) [3,4] was proposed and tested, where optical fibers and fiber couplers are used to replace discrete optic elements. Although it is compact and simple, it also focuses on single-point velocity measurement on a moving surface.…”