Few-mode fiber modal interferometers (MIs) based on cascaded fiber down-tapers and their application in curvature sensing are presented. Cascaded fiber down-taper structure can help excite more higher-order cladding modes to construct the inter-modal interference with the core mode. However, with the increase of the cascaded number of the fiber down-tapers, the curvature sensitivity of the MI is decreased accordingly. This provides a new way to control the curvature sensitivity of such device by cascading fiber down-tapers. Experimental results show that compared with the two down-tapers based MI, the curvature sensitivity of the three down-tapers one reduced by 1.64 times while the four down-tapers one reduced by 5.82 times.

Experimental setup and the microscope graph of different down-taper structures. (Image by XIOPM)