A novel Mach-Zehnder interferometer based on a multimode fiber combined with a twin-core fiber is proposed. The section of twin-core fiber is spliced between a section of multimode fiber and a single mode fiber. The curvature induced wavelength shifts on the interference fringes is experimentally monitored. A blue shift is observed. This device is simple to fabricate, and is used as a bend sensor with good sensitivity.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.