An inexpensive fiber-based displacement sensor for 2-D crack monitoring is proposed and analyzed. The device is packaged as conventional crack monitoring gauges based on sliding plates and exploits the dependence of the transmitted power between facing optical fibers with the displacement. The use of multicore polymeric fibers with high numerical aperture allows a compact form factor and simplifies the sensor assembly. The position detection algorithm has been optimized through simulations; then, experimental tests have shown a good agreement with simulations and have proved that, even with simplified layout and artisanal realization, the sensor can measure displacements in a square area of 3 mm by 3 mm with an uncertainty better than 50 μm.