In this work, an orthogonal optical grating structure is demonstrated as a displacement sensing element. The grating is made with gradient periodicity and height on both sides of a polydimethylsiloxane (PDMS) substrate using an oxygen plasma treatment of prebent PDMS. Based on Fraunhofer diffraction effect, it is experimentally shown that any displacement can be quantitatively characterized in both the x and y directions with an estimated maximum error value of 0.4% and a resolution of 300 μm− 1. With this simple and low cost technology, it is proved that this structure can operate as a single element sensor for vectorial displacement signals, which can be applied for vectorial displacement measurement and multi-axis integrated displacement sensors.