Two-dimensional (2D) van der Waals layered materials possess unique advantages as integrable sensors, due to their thinness, flexibility and sensitivity. They can be seamlessly integrated onto surfaces with different geometries where detection of near-field signal is desired. In this study, we develop a device transfer technique to integrate 2D devices onto an arbitrary smooth surface. Such technique utilizes a sacrificial polymer under layer and achieves clean and non-destructive full device transfer. For demonstration, we transferred a complete 2D multilayer InSe photodetector onto a stripped optical fiber. Due to the extreme vicinity of the 2D photodetector with the fiber core, the device can efficiently couple with the evanescent-field and accurately detect information transmitted inside the optical fiber. In addition, these super thin flexible devices can be integrated onto the fibers themselves to non-invasively monitor the optical fiber performance. The demonstration of optically coupled, conformal 2D devices on substrates of different form factors can enable a variety of near-field optical and sensor applications.