To connect a fiber light guide with a waveguide of a photonic integrated circuit fiber lenses are usually used. The parameters of these lenses must be certified. This paper describes a technique for fiber lens focal length measuring method of longitudinal displacement of a lensed fiber from which light comes out and a flat tipped fiber, which is a radiation receiver. The measurement results received by this method were compared with the results received using the Fabry-Perot interferometer. Additionally, light propagation in the system under study was modeled in the approximation of geometric optics.