Focal length measurement by fiber point diffraction longitudinal interferometry

A focal length measurement method by fiber point-diffraction longitudinal interferometry is proposed. By applying two different longitudinal displacements for the object point respectively and measuring the corresponding displacements of the image point, the lens focal length is derived by Newton formula. The displacements of the object point are introduced by glass plates with known refractive index and thickness. The corresponding displacements of the image point are measured interfeorometrically based on the modeling of the longitudinal interferometry of two point sources. Experiments and error analysis reveal that this method has an accuracy less than 0.15% under normal laboratory environment.