We present a new type of point diffraction interferometer that employs single-mode optical fibers instead of traditional pinholes. Two optical fibers with different exit endfaces are used; one is normally cut and the other obliquely cleaved. The normally cut fiber is used to generate a near-perfect spherical reference wave. The test wave is produced from the oblique fiber that performs two functions: generating a spherical wave to illuminate the test optics, and reflecting the test wave for common-path combination with the reference wave. The interferometer proposed in this investigation is found suitable for testing large size mirrors with a relatively simple overall hardware configuration.