This paper presents a simple quasi-common path point diffraction interferometer (PDI) that allows fringe contrast and fringe spatial frequency to be adjusted conveniently. The novel aspect of this PDI is the use of a polarizer with pinhole as the PDI mask - and then, with a compact circular optical setup, reference and measurement waves are obtained. Furthermore, a linear tilting modulation is added into two interfering waves and adjusted easily by tilting the polarizing beam splitter - and hence the Fourier transform method can be perfectly applied to extract the wavefront phase from the captured fringe pattern, with the highest fringe contrast and suitable carrier frequency. Detailed theoretical analysis and experimental results are presented.
