Harmonically-related gratings-based quadrature phase interferometers

We report a new method for obtaining non-trivial phase difference between the output ports of an interferometer through the use of shallow diffraction gratings. We show that as opposed to a single shallow diffraction grating-based interferometer (which provides only trivial phase shifts, i.e., 0° or 180°), a pair of harmonically-related shallow diffraction gratings can be used to design interferometers with non-trivial phase shifts between different output ports. More importantly, the phase shifts can be adjusted by simply shearing one grating with respect to the other. This approach does not change the path length relationships of the different interference beams within the interferometer, which is an advantage for metrology and low coherence interferometry applications.