The invention provides an orthogonal double-
grating based detecting device for synchronous phase shift common-light path interference and a detecting method for the orthogonal double-
grating based detecting device, belonging to the field of the detection of optical interference. The invention aims at solving the problem that the existing optical phase shift interference detecting method is complex and hard to operate, and is high in cost and low in
measurement precision caused by a high-quality
lambda / 4 wave plate. The invention has the scheme that a
light beam emitted out of a
light source is incident into a light receiving surface of a collimating and beam expanding
system through a polarizing film, an emergent
light beam collimated and expanded by the collimating and beam expanding
system is incident into a first lens through two
lambda / 4 wave plates, an object to be tested and a rectangular
window opening, an emergent
light beam collected by the first lens is incident into a second lens through the double gratings formed by a one-dimensional cyclic range
grating and a one-dimensional cyclic phase shift grating, a
diffraction light beam transmitted by the second lens is incident into a four-quadrant polarizing film set, an emergent light beam of the four-quadrant polarizing film set is received by an imaging sensor, and an
image signal output end of the imaging sensor is connected with an image input end of a computer, and obtains the phase distribution of the object to be tested.