Optical path adjusting device and method

The invention provides an optical path adjusting device and method. The optical path adjusting device adjusts the relative position of a first prism and a second prism in a self-reference interferometer so as to accurately adjust an optical path, and prevents a self-reference interference aligning system using the self-reference interferometer from generating zero-order light leakage due to a combined error of the first prism and the second prism so as to further increase the contrast of an aligning signal.