Quantitative phase imaging unit.

A simple and cost-effective method is presented for quantitative phase imaging. A common-path lateral phase shifting interferometer is realized through attaching a compact filter set to the output port of an existing microscope. The working principles, design criteria, and limitations are also derived and explained. In order to demonstrate the capability and applicability of the method, the optical phase images of a microsphere and individual human red blood cells are measured with high stability.