A fringe shift measurement system is provided and includes an optical phase mask configured to receive light fringes from optical flats. The optical phase mask has first and second halves, each half having alternating patterns of opaque rings and transparent rings. The first half pattern is phase-shifted with respect to the second half pattern. The first and second halves are configured to alternately block the light fringes or allow the light fringes to pass through the optical phase mask. A splitter is configured to direct the light fringes from the optical phase mask in desired directions. Concentrators are positioned to receive light fringes from the splitter and configured to focus the light fringes in a desired location. Detectors are configured to receive the focused light fringes from the concentrators and configured to convert the focused light fringes into digital signals. A control unit is configured to analyze the digital signals.
