A system for determining spatial coherence, temporal coherence or both of an optical signal includes a fiber bundle containing optical fibers. Optical fiber inputs are arranged in proximate groups having the same number of fibers. The groups can each receive a portion of the optical signal. Each fiber in the group has a gross length that differs from the other fibers, but each group has the same set of different gross lengths. The fibers are joined to a lens which spreads the optical signal and causes interference between portions of the signal. This interference is detected at a detector. A computer joined to the detector can measure spatial and temporal coherence from the interference. Other embodiments feature multiple detectors and reflection along the bundle.