In linear optical
interferometers (like the
Mach–Zehnder interferometer,
Michelson interferometer, and
Sagnac interferometer), interference manifests itself as
intensity oscillations over time or space, also called
fringes. Under these circumstances, the interferometric visibility is also known as the "Michelson visibility" or the "fringe visibility." For this type of interference, the sum of the intensities (powers) of the two interfering waves equals the average intensity over a given time or space domain. The visibility is written as: :\nu=A/\bar{I}, in terms of the amplitude
envelope of the oscillating intensity and the average intensity: :A=(I_\max-I_\min)/2, :\bar{I}=(I_\max+I_\min)/2. So it can be rewritten as: :\nu=\frac{I_\max-I_\min}{I_\max+I_\min}, where
Imax is the maximum intensity of the oscillations and
Imin the minimum intensity of the oscillations. :I_{max}=I_{1} + I_{2}+2*\sqrt{I_{1}*I_{2}}*| \gamma |, :I_{min}=I_{1} + I_{2}-2*\sqrt{I_{1}*I_{2}}*| \gamma |, If the two optical fields are ideally
monochromatic (consist of only single wavelength) point sources of the same
polarization, then the predicted visibility will be :\nu=\frac{2\sqrt{I_1 I_2}| \gamma |}{I_1+I_2}, where I_1 and I_2 indicate the intensity of the respective wave. \gamma indicates the phase relationship of the original electric field. Any dissimilarity between the optical fields will decrease the visibility from the ideal. In this sense, the visibility is a measure of the
coherence between two optical fields. A theoretical definition for this is given by the
degree of coherence. This definition of interference directly applies to the interference of water waves and electric signals.
Examples is constant. is maximum (80%) at the center. . At large delays the photons do not interfere. At zero delays, the detection of coincident photon pairs is suppressed. ==Visibility in quantum mechanics==