thumb|In-phase signals thumb|Out-of-phase signals thumb|Representation of phase comparison. thumb|200px|Left: the real part of a plane wave moving from top to bottom. Right: the same wave after a central section underwent a phase shift, for example, by passing through a glass of different thickness than the other parts.
thumb|In-phase signals thumb|Out-of-phase signals thumb|Representation of phase comparison. thumb|200px|Left: the real part of a plane wave moving from top to bottom. Right: the same wave after a central section underwent a phase shift, for example, by passing through a glass of different thickness than the other parts.