Differential Group Delay

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

, differential group delay is the

difference Difference, The Difference, Differences or Differently may refer to: Music * ''Difference'' (album), by Dreamtale, 2005 * ''Differently'' (album), by Cassie Davis, 2009 ** "Differently" (song), by Cassie Davis, 2009 * ''The Difference'' (al ...

in propagation time between the two

eigenmode In linear algebra, an eigenvector () or characteristic vector of a linear transformation is a nonzero vector that changes at most by a scalar factor when that linear transformation is applied to it. The corresponding eigenvalue, often denoted ...

s ''X'' and ''Y'' polarizations. Consider two

eigenmodes A normal mode of a dynamical system is a pattern of motion in which all parts of the system move sinusoidally with the same frequency and with a fixed phase relation. The free motion described by the normal modes takes place at fixed frequencies. ...

that are the 0° and 90°

linear Linearity is the property of a mathematical relationship ('' function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear ...

polarization states. If the state of polarization of the input signal is the linear state at 45° between the two eigenmodes, the input signal is divided equally into the two eigenmodes. The power of the transmitted signal ''E''_''T'',total is the combination of the transmitted signals of both ''x'' and ''y'' modes. :

E_T  =  (E_ \cdot t_x)^2 + (E_ \cdot t_y)^2 \,

The differential group delay ''D''_''t'' is defined as the difference in propagation time between the eigenmodes: ''D''_''t'' = , ''t''_''t'',''x'' − ''t''_''t'',''y'', . {{DEFAULTSORT:Differential Group Delay Optics