Fractional Fourier Transform

There are two sorts of transforms known as the fractional Fourier transform.


The linear fractional Fourier transform is a discrete Fourier transform in which the exponent is modified by the addition of a factor b,


However, such transforms may not be consistent with their inverses unless b is an integer relatively prime to N so that (b,N)=1. Fractional fourier transforms are implemented in the Wolfram Language as Fourier[list, FourierParameters -> {a, b}], where a is an additional scaling parameter. For example, the plots above show 2-dimensional fractional Fourier transforms of the function sin(x+y) for parameter b ranging from 1 to 6.

The quadratic fractional Fourier transform is defined in signal processing and optics. Here, the fractional powers F^a of the ordinary Fourier transform operation F correspond to rotation by angles api/2 in the time-frequency or space-frequency plane (phase space). So-called fractional Fourier domains correspond to oblique axes in the time-frequency plane, and thus the fractional Fourier transform (sometimes abbreviated FRT) is directly related to the Radon transforms of the Wigner distribution and the ambiguity function. Of particular interest from a signal processing perspective is the concept of filtering in fractional Fourier domains. Physically, the transform is intimately related to Fresnel diffraction in wave and beam propagation and to the quantum-mechanical harmonic oscillator.

See also

Ambiguity Function, Discrete Fourier Transform, Fourier Transform, Phase Space, Radon Transform, Time-Space Frequency Analysis, Wigner Distribution

Portions of this entry contributed by Haldun M. Ozaktas

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Ozaktas, H. M.; Zalevsky, Z.; and Kutay, M. A. The Fractional Fourier Transform, with Applications in Optics and Signal Processing. New York: Wiley, 2000.

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Fractional Fourier Transform

Cite this as:

Ozaktas, Haldun M. and Weisstein, Eric W. "Fractional Fourier Transform." From MathWorld--A Wolfram Web Resource.

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