We propose a new method to determine the wavefront of a laser beam, based on modal decomposition using
computer-generated holograms (CGHs). Thereby the beam under test illuminates the CGH with a specific,
inscribed transmission function that enables the measurement of modal amplitudes and phases by evaluating the
first diffraction order of the hologram. Since we use an angular multiplexing technique, our method is innately
capable of real-time measurements of amplitude and phase, yielding the complete information about the optical
field. A measurement of the Stokes parameters, respectively of the polarization state, provides the possibility to
calculate the Poynting vector. Two wavefront reconstruction possibilities are outlined: reconstruction from the
phase for scalar beams and reconstruction from the Poynting vector for inhomogeneously polarized beams. To
quantify single aberrations, the reconstructed wavefront is decomposed into Zernike polynomials.
Our technique is applied to beams emerging from different kinds of multimode optical fibers, such as step-index,
photonic crystal and multicore fibers, whereas in this work results are exemplarily shown for a step-index fiber
and compared to a Shack-Hartmann measurement that serves as a reference.