Fast M2 measurement for fiber beams based on modal analysis.

We report on a fast and experimentally easy technique for measuring the beam propagation ratio M(2) of light guided by optical fibers. A holographic filter enables us to determine amplitudes and phases of the excited fiber eigenmodes. The coherent superposition of modes allows the reconstruction of the optical field. With this information at hand, we are able to simulate the free-space propagation of the beam and to perform a virtual caustic measurement. Associated beam propagation ratios M(2) accurately agree with ISO-standard measurements.

[1]  D. Courjon,et al.  A versatile and stable device allowing the efficient generation of beams with radial, azimuthal or hybrid polarizations , 2005 .

[2]  Daniel Flamm,et al.  Modal analysis of beams emerging from a multi-core fiber using computer-generated holograms , 2011, LASE.

[3]  Minglun Gong,et al.  Theoretical calculation of beam quality factor of large-mode-area fiber amplifiers , 2009 .

[4]  T. Eidam,et al.  Experimental observations of the threshold-like onset of mode instabilities in high power fiber amplifiers. , 2011, Optics express.

[5]  Masud Mansuripur,et al.  Beam quality factor of higher order modes in a step-index fiber , 2006 .

[6]  Thomas Kaiser,et al.  Complete modal decomposition for optical fibers using CGH-based correlation filters. , 2009, Optics express.

[7]  Cesar Jauregui,et al.  Non-hexagonal Large-Pitch Fibers for enhanced mode discrimination. , 2011, Optics express.

[8]  D. Gloge.  Weakly guiding fibers. , 1971, Applied optics.

[9]  Cesar Jauregui,et al.  High average power large-pitch fiber amplifier with robust single-mode operation. , 2011, Optics letters.

[10]  W. H. Lee,et al.  Sampled fourier transform hologram generated by computer. , 1970, Applied optics.

[11]  Thomas Kaiser,et al.  Real-time determination of laser beam quality by modal decomposition. , 2011, Optics express.

[12]  Anthony E. Siegman,et al.  New developments in laser resonators , 1990, Photonics West - Lasers and Applications in Science and Engineering.

[13]  Daniel Flamm,et al.  Modal decomposition for photonic crystal fibers using computer-generated holograms , 2010, Photonics Europe.

[14]  A. E. Siegman,et al.  How to (Maybe) Measure Laser Beam Quality , 1998 .

[15]  Thomas Kaiser,et al.  Measuring the spatial polarization distribution of multimode beams emerging from passive step-index large-mode-area fibers. , 2010, Optics letters.

[16]  S. Wielandy,et al.  Implications of higher-order mode content in large mode area fibers with good beam quality. , 2007, Optics express.

[17]  T. Eidam,et al.  The impact of modal interference on the beam quality of high-power fiber amplifiers. , 2011, Optics express.