Both theoretical and experimental analysis of a new efficient method to measure the number and type of modes propagating in optical fibers are presented. This consists in measuring the intensity of the near field image at the end of a fiber while scanning the wavelength with a laser source signal. Modes are extracted from Fourier transformation of the spectral data at each point (x,y) of the images. A novel technique which is referred to as scalar product technique is implemented in order to reconfirm real modes and exclude spurious modes. The technique is based on the orthogonality of different modes. A standard multimode fiber has been measured to verify the technique. Three real modes LP₀₁, LP₁₁, and LP₀₂ are discovered and reconfirmed by the orthogonality with the minimum values of the scalar products. One spurious mode, which comes from the dependence of the power of the laser source on the wavelength, is thus excluded as it is not orthogonal either to the LP₁₁ mode or the LP₀₂ mode.

Date Published: 14 May 2010
PDF: 10 pages
Proc. SPIE 7717, Optical Modelling and Design, 77170V (14 May 2010); doi: 10.1117/12.853673

Published in SPIE Proceedings Vol. 7717:
Optical Modelling and Design
Frank Wyrowski; John T. Sheridan; Jani Tervo; Youri Meuret, Editor(s)