Abstract
PHASARs or Arrayed Waveguide Grating (AWG) multiplexers are key elements for Dense Wavelength Division Multiplexing (DWDM) in optical networks. The knowledge of phase errors and their impact on the characteristics of the transmission spectrum of a PHASAR is of great importance for improvements of the fabrication process. Using Fourier transform spectroscopy employing a low coherence interferometer, the power-distribution coefficients and the phase distribution in such components are evaluated. A calculation of the transmission spectrum with the phase and power coefficients shows excellent agreement with direct transmission measurements of a 16 channel 100 GHz PHASAR. The behaviour of phase deviations on the transmission peak shape is evaluated by simulations with linear, parabolic, periodic and single phase fluctuations. In consequence wavelength shift, peak broadening, increase of crosstalk and the existence of sidelobes at characteristic wavelength positions can be assigned to certain types of phase distributions. Even only one particular phase error significantly enhances the crosstalk of a device. In detail, the observed sidelobes in the transmission spectrum of a 16 channel PHASAR with 100 GHz channel spacing can be assigned to sinusoidal phase deviations with periodicities of 20 and 11 waveguides. This corresponds to a length scale of 800-900 μm for changes in refractive index and/or layer thickness. Thus, improvements in fabrication processes of PHASARs can be monitored by this technique.
Published Version
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