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Phase error distribution and spectral response in silica-based AWG multiplexers

PHASARs or Arrayed Waveguide Grating (AWG) multiplexers for application in Dense Wavelength Division Multiplexing optical networks have been realized using silica-waveguide technology. Using waveguide tapers, a flat-top passband characteristic is obtained. Using Fourier transform spectroscopy employing a low coherence interferometer, the power-distribution coefficients and the phase error distribution in such components is evaluated. Because of the coherence length of the used light source being smaller than the optical path length difference in the PHASAR, it is possible to resolve individual waveguides of the array. Thus, the transfer functions of the individual optical paths are accessible to the measurement, enabling the full simulation of the PHASAR transmission spectrum. It is demonstrated that the measured phase error distribution in tapered PHASAR devices consists of contributions from both tapered waveguides and arrayed waveguide grating regions. An evaluation method suitable for investigating both contributions separately is developed. Phase shift introduced by the waveguide tapers is in good agreement with simulation calculations based on the Beam Propagation Method. An analytic transmission calculation based on measured phase and power-distribution coefficients enables a full simulation of PHASARs including insertion loss, bandwidth and crosstalk performance. Excellent agreement with transmission measurements is performed.