Spectral width requirement for measuring return loss of arrayed waveguide gratings by using optical low coherence reflectometry

The reflection from a half wave plate incorporated in an arrayed waveguide grating (AWG) for polarisation-independent operation has a strong wavelength dependence. The error is derived as a function of the full width at half maximum (FWHM) of the Gaussian light spectrum when the reflectivity at the plate is measured with an optical low coherence reflectometer. This error can be reduced to <4 dB when the FWHM is less than the channel spacing of the AWG