An optical low coherence interferometer was built and used to characterize the optical performance of planar arrayed-waveguide grating (AWG) devices. The phase error and amplitude distributions of individual waveguides in an AWG were extracted by sectioning individual interferograms from the low coherence interferometer. Using a large amount of oversampling to improve signal-to-noise in combination with Hilbert transformation method, phase errors of less than λ/300 in our AWG’s were achieved and correlated to fabrication variations from the waveguide device design. This was subsequently used to improve the performance of our devices. In addition, the group delay (GD) and chromatic dispersion (CD) were also derived from the measured phase error using a Fourier transform method. The derived GD and CD matched well with those directly measured from commercial chromatic dispersion equipment based on the phase modulation method. The relationship between the phase and amplitude errors with different frequencies and the variation of GD or CD will be discussed.
We first report an optical image processing technique using acousto-optic Bragg diffraction. Instead of using frequency-plane filters, we demonstrate experimentally the programmable filter characteristic of the acousto-optic cell by changing the peak phase delay (alpha) . High- pass and low-pass filtering can exist simultaneously in different diffracted orders. Furthermore, we demonstrate the use of an acousto-optic device in modeling controllable partically incoherent illumination of phase gratings, or the propagation of images through a random medium with a given power density spectrum.