Silicon Photonics: Fundamentals and Devices

12.4 Methods for Improving Performance

This section discusses briefly the methods employed to make the grating insensitive to changes in polarization and temperature and to achieve flat frequency response.

12.4.1 Flat Frequency Response

The dispersion of focal position x with respect to wavelength is almost constant. The transmission loss in each channel of the normal AWG increases monotonically from the center wavelength. Furthermore optical signals pass through several filters in the network, and therefore their frequency response also affects the overall response in the channel, making it still narrower. This necessitates the design of flattened and broadened frequency response for AWG multiplexers.

Several approaches have been proposed to achieve a flat frequency response for the passband of AWGs. A flat-response AWG multiplexer with parabolic waveguide horns in the input waveguide with satisfactory performance has been reported in 14.

It has been confirmed that in order to obtain a flat spectral response, a rectangular electric field profile must be produced at the focal plane, that is, the interface between the second slab and output waveguides. The electric field profile in the focal plane is, in turn, the Fourier transform of the field in the output array aperture, that is, the interface between the array waveguide and the second slab. The needed electric field profile at the array output aperture is the sinc-type, which obeys a distribution, where is measured along the ...