Chirping of the waveguide grating router for free-spectral-range mode selection in the multifrequency laser

Because the transmission through each input-output combination of a conventional waveguide grating router consists of a periodic sequence of equal-height passbands spaced by the router free spectral range, the absolute laser oscillation wavelength and single-passband oscillation can be difficult to control for all the channels in the multifrequency waveguide grating router laser. However, the router can be designed to have one dominant passband, with the neighboring passbands experiencing lower transmission coefficients for all the input output combinations by means of chirping of the waveguide grating. Such chirping is discussed theoretically and is demonstrated experimentally.