Fast-Light Based Pulse Compression in 2-D Photonic Crystal Waveguides

Chirped-pulse propagation close to a mini-stopband (MSB) in short photonic crystal (PhC) waveguides is studied using the 2-D finite-difference time-domain method. The group delay (GD) is calculated for different length waveguides and is shown to have a nonlinear relationship with length, implying that dispersion diagram based design approaches may not be applicable in these cases. Pulse compression is then observed directly in the time domain, and a GD-based analysis is used to explain the results. It is shown that the fast-light or negative GD region that is found within the MSB plays a more important role than pulse filtering effects, which can also induce compression. The GD analysis is then used to find the optimum length waveguide for the maximum pulse compression, and this is found to be in agreement with direct time-domain results. Finally, a different PhC waveguide structure is studied based on square holes, which results in an increased GD and, hence, increased pulse compression.