Efficient coupling of self-collimated beams to slow light modes of a coupled zigzag-box resonator via antireflection structures in a photonic crystal

We show that reflections of self-collimated beams at the boundaries of a finite-size coupled zigzag-box resonator, which is designed to slow down the speed of self-collimated beams in a photonic crystal, can be minimized by introducing antireflection structures. The optimal values of design parameters for minimal reflection can be obtained by using one-dimensional antireflection coating theory and finite-difference time-domain simulations. It is shown that the optimized antireflection structures significantly reduce unnecessary finite-size effects, such as strong Fabry- Perot oscillations in the transmission spectrum and variations in the group velocity curve. Our results could be useful in implementing devices to control self-collimated beams in the time domain.