Manipulating wavelength-selective emission with heterogeneous photonic crystals

The usual near-field radiation profile of a light beam emanating from a photonic crystal waveguide (PCW) has a main lobe at the center line of the waveguide. However, a centrally symmetric profile for the emission pattern with two sidelobes can be required in some applications, e.g., Y-type power dividers, wavelength multiplexers, and semiconductor lasers. With such motivations in mind, we present the design of a compact structure that deflects the beam propagation direction in this manner. The idea utilizes the manipulation of the dispersion diagram of cascaded photonic crystals by exploiting the bandgap and self-collimation properties. The waveguide mode in the PCW can be transformed from a propagating mode into a diffusive one by altering the filling factor, which, in turn, leads to off-axis light emission. By using the finite-difference time-domain method, we show that the emission takes place into free space at the inclined output surfaces of the PCW with deviation angles of ±45°.