Mode conversion of ultrafast pulses by grating structures in layered dielectric waveguides

Various grating configurations are introduced to develop structures for the mode conversion of an ultrafast, ultrawide-bandwidth optical pulse propagating in a layered dielectric waveguide. Introducing a new technique for efficient, real-time mode extraction, we examine these schemes with a full-wave, vector, finite difference time domain (FDTD) Maxwell equation simulator. The resulting FDTD simulator is very flexible and accurate; it is capable of modeling the interaction of few- or many-cycle optical pulsed modes with finite, aperiodic gratings with complex material configurations. The grating structure can be tailored to the pulsed optical modes of interest with this FDTD simulator. It is used to design a composite mode-conversion grating structure that realizes a 29.45% increase in the converted mode energy for an ultrafast six-cycle optical pulse over that achieved with standard uniform grating convertors