Analysis of High-Order Slotted Surface Gratings by the 2-D Finite-Difference Time-Domain Method

High-order slotted surface gratings are analyzed by the finite-difference time-domain method. The power reflection, transmission and loss are calculated for these gratings. Results show good agreement with those calculated by the 2-D scattering matrix method. Simulations predict that such slotted surface gratings will yield the lowest loss with slot width equal to a quarter-wavelength (lambda/4) in the slot area. The calculated field distribution shows that a wider slot width results in a larger scattering loss from the gratings. It is also found that for the gratings with slot width of 5 lambda/4, the power reflection will increase by more than 45% while the loss will drop to just half of the value for the 9 lambda/4 slot width grating that was used in previous designs. Moreover, it can still be fabricated by standard photolithography since the slot width is around 610 nm, which means that lasers based on such gratings can be easily fabricated and will have a lower threshold current with higher slope efficiency than previous designs.