Curved Directional Coupler

Curved directional couplers have a curvature which continuously changes the local effective index and gap between the waveguides. Their transmission output changes more gradually with wavelength in comparison to conventional directional couplers, making them a broadband device. 

This broadband property is shown by sweeping a range of wavelengths with MT-FIMMPROP's native scanner. The scans run locally on a laptop in less than a minute without the need for cloud computing. 

The quick runtime is thanks to FIMMPROP's use of Eigen Mode Expansion (EME) as well as MT-FIMMPROP tailoring computational regions to follow the contours of the device, rather than simulating the whole volume. MT-FIMMPROP exploits symmetry and sub-sections being reused and recycled to reduce EME runtime, which scales with number of unique cross sections.

A conventional directional coupler with the same waveguides is set up also to achieve a 50:50 splitting ratio at 1.55 um, the spectral response of this and the broadband curved directional coupler are shown.

By setting both types of directional couplers to occupy the same relative length on a PIC, the curved directional coupler exhibits a much steadier change in transmission. 

For another example of a broadband directional coupler, see the grating directional coupler simulated in Photon Design's OmniSim. 

To see how fast this demo runs live, get in contact with us via the form below.