Directional coupler PCell

[lukasc-ubc]

We have a CML for the regular DC, namely ebeam_dc_te1550, but we don't have a KLayout PCell.

Xu implemented the CML, so you can check with him for parameters, FDTD model, etc.
See page 9 of ebeam_Lumerical_CML_User_Guide_2015_08_24.pdf

Also add automated CML generation via FDTD.

Parameters:

• gap: gap
• radius: Radius of the bus. Assume the output is 2 conventional bends
• pitch: vertical pitch (separation + w) for the in/output waveguides.
• wg_width: Waveguide width
• coupling_length: coupling length
• polarization: 'TE' or 'TM'; for use in INTERCONNECT calling FDTD to simulate one of these if pol is defined, or simulate both if undefined.
• wavelength: default 1550. Consider a simulation bandwidth of 10% of the central wavelength. Used by the INTERCONNECT-FDTD simulation.

Annotation:

• kappa
• t
• excess loss

[lukasc-ubc]

Implement using the new INTERCONNECT-FDTD communication protocol, in beta version.

Aim for June 15 release.