Photonic Solutions Enewsletter

December 2014

New CAD Circuit Reference and Dynamic Array Features

The RSoft CAD is the core program of the RSoft Component Design Suite, and acts as a control program for all of RSoft’s passive device simulation modules. It is used to define the most important input required by the RSoft simulation modules: the material properties and structural geometry of a photonic device.

Following are some tips for using circuit references and dynamically sized arrays in v2014.09. Wisely using these features will help your design work become a quicker and easier task.

  • Dynamic Arrays

Dynamically sized arrays allow child circuits (a unit cell) to be periodically repeated to create a lattice. To use this feature, first create a design file that represents the unit cell and save it. Then, in the main design file that will contain the lattice, insert a circuit reference to the unit cell by clicking the Dynamic Array button in the left CAD toolbar. Several built-in unit cells are available once inserted: you can choose the lattice properties such as the lattice type, period, size, and other options. See Section 6.F.3 in the RSoft CAD manual for more details.

Select Index File

You can also choose a user-made unit cell. As an example, consider the moth-eye patterned LED for enhancing extraction ratio shown below. The unit cell of the lattice is created in the RSoft CAD (inset), and a dynamic array was used to create the lattice. Variables can be used to express all lattice parameters in the Lattice Properties dialog shown. When these variables are changed, the lattice structure will be adjusted automatically. This offers flexibility by eliminating the need to rebuild structures.

Lattice Properties

  • Embedded Circuits

The child circuit of a circuit reference, including dynamically sized arrays, can optionally be stored within the parent file. Among other things, this makes sharing files convenient (for example, no need to send separate files). To embed a circuit, simply enable the “Embedded” option in the Circuit Reference properties dialog. The embedded file will be listed in the component tree on the right side of the CAD window.

Circuit Reference properties dialog

  • Controlling Child Circuit Options from the Parent Circuit

Hierarchy allows for variables to be inherited by the child circuit from the parent circuit. In order to do this, the circuit reference dialog has two symbol tables: a Global Symbol Table, which is the same symbol table used in the parent circuit, and a Local Symbol Table, which allows symbols to be passed on to the child circuit. The variables on the left will override the values in the child, and the values on the right are evaluated in the context of the parent’s symbol table.

Local Symbol Table

As an example, consider the Local Symbol Table taken from the moth-eye example above. The symbol height in the child file will be set to the value of the radius symbol in the parent file. The symbol H in the child file will be set as the same of H symbol in parent file. These settings are used to control the radius and height of the moth-eye structure from the parent design file.