When stringing multiple parts together, it is important to check a lightwave system for losses. BeamPROP Simulator, part of the Rsoft package will display any losses in a waveguide pathway. Here we have an example of an S-bend simulation. There appears to be losses in a few sections.
Here, the design for the S-bend waveguide has a few locations that are leaking, as indicated by the BeamPROP simulation.
The discontinuities are shown below, which are a possible source of loss:
After fixing these discontinuities, the waveguide can be simulated again using BeamPROP. In fact the losses are not fixed. This loss is called bending loss.
Bending loss is an important topic for wavguides and becomes critical in Photonic Integrated Circuits (PIC).
BeamPROP is a simulator found in the Rsoft package. Here, we will use BeamPROP to calculate the field distributions of our tapered waveguides. Other methods built withing Rsoft CAD are will also be explored.
The tapered waveguide that we are simulating is found below. We will use the BeamPROP tool to simulate the field distributions in the waveguide. We will also use the mode calculation tool to simulate the mode profile at each end of the waveguide.
BeamPROP Simulation Results
Mode Profile Simulation
The mode simulation tool is found on the sidebar:
Before choosing the parameters of the Mode Simulator, let’s first take a look at the coordinates of the beginning and end of the waveguide. This dialog is found by right-clicking on the component. The window shows that the starting point along the z axis is 1 and the ending point is 43 (the units are actually micrometers, by the way). We will choose locations along the waveguide close to the ends of the waveguide at z equals 1.5 and 42.5.
Parameter selection window:
Results at z = 1.5:
Results at z = 42.5:
Rsoft is a powerful tool for optical and photonic simulations and design. Rsoft and Synopsys packages come with a number of different tools and simulators, such as BeamPROP, FullWAVE and more. There are also other programs typically found with Rsoft such a OptoDesigner, LaserMOD and OptSim. Here we focus on the very basics of using the Rsoft CAD environment. I am using a student version, which is free for all students in the United States.
New File & Environment
When starting a new file, the following window is opened. We can select the simulation tools needed, the refractive index of the environment (“background index”) and other parameters. Under dimensions, “3D” is selected.
The 3D environment is displayed:
On the side bar, select “Edit Symbols.” Here we can introduce a new symbol and assign it a value using “New Symbol,” filling out the name and expression and selecting “Accept Symbol.”
Next we will draw a rectangle, which will be our waveguide. Select the rectangular segment below:
Now, select the bounds of the rectangle. See example below:
Editing Component Parameters
Right click on the component to edit parameters. Here, we will now change the refractive index and the length of the component. The Index Difference tab is the difference in refractive index compared to the background index, which was defined when we created the file. We’ll set it to 0.1 and since our background index was 1.0, that means the refractive index of the waveguide is 1.1. Alternatively, the value delta that was in the box may be edited from the Symbol menu. We also want to use our symbol “Length” to define the length of our waveguide. We also want this waveguide to be tapered, so the ending vertex will be set to width*4. Note that width may also be edited in the symbol list.
Here, we have a tapered waveguide: