In this example, we will demonstrate how INTERCONNECT can be used to design and simulate a ring resonator. Ring resonators can also be simulated at the component level with FDTD and MODE.
To simulate a ring resonator in INTERCONNECT, we can start by breaking it into different segments:
and simulating each piece with a Straight Waveguide or Waveguide Coupler element from the Element Library.
NOTE: Alternatively, we can also use the Double Bus Ring Resonator element
from the Element Library to model this element directly.
A single ring resonator can be simulated both on the device/element level with a physics based simulation tool such as FDTD or MODE, or on the system/circuit level with INTERCONNECT:
If we are only interested in varying the parameters at the device/element level (for example, varying the length or the gap of the coupler segment to achieve the target Q factor), this is best done in FDTD or MODE. Please see the following Getting Started Examples if you are interested in simulating a ring resonator at the device/element level:
The motivation for simulating ring resonators on the system/circuit level with INTERCONNECT is that circuits that are constructed with many elements like ring resonators would be very difficult to simulate on the device/element level. In addition, a good design at the device/element level may not translate to a good design at the system/circuit level, and it is important to test the design's overall circuit performance against the target specifications. To fully design and characterize a realistic system often involves going back and forth between device/element level simulations and system/circuit level simulations.
Transmission (TE mode)
Set up the ring resonator simulation as described in the "Modeling instructions" page or simply download the project file provided on the first page and run the simulation by clicking on the
button. Once the simulation finishes, the transmission at the "through" and "drop" port of the ring resonator will be available in the Result View window of ONA_1. Right click on the "transmission" result under "input 1", "mode 1" and select Visualize > New Visualizer. The transmission at the through port of the ring resonator will appear in a new window (see figure on the left). To see the amount of transmitted power select the "Abs^2" option in the "scalar operation" column. Similarly visualize the "transmission" result under "input 2", "mode 1" to view the transmission through the drop port (see figure on the right). Note that these transmission values are for the TE mode since the orthogonal identifier of the ONA was set to 1.
Power transmission at the through port (TE mode)
Power transmission at the drop port (TE mode)
The peak analysis option in the ONA allows the user to automatically extract different figures of merit based on the signal at each input. By default the peak analysis detects the peaks (maxima) in the transmission and calculates figures of merit such as free spectral range (FSR) and quality factor (Q). Since the transmission of the drop port peaks at the resonant wavelengths, we can perform peak analysis on the results from input 2 of the ONA to calculate the FSR and Q factor of the ring resonator. Right click on the "free spectral range" result under "input 2", mode 1", "peak" and select Visualize > New Visualizer. The FSR of the ring resonator is reported to be approximately 0.3 THz (see figure below on the left) which is consistent with analytic value calculated as, \(FSR = c/(n_g.L)\) where c is the speed of light, \(n_g\) is the group index of TE mode and L is the length of the ring (2*pi*radius) which gives a value of 0.3059 THz.
We can also visualize the Q factor from peak analysis. For this we will have to perform peak analysis on the through port (input 1). Right click on "quality factor" result under "input 1", mode 1", "peak" and select Visualize > New Visualizer. The Q factor of the ring is reported to be approximately 675 (see figure above on the right).
Transmission (TM mode)
Next we will investigate the transmission through the ring in TM mode. To do this, first we have switch back to design mode by clicking on the
button. We will now have to edit the property of the ONA to inject TM mode into the circuit. This can be done by setting the value of the "orthogonal identifier" to 2. Run the simulation again after setting the "orthogonal identifier" value. Right click on the "transmission" result under "input 1", "mode 1" and select Visualize > New Visualizer. Choose the "Abs_2" option to view the power transmission in the through port of the ring in TM mode.
Power transmission at the through port (TM mode)