This is an article on the use of an Optical Network Analyzer to investigate optical transmission through a waveguide.
Download the [[straight_waveguide.icp]] file provided above and open in INTERCONNECT. The simulation setup includes a single “Straight Waveguide” element along with an Optical Network Analyzer (ONA). The properties of the waveguide have been set as follows:
The ONA has a center frequency of 193.1 THz and a frequency range of 100 GHz. The orthogonal identifier is set to 1 to excite the TE mode of the waveguide. The “analysis type” has been set to “scattering data” to perform a frequency domain simulation.
The output and input ports of the ONA have been connected to port 1 and port 2 of the waveguide, respectively.
Results and Discussion
Load the [[straight_waveguide.icp]] file and run the simulation. Once the simulation finishes running the results are available in the “Result View” window of the ONA.
Transmission Power and Phase
The “transmission” result reports the transmission through the waveguide. Right-click “transmission” under “input 1”, “mode 1” in the ONA “Result View” window and select Visualize > New Visualizer. In the visualizer window, select the “Abs^2” option in the scalar operation column to view the power transmission through the waveguide (figure below left). The transmission is approximately 1 indicating that the amount of loss in the waveguide is negligible. We can also choose the “Angle” option in the scalar operation to view the phase of the transmitted optical signal in radian (figure below left). The phase can also be plotted by visualizing the “angle” result in the Result View window.
|[[NOTE: ]]The value of Abs^2 of transmission initially looks very noisy due to the extremely small y span of the plot. This can be fixed by clicking on the “show/hide chart setting” button and selecting the “Set axis limit” button to set the y min and y max values to have a slightly larger y span.|
Group Delay and Group Velocity
Next, we will plot the group delay of the waveguide. The ONA automatically calculates the group delay of the waveguide and provides it in the Result View window. Right-click the “group delay” result under “input 1”, “mode 1” in the ONA “Result View” window and select Visualize > New Visualizer. The group delay of the waveguide can be calculated as L*n_g/c giving a group delay of 1.3009e-12 sec which agrees with the result provided by the ONA (figure below left). The “group velocity” result can also be visualized to get the group velocity of light through the waveguide (figure below right). Note that since the ONA does not know the length of the waveguide (which is more easily understood if we were simulating an S-parameter element instead of a waveguide), the unit for group velocity is actually 1/s. We can calculate the group velocity by multiplying this value by the length of the waveguide which gives us a group velocity of 7.687e7 m/s which is consistent with the analytic value given by c/n_g.
So far we have used a value of 1 for the “orthogonal identifier” of the ONA. This injects a TE mode optical signal through the waveguide and therefore the transmission and phase information that we have seen so far are for the TE mode. In order to calculate the TM mode transmission through the waveguide, we have to set the value of the “orthogonal identifier” of the ONA to 2 from the “Property View” window. Once the value is set, run the simulation and plot the “transmission” result under “input 1”, “mode 1” in the ONA “Result View” window and select Visualize > New Visualizer. In the visualizer window, select the “Abs^2” option in the scalar operation column to view the TM mode power transmission through the waveguide (figure below left). We can also plot the “group delay” in a new window (figure below right). Note that the value is different from what we got for TE mode and is consistent with the analytic value from L*n_g/c which gives a group delay of 1.067e-12 sec.