Photonic Band Gap Experiments (1114x976)
Table of Contents
Welcome to the photonic band gap simulation. Simulations are computed in real time using FDTD solutions to Maxwell's equations. Simulations give actual interactions between light and objects in an interpretable solution. For this simulation, the interaction is between monochromatic light and a 2-D crystal structure called a photonic band gap. Photonic band gaps are built as periodic changes in dielectric materials that allow some light to pass right through and others to be reflected back. The following is a guide to help set up parameters and properly use the simulation.
This is where the wavelength of light is selected. The wavelength is easily changed by left-clicking on the slider and moving the mouse left and right. The wavelength can also be changed by selecting the text box and typing in the desired wavelength. Each color of electromagnetic spectrum has its own corresponding wavelength. For this simulation, wavelength varies in intervals of 10 nm and ranges between 300 nm and 990 nm inclusive. Input outside of this range will result in the parameters resetting to default values when simulation is run.
This legend is used to help decipher what is happening with the light that is traveling through. The legend shows the magnitude of the electric field for light. In this case, when the light is a bright red (right side of the scale) then the electric field is equivalent to coming out of the screen. When the light is white, there is no electric field in that space. When the light is a dark red the electric field is equivalent to going into the screen. This allows 3 dimensions to be represented in a 2D simulation.
This is where the diameter of the individual particles is changed. In this simulation, the crystals are thought of as combining many similar circular particles. Changing the diameter of the particle affects how the light interacts with the photonic crystals. An increase in particle size increases the spacing between adjacent particles. The diameter can be changed by left-clicking the slider and moving the mouse left and right. The diameter can also be changed by directly inputting the desired size in the input box. Particle diameters vary by increments of 10nm and range between 200nm and 400nm inclusive.
This is where the rotation of the photonic crystal is changed.
The incident angle of the photonic crystal is shown here as θ:
Rotating the photonic crystal will give a different effect with light than if it were perpendicular to the light. Left-clicking the slider and moving the mouse left and right changes the value of the incident angle. The incident angle can also be changed by directly entering the desired value in the input box. The incident angle varies in increments of 1˚ and ranges between 0˚ and 45˚. Entering a value outside of these restrictions will cause the parameters to reset to the default.
Due to interactions between the light and the photonic crystal, the graphic of what the photonic crystal can't be displayed at all times. There are interactions between the crystal's particles that need to be seen. The images below show how to get a preview of what the crystal will look like before simulating. A preview is useful to verify that set up is correct without having and being able to quickly change the set up is not correct without having to run through an undesired simulation. To get a preview of the photonic crystal:
If the parameters are correct:
- Highlight and left-click the Preview Only radio button making sure the green check mark is gone
- Highlight and left-click the Run Test button
- Simulation will begin
If the parameters aren't correct:
- Change the parameters to desired ones
- Verify that the Preview Only radio button has a green check mark in it, if not left-click on it
- Highlight and left-click the Run Test button
- Preview will appear on screen
After setting up the parameters click the Run Test button while the Preview Only radio button is unchecked to start the simulation.
When the Run Test button is pressed, the above picture will change to:
Do not exit out of the browser when this is shown. If the browser is closed during this time, the simulation will crash and become unusable. The simulation will be in progress computing the FDTD solution to Maxwell''s equations. The simulation computes 15 frames at 20 femtoseconds (10-15 seconds) per frame. Each frame will take about 30 seconds to load. When loaded, the visualization of the simulation will appear in the browser.
Once all the frames are computed and loaded, the Run Test button will revert back to normal.
The simulation has been computed in real time. To playback the animation, click the Animate button. The Animate button will cause the frames to run through in continuous sequence. When the last frame is done, it will loop back to the first frame. Pressing the Stop button will stop the animation and allow viewing of specific frames.
Left-clicking on the slider and moving the mouse allows selecting specific frames.
The simulation field is where the simulation will display what is computed. Light will be seen propagating left to right, interacting with the photonic crystal when the two meet. Along the bottom and the left side are scales for how large the simulation frame is. The photonic crystal will only appear in the simulation field during the preview. When the simulation begins, the photonic crystal will become transparent allowing sight for the light interactions within the crystal. When the frames are changed, the simulation field automatically shows the simulation at the time listed under the animation slider.
When the simulation field is left-clicked, a zoomed in version of the frame shown will pop-up.
The picture above has been zoomed in and then cut to 40% of its original size. Some detail has been lost. Higher quality pictures are in the simulation. Zooming in allows for a better understanding of what is happening to the light interacting with the single slit.
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1. Next steps |
To get a further understanding of the simulations, it is suggested to look at activities in the Manipulation of Light in the Nanoworld educational module
