How does using different wavelengths of light allow multiple messages to be sent in a single channel at the same time?
This resource was originally published in PhysicsQuest 2023: Making Waves.
How does using different wavelengths of light allow multiple messages to be sent in a single channel at the same time?
Multiplexing is a key innovation in communication technology. When signals are multiplexed, they’re layered over one another in a single channel but are encoded using different wavelengths and so can be separately decoded by devices. This activity is an introduction to what it means to multiplex messages.
After reading the introduction, what is your essential question or objective for this activity?
Older calculators and digital watches used seven-segment displays to make numbers — each symbol space contained seven segments, each of which could be illuminated or not, depending on what number was desired: 1234567890. You can also use these displays to make some Latin letters:
ABCDEFGHIJLnopsu
Count how many places you see a seven-segment display during the course of your day. Keep track of them! On what kind of devices did you find them?
Fiber optic internet is a light signal sent through a fiber optic cable. If you and your neighbors all get internet at your respective homes, and all those internet signals are sent through a single fiber optic cable, how do those signals not get mixed up? How do you get your funny cat videos and your neighbor gets DIY shoelace videos?
Get paper and red and blue colored pencils from your teacher.
Making overlapping letters with different colors allows you to transmit two different messages on the same piece of paper; you can see one message with the red lens in the 3D glasses, and the other message with the cyan lens. It’s important to use markers, highlighters, or colored pencils that are tuned to the wavelength of light that each filter transmits.
How does multiplexing allow you to use a single channel for multiple messages simultaneously?
Multiplexing is common in telecommunication systems and computer networks that use laser systems to send light signals over fiber optic cables. Multiple signals can be consolidated and sent in the same cable, because each signal is transmitted in a different wavelength, allowing them to be sorted out again later. How do you think the different wavelengths of laser signals are separated out later? What device might be used to accomplish this? (Think back to some of our earlier experiments!)
Explore the PhysicsQuest 23: Making Waves Physics Career and Concept Map. What careers that use this content sound most appealing to you? Why?
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