The Science of Telecommunications: Sending Sound on a Lightwave
Updated: Oct 8
By Craig Beals
Have you ever stopped to wonder how your smartphone sends your voice across the country without a single wire? Or how your Bluetooth headphones pull music right out of thin air? It feels like absolute magic —but it’s not magic, it is the science of light waves!
I teamed up with the legendary Glenn Govertsen (better known as Mr. G from the Mr. G Science Show) to demonstrate something that absolutely blew my mind: we are sending real audio information directly over a laser beam!
Check out the full experiment video below, and then keep reading to learn how to build your very own laser communicator right in your classroom or kitchen!
How It Works: The Simple Science
At its core, wireless telecommunication is just about two things: a transmitter that sends a signal and a receiver that catches it.
The Receiver (The Solar Cell): Normally, when light hits a solar cell, it generates a tiny bit of electrical voltage and current. If we hook that cell up to an amplified speaker, any constant light source gives us total silence. But, if we change or interrupt that light beam, the electricity changes, causing the speaker to vibrate and create sound!
The Transmitter (The Laser): By connecting an audio source (like a phone or a computer) directly to the laser's power switch, the audio signal forces the laser beam to flicker on and off at incredibly high frequencies.
When that flickering laser beam hits our solar cell across the room, the cell instantly translates those rapid light pulses back into electrical currents, which the speaker pumps out as crystal-clear music or voice. It works over massive distances—as long as the light can reach the receptor, you can send the signal!
**Since making this video, some of the supplies have become unavailable so I updated the setup with equipmetent that is currently available (and less expensive). The supplies and setup outlined below is up to date and shows everything you need to perform this activity.*
Supplies List & Materials
Refer to the diagram below for a visual explanation of each component. Links direct to products on Amazon. Beals Science is an affiliate and may earn commissions on linked purchases:
A - Music Source: Computer, phone, etc.
B - 3.5 mm to 3.5mm Audio Cable cut in half.
Cut in half and strip wires to access the two wires. Use 1/2 for computer connection and the other 1/2 for Solar Cell to Amplifier Connection
C - Wire Connectors
Note: These connectors are suggested but not required. You can use tape or twist wires together.
D - Battery Power Source AA Battery Holder 4.5 Volts
E - Laser Diode 650nm 5mW
F - Solar Cell
H - Amplifier
J - Speaker Powered speaker is preferred to boost electrical signal
Step-by-Step Build Instructions
Part 1: Setting up the Receiver (The Ear)
Connect the Solar Cell: Attach alligator clip leads to the small positive and negative wires coming out of your solar cell [F and G on diagram] (2:17).
Adapt to Audio: Connect those alligator clips to the 3.5mm headphone cable that you cut in half. Attach the clips to the bare wires on the cut end. [B and G on diagram] (7:17). The video shows how to use a 3.5mm to RCA connector which works well but in my updated version I just cut the wire to make it easier. If using the 3.5mm to RCA, attach the white clip to the center pin of the RCA jack and the red clip to the outside ground ring (7:23).
Plug into the Amp: Plug the 3.5mm jack into your mini amplifier, and connect the amplifier out into your speaker with the 3.5mm to 3.5mm cable. [B and H on diagram]
Block Ambient Light: Cover or shade your solar cell slightly (7:10). Overhead fluorescent lights flicker naturally and can cause a loud humming interference (7:10)!
Part 2: Setting up the Transmitter (The Voice)
The Laser: I've altered my setup since the video was made because the laser pointer in the video is no longer available. So, connect the laser diode to a power supply and one end to a 3.5mm audio cable that that has been cut to expose the wires. [D and B on diagram]
Connect Audio Out: Plug a 3.5mm audio jack into your computer or cell phone [A and B on diagram](4:14). If using a 3.5mm to RCA connector like in the video, attach alligator clips to the corresponding RCA ends (6:30).
Complete the Circuit: Clip the alligator leads onto either side of the laser's internal power connection/resistor (2:01).
Aim and Fire: Point your modulated laser beam directly at the solar cell (2:41). Play a track on your phone and listen to the music cross the room on a beam of light! (2:50)
Fun Challenges to Try in the Classroom!
Once you have the sound streaming smoothly, try experimenting with the beam (1:41):
The Comb Test: Run a plastic comb through the laser beam while music is playing to add a hilariously choppy "hip-hop" remix effect (3:02).
The Dust Storm: Lightly spray some dust or powder into the beam path and listen to how it alters the electrical current and drops the audio volume (3:20).
The Fan Blade: Pass a small spinning fan through the light path to hear a high-frequency, synthetic note generated by the rhythmic chopping of the light! (3:11)
The Remote Control Test: Aim a standard television remote control directly at your solar cell receiver and press a button (3:28). You'll instantly hear a rhythmic series of beeps, letting your students "hear" the hidden infrared light pulses (3:40)!
SAFETY FIRST: Always remember that lasers can cause permanent eye damage. Never look directly into the laser beam or point it toward anyone's eyes. Adult supervision is required for hacking electrical components.
For Teachers: NGSS Alignment Guide
Bring this experiment into your classroom! This hands-on demonstration provides an excellent anchor phenomenon for units on mechanical waves, light, and modern information technology.
Performance Expectations (PE)
MS-PS4-2: Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials.
HS-PS4-1: Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media.
HS-PS4-2: Evaluate questions about the advantages of using a digital transmission and storage of information.
HS-PS4-5: Communicate technical information about how devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy.
Three-Dimensional Learning Breakdown
1. Science and Engineering Practices (SEP)
Developing and Using Models: Students construct an active, physical model of a wireless telecommunication network using a laser (transmitter) and a solar cell (receiver).
Obtaining, Evaluating, and Communicating Information: Students evaluate and explain the technical mechanism of how analog auditory signals are converted into rapid light pulses and decoded back into sound waves.
2. Disciplinary Core Ideas (DCI)
PS4.A: Wave Properties: Information can be digitized and transmitted over long distances as series of wave pulses.
PS4.B: Electromagnetic Radiation: Photoelectric materials (the solar cell) capture light energy and convert it into moving electrical currents.
PS4.C: Information Technologies and Instrumentation: Multiple modern devices utilize the electromagnetic spectrum to pulse data wirelessly through light waves, microwaves, and radio waves.
3. Crosscutting Concepts (CCC)
Cause and Effect: Changes or interruptions made to the light beam path (the cause) directly generate a physical vibration and audible change in the speaker output (the effect).
Structure and Function: The internal design of the hacked laser pointer enables the structural variation of an electrical signal to dictate the flashing frequency of the light source.
Keep on Learning! ~Craig Beals
