11-08-2012, 11:59 AM
The Development of a Low-Cost Laser Communication
System for the Classroom
The Development of a Low-Cost Laser.pdf (Size: 489.59 KB / Downloads: 71)
Introduction
The Hands-On Optics project is a four-year informal science program is designed to bring the excitement of light,
color, and optics technology to tens of thousands of underserved middle school-aged students nationwide. The HOO
project1 has developed six hands-on activity modules intended to engage and enrich the math/science learning
experience for students in the middle grades. Each module offers six to seven hours of exploratory science activities
that can be grouped into 30- to 90-minute sessions. The project is aimed at after-school, museum, and science center
settings but can be adapted for the formal education classroom.
Module 6 focuses on laser communication. The first activity addresses laser light illustrating the differences
between white light and monochromatic light as well as coherent light and incoherent light. The second activity lets
the students explore using light to transmit data in the form of Morse Code. The students then learn how to build the
laser communication system. The students are given the challenge to communicate over the longest distance
possible using the largest number of optical devices. The module culminates with a demonstration of fiber optics.
The problem we encountered with this module was the cost of the laser communication system. Companies such as
Arbor Scientific2 sell ready-made laser communication kits. The kit consists of a 0.8mW Helium-Neon laser ($475)
and a Laser Voice Transmission Package ($139) consisting of a microphone, an amplified speaker, and a small
photocell. The total price of $614 was too costly for use in our kits, necessitating the development of a lower cost
system. Other laser communication systems have been described by Thomas Petruzzellis3 and Gordon McComb4.
Although these systems are robust, the circuits are more complicated and above the abilities of middle school
students to construct them.
The Low-Cost Communication System
Conducting a web search led to a potential solution to the problem. We found a posting on ihacked.com5 by Simon
Quellen Field. He described a technique using an audio output transformer from Radio Shack to modulate a
standard laser pointer. We designed a system around this concept. Our design was modified quite a bit during our
testing to optimize its performance.
For our receiver, we used the same receiver as the NASA SOFIA Active Astronomy Infrared Kit6. The receiver
consists of a small solar cell and a Radio Shack Amplified Speaker connected by a shielded audio cable. The solar
cell is very sensitive, and the system has been extensively tested by teachers in educational settings.
The transmitter was more problematic. The original design used a laser pointer wired to an external battery pack. In
order to make the transmitter easier to assemble, we decided to use a clip-activated laser pointer. You can insert this
laser into a circuit simply by attaching a wire to the clip and a second wire to the laser body.
An amplified sound source is required to modulate the laser. We found that an MP3 player or CD player would
work. However, we wanted the students to be able to transmit their own voice. Two solutions were found. The
first is a device called the Gossip Gizmo from Radio Shack