FOA Basic Skills

Lesson: Building and Testing A Fiber Optic Link - Part 1 - Duplex Link

Objectives: From this lesson you should learn:
How to build a fiber optic link using media converters
Testing the fiber optic link
Using transmitter sources to test the fiber optic link cable plant

Safety Glasses
Visual Fault Locator (VFL) or the VFL in the power meter if it has one
Fiber optic cable


Fiber Optic Media Converters

Media converters are special fiber optic transceivers used to convert from one type of cable (the media) to another, typically from copper cables to fiber optics, although some media converters will convert from one fiber type to another, e.g. multimode to singlemode. The FOA Guide has a page about media converters you should read before beginning this exercise.

We have exercises for two types of media converters. Exercise 1 uses
media converters that connect over two fibers like the majority of fiber optic links. Exercise 2 uses media converters that connect over one fiber while still providing full-duplex (simultaneous) communications bidirectionally over the one fiber. The one fiber bidirectional links are similar to those used in passive optical networks (PONs) used in FTTH (fiber to the home) and optical LANs, so Exercise 2 includes an option to build a PON demonstration.

Both types of media converters are available for purchase online at very reasonable prices. The exercises show how to use media converters that use Ethernet protocols to allow connecting computers to the Internet.

Fiber optic media converters
Typical media converters

2 singlemode fiber media converters- you will be using singlemode fiber cables from the installation exercises to connect them. If you plan to do both exercises, you will need 2 sets of media converters, one set that operates over two fibers and one set that operates over a single fiber bidirectionally.
You will connect them over 2 or 4 fiber optic cables used in the other exercises

Also you need two Cat 5e patchcords to connect your computer and router to the media converters. Purchase these online if you do not have any.

PON Splitter

If you wish to do the PON demo in exercise 2, you will need a PON splitter. Order a "1 X 4" or 4 port splitter online.

Fiber Optic Power Meter

fiber optic power meter

This fiber optic power meter measures in dBm and W and has a dB range for loss measurements.
It has adapters for SC connectors and any connector with 2.5mm ferrules.

Connecting With The Link You Build
To connect with the link, you need an Ethernet connection to the Internet and a device that can connect to the Internet over Ethernet on UTP Cat 5 cable..
Your Internet connection should have a router with Ethernet ports which can be used.
If you have a computer with an Ethernet port, that will be ideal for completing the link. You can also use a WiFi access point connected to your router over UTP Cat 5e cable for the exercise.


Lennie works safely

Always wear safety glasses when doing any of these exercises and dispose of all fiber scraps properly.

Safety Rules - Read before beginning any exercises.

Do not look directly into the light from the visual fault locator - it's bright!


Before you start, review the use of fiber optic media converters from the FOA YouTube video on media converters, the FOA Guide page on media converters or the Fiber U MiniCourse on media converters

Watch the FOA YouTube Video Of This DIY Link Demo Exercise   

Check Your Cables

Attach your cables to the Visual Fault Locator (VFL)

2. Turn the VFL on and ensure the light travels through the fiber. You can see how bright the glow is at the end of the fiber, diffused through the fiber protective cap. This shows how fiber transmits light by total internal reflection as you learned in the lesson on optical fiber.


Repeat for all the cable you are using in this exercise.

Exercise 1

Build A Fiber Optic Link

Exercise 1 uses media converters that connect over two fibers like the majority of fiber optic links. build a fiber optic link

This link uses two media converters that convert Ethernet on Cat 5 to fiber optics. The diagram above is the link we will build.

1. Assemble the equipment you need.
2. Power up the media converters and confirm the power light.

media converter

3. Connect the two media converters with duplex cables, preferably 3 cables connected with mating adapters. Did your link show the link connection light? If not did you remember that the fibers must be crossed to connect the transmitter output of one to the receiver input of the other.

media converter
Note how blue and white connectors are reversed to make transmitter to receiver connections. You should now have the middle indicator light on, showing the fiber link is working.

media converter link lights

4. Connect your Ethernet devices to the link with UTP Cat 5e cables and confirm the link transmits data. You can check the indicator lights to ensure the bottom light is flashing which shows data is being transmitted.

media converter link lights

Here is our link transmitting data, connecting our laptop to the Internet over fiber optics.

Media converter

Here we're watching a FOA YouTube video on cleaning fiber optic connectors.

media convreter

The Ethernet fiber optic link you have built is essentially the same as every digital fiber optic link.

Test Your Fiber Optic Link

Next we will test the link we have built. We want to test transmitter power, receiver power and use them to determine the loss of the cable plant we are using.

media converter test linlk

If we know the output of the transmitter, we can set that as our "0dB" reference and when we measure the receiver power, it will be lower by the loss of the cable plant. This is just like making an insertion loss test except we are using the transmitter as our test source.

Turn on your power meter and set the range to dBM to measure the power. Disconnect the patch cord connecting the transmitter of one of the media converters and plug it into the power meter.

media converter test

The output of this transmitter is -7.19dBm (middle display) so we can confirm the transmitter source is operating and we have set this to be our "0dB" reference for testing the cable plant. Reconnect this patchcord to our cables.

Next disconnect the receiver input of the other media converter and plug that into the meter.

media converter test

The meter is still set to read dB on the lower scale and the loss of the cable plant is 0.89dB. The middle display still shows the transmitter output which we used for a 0dB reference.

We can also measure the input power of the receiver of this module by switching the display to dB/W.

media converter test

The input to the receiver of this media converter is -8.00 dBm or 155.5nW ().156mW).

Our exercise showed how to test the transmitter power and receiver power and how to use the transmitter as a test source to measure the loss of the cable plant.

You have successfully completed this exercise when you have built a fiber optic link using the media converters and used it to transmit data. You also should have tested the power in the link at the transmitter and receiver and use the transmitter to test the cable plant.

Complete the exercise and fill in your Scorecard.

Exercise 2

Build A Bidirectional Fiber Optic Link And A Passive Optical Network (PON)

Media converter bidirectional link

Media converter bidirectional demo

Return to Lesson Plan

This information is provided by The Fiber Optic Association, Inc. as a benefit to those interested in teaching, designing, manufacturing, selling, installing or using fiber optic communications systems or networks. It is intended to be used as an overview and/or basic guidelines and in no way should be considered to be complete or comprehensive. These guidelines are strictly the opinion of the FOA and the reader is expected to use them as a basis for learning, as a reference and for creating their own documentation, project specifications, etc. Those working with fiber optics in the classroom, laboratory or field should follow all safety rules carefully. The FOA assumes no liability for the use of any of this material.


Table of Contents: The FOA Reference Guide To Fiber Optics

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