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Making sense out of complex Pro A/V and Broadcast technologies.

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Guide

Learn how this simple tool can minimize

your troubleshooting efforts.

An educational resource published by Communications Specialties, Inc..

The Optical Power Meter:

The Indispensable Tool for

Working with Fiber Optic Systems

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Guide

Making sense out of complex Pro A/V and Broadcast technologies.

Communications Specialties, Inc. is committed to

increased education and knowledge in the Pro A/V

and Broadcast industries.

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©2009 Communications Specialties, Inc. All Rights Reserved.

Specifications, claims or other product information contained in this document are subject to

change without notice. This document may not be reproduced, in whole or in part, without the

express written consent of Communications Specialties, Inc.,

Fiberlink, Pure Digital Fiberlink, the starburst logo, Scan Do and Deuce are registered trademarks

of Communications Specialties, Inc. CSI and the triangle designs are trademarks of

Communications Specialties, Inc.

October 8, 2009



Introduction

This eduGuide is provided to assist all those charged with installing

and supporting fiber optic systems of all kinds. This brief eduGuide will

demonstrate how a simple fiber optic power meter can be used to properly

install and maintain these systems. The Communications Specialties

Fiberlink® 6615 is a compact battery operated power meter that is both

accurate and easy to use.

The power meter, as it is commonly called, measures the optical power of light

present on a fiber optic cable. This light can be generated directly from the

output of a fiber optic transmitter device or from another common fiber optic

testing device: a laser light, such as the Fiberlink® 6620. Your optical power is

measured in dBm or in mW.

Using the Power Meter During System Design

The first thing a system designer needs to know about a fiber optic link is how

much optical loss will be experienced between the end points of any fiber

optic cable. All fiber optic transmitters and receivers will specify a maximum

amount of optical attenuation, or loss budget, that can be tolerated before the

equipment will no longer work properly. This loss budget is specified in dB and

can vary from as little as 5 dB to as high as 30 dB depending on the product’s

design.

Before determining an optical loss measurement,

you need to know two things:

•

The type of fiber being used - either single mode or multimode.

We strongly recommend the use of single mode fiber

whenever possible.

•

The operating wavelength of the transmitter you are using for

the light source you are injecting into the fiber. This is usually

850nm, 1310nm or 1550nm

You will need two devices to determine the optical loss measurement:

•

An optical power meter, such as the Fiberlink® 6615

•

A light source, as described above, to launch a beam of light into

the fiber. This can be an existing fiber optic transmitter or a light

source such as the Fiberlink® 6620 Three Wavelength Laser Light

Source

The Optical Power Meter

3



The procedure to measure the optical loss

in the fiber optic cable is as follows:

•

Set the power meter to the wavelength

of the light source you are using

•

Connect a short fiber jumper cable between

the light source and the power meter. See Figure A.

•

Make note of the power level, in dBm. We will call this “Reading A”.

•

Connect the fiber cable under test to the output

of the light source

•

Connect the power meter, set at the same wavelength as the

power source, to the far end of the fiber cable under test.

See Figure B.

•

Make note of the power level, in dBm. We will call this “Reading B”.

•

The optical loss in the fiber cable is equal to

“Reading A” minus “Reading B

Optical Loss = “Reading A” – “Reading B”

Figure A:

Transmitter

Receiver

Optical

Optical

Powe

r Meter

Powe

r Meter

29.98

ON

Power Meter

l

/dBm/OFF

ON

l

/dBm/OFF

Model

Model

6615

6615

Figure B:

Transmitter

Receiver

Power Meter

Optical

Powe

r Meter

Optical

Powe

r Meter

27.32

ON

l

/dBm/OFF

ON

l

/dBm/OFF

Model

Model

6615

6615

4

The Optical Power Meter



When multimode fiber is used, measurements should be made at 850nm

or 1310nm. It is preferred that measurements be made at both wavelengths,

if possible, as the optical loss can vary significantly as the wavelength varies

when multimode fiber is used.

When single mode fiber is used, measurements should be made at 1310nm as

this is the most common wavelength used with single mode fiber.

These measurement procedures should be repeated for every fiber cable

in the system.

Using the Power Meter During System Installation

During system installation, the use of the power meter will be essential

to verifying that the fiber cable you are working with is performing as well

as it should. Typical problems include dirty fiber connectors, breaks, kinks

and knots in the fiber, poor splices, faulty connector terminations and the

use of incorrect patch cables based on the type of fiber used (multimode

or single mode).

During the installation, it is assumed you have a working fiber optic

transmitter unit that you intend to install. On this transmitter, please note

the following:

•

The operating wavelength (850nm, 1310nm, or 1550nm)

•

Whether it is designed to operate with single mode,

multimode or both fiber types

Next, determine the type of fiber installed. The jacket of the fiber cable

should be marked.

•

For multimode fiber, it may be marked:

• multimode

• 62.5/125

• 50/125

•

For single mode fiber, it may be marked:

• single mode

• 9/125

The Optical Power Meter

5



The procedure to measure the optical loss

in the complete fiber optic link is as follows:

•

Set the power meter to the wavelength of the fiber optic

transmitter you are using

•

Connect a short fiber jumper cable between the fiber transmitter

and the power meter. See Figure A.

•

Make note of the power level, in dBm. We will call this “Reading A”

•

Connect the fiber cable under test to the output

of the light source

•

Connect the power meter, set at the same wavelength as

the fiber transmitter, to the far end of the fiber cable under test.

See Figure B.

repeaters, routers, etc., in line with the fiber cable you are measuring

•

Make sure there are no active components such as amplifiers,

•

Make note of the power level, in dBm. We will call this “Reading B”

•

The optical loss in the fiber cable is equal to

“Reading A” minus “Reading B”

Optical Loss = “Reading A” – “Reading B”

Figure A:

Transmitter

Patch Panel

Receiver

Optical

Optical

Powe

r Meter

Powe

r Meter

29.98

ON

Power Meter

l

/dBm/OFF

ON

l

/dBm/OFF

Model

M

15

odel 66

6615

Figure B:

Transmitter

Patch Panel

Receiver

Power Meter

Optical

Powe

r Meter

Optical

Powe

r Meter

26.32

ON

l

/dBm/OFF

ON

l

/dBm/OFF

Model

Model

6615

6615

6

The Optical Power Meter



If patch panels are part of the optical link they should be connected and

operational so as to be part of the end-to-end measurement. Ensure that

the fiber cable used to make the patch is utilizing the same type of fiber

(multimode or single mode) as the fiber cable itself. In fact, improper pairing

of fiber optic cabling types at the switch and/or router is a common

occurrence.

Having made these measurements you will be able to determine if your fiber

cable is performing properly. That is, does it have too much optical loss. Of

course, some optical loss is not only expected, it’s quite normal. Use the

following table to determine the amount of optical loss you should typically

expect from your fiber optic link:

Typical Optical Loss to Expect

Cables

62.5u Multimode Fiber at 850nm

62.5u Multimode Fiber at 1310nm

50u Multimode Fiber at 850nm

50u Multimode Fiber at 1310nm

Single Mode Fiber at 1310nm

Single Mode Fiber at 1550nm

Connectors, Splices and More

Each Connector

Each Splice

Each Jack on a Jack Field

Each Patch Cord

Optical Loss

3 dB per km

1 dB per km

1 dB per km

1 dB per km

0.35 dB per km

0.25 dB per km

Optical Loss

0.2 dB

0.3 dB

0.2 dB

0.2 dB

Add up all the losses for your system based on the above estimates and

compare this total to the loss you measured using the power meter. If

your fiber cable link is properly installed, the measured loss on the power

meter should be the same or less than the estimated loss using the above

numbers. If your measured loss is significantly more (i.e. >25%) you should

investigate where the excess loss might be occurring, even if your link is

operational, as this is a sign of future trouble. Start with cleaning the tips of all

fiber connectors in the optical link from beginning to end and verifying the

integrity of all connections and terminations.

When you are finished installing the system and all links are operating

normally, it is a great idea to measure the optical loss in all of your fiber optic

links and record them for future reference. You can use this data to compare it

against future measurements.

The Optical Power Meter

7



Using the Power Meter to Troubleshoot and Maintain a System

You now have a working fiber optic system. Optical link losses are as they

should be and the system is functioning normally. What should you do to

maintain the system over time to extend the useful life of the system?

In a digital fiber optic system, where the baseband signals are transmitted

digitally over the fiber, small variations of optical loss in the fiber link will not

be noticed. Usually, a properly operating link will have ample margin in the

loss budget such that a 1 to 3 dB variation in optical loss can be tolerated with

no adverse effect. However, a slow deterioration of the optical power in the

link can be a sign of system problems or a failure to come.

There are several periodic things you can do when you suspect

the link loss may be increasing:

•

Over time, small amounts of dirt and film may build up on these

connectors. Start by cleaning all optical connectors in the fiber

optic link. No exceptions. This can be done with a small alcohol

pad applied to the tip of the connector.

Use your optical power meter, as described in the procedure

Using the Power Meter During System Installation

to check the optical

loss in the fiber links you suspect may be excessive. Compare the

loss you measure now to the loss you measured when you first

installed the link.

Substitute a known good fiber optic transmitter of the same type for

the one currently installed to see if performance improves. Measure

the output power of the new transmitter and compare it the old

transmitter. They should match within 1 to 2 dB.

•

•

Conclusions

Designing, installing and troubleshooting a fiber optic system is not a difficult

task. However, an optical power meter is an indispensable tool for installing,

maintaining and troubleshooting fiber optic links. Think of it as the digital

voltmeter (DVM) of the fiber optic world. The power meter, together with

common troubleshooting techniques, are all you will need in most cases.

And remember to keep the connectors clean and the fiber cables free of kinks.

8

The Optical Power Meter



Other issues in the eduGuide Series

Introduction to Fiber Optics

Undisputably, fiber is the future. Learn all about the benefits

of fiber optic technology in this easy-to-read guide.

Advantages of Digital Fiber Optics

Examine how digital signals over fiber are accomplished,

the phenomenal results they achieve, and how cost-effective it is.

Fiber Optic Cables, Connectors and Integration

Learn how easy it is to terminate and fabricate your own fiber optic cables,

what types of fiber and fiber jackets are available and how to design

and integrate a fiber optic system.

Scan Converters Buyer’s Guide

Everything you need to evaluate and decide on the perfect Scan Converter.

Video Scaling

A comprehensive overview of the technology, how it works

and when to use this technology effectively.

Advanced Video Scaling

Easy explanations of Inverse 3:2 Pulldown, Anamorphic Scaling and Other

Confusing Concepts.

Other Educational Resources

commspecial.com

Visit our website for online education resources, product literature and more!

Pure Digital Fiberlink® Application Brief – Everyday Pro A/V

This application brief illustrates the benefits of using Pure Digital Fiberlink®

in any Pro A/V installation. Regardless of your Pro A/V market specialty,

this Application Brief is a valuable guide to integrating and specifying

Pure Digital Fiberlink® products.

Pure Digital Fiberlink® Intelligence Brief – Government/Military

Detailed analysis of how Pure Digital Fiberlink® has become the solution of

choice for mission critical government, intelligence and military applications.

If you are involved in this market segment, this document will prove to be

valuable during your next project specification.

The Optical Power Meter

9



About Communications Specialties, Inc.

Communications Specialties, Inc. (CSI) is an award-winning, Long Island

based company that manufactures and sells a variety of products for the

distribution, conversion or transmission of television and computer video

signals, including fiber optic transmission systems, scan converters and video

scalers.

The company was founded in 1983 by veterans of the broadcast industry.

Since then, CSI has managed to consistently design innovative products that

are used worldwide by Fortune 500 Companies and Government Agencies in

a variety of markets such as Broadcast, Professional A/V, Videoconferencing,

Education, Home Theater, Security, ITS, Industrial Monitoring, Digital Signage,

Government/Military and more!

The

Pure Digital Fiberlink®

line offers an extensive and affordable family

of fiber optic transmission systems for the Professional A/V marketplace

and includes several ground-breaking products for the transmission of

high-resolution RGB signals. Systems for point-to-point and

point-to-multipoint signal distribution make these products highly

desirable for any Pro A/V applications.

Our premier product line, the

Scan Do®

family of computer to video scan

converters, has redefined industry standards in computer video to NTSC/

PAL technology with unsurpassed performance in its price range. All models

support high resolutions and refresh rates and are VGA and Mac® compatible.

The feature-rich and versatile Scan Do family offers the widest range of scan

converters on the market.

The award-winning,

Deuce®

video scalers convert NTSC and PAL to high-

resolution, non-interlaced video and offer a far superior and affordable

alternative to line doubling and quadrupling. The new generation of Deuce

products offer a wide range of non-interlaced resolutions and refresh rates

for every application, from professional A/V installations to home theater,

including a model designed especially for use with HDTV displays.

In addition, CSI manufactures a comprehensive selection of distribution

amplifiers, VGA monitor, keyboard and mouse extenders and accessories for

our entire product line.

10

The Optical Power Meter



Communications Specialties and its products have been the recipient of

numerous industry awards. In 2005, the Pure Digital Fiberlink® 7220 Series

for high-resolution RGB and Stereo Audio was honored as one of the AV

industry’s best technological innovations of the year by receiving a “rAVe

Radical Product of the Year” award as “Best New Analog Signal Processing

Product”. The rAVe email newsletter is published by professional audiovisual

industry veterans and is read industry-wide.

Among CSI’s many other awards are AV Video Magazine’s Platinum Award

(given to Scan Do® Ultra and Deuce®) and the Video Systems’ Vanguard

Award (given to Deuce).

The company is headquartered in the United States on Long Island,

New York, with Sales Offices in Florida, Indiana and Virginia. Research,

development, design, engineering, manufacturing and customer support

operations are performed at the New York headquarters. Other locations

include Communications Specialties Pte Ltd (CSPL) - a wholly owned

subsidiary office in Singapore that provides support to distributors in the Far

East and Pacific Rim.

Our in-house sales department handles complete product-line sales directly

to end-users as well as to an international network of representatives and

resellers. All of our products are backed by an exceptional warranty.

The Optical Power Meter

11



Learn

Making sense out of complex Pro A/V and Broadcast technologies.

edu

Guide

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An educational resource published by Communications Specialties, Inc..

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Tel: +65 6391 8790

Fax: +65 6396 0138

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