HP 86037B User manual

User’s Guide
HP 86037B Chromatic
Dispersion Test System

ii
© Copyright Hewlett-Packard
Company 1999
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HP Part No. 86037-90017
Printed in USA
July 1999
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ISM1-A

iii
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iv
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Contents
Contents-1
General Safety Considerations iv
1QuickStart
A Quick Tour 1-4
Measuring Fiber Devices 1-8
Measuring Grating Devices 1-11
2Operation
The Main Window 2-3
The Review Data Window 2-23
Using Database Files 2-33
Checking Test Fiber Stability 2-36
3 Normalization
Normalizing the Test Setup 3-4
Verifying a Test Setup Normalization 3-6
Adjusting the Modulator Bias 3-7
Normalizing the Laser 3-8
Adjusting the Power Monitor 3-10
Setting Normalization Preferences 3-13
4RemoteControl
Setting up a Measurement 4-4
Performing a Measurement 4-13
Reading the Measurement Results 4-16
TES Parameters 4-21
TES Min/Max Parameters 4-38
Output Parameters 4-41
5 Maintenance
Troubleshooting Common Problems 5-3
Verification Tests 5-9
Reinstalling the System Software 5-16
HP Support and Maintenance 5-18
Cleaning Connections for Accurate Measurements 5-20
Electrostatic Discharge Information 5-31
Returning the Instrument for Service 5-33

Contents-2
Contents
Hewlett-Packard Sales and Service Offices 5-36
6 Installation
7 Reference
Theory of Operation 7-2
Rack Diagram 7-6
Chromatic Dispersion–theory and management 7-8
Measurement Repeatability 7-11
Material Lists 7-13
Power Cords 7-18
System Options 7-19
8 Specifications and Regulatory Information
Specifications 8-3
Regulatory Information 8-7

1
Operation—at a glance 1-2
A Quick Tour 1-4
Measuring Fiber Devices 1-8
Measuring Grating Devices 1-11
Quick Start

1-2
Quick Start
Operation—at a glance
Operation—at a glance
The HP 86037B is a complete solution for measuring chromatic dispersion in
fiber-optic cables, dispersion compensating devices, gratings, and other com-
ponents. The system performs near-end measurements where there is access
to both ends of a test device at the same location.
Your HP 86037B should have already been installed by an HP engineer. If in
the future, you should need to review the installation procedures, refer to
Chapter 6, “Installation”.
Learn about your system
• To learn how to make measurements, read “A Quick Tour” on page 1-4.
• If your measuring grating based devices, read “Measuring Grating Devices”
on page 1-11.
• To learn about chromatic dispersion theory, refer to “Chromatic Disper-
sion–theory and management” on page 7-8. Also, refer to Fiber Optic Test
and Measurement a Hewlett-Packard Professional Book available from
Prentice Hall (ISBN 0-13-534330-5).
• To learn about available support options, refer to “HP Support and Mainte-
nance” on page 5-18.
• The HP 86037B system uses the Windows NT®*operating system. To learn
about Windows NT, refer to your Microsoft®†Windows NT User’s Guide.
Single band versus dual band systems
This chapter describes how to operate both the single band and dual band ver-
sions of the HP 86037B. With a few minor exceptions, their operation is identi-
cal. Some of the figures in this chapter show features only found on the dual
band systems. If you’re using a single band system, simply ignore the features
which are not found on your system.
*. Windows NT® is a U.S. registered trademark of Microsoft Corporation.
†. Microsoft® is a U.S. registered trademark of Microsoft Corporation.

1-3
Quick Start
Operation—at a glance
WARNING HP 86037B and HP 83427A: If the system or test set products are not
used as specified, the protection provided by the equipment could be
impaired. These products must be used in a normal condition (in which
all means for protection are intact) only.
WARNING During measurements, laser light emits from the front-panel
SOURCE OUTPUT connector. This light originates from the
system’s tunable laser source. Always keep the SOURCE OUTPUT
connector covered when not in use.
CAUTION The warranty and calibration will be voided on systems where the individual
instruments, including fiberoptic cables, RF cables, or GPIB cables are
removed by the customer. The system should only be disassembled by a
Hewlett-Packard Customer Engineer. Instruments should not be swapped or
removed by non-Hewlett-Packard personnel.
SOURCE OUTPUT
(light output)
System power
switch
RECEIVER INPUT
Measurement accuracy—it’s up to you!
Fiber-optic connectors are easily damaged when connected to dirty or damaged cables
and accessories. The HP 86037B’s front-panel SOURCE OUTPUT and RECEIVER INPUT
connectors are no exception. When you use improper cleaning and handling techniques,
you risk expensive instrument repairs, damaged cables, and compromised measure-
ments. Before you connect any fiber-optic cable to the HP 86037B, refer to “Cleaning
Connections for Accurate Measurements” on page 5-20.

1-4
Quick Start
A Quick Tour
A Quick Tour
This procedure steps you through the process of making your first chromatic
dispersion measurement. Because the system defaults to measuring fiber-
based devices (versus grating-based devices) use a fiber-based device for test-
ing in this procedure. It should take approximately 20 minutes to complete.
1Press the system power switch to turn on the system.
2When the Windows desktop appears, click on the HP CD icon.
3The two procedures listed below should have been performed as part of the
system installation procedure. If they have not yet been performed, perform
them at this time.
❒“Normalizing the Laser” on page 3-8.
❒“Adjusting the Power Monitor” on page 3-10.
4On the Service menu, click Select TLS. Click the appropriate button to enable the
tunable laser source. For safety reasons, the default value is OFF.
5Enter the test identification information for your test. See the “Test
identification area” in Figure 1-1 on page 1-5. This includes items such as the
type of fiber, a descriptive name, the manager and operator’s names.
System power
switch

1-5
Quick Start
A Quick Tour
Figure 1-1. Application features
6In the “Measurement range” area, enter the the start, stop, and step
wavelengths.
7On the SetParametersFor menu, click CD/
Gain Meas. In the dialog box, click Set HP
Defaults and then OK.
8On the SetParametersFor menu, click Length
Meas. In the dialog box, click Set HP Defaults and then OK.
Normalization
data
Test identification
area
Measurement
range
Message area
Measurement
speed
Fiber
parameters
Open
Windows
Notepad
Adjust
modulator bias
Normalize
test setup
Start
measurement
Test the
connections
Verify current
normalization
View
measurement
data
Grating parameters Status area

1-6
Quick Start
A Quick Tour
9On the File menu, click Save Setup As to
save all of the settings made so far into a
setup file.
The title bar displays the name of the setup file that is currently open. You can
recall this file at any time to automatically configure the system to your spe-
cific measurement settings. You can create as many setup files as you may
need.
Normalizing the test setup
The system must warm up for two hours before test setup normalizations and
measurements can be made. While your system is warming up, spend some
time familiarizing yourself with the remaining information in this chapter.
10 Connect the device being tested to the system.
Use patch cords to connect the SOURCE OUTPUT and RECEIVER INPUT connectors
to the device you are testing. This step determines the cables required in
order to protect the system’s fiber-optic connectors from wear.
11 Remove the device being tested from the test setup and replace the device
with a patch cord. Retain as many of the test setup cables as possible.
12 Click Power Monitor, and confirm that the power levels indicate that good low-
loss connections have been made.
13 Click New Normalization to normalize the measurement setup. Then, click Start
Normalization.
Chapter 3, “Normalization” describes the various normalization procedures
and adjustments available for your system.
14 After the normalization has completed, click Close.
Performing a measurement
15 Remove the patch cord inserted in Step 11 and reinsert the device being tested.
Be sure to use the same cables that you used in Step 10.
16 Click Power Monitor, and confirm that the power levels indicate that good low-
loss connections have been made.
17 Click Verify Normalization.
Use this step to confirm that the normalization is still valid.
18 Click Start Test to begin a CD measurement.

1-7
Quick Start
A Quick Tour
Messages in the status line (located at the bottom of the display) show the
test’s progress. After a few seconds, the Data Monitor window appears. While
the test is in progress, you can toggle the views between displayed graph and
list panes.
• After the test has completed, the Data Review window is automatically dis-
played. Refer to “The Review Data Window” on page 2-23 to learn about the
available options for viewing your data.
• Measurement results can be saved for future review. Refer to “Using Data-
base Files” on page 2-33 to learn about this capability.
Figure 1-2. Measurement progress shown in the Graph and List panes
Turning the system off
CAUTION Turning the system off without performing the following steps may damage the
application files.
19 On the File menu, click Exit, and move the mouse pointer to the bottom of the
display to show the Windows NT taskbar.
20 Click on Start and then Shut Down.
21 When the computer screen indicates that the computer can be turned off, press
the system’s power switch.

1-8
Quick Start
Measuring Fiber Devices
Measuring Fiber Devices
In this section, you’ll learn how to optimize measurements on fiber devices.
You can, of course, skip this section and immediately begin making measure-
ments on your devices. However, be sure to read this material later to increase
your understanding of chromatic dispersion measurements.
By adjusting the RF modulation frequency, you can optimize measurement
accuracy. (Refer to the sidebar, “Assumptions required for this optimization
method” on page 1-10.) For information on changing the modulation fre-
quency, refer to “CD/Gain Meas command” on page 2-15.
Because the system’s accuracy varies as a function of RF modulation fre-
quency, for optimum accuracy keep the modulation frequency above 1 GHz
and preferably at 2 GHz. This puts some restrictions on the wavelength step
size because too large of a step size results in a phase "wrap-around" where
the phase jump exceeds 360°as the wavelength is stepped. Use the following
formula to determine the maximum step size:
where:
(∆λ
∆λ∆λ
∆λ)MAX is the maximum allowed step size (in nm) to keep the modulation
frequency at the desired value fm.
fm is the desired modulation frequency (in GHz).
S0is the dispersion slope in ps/(nm2×km).
λSPAN is the spectral span (stop λ– start λ) of the measurement in nm.
Lis the length of the system/fiber in km.
Suppose, for example, that you wanted to measure chromatic dispersion on a
70 km spool of dispersion shifted fiber between 1515 nm and 1575 nm. Select
the optimum modulation frequency of 2 GHz, and use the above equation to
determine the maximum allowed wavelength step size. Assuming the fiber’s
dispersion slope is 0.07 ps/(nm2km), then:
500
S
o
ƒ
m
λ
SPAN
L
(∆λ)
MAX
=

1-9
Quick Start
Measuring Fiber Devices
fm is 2 GHz.
S0is 0.07 ps/(nm2×km).
λSPAN is 60 nm.
Lis 70 km.
Substituting these values into the above equation, we have:
Note that 0.85 nm is the maximum allowed step size. Steps shorter than 0.85
nm are permitted. The 0.85 nm step size results in about 70 steps for the mea-
surement.
You can reduce the measurement time using the following techniques:
• Sacrifice accuracy for measurement speed by choosing a lower modulation fre-
quency.
For the example above, if we make fm equal to 1 GHz, the step size can be
increased to 1.7 nm. This results in about 35 steps for the measurement and
thereby halving the measurement time.
• Make a survey measurement with a wide wavelength range and a lower modu-
lation frequency, for example, 500 MHz. Then, raise the modulation frequency,
for example, to 2 GHz, but narrow down λSPAN by zooming into the wavelength
range of interest.
In the above equation, a reduction of λSPAN by a factor of 2 will increase the
maximum allowed step size (∆λ)MAX by 2. The number of steps, ∝λSPAN /
(∆λ)MAX, and therefore the measurement time, will decrease by a factor of 4.
In this example, reducing the measurement span from 60 to 30 nm increases
the maximum allowed step size from 0.85 nm to 1.7 nm. The measurement
time decreases from about 9 minutes to about 2 minutes and 15 seconds.
(∆λ)
MAX
=
500
0.07 ps
nm
2.
KM
X 2 GHz X 60nm X 70km

1-10
Quick Start
Measuring Fiber Devices
Assumptions required for this optimization method
Assumption 1. The group delay can be modeled by the quadratic equation:
Where S0is the dispersion slope, λis the wavelength, λ0is the zero dispersion wave-
length, and L is the fiber length. The precise details of the quadratic fit to the data are not
critical; the only requirement is that the group delay curve should have the shape of a par-
abolic curve. In fact, the results presented here are valid even if the three-term or the five-
term Sellmeier fits are used, as those two models also have the parabolic shape. This
assumption is valid for systems consisting mostly of dispersion-shifted fiber.
Assumption 2. The dispersion slope S0[in ps/(nm2×km)] is known. For example, the dis-
persion slope, S0, is approximately 0.07 ps/ (nm2×km) for most dispersion shifted fiber. The
zero dispersion wavelength λ0need not be known but should lie within the spectral range
of the measurement.
τ
g
(λ) = (λ − λο)
2
L
S
o
2

1-11
Quick Start
Measuring Grating Devices
Measuring Grating Devices
In this section, you’ll learn how to make measurements on grating based
devices such as Bragg fiber gratings. It is recommended that you do not skip
this section. Since the HP 86037B, by default, is set for making measurements
on fiber devices, before measuring grating devices, perform the following
steps:
1Select Absolute Group Delay
Measurement in the Grating Related
Parameters area in the main
window. (By default, relative
group delay is measured.) Refer
to “Absolute Group Delay Measurement” on page 2-14.
In addition to selecting absolute group delay, this selection turns off the
review data window’s curve fit selection. Although, curve fitting is a standard
method used to reduce the effects of noise when measuring fiber based
devices, there is currently no standard for grating based devices. You can, of
course, export the data and apply your own corrections.
2Set the Test Modulation Frequency to the
Manual setting. Refer to “CD/Gain Meas
command” on page 2-15 to configure this
setting.
For details on determining the proper RF test modulation frequency, refer to
“Setting the RF modulation frequency” on page 1-12.
3Use larger wavelength steps during test setup normalization compared to
during the measurement. This reduces overall test time.
Since patch cords used during normalization have very low dispersion, the
system is able to interpolate accurate values for use with grating measure-
ments. For example, if you are measuring a grating with 5 nm wavelength
range, you could use 1 nm steps during normalization and 1 pm steps during
measurements.
4Expect large jumps in measured dispersion.

1-12
Quick Start
Measuring Grating Devices
Without the benefit of curve fitting and since dispersion is the derivative of the
group delay, the effect of any noise is exaggerated. For example, large
amounts of noise will be measured at wavelengths in a filter’s cutoff region.
5Use a 2 GHz RF modulation frequency with a small wavelength step size. Step
sizes down to 1 pm are possible. To set the step size, refer to “Wavelength
Selection area” on page 2-6.
Setting the RF modulation frequency
When selecting the RF modulation frequency, you’ll want to select the highest frequency
possible without introducing 360°phase shifts. This requires that you know the approxi-
mate group delay variation (between measurement wavelength steps) expected on the
device that you are measuring.
Set the RF modulation frequency to a value which has a period that is at least twice the
anticipated group delay between wavelength steps.
For example, when measuring a grating device that has a variation in group delay of as
much as 500 ps between wavelength steps, set the RF modulation frequency to 1 GHz or
less. If you specify a wavelength step size of 2 pm to 100 pm, it is unlikely that any but the
fastest gratings (such as tuning filters or dispersion compensation gratings) would require
less than the default 2 GHz frequency.
RF modulation frequency 1
2 group delay between wavelength steps
()
-----------------------------------------------------------------------------------------------------------------
≤

2
The Main Window 2-3
Test and Tool buttons 2-5
Wavelength Selection area 2-6
Test Identification area 2-8
Normalization area 2-9
Measurement Speed Parameters area 2-10
Fiber Related Parameters area 2-12
Grating Related Parameters area 2-14
File menu 2-15
SetParametersFor menu 2-15
Range menu 2-18
System menu 2-19
Service menu 2-22
The Review Data Window 2-23
Measurement review tabs 2-25
File menu 2-29
Edit menu 2-32
Preferences menu 2-32
Using Database Files 2-33
Checking Test Fiber Stability 2-36
Operation

2-2
Operation
Operation—at a glance
Operation—at a glance
In this chapter, you’ll find descriptions of the chromatic dispersion applica-
tion’s two window views along with their menu selections. The two window
views (main and data review) are each described in a separate section. Addi-
tional sections describe database files and test fiber stability.
The chromatic dispersion application starts up in the main window from which
you perform all measurements. After performing a measurement, the applica-
tion automatically switches to the data review window.