THORLABS ERM200 User manual

ERM200, ERM210, ERM220
Extinction Ratio Meter
2023
User Guide

Version:
Date: 1.0 24-Jul-2023
Copyright © 2023Thorlabs

ERM2xx Series Extinction Ratio Meter
Table of Contents
Chapter 1 Safety 1
Chapter 2 Intended Use 2
Chapter 3 Introduction 3
33.1 Ordering Codes and Accessories
Chapter 4 Getting Started 4
44.1 Parts List
Chapter 5 Operating Instructions 4
55.1 Operating Elements
55.2 Setup
65.3 Adapter Mounting
65.4 Direct Operation
75.4.1 ER Measurement View
85.4.2 Power View
85.4.3 Settings View
95.4.4 Monitor Out Port
95.5 Remote Operation via Custom Software
105.5.1 32-bit Operating System
125.5.2 64-bit Operating System
145.6 Operating Principle
145.7 Applications
155.7.1 Light Source Considerations
155.7.2 Aligning a Laser Diode to a PMFiber
165.7.3 Aligning a PMFiber Patch Cable
175.7.4 Aligning the Connector Key to a PMFiber
Chapter 6 Specifications 18
196.1 Dimensions
196.2 Responsivities
Chapter 7 Maintenance and Service 20
207.1 Replacing Mains Fuse
Chapter 8 Certifications and Compliances 21
Chapter 9 Warranty and RMA Information 22
229.1 Return of Devices
229.2 WEEE Policy

ERM2xx Series Extinction Ratio Meter
Chapter 10 Manufacturer Address 22
Chapter 11 Copyright and Exclusion of Liability 23
Chapter 12 Thorlabs Worldwide Contacts 24

Rev: 1.0, 24-Jul-2023 © 2023 Thorlabs Page 1
ERM2xx Series Extinction Ratio Meter Chapter 1 Safety
Chapter 1 Safety
Attention
The safety of any system incorporating the equipment is the responsibility of the assembler of the sys-
tem.
All statements regarding safety of operation and technical data in this instruction manual will only ap-
ply when the unit is operated correctly as it was designed for.
The ERM2xx Series must not be operated in explosion endangered environments!
Do not obstruct the air ventilation slots in the housing!
Do not remove covers!
Do not open the cabinet. There are no user-serviceable parts inside!
This precision device is only serviceable if returned and properly packed into the complete original
packaging including the cardboard inserts. If necessary, ask for replacement packaging.
Refer servicing to qualified personnel!
Changes to this device cannot be made nor may components not supplied by Thorlabs be used without
written consent from Thorlabs.
Attention
Prior to applying power to the ERM2xx Series, make sure that the protective conductor of the 3 con-
ductor mains power cord is correctly connected to the protective earth ground contact of the socket
outlet! Improper grounding can cause electric shock resulting in damage to your health or even death!
Ensure that the corresponding fuse is inserted. If not, please change the mains fuse (see section Repla-
cing the Mains Fuse).
To avoid risk of fire, only the appropriate fuse for the corresponding line voltage must be used.
All modules must only be operated with duly shielded connection cables.
Attention
The following statement applies to the products covered in this manual, unless otherwise specified
herein. The statement for other products will appear in the respective accompanying documentation.
Note: This equipment has been tested and found to comply with the limits for a Class B digital device,
pursuant to Part 15of the FCC Rules and meets all requirements of the Canadian Interference-Causing
Equipment Standard ICES-003 for digital apparatus. These limits are designed to provide reasonable
protection against harmful interference in a residential installation. This equipment generates, uses,
and can radiate radio frequency energy and, if not installed and used in accordance with the instruc-
tions, may cause harmful interference to radio communications. However, there is no guarantee that
interference will not occur in a particular installation. If this equipment does cause harmful interfer-
ence to radio or television reception, which can be determined by turning the equipment off and on,
the user is encouraged to try to correct the interference by one or more of the following measures:
·Reorient or relocate the receiving antenna.
·Increase the separation between the equipment and receiver.
·Connect the equipment into an outlet on a circuit different from that to which the receiver is connec-
ted.
·Consult the dealer or an experienced radio/T.V. technician for help.

Page 2 MTN033660-D02
ERM2xx Series Extinction Ratio Meter Chapter 1 Safety
Users that change or modify the product described in this manual in a way not expressly approved by
Thorlabs (party responsible for compliance) could void the user’s authority to operate the equipment.
Thorlabs is not responsible for any radio television interference caused by modifications of this equip-
ment or the substitution or attachment of connecting cables and equipment other than those specified
by Thorlabs. The correction of interference caused by such unauthorized modification, substitution or
attachment will be the responsibility of the user.
The use of shielded I/O cables is required when connecting this equipment to any and all optional peri-
pheral or host devices. Failure to do so may violate FCC and ICES rules.
Chapter 2 Intended Use
The ERM200, ERM210, and ERM220 extinction ratio meters measure the polarization extinction ratio of
polarization-maintaining fibers. The ERM200, ERM210, and ERM220 devices are used in photonics re-
search and development applications.
The ERM200, ERM210, and ERM220 devices are designed for laboratory use only. These devices may not
be used or integrated into equipment that is applied in pharmaceutical, medical or military applica-
tions.
Thorlabs, Inc. Life Support and Military Use Application Policy is stated below:
THORLABS’ PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS OR IN ANY MILITARY APPLICATION WITHOUT THE EXPRESS WRITTEN APPROVAL OF
THE PRESIDENT OF THORLABS, INC. As used herein:
1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and whose failure to perform, when properly used in ac-
cordance with instructions for use provided in the labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component in a life support device or system whose failure to perform
can be reasonably expected to cause the failure of the life support device or system or to affect its
safety or effectiveness.
3. The Thorlabs products described in this document are not intended nor warranted for usage in Milit-
ary Applications.

Rev: 1.0, 24-Jul-2023 © 2023 Thorlabs Page 3
ERM2xx Series Extinction Ratio Meter Chapter 2 Intended Use
Chapter 3 Introduction
The ERM2xx benchtop extinction ratio meters are designed to measure the polarization extinction ratio
and the polarization angle of polarization-maintaining fibers (PM fibers) for any kind of alignment ap-
plication such as connectorization of PMfibers or pigtailing of laser diodes with PMfibers.
The ERM2xx series models cover different wavelength ranges from 400 nm up to 2500 nm. The ERM200
module is optimized for 600nm to 1600nm, the ERM210 module for 400 nm to 700 nm, and the ERM220
module for 1200 nm to 2500 nm.
The front panel features a connection port for light input. To test PM fibers equipped with the fiber
connectors FC/PC (narrow- or wide-key), FC/APC (narrow- or wide-key), LC/PC, and SC/PC, Thorlabs of-
fers fiber adapters as listed in the chapter Ordering Codes and Accessories.
The ERM2xx extinction ratio meters can be operated using the front panel display and control knobs or
with custom-made software via the USB interface. This provides access to integration into variable
setups in a wide range of applications in manufacturing, quality control, quality assurance, and R&D. To
write custom-made software for the remote control of an ERM2xx device, Thorlabs provides the drivers
for LabVIEW™ and C. Please see the chapter Remote Operation via Custom Software.
Attention
Please find all safety information and warnings concerning this product in the chapter Safety.
3.1 Ordering Codes and Accessories
ERM200
Benchtop Extinction Ratio Meter with Exchangeable Fiber Adapter Connection Port,
Wavelength Range 600nm to 1600 nm
ERM210
Benchtop Extinction Ratio Meter with Exchangeable Fiber Adapter Connection Port,
Wavelength Range 400nm to 700nm
ERM220
Benchtop Extinction Ratio Meter with Exchangeable Fiber Adapter Connection Port,
Wavelength Range 1200nm to 2500nm
Required Accessories:
ERM2x Fiber Connector
Please find a list of compatible fiber adapters below:
ERM2F Fiber Adapter to Connect Wide-Key FC/PC Connectors to the ERM2xx Benchtop Extinction
Ratio Meter
ERM2F2 Fiber Adapter to Connect Narrow-Key FC/PC Connectors to the ERM2xx Benchtop Extinction
Ratio Meter
ERM2A Fiber Adapter to Connect Wide-Key FC/APC Connectors to the ERM2xx Benchtop Extinction
Ratio Meter
ERM2A2 Fiber Adapter to Connect Narrow-Key FC/APC Connectors to the ERM2xx Benchtop Extinc-
tion Ratio Meter
ERM2L Fiber Adapter to Connect LC/PC Connectors to the ERM2xx Benchtop Extinction Ratio Meter
ERM2S Fiber Adapter to Connect SC/PC Connectors to the ERM2xx Benchtop Extinction Ratio Meter

Page 4 MTN033660-D02
ERM2xx Series Extinction Ratio Meter Chapter 4 Getting Started
Chapter 4 Getting Started
4.1 Parts List
Please inspect the shipping container for damage. Please do not cut through the cardboard, as the box
might be needed for storage or returns.
If the shipping container appears to be damaged, keep it until you have inspected the contents for
completeness and tested the ERM2xx device mechanically and electrically.
Verify that you have received the following items within the package:
1. ERM200, ERM210, or ERM220Extinction Ratio Meter
2. USB 2.0 Cable Type A-B, 2 m
3. Region-Specific Power Cord
4. Test Report
5. Quick Reference
Chapter 5 Operating Instructions
The ERM2xx modules utilize a rotating polarizer followed by a photodiode for light detection to provide
fast and accurate measurements of the polarization extinction ratio (PER) of PM fibers. Additionally,
the polarization angle and the power of the input light beam is measured.
To set up the ERM2xx module, please read the chapter Setup.
The chapter Direct Operation explains how to run the ERM2xx polarization extinction ratio meter on the
device via the display and control knobs.
Running an ERM2xx module remotely via USB requires custom-made software. Thorlabs provides the
necessary drivers for LabVIEW™ and C. Please see the chapter Remote Operation via Custom Software
for more information.
Fiber Connector Adapters
To accommodate for the use of the ERM2xx modules with different PM fiber connectors, Thorlabs of-
fers 6 different adapters for the connectors noted in parentheses: ERM2F (Wide-Key FC/PC), ERM2F2
(Narrow-Key FC/PC), ERM2A (Wide-Key FC/APC), ERM2A2 (Narrow-Key FC/APC), ERM2L (LC/PC), and
ERM2S (SC/PC). These adapters, which are not included with the extinction ratio meter, can be moun-
ted to the ERM2xx device. Please find more information in the chapter Adapter Mounting.

Rev: 1.0, 24-Jul-2023 © 2023 Thorlabs Page 5
ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
5.1 Operating Elements
ERM200, ERM210, and ERM220 outer dimensions are identical. ERM200 device is shown.
Rear Panel
5.2 Setup
1. Place the ERM2xx module such that the power cord can be easily connected and disconnected.
2. Connect the ERM2xx module to the power network using the supplied power cord.
3. Identify the fiber adapter for the ERM2xx module which matches the connector on the fiber un-
der investigation. The available Thorlabs fiber adapters for the ERM2xx series are listed in the
chapter Ordering Codes and Accessories. Please note that the adapters need to be ordered sep-
arately.
4. Screw this fiber adapter to the fiber adapter connection port on the front panel of the ERM2xx
module (see the Adapter Mounting chapter for details).
5. Connect the fiber connector or the fiber cable to the fiber adapter.
6. Adapters and fibers may also be connected or exchanged at a later point.
7. To switch on the ERM2xx module, short press the power button (<3seconds). The power button
is illuminated when the device is powered up. The following screen will appear on the display:

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ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
8. The ERM2xx module is ready for operation after a 15minute warmup period.
9. If not already done, connect the fiber adapter and optical fiber to the device.
10. Use the button MENUto get to the settings for the ERM2xx module and configure the ERM2xx
module.
5.3 Adapter Mounting
In order to measure polarization extinction ratios based of PM fibers mounted to fiber connectors,
Thorlabs offers adapters for the input port on the ERM2xx modules.
Please choose the correct adapter from the table below:
Item #
Fiber Connector Type
ERM2F
Wide-Key FC/PC
ERM2F2
Narrow-Key FC/PC
ERM2A
Wide-Key FC/APC
ERM2A2
Narrow-Key FC/APC
ERM2L
LC/PC
ERM2S
SC/PC
Mounting steps
1. Push the adapter with the side labeled "Thorlabs" onto the fiber adapter connection port.
2. Screw the locking ring on the adapter to the port to secure the connection.
3. Mount the fiber connector to the adapter on the ERM2xx device.
5.4 Direct Operation
The ERM2xx modules are controlled by three buttons on the front. The display on the front panel shows
all measurement data in various display configurations. Changes to all necessary settings can be ex-
ecuted using the control buttons and will be shown on the display.
The display features three display modes: Extinction Ration (ER) Measurement View, Power View, and
Settings View. The actual measurement data are displayed in the ER Measurement View. The Power
View shows the optical input power in dBm or Watt, and the wavelength in nm. In the Settings View,

Rev: 1.0, 24-Jul-2023 © 2023 Thorlabs Page 7
ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
measurement parameters can be modified and system information will be shown. The button MENU is
used to get to the Settings View.
5.4.1 ER Measurement View
The ER Measurement View shows the results of the polarization extinction ratio.
The ERM2xx module will initially be in the ER Measurement View. To switch to the Measurement View
from the menu, push the MENU button. To go to the Measurement View from the Power View, use the
rotary knob.
Three different datasets are available for display in the ER Measurement View, selected via Mode:
1. ERdisplays the currently measured polarization extinction ratio in dB and the current misalignment
angle in degrees. The measured ER is displayed when the ER was selected as Mode in the Settings
View. Press the MENU button to go to the Settings View, select mode by turning the knob and press
the rotary knob until the Mode is ER (not ERmin or ERmax):
2. ERmin shows the minimum extinction ratio in dB since the last ERmin-monitor reset was performed.
It also shows the corresponding misalignment angle in degrees:
To get to the ERmin mode, go to the Settings View and select ER_min from the mode parameter as
described above.
To redetermine the minimum extinction ratio, press the MENU button after selecting the ERmin
mode:
Then press RETURN. The minimum ER value measured at that moment is then displayed in the
ERmin display.
3. ERmax shows the maximum extinction ratio in dB since the last ERmax-monitor reset was per-
formed. It also shows the corresponding misalignment angle in degrees:

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ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
To get to the ERmax mode, go to the Settings View and select ER_max from the mode parameter as
described above.
To redetermine the maximum extinction ratio, press the MENU button after selecting the ERmax
mode:
Then press RETURN. The maximum ER value measured at that moment is then displayed in the
ERmax display.
5.4.2 Power View
The Power View shows the optical input power in Watt or dBm for the wavelength selected in the Set-
tings View.
To go to the Power View, turn the rotary knob from the ER Measurement View.
The units can be set in the Settings View under Power Unit.
Press the MENUbutton to show the Settings View.
5.4.3 Settings View
Access the ERM2xx device settings via the menu in the Settings View by pressing the button MENU.

Rev: 1.0, 24-Jul-2023 © 2023 Thorlabs Page 9
ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
To switch between parameters, turn the rotary navigation and control knob. Press this knob to select
the parameter, show the subpage for the selected parameter, or confirm the selection. Use the rotary
knob to change parameter values. Press the button MENU again to go back to the previously shown
Measurement View or Power View.
The settings listed below can be changed.
1. Mode to choose between ER, ERmin, or ERmax
2. Wavelength for the wavelength of interest
3. Averaging: The ERM2xx devices acquire 10 samples per second. With AVERAGING, up to 30 samples
can be averaged for the display values. A higher AVERAGING value will result in lower display rate.
The AVERAGING value has no effect on the measurement data transferred by the remote interface.
4. Power Unit to choose the unit for the Power View
5. Remote: The ERM2xx devices can be controlled remotely via custom-made software. Please see the
chapter Remote Operation via Custom Software.
6. System Info shows system information and parameters.
Press the button MENU to return to the Settings View.
5.4.4 Monitor Out Port
The monitor output port (BNC) provides the measured PER as voltage signal between 0V to 5 V (High-Z,
Conversion Factor 0.1V/dB). This is convenient for active alignment of PM fibers. The BNC Monitor Out
connector is compatible with Thorlabs Vytran® PMFusion Splicers.
5.5 Remote Operation via Custom Software
The ERM2xx Series of ER meters can be controlled remotely by a host computer with custom-made soft-
ware. Connection to the computer is established by the USB 2.0 connector and the included USB cable
with a male type ‘A’ connector at the PC side and a type ‘B’ connector on the instrument side.
In order to generate custom-made software to control the ERM2xx module remotely, a specific instru-
ment driver and some tools for use in different programming environments are required. The driver
and tools are installed to your computer during the installation of the driver and cannot be found in the
installation package folder.
The driver package can be downloaded from the website via the Driver Package tab on the ERM2xx Ser-
ies website:
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=15943

Page 10 MTN033660-D02
ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
In this section the location of drivers and files required for programming in different environments are
given for installation under Windows 8.1, Windows 10(32and 64 bit) and Windows 11 (32and 64-bit).
Note
The ERM2-Series driver contains 32-bit and 64-bit versions.
In 32-bit systems, only the 32-bit components are installed to
C:\Program Files\...
In 64-bit systems the 64-bit components are being installed to
C:\Program Files\...
while 32-bit components can be found at
C:\Program Files (x86)\...
Please find a summary of what files are required for particular programming environments in the table
below
Programming environment
Necessary files
C, C++, CVI
*.h (header file)
*.lib (static library)
C#
.net wrapper dll
LabView
*.fp (function panel) and NI VISA instrument driver
Beside that, LabVIEW™ driver vi's are provided with the *.llb container
file.
Note LabVIEW™ drivers and components are installed only if a
LabVIEW™ installation was recognized.
Note:
All above environments require also the VXIpnp Instrument Driver dll!
During installation, a system environment variable VXIPNPPATH for including files is created. It con-
tains the information where the drivers are installed to, usually to C:\Program Files\IVI
Foundation\VISA\WinNT\.
In the next sections the locations of above files are described in detail.
5.5.1 32-bit Operating System
Note
According to the VPP6 (Rev6.1) Standard the installation of the 32 bit VXIpnp driver includes both the
WINNT and GWINNT frameworks.
VXIpnp Instrument driver:
C:\Program Files\IVI Foundation\VISA\WinNT\Bin\TLERM200_32.dll
Note
This instrument driver is required for all development environments!
Header file
C:\Program Files\IVI Foundation\VISA\WinNT\include\TLERM200.h

Rev: 1.0, 24-Jul-2023 © 2023 Thorlabs Page 11
ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
Static Library
C:\Program Files\IVI Foundation\VISA\WinNT\lib\msc\TLERM200_32.lib
Function Panel
C:\Program Files\IVI Foundation\VISA\WinNT\TLERM200\TLERM200.fp
Online Help for VXIpnp Instrument driver:
C:\Program Files\IVI Founda-
tion\VISA\WinNT\TLERM200\Manual\TLERM200.html
NI LabVIEW™ driver
The LabVIEW™ Driver is a 32-bit driver and compatible with 32bit NI- LabVIEW™ versions 8.5 and higher
only.
C:\Program Files\National Instruments\LabVIEW xxxx\Instr.lib\TLERM200\
TLERM200.llb
(LabVIEW™ container file with driver vi's and an example. "LabVIEW xxxx" stands for actual LabVIEW™
installation folder.)
.net wrapper dll
C:\Program Files\Microsoft.NET\Primary Interop Assemblies…
…\Thorlabs.ERM200_32.Interop.dll
C:\Program Files\IVI Foundation\VISA\VisaCom\…
…\Primary Interop Assemblies\Thorlabs.ERM200_32.Interop.dll
Example for C
Project file:
C:\Program Files\IVI Foundation\VISA\WinNT\TLERM200\Examples\CVI C
Sample\sample.prj
Source file:
C:\Program Files\IVI Foundation\VISA\WinNT\TLERM200\Examples\CVI C
Sample\sample.c
Example for C#
Solution file:
C:\Program Files\IVI Foundation\visa\WinNT\TLERM200\Examples\MS VS
2012 CSharp Demo\Thorlabs.ERM200.CSharp_Sample.sln
Project file:
C:\Program Files\IVI Foundation\visa\WinNT\TLERM200\Examples\MS VS
2012 CSharp Demo\Thorlabs.ERM200.CSharp_Sample.csproj
Example for LabVIEW™
C:\Program Files\National Instruments\LabVIEW xxxx\In-
str.lib\TLERM200\TLERM200.llb

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ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
(LabVIEW™ container file with driver vi's and an example. "LabVIEW xxxx" stands for actual LabVIEW™
installation folder.)
5.5.2 64-bit Operating System
Note
According to the VPP6 (Rev6.1) Standard the installation of the 64-bit VXIpnp driver includes the
WINNT, WIN64, GWINNT and GWIN64 frameworks. This means that the 64-bit driver includes the 32-bit
driver as well.
In case of a 64-bit operating system, 64-bit drivers and applications are installed to
C:\Program Files\...
while the 32-bit files - to
C:\Program Files (x86\...
Below, both installation locations are listed.
VXIpnp Instrument driver:
C:\Program Files (x86)\IVI Foundation\visa\WinNT\Bin\TLERM200_32.dll
C:\Program Files\IVI Foundation\VISA\Win64\Bin\TLERM200_32.dll
C:\Program Files\IVI Foundation\VISA\Win64\Bin\TLERM200_64.dll
Note
This instrument driver is required for all development environments!
Header file
C:\Program Files (x86)\IVI Foundation\visa\WinNT\Include\TLERM200.h
C:\Program Files\IVI Foundation\visa\WinNT\Include\TLERM200.h
Static Library
C:\Program Files (x86)\IVIFoundation\visa\WinNT\lib\msc...
...\TLERM200_32.lib
C:\Program Files (x86)\IVIFoundation\visa\WinNT\Lib_x64\msc...
...\TLERM200_64.lib
C:\Program Files\IVI Foundation\VISA\Win64\Lib_x64\msc\TLERM200_64.lib
Function Panel
C:\Program Files (x86)\IVI Foundation\visa\WinNT\TLERM200\TLERM200.fp
Online Help for VXIpnp Instrument driver:
C:\Program Files (x86)\IVI Founda-
tion\VISA\WinNT\TLERM200\Manual\TLERM200.html
NI LabVIEW™ driver
The LabVIEW™ Driver supports 32bit and 64bit NI-LabVIEW2009 and higher.
C:\Program Files\National Instruments\LabVIEW xxxx\Instr.lib\TLERM200…
…\TLERM200.llb
C:\Program Files (x86)\National Instruments\LabVIEW xxxx\In-
str.lib\TLERM200\TLERM200.llb
(LabVIEW™ container file with driver vi's and an example. "LabVIEW xxxx" stands for actual LabVIEW™
installation folder.)

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ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
.net wrapper dll
C:\Program Files (x86)\Microsoft.NET\Primary Interop Assemblies…
…\Thorlabs.ERM200_32.Interop.dll
C:\Program Files (x86)\Microsoft.NET\Primary Interop Assemblies…
…\Thorlabs.ERM200_64.Interop.dll
C:\Program Files (x86)\IVI Foundation\VISA\VisaCom\…
…\Primary Interop Assemblies\Thorlabs.ERM200_32.Interop.dll
Example for LabView™
C:\Program Files\National Instruments\LabVIEW xxxx\Instr.lib\XXXX…
…\TLERM200.llb
(LabVIEW™ container file with driver vi's and an example. "LabVIEW xxxx" stands for actual LabVIEW™
installation folder.)

Page 14 MTN033660-D02
ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
5.6 Operating Principle
The ERM2xx models are based on a rotating polarizer which transmits light depending on the transmis-
sion axis of the polarizer and the polarization of the analyzed light. A photodiode positioned behind
the rotating polarizer quantifies the transmitted light. Thus, whenever the analyzed light is linearly po-
larized and the transmission axis of the rotating polarizer is oriented parallel to the polarization axis, a
peak in optical power is detected. The higher the degree of polarization (DOP) of the analyzed light,
the lower the minimum polarization extinction will be.
In theory, if the input light is completely linearly polarized and the DOP is 100%, the measured photo
current is sinusoidal with its minimum at zero. If the minimum is not equal to zero, it might be due to
an elliptical input polarization or due to a DOP less than 100%. This occurs when the light has an unpo-
larized contribution. Aside from the DOP, other factors may influence the measurement data, such as
dark current or noise of the detection system.
Circularly polarized light with a DOP of 100% would result in a DC photo current in the ERM2xx module.
A purely unpolarized input light would also generate a DC photo current.
The following table shows the measured ER value in relation to the DOP assuming an ideal linear polar-
ization.
DOP [%]
90.0
98.0
99.0
99.8
99.9
99.94
99.98
99.99
99.998
PER [dB]
12.8
20.0
23.0
30.0
33.0
35.0
40.0
43.0
50.0
If the DOP posts a challenge in a particular PER measurement application, a more complex measure-
ment system like Thorlabs' Polarization Measurement System PAX1000Series is required.
PERand PM fibers
As long as the linearly-polarized light of a broadband source travels along the slow (or fast) axis the po-
larization is maintained and the ERM2xx module will show a high PER. If the linearly-polarized light is
not coupled into one of the main axes of the PMfiber the linearly-polarized light is separated into two
parts. One is traveling along the fast axis and the other along the slow axis. Both parts will travel with
different speeds. Depending on the birefringence of the fiber, its length, and the induced stress (for
example by bending or temperature), the output polarization is not predictable and can vary over time.
Furthermore, the birefringence is wavelength dependent. The output of each wavelength of the spec-
trum of the broadband source will be different. This leads to a certain degree of depolarization of the
light coupled into the fiber and leads to a lower extinction ratio measured by the ERM2xx module.
Light with an elliptical polarization or linearly-polarized light which is not parallel to one of the main
axis will not preserve its polarization state along the fiber.
5.7 Applications
Measurement setups and procedures differ depending on the task. For example, the requirements for
testing the coupling of linearly-polarized light into a main axis of a PM fiber and the alignment of a
laser diode to a PM fiber are different, and differ again from the requirements for testing a PM fiber
patch cable.
This chapter suggests application procedures for widely used tasks.
For the cases described below, we assume perfect optical elements.

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ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
5.7.1 Light Source Considerations
One common application is the optimization of the PMfiber orientation to best maintain the polariza-
tion of light.
A key factor is the light source. A broadband source like a source using amplified spontaneous emission
(ASE) or an SLD will simplify the alignment procedure compared to a narrowband source like a DFB
laser.
Narrow bandwidth light source (DFB laser)
Light emitted from a narrow bandwidth laser light source is coherent and can result in unstable meas-
urement results and an apparent, artificial contribution to the PER.
In many cases, it is not sufficient to simply measure a current PER value to characterize the quality of
the PMfiber alignment because the output polarization, as measured by the extinction ratio meter, can
be linear even when a misaligned linear polarization or an elliptical polarization was entered into the
input. While misaligned linear polarization or other contributions to the transmitted apparently polar-
ized light will be eliminated when a fiber is stressed (mechanically or by temperature), linearly-polar-
ized light transmitted via amain axis will not change its polarization. Therefore, a conservative PER can
be determined when the PMfiber is under stress.
An easy way to determine the ERmin is to stress the fiber by pulling it gently or with increased temper-
ature. Stress is induced and the PER will vary while the polarization of the light in the main axis is main-
tained. This results in a very conservative extinction ratio, the ERmin.
SLD and ASE Source
Instead of a laser diode, an SLD(super-luminescent diode) or an ASE may be used as a light source.
Broadband sources emit light with unknown state of polarization. Therefore, light emitted from the
broadband source needs to be polarized with the help of a polarizer prior to fiber input. It is recom-
mended to mount the polarizer with its transmission axis vertical to the base plate, between the light
source and the PMfiber.
The light is fed into the slow axis of the PMfiber if the slow axis is orientated to the connectors key and
the key is vertical aligned.
5.7.2 Aligning a Laser Diode to a PM Fiber
To align a laser diode to a PM fiber, the user needs to take the coherent nature of laser light into ac-
count, which adds an artificial contribution to the PER. It is therefore not sufficient to optimize the cur-
rent extinction ratio (ER). Additionally, as described above, the lowest extinction ratio (ERmin) should
be determined when the fiber is under stress to reduce artificial polarized light contributions. This will
result in a conservative ERmin value with the optimal PMfiber orientation.
The alignment of a laser diode to a PMfiber can be done in the following way:
1. The output connector of the fiber is entered into the fiber adapter on the connection port of the
ERM2xx model and the unit is switched on.
2. Toggle to the ER display to receive the actual ER value. Press the MENU button to go to the Settings
View, select Mode by turning the knob and press the rotary knob until the Mode is ER (not ERmin or
ERmax).
3. Rotate the PM fiber relative to the laser diode until the displayed ER value is at a peak. To receive
more stable readings, increase averaging. Rotate the fiber only slightly relative to the laser diode.
4. To determine and set the ERmin value, change to the ERmin mode.

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ERM2xx Series Extinction Ratio Meter Chapter 5 Operating Instructions
a. Go to the Settings View and select ER_min from the Mode parameter.
b. To redetermine the minimum extinction, press the RETURN button after selecting the ERmin
mode. ERmin is updated whenever a lower value is measured.
c. Repeat the procedure while stressing the fiber mechanically or with temperature.
5. The orientation of the PMfiber can be optimized by a trial and error method. Rotate the fiber relat-
ive to the laser diode in one direction, however only slightly and slower than in the crude first ad-
justment (3). The ERmin will be saved. Repeat steps 4b and 4c stepwise, rotating the fiber slightly
and putting it under stress until the ERmin peaks.
Note
The ERM2xx modules cannot distinguish between the fast and slow axis of a PM fiber. A pre-adjust-
ment to the desired main axis is required to align the device under test (DUT) to the slow (or fast) axis
of the PMfiber.
5.7.3 Aligning a PM Fiber Patch Cable
This section describes how to use the ERM2xx module to align a PMfiber patch cable.
For this, Thorlabs recommends using an SLD or ASE as a light source rather than a laser diode.
The Extinction Ratio measurement of a PMfiber with an SLDcan be done in the following way:
1. The output connector of the fiber is entered into the fiber adapter on the connection port of the
ERM2xx model and the unit is switched on.
2. Connect the SLD to the input of the fiber bench with the polarizer.
3. Connect the input of the PMfiber to the output of the fiber bench.