THORLABS EO-PM-NR-Cx User manual
EO-PM-NR-Cx
EO-PM-R-20-Cx
Electro-Optic Phase
Modulator
Operating Manual
Electro-Optic Phase Modulator
Page 1 15952-D02 Rev.B, 1/26/2012
Table of Contents
Chapter 1 Description .........................................................................2
1.1. Overview ...................................................................2
1.2. EO Amplitude Modulator Versions..............................2
1.3. Standard Features......................................................3
1.4. EO-PM Specifications .................................................3
Chapter 2 Setup ...................................................................................5
2.1. Unpacking .................................................................5
2.2. Generating RF Sidebands ...........................................5
Chapter 3 Photorefractive Limits.......................................................8
Chapter 4 Cleaning and Maintenance................................................9
4.1. Cleaning the Optics ....................................................9
4.2. Cleaning the Modulator Housing ................................9
Chapter 5 Mechanical Drawings ......................................................10
Chapter 6 Warranty Information.......................................................11
6.1. General Product Warranty .......................................11
6.2. Opto-Mechanics.......................................................11
6.3. Optical Tables and Breadboards ...............................11
6.4. Lasers and Imaging Systems.....................................11
6.5. Opto-Electronics, Control Electronics, Optics, and Non-
Positioning Product Lines..........................................................11
6.6. Warranty Exclusions.................................................12
Chapter 7 Regulatory ........................................................................13
7.1. Waste Treatment is Your Own Responsibility ............13
7.2. Ecological Background .............................................13
Chapter 8 Thorlabs Worldwide Contacts ........................................14
Chapter 1: Description
Page 2
Chapter 1 Description
1.1. Overview
The electro-optic phase modulator (EO-PM) consists of an electro-optic crystal,
lithium niobate, packaged in a compact housing with an RF input connector. By
applying an appropriate voltage to the RF input, a corresponding change in the
extraordinary refractive index will occur. If the optical input is both linearly
polarized and aligned with the extraordinary axis of the modulator crystal, the
output will undergo a pure phase shift with no change in the state of polarization.
This effect is utilized in applications where only a phase shift is required (i.e.,
generating RF sidebands and Mach Zhender interferometers).
The extraordinary axis (the crystal Z-axis or optic axis) is oriented vertically with
respect to the modulator package. With linearly polarized input light, the angle of
the input polarization with respect to the optic axis determines how the output will
be affected: When the input polarization is vertically aligned, a pure phase shift
will occur. If the input polarization is horizontal, a pure phase shift will also occur
but with approximately 30% less efficiency than for vertical polarization (r13/r33 =
30% for Lithium Niobate). If the input polarization is at 45, the output polarization
will undergo a change from linear to elliptical. In this mode, the modulator can be
considered an electronically tunable waveplate.
1.2. EO Phase Modulator Versions
Thorlabs offers the EO phase modulators in two basic versions:
1. DC-coupled Broadband Version: The electro-optic crystal is directly
coupled to the RF modulation input connector, allowing the full
bandwidth of the crystal to be utilized. The broadband version can be
driven from DC up to the frequency limit of the RF driver (Note: The
external driver must be capable of driving the capacitive load of the
crystal).
2. High Q Resonant Mode Modulator: A high Q tank circuit is used to
boost the RF input voltage up to the high voltage needed by the EO
crystal. An impedance matching network transforms the reactive crystal
load to a 50 input to allow for easy matching to standard RF drivers
and function generators.
Note: By definition, high Q circuits have a narrow operating bandwidth. The
resonant EO modulators have a typical operating bandwidth that is 5% of the
center frequency. Therefore, the operating frequency must be specified at time
of purchase.
Electro-Optic Phase Modulator
Page 3 15952-D02 Rev.B, 1/26/2012
1.3. Standard Features
Broadband DC coupled and High Q Resonant models
MgO doped Lithium Niobate crystal
Standard Broadband AR coatings cover 400 to 1650 nm range
2 mm diameter clear aperture
SMA RF modulation input connector
DC to 100 MHz
Flange with thru holes on housing for secure mounting
#1/4-20 and #8-32 tapped mounting holes on bottom
Custom OEM versions available
1.4. EO-PM Specifications
Specification
Value
Modulator Crystal
MgO Doped Lithium Niobate
(LiNbO3)
Wavelength Range
C1
600 to 900 nm
C2
900 to 1250 nm
C3
1250 to 1650 nm
C4
400 to 600 nm
Clear Aperture
2 mm diameter
Input Connector
SMA Female
Halfwave Voltage, V, Non-Resonant
135 V @ 633 nm (See Figure
1)
Halfwave Voltage, V, Resonant
15 V @ 633 nm
Input Capacitance, Non-Resonant
14 pF (typical)
Input Impedance, Resonant
50 ohms
Maximum RF Input Power, Resonant
3 W (35 Vpp)
Maximum Optical Power Density
2 W/mm2@ 532 nm
4 W/mm2@ 1064 nm
Chapter 1: Description
Page 4
0
50
100
150
200
250
300
350
400
450
400 600 800 1000 1200 1400 1600
Half-Wave Voltage
Wavelength (nm)
EO-PM Halfwave Votage vs. Wavelength
Non-Resonant
Resonant
Figure 1 Halfwave Voltage
Electro-Optic Phase Modulator
Page 5 15952-D02 Rev.B, 1/26/2012
Chapter 2 Setup
WARNING
Do not remove cover. High voltages are used to drive the crystals. Contact
with these high voltages may be harmful to the user.
2.1. Unpacking
The modulator is shipped form the factory ready to be placed into your setup.
Carefully unpack the modulator and inspect the optics by looking through the
aperture. If the modulator is shipped with protective tape over the optical
apertures, it will need to be removed prior to operation.
2.2. Generating RF Sidebands
An EO phase modulator is ideal for generating RF sidebands on top of a laser
line. By applying a sinusoidal varying RD drive voltage, the phase of the optical
signal will have a time varying sinusoidal modulation at the same frequency as
the modulating signal. This phase modulation will result in a frequency
modulation of the optical signal.
If the frequency modulated signal is viewed with a spectrum analyzer (i.e., with
Thorlabs Scanning Fabry-Perot Interferometer), a series of sidebands can be
easily observed. These sidebands are an infinite series with each pair of
sidebands spaced symmetrically about the fundamental with a separation equal
to a multiple of the modulation frequency (i.e. with a laser operating at a
fundamental of fo, and a modulation frequency of fm, the first pair of side bands
will be at fo± fm, the second pair of sidebands will be at fo± 2*fm, etc.).
The amount of energy transferred from the fundamental to the nth sideband with
a phase modulation depth of radians is described by the square of the Bessel
function of order n, Jn()2. Figure 2 on page 6 shows the relative power of the
fundamental and the first three sidebands as a function of the phase modulation
depth.
Chapter 2: Setup
Page 6
Figure 2 Sideband Power Versus Phase Shift
Note: At a depth of about 2.4 rad, almost all of the energy is transferred from the
fundamental to the sidebands.
Figure 3 Typical Setup for Sideband Generation
Showing FM Sidebands
Thorlabs Fabry-Perot
NOVA PHASE
Electro-Optic
Phase Modulator
Laser
Glan Thompson
Polarizer
EO Phase Modulator
RF Drive Signal
Interferometer
Spectrum Analyzer Output
THORLABS
Electro-Optic
Phase Modulator
Electro-Optic Phase Modulator
Page 7 15952-D02 Rev.B, 1/26/2012
Sideband Generation Example: Figure 4 below is an actual oscilloscope trace
from the output of a scanning Fabry-Perot spectrum analyzer. The modulator
was a resonant mode EO-PM operating at 30 MHz and being driven from 8 Vpeak
sine wave.
Note the suppression of the fundamental (center band) indicating a very good
depth of modulation (2.1 rad).
Figure 4 Sideband Generation Sample
Chapter 3: Photorefractive Limits
Page 8
Chapter 3 Photorefractive Limits
Lithium Niobate, LiNbO3, has an optical transparency range from 320 nm to over
5 µm and can withstand pulsed power densities up to 1 MW/cm2. However, short
wavelength operation is limited by photorefractive effects which lead to color
center formation and progressively increasing absorption. Photorefractive
damage is noted by increase scattering and absorption in the optical path along
with gray appearance in the crystal (gray tracking).
Photorefractive limits are a concern in the visible region (400 –700 nm)
particularly with frequency- doubled lasers.
The lithium niobate crystals in Thorlabs’EO modulators are MgO-doped for
increased resistance to photorefractive damage.
Electro-Optic Phase Modulator
Page 9 15952-D02 Rev.B, 1/26/2012
Chapter 4 Cleaning and Maintenance
Under normal operating conditions, the modulator needs very little, if any
maintenance.
4.1. Cleaning the Optics
The modulator crystal is recessed inside the housing and under normal
conditions, the crystal faces should not need cleaning. If necessary, use a gentle
stream of compressed air (dry nitrogen under low pressure or a can of
compressed air made specifically for cleaning optics).
WARNING
Damage may result from excessive cleaning air pressure or if condensation is
allowed to build up from using a stream of compressed air from an inverted
can.
4.2. Cleaning the Modulator Housing
The housing can be wiped clean with a lint free rag wetted with propanol or a
commercial window cleaner. Do not soak the housing –it is not watertight and
any moisture introduced inside the modulator may cause condensation problems.
Chapter 5: Mechanical Drawings
Page 10
Chapter 5 Mechanical Drawings
Electro-Optic Phase Modulator
Page 11 15952-D02 Rev.B, 1/26/2012
Chapter 6 Warranty Information
6.1. General Product Warranty
Thorlabs warrants that all products sold will be free from defects in material and
workmanship, and will conform to the published specifications under normal use
and service when correctly installed and maintained.
6.2. Opto-Mechanics
Lifetime Warranty: Thorlabs offers a lifetime warranty on all opto-mechanical
components. Thorlabs will repair or replace any opto-mechanical product which
after evaluation has failed to perform in the above conditions.
6.3. Optical Tables and Breadboards
Lifetime Warranty: We provide a lifetime guarantee that all of our passively
damped optical tables and breadboards will meet all originally stated
performance specifications under normal use and proper handling. We
additionally guarantee that all our table tops and breadboards, both active and
passive, will be free from defects in workmanship, including de-lamination of the
skins under normal use and handling.
6.4. Lasers and Imaging Systems
Thorlabs offers a one year warranty on all lasers and imaging systems, with the
exceptions of laser diodes. Some products are warranted for the number of hours
specified in the operating manual of each laser.
6.5. Opto-Electronics, Control Electronics, Optics, and
Non-Positioning Product Lines
Thorlabs offers a two year warranty on the above mentioned product lines,
providing normal use and maintenance of the products and when properly
handled and correctly installed.
Thorlabs shall repair or replace any defective or nonconforming product as
detailed above. We ask that the buyer contact Thorlabs for a Return Material
Authorization number (RMA#) from our Customer Service/Returns department in
order to most efficiently process the return and/or repair.
Products returned for repair that are not covered under warranty, a Thorlabs
standard repair charge shall be applicable in addition to all shipping expenses.
This repair charge will be quoted to the customer before the work is performed.
Chapter 6: Warranty Information
Page 12
6.6. Warranty Exclusions
The stated warranty does not apply to products which are (a) specials,
modifications, or customized items (including custom patch cables) meeting the
specifications you provide; (b) ESD sensitive items whose static protection
packaging has been opened; (c) items repaired, modified, or altered by any party
other than Thorlabs; (d) items used in conjunction with equipment not provided
by, or acknowledged as compatible by Thorlabs; € subjected to unusual physical,
thermal, or electrical stress; (f) damaged due to improper installation, misuse,
abuse, or storage; (g) damaged due to accident or negligence in use, storage,
transportation, or handling.
Electro-Optic Phase Modulator
Page 13 15952-D02 Rev.B, 1/26/2012
Chapter 7 Regulatory
As required by the WEEE (Waste Electrical and Electronic Equipment Directive)
of the European Community and the corresponding national laws, Thorlabs offers
all end users in the EC the possibility to return “end of life” units without incurring
disposal charges.
This offer is valid for Thorlabs electrical and electronic equipment:
Sold after August 13, 2005
Marked correspondingly with the crossed out
“wheelie bin” logo (see right)
Sold to a company or institute within the EC
Currently owned by a company or institute
within the EC
Still complete, not disassembled and not
contaminated
As the WEEE directive applies to self-contained
operational electrical and electronic products, this end of
life take back service does not refer to other Thorlabs products, such as:
Pure OEM products, that means assemblies to be built into a unit by the
user (e.g. OEM laser driver cards)
Components
Mechanics and optics
Left over parts of units disassembled by the user (PCB’s, housings etc.).
If you wish to return a Thorlabs unit for waste recovery, please contact Thorlabs
or your nearest dealer for further information.
7.1. Waste Treatment is Your Own Responsibility
If you do not return an “end of life” unit to Thorlabs, you must hand it to a
company specialized in waste recovery. Do not dispose of the unit in a litter bin
or at a public waste disposal site.
7.2. Ecological Background
It is well known that WEEE pollutes the environment by releasing toxic products
during decomposition. The aim of the European RoHS directive is to reduce the
content of toxic substances in electronic products in the future.
The intent of the WEEE directive is to enforce the recycling of WEEE. A
controlled recycling of end of life products will thereby avoid negative impacts on
the environment.
Wheelie Bin Logo
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Page '5HY%
Chapter Thorlabs Worldwide Contacts
For technical support or sales inquiries, please visit us at
www.thorlabs.com/contact for our most up-to-date contact information.
USA, Canada, and South America
Thorlabs, Inc.
Europe
Thorlabs GmbH
France
Thorlabs SAS
Japan
Thorlabs Japan, Inc.
UK and Ireland
Thorlabs Ltd.
Scandinavia
Thorlabs Sweden AB
Brazil
Thorlabs Vendas de Fotônicos Ltda.
China
Thorlabs China
www.thorlabs.com
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