THORLABS MX10B Series User manual

MX10B Series
12.5 Gb/s Optical Transmitters
MX40B Series
40 Gb/s Optical Transmitters
User Guide

MX10B, MX40B Series of Optical Transmitters
Table of Contents
Chapter 1Introduction .............................................................................................................................................................. 1
1.1Description ..................................................................................................................................................... 1
1.2Parts List ........................................................................................................................................................ 1
1.3Block Diagram................................................................................................................................................ 2
1.4Front and Back Panel Overview ................................................................................................................... 3
Chapter 2Safety......................................................................................................................................................................... 5
2.1Precautions .................................................................................................................................................... 6
Chapter 3Quick Start Guide ..................................................................................................................................................... 7
3.1Hardware Set Up ............................................................................................................................................ 7
3.2Controls on the Home Page .......................................................................................................................... 8
3.3System Wavelength Setting .......................................................................................................................... 9
3.4Controls on the Settings Pages .................................................................................................................. 10
Chapter 4Operating Instructions ........................................................................................................................................... 11
4.1The Modulator Transmission Function ...................................................................................................... 11
4.2Control Loop Diagram ................................................................................................................................. 11
4.3Bias Settings Page ...................................................................................................................................... 12
4.3.1Quadrature Mode .............................................................................................................................. 13
4.3.2Peak Mode ........................................................................................................................................ 15
4.3.3Null Mode .......................................................................................................................................... 15
4.3.4Manual Mode .................................................................................................................................... 16
4.4Amplifier Settings Page .............................................................................................................................. 18
4.5Variable Optical Attenuator Settings Page ................................................................................................ 20
4.6Laser Settings Page .................................................................................................................................... 21
4.7Load Page .................................................................................................................................................... 22
4.8Menu Page .................................................................................................................................................... 23
4.8.1Display and Sound Settings Page ..................................................................................................... 23
4.8.2System Information Page .................................................................................................................. 24
4.8.3Accent LED Settings Page ................................................................................................................ 24
4.8.4Thorlabs Help Page .......................................................................................................................... 25
Chapter 5Specifications ......................................................................................................................................................... 26
5.1General System Specifications .................................................................................................................. 26
5.2Power and Environmental Specifications ................................................................................................. 27
5.3Internal Control Specifications ................................................................................................................... 27
5.4Internal Amplifier Specifications ................................................................................................................ 27
5.5Internal Modulator Specifications .............................................................................................................. 27
5.6Laser Specifications .................................................................................................................................... 28
Chapter 6Control and PC Connections ................................................................................................................................. 29
6.1General Purpose I/O, RS-232, and USB Connections ............................................................................... 29
6.2The Laser Safety Interlock .......................................................................................................................... 30
Chapter 7Mechanical Drawings ............................................................................................................................................. 31
7.1MX10B Series ............................................................................................................................................... 31

MX10B, MX40B Series of Optical Transmitters
7.2MX40B Series ............................................................................................................................................... 32
Chapter 8Maintenance, Repair, and Fuses ........................................................................................................................... 33
8.1Maintenance and Repair ............................................................................................................................. 33
8.2Replacement Parts ...................................................................................................................................... 33
8.3Replacing the Main Fuse ............................................................................................................................. 34
Chapter 9Troubleshooting ..................................................................................................................................................... 35
Chapter 10Declarations of Conformity ......................................................................................................................... 36
Chapter 11Thorlabs Worldwide Contacts .................................................................................................................... 38

MX10B, MX40B Series of Optical Transmitters Chapter 1: Introduction
Rev. D, March 19, 2019 Page 1
Chapter 1 Introduction
1.1 Description
Thorlabs' MX10B and MX40B series of reference transmitters are designed for high-speed fiber optic test and measurement
applications. They are fully-integrated and user-configurable solutions based on proven lithium niobate (LiNbO3) modulator
technology driven by high-fidelity digital RF amplifiers. They are designed for digital applications, and the maximum output swing
of their limiting RF amplifiers is user-adjustable. Variable optical attenuators (VOAs) and power monitors enable completely
automatic control and stabilization of the optical output power. Transmitters in the MX10B series include an external loop-back
cable for the driver RF output and modulator RF input ports, which provides the opportunity to use an external driver, if desired.
The MX10B/MX40B, MX10B-LB/MX40B-LB, and MX10B-1310/MX40B-1310 include a tunable C-band laser, a tunable L-band
laser, and a 1310 nm fixed-wavelength laser, respectively. Both the C- and L-band laser sources are tunable on the ITU 50 GHz
grid and include a dither feature for wavelength stabilization. An external laser source, operating from 1250 nm to 1610 nm, can
also be used with all models to provide the optical input.
These instruments can be controlled in two ways. The simplest method is directly via the built-in graphical user interface (GUI)
and touchscreen. The instrument can also be operated remotely via the RS-232 or USB ports on the back panel. Remote control
is enabled using simple SCPI-type serial commands from a PC. See the remote control user guide (RCUG), which can be
downloaded from https://www.thorlabs.com/manuals.cfm, for details.
The most recent firmware and remote control software tools can be downloaded by visiting
https://www.thorlabs.com/navigation.cfm?Guide_ID=2191 and entering the Item # into the search field. Thorlabs’ technical
support can provide up-to-date information on available firmware revisions and control functions.
NOTE: This manual covers both the MX10B and MX40B series of models, as their architectures are very similar. Their
differences are clearly noted in the following sections.
1.2 Parts List
Inspect the shipping container for damage. If the shipping container seems to be damaged, keep it until you have inspected the
contents and tested the unit mechanically and electrically. Verify that you have received the following items within the package:
1. MX10B or MX40B Series Optical Transmitter Main Unit
2. Power Cord According to Local Power Supply
3. PM Loopback Fiber Optic Cable
4. SMA Loopback RF Cable (not required for MX40B series)
5. Interlock Keys
6. 2.5 mm Interlock Pin (in back panel)
7. 1.25 A 250 VAC Fuse
8. USB Type A to Type B Cable, 6' Long


MX10B, MX40B Series of Optical Transmitters Chapter 1: Introduction
Page 2 TTN048897-D02
1.3 Block Diagram
These instruments are fully integrated and contain both the laser source and the intensity modulator. The modulator is a Mach-
Zehnder configuration and will often be referred to as the MZM. All the user needs to supply is the signal source to the Amplifier
RF In port. The user can choose to use the internal laser source (via loop-back fiber) or an external laser source of their own.
The Laser In port uses PM fiber with light linearly polarized along the slow axis as shown on the front panel. Maximum input
power is 20 dBm (100 mW). In the MX10B series of transmitters, the user also has the option of using their own modulator driver
connected to the Modulator RF In port. The MX40B series does not have this option in order to preserve signal integrity. Optical
power is monitored in three places (Mon-1,-2,-3) for the purpose of enabling bias and power control. These power values are
also available at the I/O port. Mon-1 is at the Laser Input, Mon-2 is at the MZM Output, and Mon-3 is at the final Optical Output.
Figure 1 Block Diagram of the MX10B and MX40B Series


MX10B, MX40B Series of Optical Transmitters Chapter 1: Introduction
Rev. D, March 19, 2019 Page 3
1.4 Front and Back Panel Overview
Figure 2 Front Panel
Callout Description MX10B Series MX40B Series
A Touchscreen Display - -
B Adjustment Knob - -
C
Key Switch and Indicator
Lasing Disabled; Lasing
Enabled
- -
D
Grounding Jack (Banana
Connector)
Earth Ground
Banana Banana
E Laser Output PM FC/PC PM FC/PC
F Laser Input PM FC/PC PM FC/PC
G Optical Output FC/PC FC/PC
J Amplifier RF Output SMA Not Available
K Modulator RF Input SMA Not Available
L Amplifier RF Input SMA 2.92 mm
M Standby Button - -

C
D
A B
M
L
K
J
G
F
E

MX10B, MX40B Series of Optical Transmitters Chapter 1: Introduction
Page 4 TTN048897-D02
Figure 3 Back Panel
Callout Description MX10B Series MX40B Series
N I/O Port DB-15 DB-15
O Option Label - -
P RS-232 Port DB-9 DB-9
Q USB Port, Type B - -
R Laser Interlock 2.5 mm 2.5 mm
S Power Connector - -
T Fuse Tray - -
U Power Switch
Supply On; Supply Off - -
Q
P
O
N
U
R
T
S

MX10B, MX40B Series of Optical Transmitters Chapter 2: Safety
Rev. D, March 19, 2019 Page 5
Chapter 2 Safety
All statements regarding safety of operation and technical data in this instruction manual will only apply when the unit is operated
correctly. If equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be
impaired. Only with written consent from Thorlabs may changes to single components be carried out or components not supplied
by Thorlabs be used.
Warning: Risk of Electrical Shock
Before applying power to the instrument, make sure that the protective conductor of the 3 conductor mains power
cord is correctly connected to the protective earth contact of the socket outlet. Improper grounding can cause electric
shock with damage to your health or even death. The local supply voltage must be in the range specified on the back
panel, and the correct fuse must be installed in the fuse holder. If not, please replace the main fuse (see section on
instrument maintenance). Only use mains cable with sufficient current and voltage ratings for this instrument. Do not
position equipment in a way that makes it difficult for the user to operate the disconnecting device. Do not remove
covers. Refer servicing to qualified personnel.
Warning: Risk of Explosion
The instrument must not be operated in explosion endangered environments.
Warning: Laser Radiation
Avoid Exposure – Radiation emitted from apertures. Do not look into the laser
aperture while the laser is on. Injury to the eye may result. Laser should not be turned
on unless there is an optical fiber connected to the laser output port.
Caution – Use of controls or adjustments or performance of procedures other than
those specified herein may result in hazardous radiation exposure.
Caution: ESD Sensitive Component
The components inside this instrument are ESD sensitive. Take all appropriate precautions to discharge personnel
and equipment before making any connections to the unit. A front panel grounding jack is provided for connection to
a wrist strap.
Caution: Components not Water Resistant
This instrument should be kept clear of environments where liquid spills or condensing moisture are likely. It is not
water resistant. To avoid damage to the instrument, do not expose it to spray, liquids, or solvents.
Caution: Follow Intended Usage Guidelines
This product is not suitable for household room illumination.
Inputs and outputs must only be connected with shielded connection cables.
Do not obstruct the air ventilation slots in housing.
Mobile telephones, cellular phones or other radio transmitters are not to be used within the range of three meters of
this unit since the electromagnetic field intensity may then exceed the maximum allowed disturbance values according
to IEC 61326-1.

LASER RADIATION
DO NOT VIEW DIRECTLY WITH
OPTICAL INSTRUMENTS
CLASS 1M LASER PRODUCT

MX10B, MX40B Series of Optical Transmitters Chapter 2: Safety
Page 6 TTN048897-D02
2.1 Precautions
The following statement applies to the products covered in this manual, unless otherwise specified herein. The statement for
other products will appear in the accompanying documentation.
Note: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of 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
instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not
occur in a particular installation.
This product has been tested and found to comply with the limits according to IEC 61326-1 for using connection cables shorter
than 3 meters (9.8 feet).
Thorlabs is not responsible for any radio television interference caused by modifications of this equipment 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 peripheral or host devices. Failure to do so may violate FCC
and ICES rules.
This precision device should only be shipped if packed into the complete original packaging including the custom cut foam
padding. If necessary, ask for replacement packing material.

MX10B, MX40B Series of Optical Transmitters Chapter 3: Quick Start Guide
Rev. D, March 19, 2019 Page 7
Chapter 3 Quick Start Guide
3.1 Hardware Set Up
For first use, plug the main power cable into the back panel connector, and then plug the other end into an AC wall
receptacle. Flip the power switch on the back panel to the ON (I) position. The unit will now be in the “Standby” mode,
and the front panel standby button should glow amber.
Figure 4 Power Cable Port, Fuse, and Power
Switch
Figure 5 Indicator Glows Amber when Instrument
is In Standby
Attach the polarization-maintaining (PM) loopback fiber optic cable between the Laser Out and Laser In PC/FC connectors on
the front panel. Be sure to clean both ends of the fiber as described in the Maintenance Section of this manual. For the MX10B
series: attach the SMA loopback RF cable between the Amplifier RF Out and Modulator RF In SMA connectors on the front
panel. (This instruction does not apply to the MX40B series, as it does not have an Amplifier RF Out port.)
Figure 6 PM Loopback Fiber Cable Installed Figure 7 Amplifier RF Out present only on the
MX10B series of transmitters. This cable is not
installed on the MX40B transmitter series.
Insert the key into the interlock switch and turn it towards the unlock symbol ( ). This allows the laser to be turned on, but the
LASER ON indicator will not glow green until the laser is actually turned on by the touchscreen button. Turn on the unit by
pressing the amber standby button on the front panel which will then turn green to indicate the unit is fully on. The touchscreen
display will come up with a boot screen for about 5 seconds and then go to the home page. The unit will initialize in the factory
default state with all functions OFF.
Figure 8 Interlock Key Switch
Figure 9 Indicator Glows Green when Instrument is
Fully Enabled

MX10B, MX40B Series of Optical Transmitters Chapter 3: Quick Start Guide
Page 8 TTN048897-D02
3.2 Controls on the Home Page
The MX10B and MX40B series of transmitters can be fully controlled by using the resistive touchscreen display for all functions.
The screen is sensitive to the touch of a finger or a plastic stylus, and selections are made by tapping the on-screen button of
interest. In addition, the knob on the front panel can be used in place of the on-screen arrow buttons for quickly changing set-
point values. Pressing (clicking) the knob will confirm a new set-point value.
Figure 10 Home Screen Features
The Home screen (or dashboard) is organized into three main sections.
The left side contains the ON/OFF buttons for each of the main instrument functions. Tapping any of these buttons will toggle
the function on and off. The same ON/OFF functionality is also available on the individual Settings pages. The power buttons
turn green to indicate the function is ON, and turn red to indicate the function is disabled.
The central section is the main dashboard for reporting operational values of each section. Tapping the screen in this middle
area will take the user to the corresponding Settings page for each section. Note that the green dot in each of these sections
indicates the function is stable. A blinking green dot indicates the function is still stabilizing.
The right side of the screen provides access to the main utility functions of the box.
The screen shot below shows some of the common warning indicators on the HOME page. Some functions can be disabled
when the laser power is low. In this case, buttons may be disabled and warnings indicators may appear.
Figure 11 Home Screen Warnings and Indicators
Tap these buttons
to turn functions
ON or OFF
Tap in these areas
to go to the related
Settings pages.
Blue Button:
Utility Functions
Green Dot:
Stability Indicator
Power units (dBm or
mW) are set in the
VOA Settings page.
Disabled
Functions
Low Power
Warnings
Interlock
Warning

MX10B, MX40B Series of Optical Transmitters Chapter 3: Quick Start Guide
Rev. D, March 19, 2019 Page 9
3.3 System Wavelength Setting
The operational wavelength range of the MX10B and MX40B series extends from 1250 nm to 1610 nm. The three calibration
wavelengths of the power monitors, 1310 nm, 1550 nm, and 1590 nm, represent the centers of the O-band, C-band, and L-band
and provide the user with accurate power readings at or near those wavelengths.
The system wavelength should always be set to the wavelength closest to that of the laser source coupled to the Laser In
bulkhead. The instrument’s system wavelength is factory-preset to correspond to the wavelength band of the integrated laser
source. If an external laser is to be used with the instrument, the system wavelength may need to be changed. This function
exists in the Utility Menu.
From the Home screen, tap the MENU button to bring up the Utility Menu as shown.

Figure 12 Accessing the Utility Menu from the Home Screen
Then tap the System Wavelength bar as shown below to bring up the three wavelength choices. Tap the desired wavelength to
set the System Wavelength.
Figure 13 System Wavelength is Selected from the Utility Menu

Tap the MENU button to
access the Utility Menu.
Tap here to activate
wavelength selection.
Choose one of these
wavelengths.

MX10B, MX40B Series of Optical Transmitters Chapter 3: Quick Start Guide
Page 10 TTN048897-D02
3.4 Controls on the Settings Pages
The Settings pages all follow the same general design and functionality as shown in the example screen shot below. The upper
section with white letters displays the parameters that can be changed. Simply tap on the parameter of interest to highlight it,
and the controls for that parameter will be presented.
The lower section with amber letters displays selected values that are convenient to monitor on that page.
The right-hand column provides the controls for changing the values for the selected parameters. The main control knob on the
front panel can also be used to adjust and confirm selected values. The screen shots below show examples of the touch-screen
controls.
Figure 14 Controls used to Adjust and Save Values of Selected Parameters
Fields that have adjustable values will show a flag if the minimum or maximum values have been reached. These are set by
firmware at the factory.
Figure 15 MIN and MAX Flags Indicate Bounds of Adjustable Value Ranges

Tap to select parameter.
Yellow highlight will appear.
Increase value
Decrease value
Change step size
Confirm new value
Cancel any changes
Monitor area
MIN / MAX warnings
indicate that the setting
limit for a particular
parameter has been
reached.

MX10B, MX40B Series of Optical Transmitters Chapter 4: Operating Instructions
Rev. D, March 19, 2019 Page 11
Chapter 4 Operating Instructions
4.1 The Modulator Transmission Function
The Mach-Zehnder Modulator (MZM) has a repetitive transmission function with applied voltage as can be seen in the diagram
below. In order for it to work correctly, a DC bias voltage must be applied and maintained at the desired set point. The high-
frequency AC signal can then be applied to the modulator to enable the correct optical modulation of the laser beam. The most
common operating points are the peak, null, and quadrature points as shown below.
The purpose of the Bias settings is to hold the modulator at one of these chosen points. Note that a real transmission function
does not go perfectly from 0% to 100%. This is characterized by the Extinction Ratio of the modulator (Peak power / Null power).
The efficiency of the modulator is also characterized by Vπ, which is defined as the voltage necessary to change the transmission
from Null to Peak. The most linear response of the modulator is achieved by biasing it at one of the Quadrature points where
the transmission is closest to 50%. Some non-linear, frequency doubling, and phase modulation applications require biasing at
the Null or Peak.
Figure 16 Illustration of the Modulator Transmission Function
4.2 Control Loop Diagram
The following diagram shows the control loops added to the block diagram. From this picture, the user can see how the power
monitors and VOA are used to provide stability and control to the whole system. It will be helpful to refer to this diagram to gain
a better understanding of the functionality of the unit as described in the upcoming sections of the manual. Note the MX40B
series does not have the external RF loopback.
Figure 17 Control Loops Overlaid on Block Diagram

MX10B, MX40B Series of Optical Transmitters Chapter 4: Operating Instructions
Page 12 TTN048897-D02
4.3 Bias Settings Page
To get to the Bias Settings page tap the Bias monitors pane on the Home page. The Bias page contains the settings for controlling
the modulator bias and operating modes. There are four modes for MZM bias control: 1) Quadrature, 2) Peak, 3) Null, and 4)
Manual. The screen shot below is an example of how the bias settings page opens up if the controller is in the Quadrature mode.
The blue buttons enable switching between modes.
Figure 18 Bias Settings Page
Active control of the MZM bias point is essential as the modulator is temperature sensitive and will drift over time. The
Quadrature, Peak, and Null modes use a dither tone as part of a lock-in control scheme to keep the MZM bias stable. The dither
tone allows the control algorithm to track the drifting, but at the cost of decreased signal-to-noise ratio (SNR) due to the injection
of a single frequency tone into the MZM bias.
The first time you turn on the MZM Bias control, the instrument will perform a calibration routine to determine the approximate
bias voltages required for the various MZM operating points. This allows the instrument to quickly and effectively switch between
Bias modes. The user may perform this calibration anytime by pressing the Reset Auto Bias button on the right side of the Bias
Settings page. This button is not available if the Bias is off or in Manual mode.
Figure 19 Buttons to Manually Initiate Modulator Calibration Routine

Tap to select Peak Mode
Tap to select Quadrature Mode
Tap to select Null Mode
Tap to select Manual Mode
Tap to turn Bias On/Off
Tap to Reset Modulator Bias
New set points will be stored

MX10B, MX40B Series of Optical Transmitters Chapter 4: Operating Instructions
Rev. D, March 19, 2019 Page 13
4.3.1 Quadrature Mode
Quadrature is the default mode and biases the MZM at the 50% point on the MZM transmission curve (see figure). This is the
recommended mode for digital signals such as On-Off-Keying (OOK) that require a high extinction ratio. The screen-shot below
shows the parameters that can be controlled in the Quadrature mode.
Figure 20 Buttons to Select Preset and Define Custom Dither Frequencies
The bias control circuit uses an AC dither tone to stabilize the bias point of the modulator. The graphic below shows how it works:
Figure 21 Illustration Showing How Dither is Used to Stabilize Modulator Bias Point
A small AC voltage is applied to the DC bias so that the optical output is also slightly modulated. Both the amplitude and the
frequency of AC dither tone can be selected by the user. The modulated optical output is detected by a frequency and phase
sensitive detector which can then interpret whether the DC bias is at the correct level for the chosen set-point (Quad, Peak or
Null). The DC bias voltage is then continuously adjusted to maintain the correct set-point.
The frequency of the dither tone (under 10 kHz) is usually well below the low frequency cut-off for the RF signal of interest, so
it does not interfere. The dither tone can also be turned if other methods of bias control are desired (e.g. manual control, or
input/output ratio control as described later).
Select your own Dither
Frequency here.
Choose one of three preset
Dither Frequencies.

MX10B, MX40B Series of Optical Transmitters Chapter 4: Operating Instructions
Page 14 TTN048897-D02
The dither tone frequency may be changed by tapping the Dither Frequency field. Standard frequencies are available on the
blue buttons, or a custom frequency may be chosen by pressing User Define. The dither tone frequency usually has very little
effect on the accuracy of the bias control, but in some cases a different frequency may work better or be desirable depending
on the RF signal applied, or the specific application. The User Define button allows for the selection of an arbitrary frequency
between 1 kHz and 10 kHz with 10 Hz resolution.
Figure 22 Adjust, Enable, or Disable the Dither Used to Stabilize the Bias Point
The dither tone amplitude can also be adjusted to any amplitude between 20 mV and 2 V with 1 mV resolution. Higher
amplitude will typically be more stable in the presence of MZM drift and broadband RF signals, but larger dither tones also
decrease SNR. If the amplitude is too low, the MZM bias may not stay locked. Typically, a value between 300 mV and 500 mV
is a good starting point.
In applications where the highest SNR is desired, there is also the option to disable the dither tone. This allows the user to
quickly turn the dither off, perform a measurement requiring low noise, and then turn the dither back on. When the dither is
turned off, the bias is simply held at the previous bias voltage. For longer term measurements without dither, you can switch to
Manual Mode and use a constant ratio method for stabilizing the bias point. (See the Manual Mode section.)
Figure 23 Locate Bias Point on Positive or Negative Slope
The Quadrature mode also allows the user to select between two operating points by selecting the Slope field. Positive slope is
the non-inverting operating point where increasing voltage on the MZM results in increasing optical output power. Negative
slope is the inverting operating point where increasing voltage on the MZM results in decreasing optical output power. This
effectively changes the phase of the response function.

Tap here to turn Dither On/Off.
A
djust the Dither Amplitude
from this screen.
Select Positive Slope
Select Negative Slope
Tap here to change Slope.

MX10B, MX40B Series of Optical Transmitters Chapter 4: Operating Instructions
Rev. D, March 19, 2019 Page 15
4.3.2 Peak Mode
The Peak Mode adjusts the DC bias voltage so the transmission is centered at a nearby transmission maximum. In this mode
only dither frequency and amplitude settings are available. These controls and settings are the same as previously described
for the Quadrature mode.
Peak and Null modes are often used to obtain phase modulation and non-linear frequency doubling. The optical phase is 180°
shifted on opposite sides of the Null point.


Figure 24 Peak Mode Settings
4.3.3 Null Mode
The Null Mode adjusts the DC bias voltage so the transmission is centered at a nearby transmission minimum. In the Null
mode only dither frequency and amplitude settings are available. These settings are the same as previously described for the
Quadrature mode.
Figure 25 Null Mode Settings
Bias control in Peak mode;
Tap to change.
Tap here to reset the Bias
calibration and return to
Peak mode.
Bias control in Null mode;
Tap to change.
Tap here to reset the Bias
calibration and return to Null
mode.

MX10B, MX40B Series of Optical Transmitters Chapter 4: Operating Instructions
Page 16 TTN048897-D02
4.3.4 Manual Mode
The Manual mode allows the user to bias the modulator at any point of the transmission function desired. Manual mode offers
two modes of operation: 1) Constant Bias, and 2) Constant Ratio. In both of these modes, the dither function is not active, and
the controller uses different techniques to hold the bias steady.
Figure 26 Constant Bias Manual Mode Settings
Constant Bias is the most basic mode of operation and will apply a user selected DC voltage to the MZM. This can be useful
for performing brief measurements that only take a few minutes. During longer duration experiments, the MZM is more likely
to drift.
The Constant Ratio mode employs active control of the MZM bias, but without using a dither tone. As a result, it can achieve
superior SNR compared to the Quadrature mode. This mode is recommended for analog signals or higher level Pulse-
Amplitude Modulation (PAM) formats.
Constant Ratio works by holding the MZM ratio of input light (at Mon-1) to output light (at Mon-2) at a constant value (typically
at or close to Quadrature). Note that it does NOT take into account the insertion loss of the MZM. Therefore, the user must
have some knowledge of the IL between the Monitors. For example. If the modulator has an IL of 3 dB, then the I/O ratio at
maximum transmission is already 2:1. To bias the modulator at the 50% point, the ratio must be doubled to 4:1. The MZM
insertion loss is listed in the specifications.
Figure 27 Constant Ratio Manual Modes Settings
Bias control in Manual mode;
Tap here to change mode.
Tap here to adjust Bias voltage.
Tap here to select Hold mode:
Constant Bias or Constant Ratio
Tap here to manually adjust the
modulator transmission ratio in
Constant Ratio mode.
This is the ratio of modulator input
power to output power.