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Automated Bias Controller for Lithium Niobate (LiNbO3) Modulators


  • Quadrature, Peak, and Null Automated Modes
  • Ditherless and Constant Bias Modes 
  • Built-In VOA for Power Control
  • Power Calibration Points at 1310 nm, 1550 nm, and 1590 nm

Touchscreen Interface

MBX

Bias and Power Controller for External Modulators

Related Items


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MBX Bias Controller Block Diagram
Click to Enlarge

Block Diagram of the Internal Setup of the MBX Modulator Bias Controller
For additional information , see the Operation tab.

Janis Valdmanis, Ph.D. Optics
Ultrafast Optoelectronics
General Manager

We Design, Develop, and Manufacture
Equipment up to 70 GHz

Questions?

Demo Unit Requests?

Product Suggestions?

Custom or OEM Applications?

Contact Me

Features

  • Compatible with Any Fiber-Coupled LiNbO3 Intensity Modulator Operating from 1250 to 1610 nm
  • Fully Automated or Fixed-Voltage Bias Control for Intensity Modulators
    • Dithered Operation in Automated Quadrature, Peak, and Null Set Point Modes 
    • Ditherless Operation in Automated Constant Ratio Mode
    • Ditherless Operation in Fixed-Voltage (Constant Bias) Mode
  • Built-In Variable Optical Attenuator (VOA) for Automatic or Manual Power Control
  • Three Calibration Wavelengths: 1310 nm, 1550 nm, and 1590 nm
  • Control via Intuitive Touchscreen Interface or Remotely using USB or RS-232 Connections

Thorlabs' MBX Bias Controller provides complete and precise control of DC bias and optical output power for any fiber-coupled lithium niobate (LiNbO3) electro-optic intensity modulator, regardless of signal speed. The operational wavelength range of the MBX extends from 1250 nm to 1610 nm (O- through L-band), and the user may select from power calibration points at 1310 nm, 1550 nm, and 1590 nm. Whether operated in an R&D laboratory or manufacturing environment, this fully-featured modulator bias controller is ideal for use within a customized setup that uses an external laser, LiNbO3 intensity modulator, signal source, and RF amplifier.  

Several operation modes are provided. Automated bias control operation continuously adjusts the DC bias voltage to maintain the correct set point, and there are dithered and ditherless options. When operating in a dithered control mode, an adjustable dither tone with a user-selectable frequency between 1 and 10 kHz is used as a pilot tone. Each automated dithered mode biases the modulator at a different operating point (Peak, Null, or Quadrature); all operating points are referenced to the modulator transmission function described in the Operation tab. If the application requires automated, but ditherless, bias control of the modulator, Constant Ratio mode may be chosen. It is also possible to operate the MBX in the fixed-voltage and ditherless Constant Bias mode, in which a user-selected DC bias voltage is applied to the modulator. This mode can be useful for brief measurements, but its inability to track modulator drift renders it impractical for measurements longer than a few minutes. 

The MBX can be controlled in two ways. The simplest method is using the intuitive touchscreen interface, which gives the user complete control over all instrument functionality. These instruments can also be operated remotely via the RS-232 or USB ports on the back panel. The Operation tab describes graphical user interface (GUI) and user-customizable features, and we provide a remote control user guide and a remote control software tool (see the Software tab) for download.

Closely Related Items

The MBX is one of a range of LiNbO3 electro-optic modulator driver and control instruments developed by Thorlabs to meet a variety of application requirements. Our fully integrated solutions include a tunable laser and modulator in addition to the driver electronics. The key features of each instrument in the range are listed in the table at lower-left. Please contact the Ultrafast Optoelectronics Team if your application requires a driver or controller with additional customization.

The lithium niobate intensity modulators we offer are listed in the table at lower-right. Our full range of LiNbO3 modulators includes these and our phase modulators.

Modulator Drivers and All-in-One Systems
Item# Bit Rate /
Bandwidtha
Tunable Laser Internal Modulator 
(Type) 
RF Amplifier
(Type)
Bias Controller VOA
MBX N/Ab No No No Yes Yes
MX10A 12.5 Gb/s  No No Yes (Digital) Yes Yes
MX40A
40 Gb/s  No No Yes (Digital) Yes Yes
MX10B 12.5 Gb/s  Yes Yes (Intensity) Yes (Digital) Yes Yes
MX40B 40 Gb/s  Yes Yes (Intensity) Yes (Digital) Yes Yes
MX10C
12.5 Gb/s  Yes Yes (Phase) Yes (Digital) No Yes
MX40C 40 Gb/s  Yes Yes (Phase) Yes (Digital) No Yes
MX35E 35 GHz Yes Yes (Intensity) Yes (Linear) Yes Yes
MX40G 40 GHz Yes Yes (Intensity) No Yes Yes
  • Maximum Supported Digital Bit Rate or Analog Bandwidth
  • The MBX can be used with modulators of any speed or bit rate.
Fiber-Coupled LiNbO3 Intensity Modulators
Item# Freq. or Bit Rate Operating Range
LN82S-FC 9.953 Gb/s 1525 to 1605 nm
LN81S-FC 12.5 Gb/s 1525 to 1605 nm
LN05S-FC 40 Gb/s 1525 to 1605 nm
MBXa
System
Optical Input Power 
(from External Laser)
20 dBm (Maximum)
22 dBm (Absolute Maximum)
Wavelength Range 1250 to 1610 nm
Power Calibration Points 1310 nm, 1550 nm, and 1590 nm
Bias Voltage Range ±10 V
Bias Modes Quadrature (Positive and Negative Slope)
Peak
Null
Manual (Constant Ratio and Constant Bias)
Dither Frequency Rangeb 1 to 10 kHz
Dither Amplitude Rangeb 20 mV to 2 V
Automatic Mode Settling Time 1 to 5 s
Internal Optical Fiber PM Ports: PM PANDA-Style Fiber
SM Ports: SMF-28-Compatible Fiber
Internal Controlc
Power Monitor Accuracyd ±0.5 dBm 
Power Monitor Resolutiond 0.01 dBm
Power Monitor Insertion Losse 0.1 dB 
VOA Insertion Loss 0.4 dB 
VOA Response Time 1 s
Connectors
Fiber Connectorsf FC/PC, 2.0 mm Narrow Key
Bias Out  SMA Female
I/O HD DB15
RS-232 DB9
Mechanical
Dimensions  322.3 mm x 250.0 mm x  134.8 mm
(12.69" x 9.84" x 5.31")
Weight 3.8 kg (8.4 lb)
  • All values are typical unless noted otherwise.
  • Adjustable
  • Specified at 1310 nm, 1550 nm, and 1590 nm.
  • Applies to all three internal monitors.
  • Per Monitor
  • Laser Input and Output to Modulator connectors are PM FC/PC, and Return from Modulator and Final Output connectors are FC/PC.
Power and Environmental Specifications
Parameter Min Max
Main AC Voltage 100 VAC 250 VAC
Power Consumption - 60 VA
Line Frequency 50 Hz 60 Hz
Operating Temperature 10 °C 40 °C
Storage Temperature 0 °C 50 °C
Humiditya 5% Relative Humidity 85% Relative Humidity
  • Non-Condensing Environment

System Overview

The block diagram shown below illustrates the internal setup of the modulator bias controller. The fiber-coupled light path is traced by the red arrows, and the blue arrows show the electrical connections. The optical laser power is coupled to the Laser Input port and read by Monitor 1 before exiting to the external modulator. The optical output of the modulator is coupled to the Return from Modulator port and routed through the variable optical attenuator (VOA)-based power control system before exiting as the Final Optical Output. Automatic and Manual bias control is performed by referencing intensity readings from Monitor 1 and Monitor 2, and the power controller uses intensity readings from Monitor 2 and Monitor 3 to control and stabilize the output optical power. The rear panel features output ports for several additional monitor and control functions.

MBX Modulator Bias Controller Block Diagram
Block Diagram of the Internal Setup of the MBX Modulator Bias Controller
Modulator Bias Controller System Wavelength Settings Screen
Click to Enlarge

Figure 2: System Wavelength Selection Screen
Bias Controller Main Menu
Click to Enlarge

Figure 1: Home Screen of the MBX
Modulator Bias Controller Dither Settings Screen
Click to Enlarge

Figure 3: Bias Controller Settings Screen to Adjust Dither
Amplitude
Modulator Bias Controller Modulator Operating Mode Settings Screen
Click to Enlarge

Figure 4: Bias Controller Settings Screen to Adjust
Operating Mode
Modulator Bias Controller LiNbO3 EO Modulator Transmission Function
Click to Enlarge

Figure 5: Bias Points for an Intensity Modulator
Vπ is the half-wave voltage. 
Modulator Bias Controller Variable Optical Attenuator Settings Screen
Click to Enlarge

Figure 6: VOA Settings Screen to Adjust Output Power

Touchscreen Interface

Full access to all MBX modulator bias controller functions is available using the resistive touchscreen display, which is sensitive to finger pressure or the tap of a plastic stylus. Figure 1 shows the Home screen, at a time when the bias controller was disabled and the VOA enabled. 

The Home screen is organized in three main sections:

  • Left Column:
    • Buttons show the on/off status of the different instrument functions.
    • Tap a button to toggle the function on/off.
  • Middle Column: 
    • Current operating parameters of each control function are shown.
    • Tap in this column to access the Settings page for each function.
  • Right Column:
    • Buttons provide access to various utility and help functions.
    • Tap to review and customize system settings.

The system wavelength may be selected on the Menu page, which is shown in Figure 2. The choice of system wavelength specifies which calibration settings to apply to the intensity monitors in the MBX.

The bias controller and VOA settings can be adjusted using pages accessed by touching the center region of the Home page. A setting screen for the Quadrature mode of the bias controller is shown in Figure 3. The parameters written in white font are modified using the function buttons, which are customized for each parameter and stacked in the column to the right of the screen. The parameters in orange font may be monitored here, but not set. Toggle Dither on and off by tapping its value in the center column of the screen. Dither is discussed in more detail in the following section. In this screen shot, Dither Amplitude is selected and its set point value can be adjusted by tapping the arrows on the right of the touchscreen. Tap the check mark to confirm a value, and the X to cancel any changes. Set point values may also be quickly changed by dialing the knob on the front panel of the housing. Pressing (clicking) the knob will confirm a new set point value.

Bias Controller Settings 
The Bias Settings screens allow the operator to select among and customize the different operating modes, which are chosen by touching the Mode value and then navigating using the function buttons on the right of the screen. Figure 4 shows these function buttons, which are labeled PEAK, QUAD, NULL, and MAN. 

Three of the four automated operating modes, Peak, Quadrature, and Null, reference the regions labeled on the modulation transmission function, which is illustrated in Figure 5. When one of these modes is selected, a dither tone is used to hold the modulator at the respective bias point. The dither tone is part of a lock-in approach that maintains a stable bias point by compensating for modulator drift, which occurs over time due to the temperature sensitivity of the modulator. The dither tone can be set to a frequency between 1 and 10 kHz, and the amplitude of the tone can also be selected. Quadrature mode gives the option of operating on either the positive or negative slope of the function.

For those applications that require an automated, but ditherless, approach to maintaining a stable bias set point, the MBX includes the Constant Ratio mode. It is enabled by tapping the MAN function on the right of the screen shown in Figure 4 and configuring the Ratio Set Point and Slope values. This mode adjusts the bias voltage to maintain a chosen ratio between the intensity values reported by Monitor 1 and Monitor 2. The Slope setting allows the user to choose whether increasing voltage on the modulator increases or decreases the optical output power.

It can be useful to operate for brief periods of time at a bias fixed voltage and without a dither tone. The MBX allows a fixed bias voltage to be applied in one of two ways. When operating in Quadrature, Peak, or Null modes, tapping the value of Dither will toggle it between on and off states. When dither is toggled off, the value of the fixed bias voltage is held at the most recent automated bias voltage. This enables the user to make quick measurements, without the dither tone present, while the modulator is biased at one of the common modulator transmission function set points. The Constant Bias mode can also be accessed by tapping the Mode value and then the MAN function on the right of the screen. This page allows either the automated Constant Ratio or fixed-voltage Constant Bias modes to be enabled and configured.  

VOA Settings
The VOA provides the means for adjusting and stabilizing the modulated optical output power. The VOA settings screen, which is shown in Figure 6, allows the user to choose between and adjust the parameters of the two operational modes. In Constant Attenuation mode, the attenuation level between the Return from Modulator input port and the Final Optical Output port is fixed, which allows power fluctuations at the input of the power controller to be transferred to the output. In Constant Output Power Mode, the final optical output power is held constant independent of the input fluctuations. In this mode, the VOA is effectively used as a power stabilizer. Tap the Step function button at the right of the screen to change the step size by which the arrows increment or decrement the set point values.

The VOA settings screen also allows the user to select the units used to report the power readings and parameters on all pages. Use the Power Units field to choose whether power values are reported as mW or dBm.

Rear Panel
The rear panel provides additional utility functions such as the power monitor output, RS-232, and USB ports. The USB interface is currently used only for firmware upgrades that are made available on the Thorlabs website. Future revisions of the firmware will provide for remote control of the instrument’s functions.

Front Panel

MBX Modulator Bias Controller Front Panel
Click to Enlarge

MBX Modulator Bias Controller Front Panel
Callout Description
1 Touchscreen Display and Control
2 Value Adjustment Knob
3a Laser Input to Bias Controller,
Accepts PM Fiber with FC/PC Connector
4a Laser Output to Modulator Input,
Accepts PM Fiber with FC/PC Connector
5b Return from Modulator Output to Power Controller,
FC/PC Connector
6b Optical Out: Final Optical Output,
FC/PC Connector
7 Bias Output to Modulator Input,
SMA Female
8 On/Standby Button
  • Uses PM PANDA Fiber for Internal Connection
  • Uses SMF-28-Compatible Fiber for Internal Connection

Back Panel

MBX Modulator Bias Controller Back Panel
Click to Enlarge

MBX Modulator Bias Controller Back Panel
Callout Description
1a I/O Control Port, 
Outputs from Three Integrated Power Monitors,
Female HD DB15 Connector
2 Option Label
3a RS-232 Control Port,
Male DB9 Connector
4 USB Port (Type B)
5 AC Power Cord Connector
6 Fuse Tray
7 AC Power Switch
  • See the Pin Diagrams tab for pin assignments.

 I/O HD DB15 Connector


The I/O connector provides analog outputs from the three power monitors.
Pin Description Pin Description
1 Power Monitor 1a 9 Analog Ground
2 Power Monitor 2a 10 Analog Ground
3 Power Monitor 3a 11 Reserved for Future Use
4 Reserved for Future Use 12 Reserved for Future Use
5 Analog Ground 13 Monitor 1 Gain Indicatora
6 Analog Ground 14 Monitor 2 Gain Indicatora
7 Analog Ground 15 Monitor 3 Gain Indicatora
8 Analog Ground - -
  • The voltage on each Power Monitor pin is proportional to the optical power with one of two gain settings, which is reported on the corresponding Gain Indicator pin. Please see Chapter 7 of the manual for details.

RS-232 Connector


The RS-232 connector is included to support future remote operation that will be enabled by future firmware upgrades.
Pin Description
1 Not Connected
2 RS232 Input
3 RS232 Output
4 Not Connected
5 Digital Ground
6 Not Connected
7 Not Connected
8 Not Connected
9 Not Connected

USB Type B Connector

USB type B
The USB interface is provided to facilitate interfacing a computer with the MBX, so that new firmware revisions posted to the Thorlabs website can be uploaded. 

Each Modulator Bias Controller Includes:

  • Modulator Bias Controller Main Unit
  • Power Cord According to Local Power Supply (Determined by Ordering Location)
  • 1.25 A, 250 VAC Fuse
  • USB Type A to Type B Cable, 6' Long
Screen Capture of the TLX Laser Remote Control Tool Software V1.6
Click to Enlarge

The GUI of the Remote Control Software Tool 

Software for the MBX Automated Bias Controller

Control the MBX Bias Controller Remotely via Serial Commands
Serial commands sent to the MBX can control the functionality of the internal EO modulator bias controller and variable optical attenuator (VOA), as well as general system parameter settings. The commands can be sent from a computer running any operating system to the RS-232 port on the back panel of the MBX. Computers running Windows® 7, or later versions of the operating system, can send serial commands to the USB port on the back panel of the MBX. The touchscreen interface remains active while the MBX is controlled remotely. Descriptions of how to connect a controlling computer to the MBX, the serial command set, and descriptions of each command are included in the Remote Control User Guide.

Application Demonstrating GUI-Based Remote Control of the MBX
The Remote Control Software Tool, which is available for download, is an example graphical user interface (GUI) provided for testing, demonstrating, and exploring the use of the different serial commands. This program is not required to operate the MBX remotely. It opens a connection to the laser source and sends commands in response to buttons clicked by users. Commands sent to the MBX, responses from it, and status information messages are logged to the three rectangular fields located beneath the buttons. Please see the Remote Control User Guide for more information. This program can be used as a basis for the development of custom applications. Please contact us to request the source code.

Software

Version 1.6.1 (September 26, 2017)

Click on the link below to download the Remote Control Software Tool.

Software Download

Firmware Update

Version 1.6.2 (November 15, 2017)

Click on the link below to download the latest firmware.

Software Download

Janis Valdmanis, Ph.D. Optics
Ultrafast Optoelectronics
General Manager

Custom and OEM Options

When your application requirements are not met by our range of catalog products or their variety of user-configurable features, please contact me to discuss how we may serve your custom or OEM needs.  

Request a Demo Unit

Explore the benefits of using a Thorlabs high-speed instrument in your setup and under your test conditions with a demo unit. Contact me for details.

Contact Me

MX40B with cover removed
Click to Enlarge

 The MX40B Digital Reference Transmitter

Design, Manufacturing, and Testing Capabilities

Thorlabs' Ultrafast Optoelectronics Team designs, develops, and manufactures high-speed components and instrumentation for a variety of photonics applications having frequency responses up to 70 GHz. Our extensive experience in high-speed photonics is supported by core expertise in RF/microwave design, optics, fiber optics, optomechanical design, and mixed-signal electronics. As a division of Thorlabs, a company with deep vertical integration and a portfolio of over 20,000 products, we are able to provide and support a wide selection of equipment and continually expand our offerings.

Our catalog and custom products include a range of integrated fiber-optic transmitters, modulator drivers and controllers, detectors, receivers, pulsed lasers, variable optical attenuators, and a variety of accessories. Beyond these products, we welcome opportunities to design and produce custom and OEM products that fall within our range of capabilities and expertise. Some of our key capabilities are:

  • Detector and Receiver Design, to 70 GHz
  • Fiber-Optic Transmitter Design, to 70 GHz
  • RF & Microwave Design and Simulation
  • Design of Fiber-Optic and Photonics Sub-Assemblies
  • High-Speed Testing, to 70 GHz
  • Micro-Assembly and Wire Bonding
  • Hermetic Sealing of Microwave Modules
  • Fiber Splicing of Assemblies
  • Custom Laser Engraving
  • Qualification Testing

Overview of Custom and Catalog Products  

Our catalog product line includes a range of integrated fiber-optic transmitters, modulator drivers and controllers, detectors, pulsed lasers, and accessories. In addition to these, we offer related items, such as receivers and customized catalog products. The following sections give an overview of our spectrum of custom and catalog products, from fully integrated instruments to component-level modules.  

Fiber-Optic Instruments

To meet a range of requirements, our fiber-optic instruments span a variety of integration levels. Each complete transmitter includes a tunable laser, a modulator with driver amplifier and bias controller, full control of optical output power, and an intuitive touchscreen interface. The tunable lasers, modulator drivers, and modulator bias controllers are also available separately. These instruments have full remote control capability and can be addressed using serial commands sent from a PC.

  • Fiber-Optic Transmitters, to 70 GHz
  • Linear and Digital Transmitters
  • Electrical-to-Optical Converters, to 70 GHz
  • Modulator Drivers
  • Modulator Bias Controllers
  • C- and L-Band Tunable Lasers 

Customization options include internal laser sources, operating wavelength ranges, optical fiber types, and amplifier types.

Fiber-Optic Components

Our component-level, custom and catalog fiber-optic products take advantage of our module design and hermetic sealing capability. Products include detectors with frequency responses up to 50 GHz, and we also specialize in developing fiber-optic receivers, operating up to and beyond 40 GHz, for instrumentation markets. Closely related products include our amplifier modules, which we offer upon request, variable optical attenuators, microwave cables, and cable accessories.

  • Hermetically-Sealed Detectors, to 50 GHz
  • Fiber-Optic Receivers, to 40 GHz
  • Amplifier Modules
  • Electronic Variable Optical Attenuators
  • Microwave Cables and Accessories 

Customization options include single mode and multimode optical fiber options, where applicable, and detectors optimized for time or frequency domain operation.

Free-Space Instruments

Our free-space instruments include detectors with frequency responses around 1 GHz and pulsed lasers. Our pulsed lasers generate variable-width, nanosecond-duration pulses, and a range of models with different wavelengths and optical output powers are offered. User-adjustable repetition rates and trigger in/out signals provide additional flexibility, and electronic delay-line products enable experimental synchronization of multiple lasers. We can also adapt our pulsed laser catalog offerings to provide gain-switching capability for the generation of pulses in the 100 ps range.

  • Pulsed Lasers with Fixed 10 ns Pulse Duration
  • Pulsed Lasers with Variable Pulse Width and Repetition Rates
  • Electronic Delay Units to Synchronize NPL Series Pulsed Lasers
  • Amplified Detectors

Customization options for the pulsed lasers include emission wavelength, optical output powers, and sub-nanosecond pulse widths.


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