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Automated Bias Controller for Lithium Niobate (LiNbO3) Modulators
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
We Design, Develop, and Manufacture
|Modulator Drivers and All-in-One Systems|
|Item#||Bit Rate /
|Tunable Laser||Internal Modulator
|MX10A||12.5 Gb/s||No||No||Yes (Digital)||Yes||Yes|
||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|
||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|
|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)
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
|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|
|Fiber Connectorsf||FC/PC, 2.0 mm Narrow Key|
|Bias Out||SMA Female|
|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)|
|Power and Environmental Specifications|
|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|
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.
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:
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.
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.
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.
|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,
|6b||Optical Out: Final Optical Output,
|7||Bias Output to Modulator Input,
|1a||I/O Control Port,
Outputs from Three Integrated Power Monitors,
Female HD DB15 Connector
|3a||RS-232 Control Port,
Male DB9 Connector
|4||USB Port (Type B)|
|5||AC Power Cord Connector|
|7||AC Power Switch|
|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|
Each Modulator Bias Controller Includes:
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
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.
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.
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:
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.
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.
Customization options include internal laser sources, operating wavelength ranges, optical fiber types, and amplifier types.
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.
Customization options include single mode and multimode optical fiber options, where applicable, and detectors optimized for time or frequency domain operation.
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.
Customization options for the pulsed lasers include emission wavelength, optical output powers, and sub-nanosecond pulse widths.
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