MBC-AN-LAB
Operating Manual Version 2.0
MBC-AN-LAB 1 Version 2.0
Content
Legal Notice .............................................................................. 3
Disclaimers ........................................................................................................................ 3
About this Manual .................................................................... 3
Purpose ............................................................................................................................. 3
Audience ........................................................................................................................... 3
Prerequisites ..................................................................................................................... 4
Terms and Symbols in this Manual .................................................................................... 4
Electrical safety ................................................................................................................. 4
Contacting iXblue .............................................................................................................. 4
General Information ................................................................. 5
Product Overview .............................................................................................................. 5
Principle of operation ......................................................................................................... 5
Standard Specifications ..................................................................................................... 7
Panel features ........................................................................... 8
Front panel .................................................................................................................... 8
Back panel ..................................................................................................................... 9
Getting started .......................................................................... 9
Standard Accessories ........................................................................................................ 9
Installation and set up ........................................................................................................ 9
Operation................................................................................. 10
Quick start procedure .......................................................................................................10
Remarks: ..........................................................................................................................12
Calibrating the board ........................................................................................................13
Appendices ............................................................................. 17
A. Mach-Zehnder intensity modulators ..........................................................................17
B. Drift effects ...............................................................................................................18
MBC-AN-LAB 2 Version 2.0
MBC-AN-LAB 3 Version 2.0
Legal Notice
Disclaimers
No warranty: This documentation is provided « as is » without any express or implied
warranty of any kind.
Limitation of Liability: Photline does not assume any liability arising out of the
application or use of any products, or software described herein. In no event shall Photline
be liable for any damage whatsoever (including, without limitation, consequential or
incidental damages, damages for lot of profits, or otherwise) arising out of the use of the
information provided in this documentation.
The content of this publication has been carefully checked for accuracy. However,
Photline makes no warranty as to the completeness, correctness, or accuracy of the
information contained within this documentation. In the interest of continued product
improvement, Photline further reserves the right to make any change in any products
describers herein without notice. This publication is subject to change without notice.
About this Manual
Purpose
The purpose of this instruction manual is to explain how to set up the MODBOX and
to utilize the various features of the product.
Audience
This manual is aimed at professionals with the necessary technical background and
prerequisites needed to use fiber optics equipment, including lithium niobate modulators, and
the related tests equipment and accessories.
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Prerequisites
Reader is assumed to be familiar with and fiber optics technology.
Terms and Symbols in this Manual
The following terms and symbols may appear throughout this manual:
WARNING: Warning statement identifies conditions or practices that could result in injury or
loss of life.
CAUTION: Caution statement identify conditions or practices that could result in damage to
this product or other property
Electrical safety
WARNING
Operate under the proper environmental conditions
The MBC-AN-Board is designed for indoor use. To avoid injuries, do not
expose this instrument to water or excessive moisture. Do not operate the
board in the presence of flammable gases or fumes.
Contacting iXblue
For application oriented or service related requests, please contact iXblue customer
service department:
contact@ixblue.com
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General Information
Product Overview
MBC-AN-Board is a bias controller specially designed to lock the operating point of a LiNbO3
Mach-Zehnder modulator by monitoring the bias voltage applied on the DC electrodes of the
device.
Unlike classical dither signal based bias controllers, MBC-AN-board does not superimpose
any tone signal to the optical modulated signal. It is designed for application where such a
tone signal is not desired and typically for analog applications where a high purity carrier is
required.
Principle of operation
The MBC-AN bias controller is based on the comparison of the optical power before and
after the Mach-Zehnder modulator. It uses optical tap couplers and photodiodes with
a proportional integrator feedback loop to lock the operating point of the modulator at the
Quad+ or Quad- position.
The MBC-AN-BT is operated with a user supplied PC. It comes with a Windows graphical
user interface.
Figure 1: basic scheme of a modulation set-up including a modulator bias controller and 2 external
monitoring photodiodes
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A fiber coupler with a strong imbalance (10:90 or 1:99) is placed between the Mach-Zehnder
modulator and the laser. At the output of the coupler a photodiode is used to monitor the
average optical power emitted by the laser. The RF signal is applied to the RF electrodes. At
the output of the MZ modulator, a fiber coupler with a strong imbalance (10:90 or 1:99)
allows to detect a small portion of the transmitted light thanks to a monitoring photodiode.
The signal from the photodiode is amplified and compared with the signal coming from the
laser monitoring photodiode. The discrepancy between both signals are integrated and
injected into the DC electrodes of the modulators in order to maintain the operating point at
the desired position.
The principle of operation of the MBC-AN is based on a proportional integrator feedback
loop. It has been design only for locking the operating point at Quad+ or Quad-.
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Standard Specifications
Input Signals Specifications
Units
Min
Typ
Max
Electrical
Modulator Bias voltage
V
-12 +12
Photodiode Bias Voltage
V -5
Bias voltage step (in manual mode)
V
0.002
0.01
Locking point (Transfert level)
QUAD-(-50%), QUAD+(+50%)
Environmental
Operating temperature
°C
+10
+45
Storage Temperature
°C
-40 +75
Power supply
Positive bias voltage
V 0 +12
+15
Negative bias voltage
V
-15
-12
0
90-250V, 50/60Hz AC power supply
Provided
Interfaces
Photodiode Input /coupler input
FC/APC connector
Bias Output
BNC Female connector
Communication
USB Connector
Environmental
Operating temperature
°C
+10
+45
Dimensions
LAB
220 x 220 x 52mm3
Software (GUI)
Minimum computer requirements
Windows XP SP3
One USB port
Recommended computer configuration
Windows XP SP3
One USB port
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Panel features
Front panel
<1> Power button
<2> Control LED
Auto: MBC is in Auto Mode
Sat: MBC bias control voltage is saturating
<3> Bias Modulator connector (BNC)
<4>: Laser optical input
Input, fiber from laser output (coupler option)
Input, part of laser power (no coupler option)
<5>: Modulator optical input (optional)
Output of the first integrated coupler, to the input optical fiber modulator
<6>: Modulator optical output
Input, fiber from modulator output (coupler option)
Input, part of modulator output power (no coupler option)
<7>: Signal (optional)
Output of the second integrated coupler, working signal.
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Back panel
<8> Power supply connector (Jack 3.5mm, 12V 500mA)
<9> USB connector
Getting started
Standard Accessories
User Manual
Interface User Manual
Cord Kit
USB Cord
AC-DC Power Supply
Installation and set up
To set-up the MBC-AN-Board for your application you have to install the MBC-AN control
software.
Preliminary: MBC Interface software installation
Minimum computer requirements:
Windows XP/Vista/7
USB port
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Installation: Install the USB driver (PhotlineUSBinstaller.exe), and then launch the
setup.exe present on the CD.
The MBC interface software is now installed and ready to be used.
Operation
Quick start procedure
Your MBC-AN-Board has been carefully mounted so that you just need to set the
correct adjustments with the windows interface to get going. You basically just need to plug
the +12V/0/-12V supply (<3> or <4>) and connect the inputs (<1> and <2>) and the outputs
(<9>). You will find a quick start procedure below:
1. Make sure you received all the ordered parts
2. Proceed to the MBC-AN-Board system installation
3. Connect the board to the power supply
4. Connect the PD2 output connector (Signal) to a power meter using an optical fiber.
Then plug the modulator output connector to the PD2 input connector. Plug the
modulator input connector to the PD1 output connector. And plug the laser connector
to the PD1 input connector. Connect the Vbias connector to the modulator Vbias pin,
and the ground connector to the modulator ground.
Setup with an internal coupler (coupler option):
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Setup with an external coupler (no coupler option):
5. When you are done, start the laser
6. Start the MBC-AN windows control interface
7. Select the device
8. Select manual mode and adjust Vbias Mod (can go positive or negative) to get the
maximum optical power at the input of your power meter
Figure 2: Manual mode selection
9. When done check Automatic
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Figure 5: Automatic Mode selection
10. Check the Reset button to restart the integrator
11. The board should be in quad mode
Remarks:
1. If needed the MBC-AN-BOARD can be used as a manual modulator bias source by
selecting the manual mode.
Figure 6: Manual mode selection
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2. You can lock the MBC-AN next to the quad point with the “Scan” function.
Figure 7: Scan
3. In the case the MBC-AN-BOARD is not able to lock on the quad point, you have to
calibrate your MBC-AN-BOARD by using the Calibration menu in the Control
interface.
Calibrating the board
The Calibration mode is used, when you need to set-up the board, for example when you
change the modulator.
1. Select the Calibration Menu in the toolbar. Then enter the following password: trepxe
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Figure 8: Calibration mode selection
2. Select manual mode and adjust Vbias Mod (can go positive or negative) to get the
maximum optical power at the input of your power meter.
Figure 9: Manual mode selection
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3. Change the coarse gain in the PDM (PhotoDiode Modulator) settings box to get a
value around 3.5V in the PDM voltage box, and adjust with fine gain.
Figure 3: PDM adjustment
Change the coarse gain in the PDL (PhotoDiode Laser) settings box to get a value around
1.75V in the PDM voltage box, and adjust with fine gain. (PDL voltage = PDM voltage / 2)
Figure 4: PDL adjustment
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4. When done check Automatic
Figure 5: Mode selection
5. Check the Reset button to restart the integrator.
6. The board should be in quad mode. If the optical power measured at the output is
different from Pmax - 3dB, and that the LED +/-Vbias sat. are not ON, you can adjust
the power by changing the value of the fine gain and coarse gain of PD1.
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Appendices
A. Mach-Zehnder intensity modulators
Lithium Niobate (LiNbO3) Mach-Zehnder modulators (MZMs) are external
modulators that have been widely used since the mid-nineties, mostly in long haul
optical networks for their ability to modulate optical signal from 1300 nm and 1550
nm laser diodes with short transition times and without chirp compared to other
techniques (direct laser diode current modulation for instance). Thanks to their
broad wavelength performance, they currently also offer modulation solutions at
1064 nm, 850nm and other NIR laser wavelengths.
Mach-Zehnder modulators are 2-waves interferometer devices that exhibit a sine
transfer function (Figure 6). Although MZMs are highly stable components, their
operating point can suffer slow drifts due to variations of external conditions (like
pressure and temperature for instance) and those drifts may induce key
performances time fluctuations like the extinction ratio for example.
In order to adjust the operating point of LiNb MZMs independently from the RF
modulation signal applied, the design can be done with two sets of electrodes: the
RF set (the RF Electrodes) is used to apply the RF signal (PRBS data stream,
analog signal, short pulses…). The DC set (the DC Electrodes) is applied to set the
MZM operating point using a fixed voltage. Figure 7 illustrates the typical electrode
architecture of LiNbO3 MZMs.
Figure 6 : Transfer function of a Mach-Zehnder modulator and data output vs. data input at QUAD+ and
QUAD- operating point
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Figure 7: typical electrode and waveguide architecture of a Mach-Zehnder modulator
B. Drift effects
DC drift is the optical output power variation under the constant DC bias
voltage application. Figure 8 shows the output power of the modulator as a function
of the applied voltage. The broken line shows the output power as a function of
applied voltage when only AC voltage is applied (and no DC is applied, at t = 0) and
the solid line shows the same, after t = t1, when DC voltage is also applied in
addition to the previous AC signal voltage. The shift between these two curves, V,
is the measure of the DC drift.
Figure 8: Output power of the modulator as the function of the driving voltage, with/without the DC
applied voltage.
The DC drift physical mechanism and its causes are not yet well understood. But
this can be attributed to the ions movement, including OH- ions, inside the Lithium
Niobate substrate and the buffer layer. It is influenced by the balance of the RC time
constants, in both horizontal and vertical directions in the equivalent circuit model,
as is displayed in Figure 9. It was also found that the DC drift is more affected by
the buffer layer. In the circuit model of Figure 8, all layers, including the LiNbO3
substrate, the Ti:LiNbO3 optical waveguide and the buffer layer, are represented in
terms of resistances R and capacitances C, in both vertical and horizontal directions
of the crystal.
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Figure 9:Equivalent RC circuit model of the MZM crystal electric structure, with vertical and horizontal
components.
Thermal and humidity drift is the optical output power variations under
temperature (respectively humidity) changes. Once the temperature changes,
piezoelectric charges are induced on the surface of the LN substrate. This raises a
surface charge distribution across the two arms of the interferometer, affecting the
global electric field. This results into a shift in the switching curve, in the same way
that operates the DC drift. Hence, to mitigate thermal effects, there is a need to
distribute or dissipate the charges that are accumulating on the LiNbO3 crystal
surfaces and between the electrodes.
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