Modulator Bias Controller
For Single and Dual Drive IQ modulators

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The Modulator Bias Controller for IQ Modulator
The MBC-DG-Board, MBC-DG-BT and MBC-IQ-BT with or without PD option are a family ofbias controller specially designed to stabilize the operating point of LiNb03 Mach-Zehnder
modulators by monitoring the bias voltage applied on the DC electrodes of the device.
The MBC-IQ-BT model is especially designed for IQ modulator. The MBC-IQ-BT is preset atoperating point MIN and lock automatically the DC1 and DC2 from an IQ modulator (refer toappendix 1 for modulator input ports definition). Additionally, a continuous supply voltage output isavailable for manual (knob adjustable) DC3 for phase difference between the two sub-MZ's. The
MBC-IQ-BT is an efficient component for either single drive (X-cut design) and differential biasing.

MBC-IQ-BT
Potentiometer

RS 232

MBC1

RS 232

MBC2
DC1

DC in

PM

DC2

DC3
DC in

DC in

IQ
Modulator

PM

MBC-IQ-BT set-up with IQ modulator

The MBC-IQ-BT will ensure: biasing of one LiNb03 IQ modulators, DC1 and DC2 automatic, DC3 manual parallel biasing of two LiNb03 intensity modulators using the two MBC-boards
 a stable continuous supply voltage for modulator, driver, amplifiers, …biasing
 independent control of each MBC (using MBC front panel or remote by RS232)
 stabilisation of preset working point MIN, MAX, QUAD+, QUAD tuneable locked-working point
 tuning mode Manual/AutoOPTION
 Internal photodiode Tap coupler

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1423125613 147815

91016

11

17

MBC-IQ-BT-PD front panel with optional internal photodiodeThe MBC-IQ-BT-PD front panel features :

1Main display

2

MBC1, MBC2 : MBC1 and MBC2 selection

3ESC, OK,



4

A2 : Anode 2-MBC2 input port when modulator’s internal photodiode is used



5

A1 : Anode 1-MBC1 input port when modulator’s internal photodiode is used



6

K1 : Cathode 1-MBC1 input port when modulator’s internal photodiode is used



7

K2 : Cathode 2-MBC2 input port when modulator’s internal photodiode is used

8

DC1+ : Positive DC1 output port (single drive modulator)

9DC2+ : Positive DC2 output port (single drive modulator)

10

DC3+ : DC3 output port (single drive modulator)

11Display for DC3 control

12

Optical Input : Optical input port when modulator external PD is used (Opt-PD)13

GND : Ground port for DC1 and DC2

14

DC1- : Negative DC1 output port (additional port for dual drive modulator)

15

DC2- : Negative DC2 output port (additional port for dual drive modulator)

16

GND : Ground port for DC317

Knob for DC3 voltage control,: Keypad for MBC1, 2 circuit parameters control – Manual mode

The MBC-IQ-BT rear panel features two RS-232 interfaces (USB port in Option) for remoteadjustment of the bias control circuit parameters. Moreover, automatic and manual bias control
functions selection is also available.

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SPECIFICATIONS
DC1 & DC2 Optical Characteristics
PARAMETERS

Wavelength ofoperation
Input optical power
Optical dynamic
range

CONDITIONS

UNIT

MIN

TYP

MAX-nm780-

1 650dBm--4-dBm-22-

CONDITIONS

UNIT

MIN

TYP

MAXin manual mode
range over 4 user selectable
gains
gain 1gain 2gain 3
gain 4range over 4 user selectable
gains
range over 1 user selectable
gainVV-10-

0.110-

µA

3-

500

µA
µA
µA
µA

10020103-

500
200
10030dB-

22-

dB

7810VmV
mA-18-

10-

+1820

MIN
TYP
MIN (0%)

MAXwith internal PD and tap
couplerrange over 4 user selectable
gains, with internal PD & tap
coupler

DC1 & DC2 Electrical Characteristics
PARAMETERS
DC1 & DC2Bias voltage
Bias voltage step

Input photocurrent

Photocurrent
dynamic range
DC3Voltage range
Voltage step
Output current

manual-DC1 & DC2 Bias Control Characteristics
PARAMETERS

Preset locking point
Locking range
Bias voltage step
Extinction ratio(Min mode)
Extinction ratio
stability (Min mode)
Dither frequency
Dither amplitude

CONDITIONS

UNITwith IQ modulator
manual and automatic
Degreecontrolat quadDegreewith proper modulator, widthinternal PD & tap couplerdB
optionwith proper modulator,
internal PD & tap couplerdB
option, over 1 hour
by 40 Hz frequency step
Hzby 10 mV amplitude stepmV-360-

89.59090.5--50-±0.05-40050-

1 400
1 000

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Other
PARAMETERS

Operating temperature
Storage Temperature
POWER SUPPLYAC Voltage (automatic switch)
Electrical plug
DIMENSIONS
Bench-top unit
SOFTWARE
Minimum computer requirements

UNIT°C°C

MIN-10-40

TYP-MAX+45+75

V
Hz

90
110
50Rear panel

240
60

30 cm W x 21 cm H x 8 cm D
Windows 98/NT/2000/XP

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Appendix 1 : MXIQ-LN-40 modulator
A IQ modulator is basically composed of four waveguides. The two first waveguides are linked
together with input and output Y-junctions forming a first sub-Mach-Zehnder modulator (MZ1). The
two last waveguides are linked together with Y-junctions as well, forming a second sub-MachZehnder modulator (MZ2). Each output port of the Y-junctions is linked with a larger Y-junction. In
conclusion, the IQ modulator is of two Mach-Zehnder modulator nested into a larger Mach-Zehndermodulator.
Electrodes are placed parallel to the waveguide arms. Two sets of high speed electrodes allows toapplied RF signal to each of the sub-MZ's. Two sets of DC electrodes allows to control the static
phase of each sub-MZ's. A last set of DC electrodes allows to control the static phase between thetwo sub-MZ's. In (D)QPSK / SSB / OFDM / QAM modulation formats, each DC voltage (DC1 andDC2) of the sub-MZ's is adjusted in order to introduce a phase shift equal to π, while the voltage
applied to the phase difference between the two sub-MZ's is adjusted to introduce a phase shift ofπ/2.

MZ1

MZ2

Simplified Scheme of a IQ modulator integrated on an X-cut lithium niobate crystal

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