Ultra Compact DP-IQ Modulator Bias Controller Automatic Bias Controller

Short Description:

Rofea’ modulator bias controller is specially designed for Mach- Zehnder modulators to ensure a stable operation state in various operating environments. Based on its fully digitized signal processing method, the controller can provide ultra stable performance.

The controller injects a low frequency, low amplitude dither signal together with bias voltage into the modulator. It keeps reading the output from the modulator and determines the condition of the bias voltage and the related error. A new bias voltage will be applied afterwords according to the previous measurement. In this way, the modulator is ensured to work under proper bias voltage.

Product Detail

Rofea Optoelectronics offer Optical and photonics Electro-optic modulators products

Product Tags


•Simultaneously provides six automatic bias voltages for Dual Polarization IQ modulators
•Modulation format independent:
SSB, QPSK, QAM, OFDM verified.
•Plug and Play:
No manual calibration needed Everything automatic
•I, Q arms: controll on Peak and Null modes High extinction ratio:50dB max1
•P arm: controll on Q+ and Q- modes Accuracy: ± 2◦
•Low profile: 40mm(W) × 29mm(D) ×8mm(H)
•High stability: fully digital implementation Easy to use:
•Manual operation with mini jumper 2
Flexible OEM operations through UART /IO
•Two modes to provide bias voltages: a.Automatic Bias Control b.User defined bias voltage

Electro-optic modulator Electro-optical modulator Modulator Bias Controller Bias point controller IQ Modulator DP-IQ Modulator  Automatic Bias Controller


•LiNbO3 and other DP-IQ modulators
•Coherent Transmission


1 The highest extinction ratio depends on and cannot exceed 1 the system modulator maximum extinction ratio.

2 UART operation is only avaliable on some version of the controller.



Figure 1. Constellation (without controller)


Figure 2. QPSK Constellation(with controller


Figure 3. QPSK-Eye pattern


Figure 5. 16-QAM Constellation pattern


Figure 4. QPSK Spectrum


Figure 6. CS-SSB Spectrum







Controll Performance
I, Q arms are controlled on Null(Minimum) or Peak(Maximum) point
Extinction ratio  




P arm is controlled on Q+(right quadrature) or Q-( left quadrature) point
Accuracy at Quad





Stablization time





Positive power voltage





Positive power current





Negative power voltage





Negative power current





Output voltage range of YI/YQ/XI/XQ





Output voltage range of YP/XP





Dither amplitude  




Input optical power3





Input wavelength





1 MER refers to intrinsic Modulator Extinction Ratio. The extinction ratio achieved is typically the extinction ratio of the modulator specified in modulator datasheet.

2  Let Vπ  denote the bias voltage at 180 and VP  denote the most optimized bias voltage at Quad points.

3 Please be noted that the input optical power does not refer to the optical power at the selected bias point. It is the maximum optical power that the modulator can export to the controller when the bias voltage ranges from Vπ to +Vπ .

User Interface


Figure5. Assembly

Group Operation


Rest Insert jumper and pull out after 1 second Reset the controller
Power Power source for bias controller V- connects the negative electrode of the power supply
V+ connects the positive electrode of the power supply
Middle port connects with the ground electrode
UART Operate controller via UART 3.3: 3.3V reference voltage
GND: Ground
RX: Receive of controller
TX: Transmit of controller
LED Constantly on Working under stable state
On-off or off-on every 0.2s Processing data and searching for controlling point
On-off or off-on every 1s Input optical power is too weak
On-off or off-on every 3s Input optical power is too strong
Polar1 XPLRI: Insert or pull out the jumper no jumper: Null mode; with jumper: Peak mode
XPLRQ: Insert or pull out the jumper no jumper: Null mode; with jumper: Peak mode
XPLRP: Insert or pull out the jumper no jumper: Q+ mode; with jumper: Q- mode
YPLRI: Insert or pull out the jumper no jumper: Null mode; with jumper: Peak mode
YPLRQ: Insert or pull out the jumper no jumper: Null mode; with jumper: Peak mode
YPLRP: Insert or pull out the jumper no jumper: Q+ mode; with jumper: Q- mode
Bias Voltages YQp, YQn: Bias for Y polarization Q arm YQp: Positive side; YQn: Negative side or ground
YIp, YIn: Bias for Y polarization I arm YIp: Positive side; YIn: Negative side or ground
XQp, XQn: Bias for X polarization Q arm XQp: Positive side; XQn: Negative side or ground
XIp, XIn: Bias for X polarization I arm XIp: Positive side; XIn: Negative side or ground
YPp, YPn: Bias for Y polarization P arm YPp: Positive side; YPn: Negative side or ground
XPp, XPn: Bias for X polarization P arm XPp: Positive side; XPn: Negative side or ground

1 Polar depends on system RF signal. When there is no RF signal in the system, the polar should be positive. When RF signal has amplitude greater than a certain level, the polar will change from positive into negative. At this time, Null point and Peak point will switch with each other. Q+ point and Q- point will switch with each other as well. Polar switch enables user to change the

polar directly without changing operation points.

Group Operation


PD1 NC: Not Connected
Y-A: Y-polarization photodiode Anode

Y-A and Y-C: Y polarization photocurrent feedback

Y-C: Y-polarization photodiode Cathode
GND: Ground
X-C: X-polarization photodiode Cathode

X-A and X-C: X polarization photocurrent feedback

X-A: X-polarization photodiode Anode

1 Only one choice shall be chosen between using controller photodiode or using modulator photodiode. It is recommended to use controller photodiode for Lab experiments for two reasons. Firstly, controller photodiode has ensured qualities. Secondly, it is easier to adjust the input light intensity. If using modulator’s internal photodiode, please make sure that the output current of photodiode is strictly proportional to input power.

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  • Rofea Optoelectronics offers a product line of commercial Electro-optic modulators, Phase modulators, Intensity modulator, Photodetectors, Laser light sources, DFB lasers,Optical amplifiers, EDFA, SLD laser, QPSK modulation, Pulse laser, Light detector, Balanced photodetector, Laser driver, Fiber optic amplifier, Optical power meter, Broadband laser, Tunable laser, Optical detector, Laser diode driver, Fiber amplifier. We also provide many particular modulators for customization, such as 1*4 array phase modulators, ultra-low Vpi, and ultra-high extinction ratio modulators, primarily used in universities and institutes.
    Hope our products will be helpful to you and your research.

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