Photonic Control Devices

Chip-scale Optical Modulator BiasController
PSI-0204-11

Features and Benefits
Dither based control compatible with mostoptical modulators
Adjustable Dither amplitude: 20 to 200mVpp
power supply range: +/-12 to +/-18volts
Low operating current: <12mA typical
Small size: 2.5”x 0.7”, 24pin, 0.6” width DIP
Customized Designs available in micro-sizedpackages
Evaluation kit available for simple test anddesign

Product Description
The PSI—0204-11 chip-scale optical modulator bias controller(MBC) offers comprehensive control of external optical modulators from a single, small form factor circuit board. When operated
with lithium niobate (LiNbO3) modulators, the PSI-0204-11 provides automatic or manualbias control. Users may select automatic tracking of
Quad +, Quad -, Minimum orMaximum bias points asshown in Figure 1. Operation at an externally set
manual bias point may also
be selected.
Figure 1– Modulator Transfer Function

Using a dither tone, the PSI0204-11 tracks a user selected operating point to within +/- 1° at
1% dither of Vπ when operating at quadrature. Dither frequency is
set at 1 KHz and dither amplitude is user defined between 20
and 200mVpp. Bias point accuracy is maintained over a wide
operating temperature range of 0° to +50° C. Using a common
photodetector, bias point accuracy is easily maintained over a
10dB range of optical power. Wider dynamic range controllers areavailable upon request.
Designed for easy integration into the user’s optical system, thesecontrollers maintain constant bias point operation by compensating for drift in a modulator’s transfer function. An external modulation fiber optical transmitter is shown in Figure 2 to illustrate
how the controller is typically used. A dither tone is applied to themodulator bias voltage and sampled at the modulator optical output. Through use of an optical coupler and photodetector, a portion of the transmitted light is detected and fed to the MBC. User
settings determine bias point and amplitude.

Figure 2: Typical Modulator
Controller Application

Applications
••
•
•
•
••

Modulator design
Integrated Modulator/TransmittersFiber optic component evaluation
Photonic Test Systems
Spectroscopy systems
Analog communications systems
Optical transmissionBeyond standard specifications, PSI can modify the PSI-0204-11
to meet the exact requirements of your application, such as specific dither frequency, wide temperature range or very large optical input range. Smaller package sizes are offered for operation
at a single bias point; other designs may also result in microminiature packages.
An optional evaluation kit is available to aid with design-in andproof of concept activities. The evaluation board provides a convenient means to power, control and test the MBC in a laboratory
setting. Electrical connections are provided through either a DB9or Molex plug. An optical photodetector completes the feedback
loop. Included in the kit are an evaluation board with photodetector, AC power adapter and an MBC device.

978-670-4990
www.photonicsinc.com
info@photonicsinc.com

PSI-0204-11

Chip scale Optical Modulator Bias
Controller
Specifications
PhotonicSystems, Inc.
(PSI) is arecognizedexpert in thedesign, analysis

Parameter

Typical Value

Units

Modulating Signal

Analog small or large signal or DPSK—

Modulators Supported

LiNbO3—Modulator/Bias-T Load Capacitance< 0.2μFOutput DC Bias Port Impedance

100ohms

Output DC Bias Voltage

0.3 less than supply voltage

Volts

Dither Frequency

1KHz

Dither Amplitude

20 to 200; user definedmVpp

Bias Point Error @Quad + or Quad - point, 5 to 50 μa photo detector current 1

1 @1% dither of Vπ

degrees

Bias Point Error @Max or Min point, 10 to 100 μa photo detector current 1< 0.1

degrees

comprehensive
fiber optic

DC Power Supply+/- 12 to +/-18

Volts

DC Operating Current< 12mA

engineeringsolutions togovernment,military andOperating Temperature Range

0 to +50

degrees C

MBC Board Dimensions

2.5 x 0.7 (6.4 x 1.7cm) ; 24 pin dual
in-line package, 0.6” widthinches

and implementation of highperformancefiber opticsystems.
With decades ofcollectiveexperience, thePSI team offers

commercial
customers.

1. Equivalent to -23 to -13 dBm of optical power (at quadrature) applied to Fermionics FD-300 or equivalent photo detector. Wider dynamic range
controllers available at additional cost; contact PSI for details.

978-670-4990
www.photonicsinc.com
info@photonicsinc.com
Rev. F 8/18/06; Specifications subject to change without notice-2-PSI-0204-11

Chip scale Optical Modulator Bias
Controller
Device Function and Pin Descriptions
PinFunction

1PD Bias

Description
Provides internally generated bias voltage for photodetector. Normally connected together with Pin 2 to the PD cathode.

2PD Cathode3

PD Anode (Common)

Photodetector cathode connection. Normally connected to Pin 1 for PD bias.
Photodetector anode connection.

4

PD Anode (Common)

Photodetector anode connection.

5

MasterOutput of PD preamplifier. Normally connected to pin 6. May be used for control of slaved bias controllers.

6SlaveInput to dither detection circuitry. Normally connected to pin 5. May be used for control from a master bias controller.

7GroundDevice Ground

8Intg. In

Control loop integrator input. Normally unused, this input allows for modification of the bias control response time.

9-Intg. –B

Control loop integrator output. Normally connected to pin 10, this output allows for modification of the bias control response time.

10+Intg. +B

Control loop integrator output. Normally connected to pin 9, this output allows for modification of the bias control response time.

11Bias Out

Bias output

12

Manual Bias In

13

Dither Out– Lo Adj

14

Dither In

Dither input. Normally connected to pin 15 through a user selectable resistance to set dither amplitude. May be used to implement
adjustable dither in conjunction with pin 15.

15

Dither Out Adj

Dither generator output. Normally connected to pin 14 through a user selectable resistance to set dither amplitude. May be used toimplement adjustable dither in conjunction with pin 14.

16

Auto Bias Select 2

Input to set auto bias point in conjunction with pin 17. See table 1 below. Device employs internal 200k pull up resistor.

17Auto Bias Select 1Input to set auto bias point in conjunction with pin 16. See table 1 below. Device employs internal 200k pull up resistor.

18Freq. Adj (future use)

No connection- Dither frequency control in future release; not supported at this time.

19+Vlog Out20Reset

21

Auto/Manual Select

22-V

23

Ground24+VInput for control of bias in manual mode. Input voltage ranges from –V to + V for control of bias voltage over Max to Min.
Low dither voltage output. May be used for fine adjustment of dither amplitude. Normally not used.

4.5 volt reference output. Normally not used.
Control loop reset input. Ground for normal operation, allow high for reset; device employs 200k pull up resistor.
Selects Automatic or manual bias point control. Connect to ground for automatic control; open for manual control. Device employs
internal 200k pull up resistor.
Negative power supply connection. Acceptable range from –4.75 to –18 volts
Device Ground
Positive power supply connection. Acceptable range from 4.75 to 18 volts

MBC Pin Pin 17

Pin 16Q+OpenOpenQ-Ground

Open

Max

Open

GroundMin

GroundGroundBias
Point

Table 1: Auto bias control point settings.

Rev. F 8/18/06
Specifications subject to change without notice-3-978-670-4990
www.photonicsinc.com
info@photonicsinc.com