LMC10NEG3347-J28 BOOKHAM [Bookham, Inc.], LMC10NEG3347-J28 Datasheet - Page 8

• Manufacturer Part Number: LMC10NEG3347-J28
• Description: 10Gb/s Compact InP MZ Modulator with DWDM Laser
• Manufacturer: BOOKHAM [Bookham, Inc.]

8
Pin Definitions
Pin 1 MZ data DC Bias input and Pin 2 MZ data-bar DC
Bias input
DC bias voltages for data and data-bar MZ arms. These pins
must be connected to a low noise negative DC voltage,
typically around -2V (WRT case). These voltages are defined
for each Tx in the deliverable data. A precision voltage source
must be used, which is capable of sourcing up to 10mA to
each pin. Refer to Bookham applications note AN0130 for
circuit implementation and filtering suggestions.
Pin 3
Connect to ground.
Pin 4 Bias Control Tap
The MZ bias control tap pin must be biased to -5V.
The supply should be regulated if the device is used
in mode 1 as the monitor diode responsivity is voltage
dependent.
Pins 5, 7 and 9 Ground
Package ground connections.
Pin 6 MZ Data-bar modulation input and Pin 8 MZ Data
modulation input
Operation is typically using differential electrical drive voltages
applied to both the Data and Data-bar MZ Modulator inputs.
Typical amplitude is 2.0V peak-to-peak. AC RF coupling must
be used.
Pin 10 TEC (-) and Pin 11 TEC (+)
The LMC10 contains a Peltier heatpump. Applying a negative
voltage on Pin 10 with respect to Pin 11 will cause the
internal optics to be cooled relative to the case temperature.
Operating the LMC10NEG
Control Schemes for the LMC10NEG
Arm DC Bias Voltage Control
A dynamic control scheme can be implemented to maintain
the bias points on the left and right arms of the MZ modulator
at the quadrature point. This will maintain the output pulse
train with a 50% eye crossing level. The control circuit needs
to track any over life change in the bias points, thereby
maintaining the 50% eye crossing condition.
Benefits of Using Control Schemes
The product can be used without the control scheme as
discussed above. But there are benefits of implementing
the control loop:
Data Sheet
Reversing the applied voltage will cause the internal
structures to be heated. The heatpump must be used in
a feedback controlled circuit in conjunction with the
internal thermistor.
Pin 12 Laser Anode
The laser is operated with a forward bias current, the laser
cathode being connected internally to case ground.
Pin 13 Thermistor
The thermistor is used in the TEC control loop for keeping the
internal temperature at a constant value. It has a nominal
resistance of 10k Ohms at a temperature of 25ºC and is not
polarity sensitive, although one side of the thermistor is
connected to package ground. Operating current should be
limited to less than 100µA to prevent self heating errors.
The exact thermistor value is supplied with each Tx as
part of the deliverable test data to ensure the correct
operating wavelength.
Pin 14 Back Facet Monitor Diode Anode (Etalon)
The signal from this diode carries the spectral response of the
wavelength filter.
Pin 15 Back Facet Monitor Diode Common Cathode
Common connection for monitor diode cathodes.
Pin 16 Back Facet Monitor Diode Anode (Reference)
The signal from this diode is the reference signal and
indicates the power of the rear facet of the laser. The signals
from the reference and etalon monitor diodes are used in a
control loop to maintain the wavelength of the laser at the
defined lock point.
Maintaining the optical eye crossing to 50% through the life of
the product will minimise the variation in extinction ratio and
reduce variations in link dispersion penalty.
Summary
For more demanding applications at higher link lengths or
tighter link budgets the LMC10NEG may be used with a
dynamic control scheme which will provide MZ arm bias point
control for 50% optical eye crossing.
Use of the BCT in a control loop can offer improved optical
eye shape stability compared to open loop performance.