Alcatel 1660SM Technical Handbook page 417

The unit has the following building blocks (see Figure 250. on page 417).
Power and reference circuitry
The unit has a direct power supply from battery voltage on backplane: nominal value in the range –48 V
to –60 V.
Devoted to:
•
Input of main power supply with fault protecting circuitry
•
DC/DC conversion from battery voltage to 5.2 V and 3.3 V main on board power supplies (with
fault protecting circuitry and synchronizing oscillator)
•
DC/DC conversion from 5.2 V and 3.3 V main power supplies to –5.2 V, +2.5 V, –3.3 V auxiliary
power supplies (with overvoltage protecting circuitry)
•
Voltage reference generation
•
Power supplies alarm detection
Compact OFA module
Optical fibre amplifier module, an hybrid module of the Alcatel Optronics 1900 OFA family, acting as optical
gain device with built–in input and output power monitoring photodiodes.
Main components are:
•
Photodiode for monitoring of input power (fed by a coupler extracting a small fraction of light
from the main optical path)
•
Input optical isolator (preventing pump power and amplified spontaneous emission to exit from
input port)
•
A length of Erbium doped active fibre
•
Pump laser (operating at 980 nm) to generate optical pumping power
•
A WDM coupler to insert pumping power into active fibre
•
Output optical isolator to prevent external reflections (assuring stable operation of the OFA)
•
Photodiode for monitoring of output power (fed by a coupler extracting a small fraction of light
from the main optical path)
Control block
Mixed analogue and digital circuitry (with a DSP microprocessor) devoted to control:
•
Pump laser temperature
It should be stabilized in a small range around nominal value; the thermistor in OFA module is
used for temperature sensing of the laser, and a Thermo Electric Cooler/Heater (TECH) driven
by a current source/sink circuit is used for temperature control.
DSP processor can monitor TECH current via a sensing resistor, a differential amplifier and A/D
converter.
•
Optical output power
It should be stabilized around target value +10 dBm; output photodiode in OFA module is used
for sensing of output power, and the current of pump laser is adjusted consequently. Moreover
input power to OFA module is monitored via input photodiode, a transimpedance amplifier and
A/D converter.
Main functions of the block are:
•
Conditioning (i.e. level adjusting, buffering, and so on) of analogue signals from sensors internal
or external to OFA module
•
Analogue to digital conversion of the conditioned signals
•
Digital implementation of control logic in DSP microprocessor, to generate control signals
•
Digital to analogue conversion of control signals towards current sources
•
Current source circuits toward OFA module (laser diode current and TECH current)
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