Tektronix OI1125 Instruction Manual page 40

Theory of Operation
Front Panel
Rear Panel
Transmitter Board
28
The front panel of the transmitter provides access to most of the connectors and
the manual controls for the instrument. FC/APC-PM connectors are used for
both the internal laser output and the modulator laser input. An external optical
patch cord connects the two when the internal laser is used as the optical source.
A modulated electrical data signal connects to a high-quality SMA connector and
is routed internally to the modulator driver on the transmitter board. The
modulated optical signal is routed to a single-mode fiber, universal optical output
connector.
A keyswitch with a removable key enables the internal laser, and laser status is
displayed with indicators backlit by green LEDs. Potentiometers and pushbutton
switches control the front-panel adjustments.
The rear panel of the transmitter has four components: the AC line cord
connector, the power on/off switch, the laser direct modulation input connector,
and the remote interface connector.
When any of the international power cords available for the transmitter are
connected to the AC connector, the power is passed through to the power on/off
switch. When the switch is turned on, the AC line is connected to the power
supply input.
The laser direct modulation input connector is an SMA connector that accepts a
low frequency (<10 MHz) electrical signal. This signal can be used to directly
modulate the internal optical signal for identification or other special purposes.
The remote interface is a 25-pin D-connector that provides remote control of all
the front panel control features, as well as access to all status indicators. The
remote port is primarily a TTL control/status interface with analog voltage
control of the front panel control knobs.
The laser safety interlock control, which provides a redundant shutoff capability
for the internal laser, is also implemented with a control pin on the remote
interface connector.
The transmitter board is comprised of two main circuits: the internal laser, and
the modulator and related support circuitry.
Internal Laser. The internal laser is a distributed feedback (DFB) laser module
with an output power level high enough for Class IIIb rating. The laser module
includes a polarization-maintaining fiber (PMF) connection to the front panel so
that either the internal laser or an external, tunable laser can be used to drive the
modulator. The modulator requires that its input optical source has the correct
orientation of its polarization to operate properly.
OI1125 E/O Transmitter Instruction Manual