Specifications

The optical interface can be ordered with different optical connectors as specified in the
parts list (pls. ref. to 2). It is also possible without the need of using special tools to
change the optical interface by replacing the optical connector interface plate by
another one as specified in the parts list.
For an EMS (element management system) or a NMS (network management system) an
Ethernet 10/100 MBps interface is available at the rear side of the ES10-XLa. This
Ethernet interface supports SNMP and Webbrowser protocols. The IP address for the
Webbrowser interface can be set using the push buttons at the front panel or the RS232
local set-up port at the rear side.
An additional RS485 (master) interface has been implemented at the ES10-XLa to poll
other equipment like EDFAs or optical switches which are connected to the local RS485
management bus.
The ES10-La offers a RS485 for EMS or NMS. An external level converter from RS485 to
RS232 can be offered on request to connect the ES10-La to standard PC-COM1 or -COM2
interfaces.
3.2 Principle of Operation
The transmitter is based on 5 functional blocks: RF-path, CW-DFB-Laserdiode, integrated
optical modulator, control electronics and power supply. The functional diagram is
given in fig. 2.2.
The RF input signal is fed into a preamplifier comprising an automatic gain control
circuitry. The AGC stabilises the output signal of the preamplifier to maintain a stable
RMS- (root-mean-square) optical modulation index (OMI) of the optical modulator.
Input level variations are compensated as long as the AGC circuit is working in its
nominal gain range (ref. to chapter 3).
The AGC can be adjusted turned off for a constant gain operation via the push buttons,
or the Ethernet interface in order to tailor the CNR/CSO/CTB performance to the used
frequency plan and the requirements of the customer by using a different input level.
The electrical RF-signal is fed via a highpass circuit to the input of a predistortion circuit
which is foreseen to linearize the squared sine wave transmission function of the
electrooptical modulator. The predistortion circuit is requested to minimise 3rd order
intermodulations (CTB = composite triple beat). The output signal of the predistortion
circuit is amplified to proper input level for the electrooptical modulator, to establish a
sufficient modulation depth of the optical output signal.
The central core of the transmitter is the electrooptical modulator working as a Mach-
Zehnder-interferometer. The light from the laserdiode is coupled to an optical strip
waveguide. An integrated optical splitter divides the light into two identical portions
which are phase modulated by an RF signal applied to the electrodes of the modulator.
The concept of the electrodes results in an push pull phase modulation of both
branches. Following the modulating section the signals of both arms are combined and
interfere. The interference of the phase modulated signals results in an amplitude
modulation of the output light signal which is available on both outputs of the
combiner.
The necessary CW input light for the modulator is produced by a DFB laserdiode
working with a wavelength between 1550 and 1560 nm. There are two control loops
for operating the laserdiode at constant optical output power as well as at constant
temperature by means of a thermoelectric cooler. The ES10-XLa has been designed for
DWDM applications and allows to change the operation frequency (wavelength) by +/-
100 GHz in steps of 50 GHz. The laserdiode drive current is measured to detect an
increase to 130% of the initial value which could be caused e.g. due to ageing of the
laserdiode. The temperature of the laserdiode is supervised by measuring the required
drive current for the thermoelectric cooler. At 90% of the available cooler drive current
Funea Broadband Services bv product information page 8 of 31
version: 11-02