Specifications

ES10/ES26 Page 12/104

Document status: released Operating Manual rev. 01, 03.11.08

Ethernet -

Interface

RS485 -

Interface

RS 232-

Interface

Liquid crystal

display +

push buttons

Input

onitor

RF - Input

RF - Monitor

CSO

Detection

Fig. 3.2.1: ES10 Block Diagram

The central core of the transmitter is the electrooptical modulator working as a Mach-Zehnder-

interferometer. The light from the laserdiode is coupled into 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 a 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

1550 nm wavelength. 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

ES10XL has been designed for DWDM applications and allows tuning the operation frequency

(wavelength) by +/- 100 GHz in steps of 50 GHz. The laserdiode operating current is controlled in

order to compensate for ageing effects. The temperature of the laserdiode is controlled by

regulating the required drive current for the thermoelectric cooler. At 90% of the available cooler

drive current and/or >130% of the initial laserdiode operating current a warning is generated

which indicates ageing. At 100% cooler drive current the laserdiode operating current is switched

off to protect the laserdiode against irregular temperature conditions and an alarm is generated

indicating severe malfunction. Both types of indications are causing the corresponding LED on

the front plate of the optical transmitter to emit. In case of a warning the LED lights yellow since

the unit is still working properly, however close to its limits. In case of an alarm the LED is

emitting red light. The messages to the network management system are of course more

detailed. They include the actual values of the currents and temperature as well as alarm flags.