NCM-1550-EM30 (1550nm externally modulated optical transmitter) operating manual
- 4 -
Stimulated Brillouin Scattering (SBS) occurs, when the optical input power is
greater than a certain threshold value. SBS generate the lower frequency
backscattered light which will attenuate the transmission light and return to the laser
while destroying its performance. Causing optical power fluctuation, generates large
noise, and seriously deteriorates the system carrier to noise ratio (CNR). To improve
the SBS threshold, NCM-1550-EM30 series optical transmitter adopts SBS control
technology which is independent researched and developed by ourselves. The
threshold value can be set up to 19dBm.
The optical modulator has a two-way optical signal output. Parts of that signal
are routed to an InGaAs photodiode. This detection of the optical signal has two
functions:
1)
Detect whether the laser is normal working. Once the output optical power is
2dB lower than standard power, alarm will be set off.
2)
Detect CSO distortion to optimize the bias point of the optical modulator. For
working normal the detector circuit needs at least two carrier signal inputs with an
interval of 24MHz. There is a CSO initialization program in the boot process. If the
CSO install failed, the RF indicator will flash red, see details in
6.2 Troubleshooting.
Block Diagram
1.3
Product Applications
•
High-performance long-distance transmission
•
High-power distribution network
•
Redundancy loop architecture
•
FTTx network
•
RFOG application
•
DWDM network
