Olson Technology MUSCLE-EM55X - Manual (Page 25)

OTOT-EM55X/XL Optical Transmitter Rev. x1 www.olsontech.com
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Mode: AGC-on, modulated carriers (user adjustable)
There is an alternative AGC mode available for measurement purposes only: AGC-on for modulated carriers. This
mode is only required when measuring CXMA (cross modulation distortions) in HFC networks and should not be used
in normal operations of HFC networks.
In CXMA measurements with AGC on the RF signal is increased by about 3dB due to the typical 100% duty cycle in
cross modulation measurements. This leads, however, to rather poor CXMA values measured. In order to compensate
for the increased gain, the AGC-on mode for modulated carriers has been implemented. Compared to the AGC-on
mode for unmodulated CW carriers, the gain is decreased by about 3dB for measurement purposes only.
Mode: AGC-off, (user adjustable)
In this mode, which is for experienced users only, the user has the flexibility to change the gain of the internal RF am-
plifier by +3 / -6dB according to his individual requirements. This adjustment, however, changes the RF input sensi-
tivity. The OMI
totrms
is measured for the applied input signal and selected gain and can be monitored on the LCD or via
the Ethernet interface. This mode should only be used with great care since the automatic protection against over-
modulation as given in the AGC-on mode is lost.
ITU frequency adjustments in DWDM applications (OTOT-EM55XL only)
The OTOT-EM55XL offers the feature to tune the optical frequency (respectively wavelength) of the transmitter by
±100 GHz in steps of 50GHz in order to enable DWDM applications. The tuning can be performed via the buttons on
the front panel or via the Ethernet interface.
Optical Power On /Off
The transmitter can be configured as a back-up transmitter with optical output power off. This allows turning on the
transmitter within less than 10 seconds in situations when a fast switching to a redundant transmitter is requested. The
optical power on/off switching can be performed via the buttons on the front panel or via the Ethernet interface.
SBS suppression setting (OTOT-EM55XXL only)
The OTOT-EM55XL enables theuser to change the SBS suppression of the transmitter. SBS (Stimulated Brillouin
Scattering) is a well known problem in long distance, high power transmission. For extremely coherent optical light,
SBS occurs already at optical powers of around +6dBm (4mW) in standard single mode fibers. With electronic meas-
ures the coherency of the light can be degraded which increases the SBS threshold that means the optical power which
leads to strongly perturbing SBS effects, destroying the CNR and CSO performance especially in the lower transmis-
sion frequency band.
If the SBS threshold is increased, another effect, the SPM (self phase modulation) arises. This effect degrades the CSO
performance in the higher frequency band. SPM depends on the total dispersion, which is present in the transmission
system.
SBS and SPM are both nonlinear effects in optical fibers and depend on
• the launched optical power
• the fiber properties (especially fiber loss and mode field diameter)
• the link properties (number of splices and total splice loss)
Both effects are worse with
• higher optical power
• lower mode field fiber diameter
• higher quality, lower loss fiber
• fewer, lower loss splices
Olson Technology tests the SBS and SPM performance of the OTOT-EM55XL with a standard IEC rec. G652 fiber
under worst case conditions: link containing no splices and providing a fiber loss of only 0.19dB/km. For this test ar-