KWS VAROS109, Manual, Page: 64 / 78

62 Chapter 14 – Optical Receiver (Option)
10911 V01.10
Using
MODE
> Settings > Wavelength LAMBDA (second page) you can set the wavelength as 1,310 nm, 1,490 nm or
1,550 nm.
14.4 Measuring the optical power
Optical transmission involves modulation of the intensity of the light power.
The measuring device measures the average optical power in dBm. This power is also measured when the light is
supplied from an unmodulated laser source. In this case, the device can be used as a purely optical power measuring
device. Start the measurement by entering the frequency and pressing ENTER to confirm.
14.5 Measuring the optical modulation index (OMI)
The optical modulation index (OMI) is comparable with the modulation index for an amplitude modulation. The am-
plitude (intensity) of a carrier— here, the light— is modulated. The greater the difference between the maximum
intensity and the minimum intensity, the greater the OMI and the RF voltage (level) after the optical receiver. The OMI is
specified in %. With this device, the OMI is selectively measured for a certain frequency, meaning that only the RF
power within the signal bandwidth is taken into account. It is designated as the individual OMI or the channel OMI. The
attainable signal-to-noise ratio depends on the individual OMI. A value of around 4% is ideal.
Note:
The level specified after the OMI value corresponds to the internal RF level after the optical/electrical
converter. This information is only relative. This specification is primarily used to determine the relation-
ships between the levels of the individual channels..
A brief overview of the relationships between optical power, RF level and OMI is provided below:
If the optical power is increased by 1 dB for optical transmission, the RF voltage increases by 2 dB after the optical
receiver, while the optical modulation index (OMI) remains unchanged. The RF voltage is proportional to the square of
the optical power. If the optical modulation index is doubled (e.g. increased from 2 % to 4 %) with the same optical