EXFO IQS-12004B DWDM Passive Component Test System for IQS-500 - Manual (Page 420)

Definitions and Calculation Methods
408 IQS-12004B
Bandwidth (nm)
Bandwidth is the spectral width over which the transmission of the device
exceeds some stated loss value. The system can measure bandwidth at
three different power levels, called BW1, BW2, and BW3, relative to the
peak power level, as illustrated in the following diagram.
These levels are configurable by the user, but they are given the default
values of 1.0 dB, 3.0 dB, and 20.0 dB.
³
A BW1 bandpass filter (at 1.0 dB or 0.5 dB) is commonly referred to as
the passband or operating wavelength range of the device.
³
BW2 (at 3 dB) is the half-power bandwidth.
³
BW3 (at 20 dB or higher) is often used to describe the rejection or
isolation band. The BW1/BW3 ratio can be used as an indicator of
the filter shape.
I
MPORTANT
The application uses BW1 for a number of calculations (IL, ripple,
and crosstalk), and the results will depend on the selected method.
Increasing loss
1.0 dB bandwidth (BW1)
3.0 dB bandwidth (BW2)
20.0 dB bandwidth (BW3)
Wavelength