98 – Operating and Maintenance Instructions
Example Application: Characterizing Fiber Bragg Gratings in Reflection
Fiber Bragg Gratings work by reflecting the light back into the wavelength region that they are
designed to filter out. When measuring the gratings in transmission considerable light is
reflected back into the Control Module. The Control Module is designed to accommodate this
phenomenon.
A circulator is needed for this measurement. In addition, a 100% reflector is required for the
reference. It is not recommended that the device be measured in both transmission and
reflection simultaneously. Also, special care needs to be taken that the transmitted portion of the
light is prevented from corrupting the measurement in reflection. As in any SWS measurement,
the first step is to acquire the zero loss reference. Next, the device is connected and the
measurement is performed.
Measuring Insertion Loss of an FBG
To measure the insertion loss of the FBG in reflection:
1. Connect the FBG to the system, as shown in Figure 81.
Figure 81: Setup for Characterizing the FBG
2. To perform the reflection measurement, replace the reflector with the FBG and terminate the
transmitted output of the FBG using a mandrel termination or similar technique. The mandrel
termination is used to prevent possible reflection of light to Port 2 back through the grating
and the corruption of the insertion loss measurement by the reflected light. Corruption can
reduce the insertion loss by as much as 10 dB. The reflection measurement is made on
Channel 2 of the receiver, which is consistent with the way the zero loss measurements are
performed.
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Содержание SWS15100
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