Performance of the Optical Links

The optical signals pass four connection points before they are translated into electronic signals in the FED modules in the service room a single-fiber (MU) connection on the supply tube located at 2 m distance from the laser, a multi-fiber (ribbon) connection at the pixel detector PPO at a distance of 3 m, a multi-ribbon connection at the strip tracker PPl at 7 m distance and a connection to the FED modules at 63 m distance. The latter connection at the strip tracker end-flange was not accessible anymore at the time of the BPIX installation. 

In addition, a bad PPl connection was found. The four fibers passing through that connection could be recovered by using a spare ribbon. An example of the OTDR measurement of a fiber with a reflection at the MU and the PPl connection is shown in Fig. 8.16. 

The visual inspection of the connection to the FED was performed with a microscope and 19 ribbons with marks on the fibers were spotted. In about 50% of the cases cleaning was successful and slightly improved the noise behavior. A microscopic view of the FED connection with marks on the fibers can be seen in Fig. 8.17. 

Not a single optical fiber of the BPIX detector was lost during all operations. 

Although the testing after the transport of the BPIX detector has not revealed any damage (in addition to the four modules known to be non-working), after the installation five more broken modules were identified. The failure modes are  

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