Dr. Tobias Flick

TX Plugin Investigation

A list of investigations going on in the field of understanding the VCSEL problems encountered in the ATLAS Pixel Off-detector part of the optical data transmission link. On this page information are collected and linked.

Rate of death (more information about the current death rates and replacements is here)

• IV-curves taken from dead VCSELs.
• Measurements of the optical spectra from Tx-plugins VCSELs
• Measurements of the optical spectra from the optoboard VCSEL installed in the ATLAS Pixel Detector
• Measurements of the optical spectra from optoboards in a stresstest
• Studies of the thermal behaviour of the VCSEL on a Tx-plugin
• Picture from the VCSEL surfaces
• Tx Plugins longterm test.

IV curves:

For three plugins disassembled from the detector, we have measured the IV-curves of the laser diode. For a plugin assembled with a BPM chip this can only be done in forward direction.

The result is the same as achieved last year looking at the ESD damages devices:
The dead channel shows a changed IV-characteristic. The knee voltage and the rise of the curve is changed from the normal behavior.

More details can be found here.

TX Plugin VCSEL Spectrum Measurements:

Description Measuring the optical spectrum of the devices, it can be seen that the spectrum for used channels
is narrowing. It is not yet clear, how this develops with time, if it is to be expected, if this is the reason for failures etc.
Further investigations are ongoing. A typical spectrum can be seen here (for a 12 channel array out of which the
middle eight have been operated).

More details can be found here.

TX Plugin VCSEL Thermal Behavior Spectrum Studies:

More details can be found here.

Optoboard VCSEL Spectrum Measurements from the Pit:

More details can be found here.

Optoboard VCSEL Spectrum Measurements from Stresstest:

More details can be found here.

TX Plugin VCSEL Surface Inspection:

The VCSEL surface has been observed under a microscope. Pictures like the following can be found here.

TX Plugin and Optoboard VCSEL Stresstest:

More details can be found here.