The radiation hardness and temperature stability of Planar Light-wave Circuit splitters for the High Luminosity LHC

Abstract

High Luminosity LHC (HL-LHC) Inner Tracker designs may include the sharing of Timing, Trigger and Control (TTC) signals between several tracker modules.This is possible because the highest frequency signals are common to all modules.Such designs are an attractive option because they reduce the number of optical links required and hence the cost.These designs will require optical signal splitters that are radiation hard up to high doses and capable of operating in cold temperatures.Optical splitters are available as either fused-fibre splitters or Planar Light-wave Circuit (PLC) splitters.PLC splitters are preferable because they are smaller than fused-fibre splitters. A selection of PLC splitters from different manufacturers and of two different technologies (silica and glass based) have been tested for radiation hardness up to a dose of 500 kGy(Si) and for temperature stability.All the tested splitters displayed small increases in insertion losses ( < 0.1 dB) in reducing the operating temperature from 25°C to −25°C.The silica based splitters from all manufacturers did not exhibit significant radiation induced insertion losses, despite the high dose they were exposed to.The glass based sample, however, had a per channel radiation induced insertion loss of up to 1.16 dB.Whilst the silica based splitters can be considered as qualified for HL-LHC use with regards to radiation hardness, the glass technology would require further testing at a lower, more realistic, dose to also be considered as a potential component for HL-LHC upgrade designs.