J. Troska

Optical readout and control systems for the CMS tracker

The Compact Muon Solenoid (CMS) Experiment will be installed at the CERN Large Hadron Collider (LHC) in 2007. The readout system for the CMS Tracker consists of /spl sim/10 million individual detector channels that are time-multiplexed onto /spl sim/40000 uni-directional analogue (40MS/s) optical links for transmission between the detector and the /spl sim/65m distant counting room. The corresponding control system consists of /spl sim/2500 bi-directional digital (40Mb/s) optical links based upon the same components as far as possible. The on-detector elements (lasers and photodiodes) of both readout and control links will be distributed throughout the detector volume in close proximity to the silicon detector elements. For this reason, strict requirements are placed on minimal package size, mass, power dissipation, immunity to magnetic field and radiation hardness. It has been possible to meet the requirements with the extensive use of commercially available components with a minimum of customization. The project has now entered its volume production phase after successful completion of technical feasibility. Components have been identified that meet both the stringent analogue performance targets and are sufficiently radiation-hard for use in the CMS Tracker, where lifetime radiation exposure is expected to reach /spl sim/3.4/spl times/10/sup 14//cm/sup 2/ fluence and /spl sim/150kGy dose. Analogue and digital system performance, as well as the component radiation hardness and quality assurance procedures, are reviewed this paper.

Radiation Damage Studies of Lasers and Photodiodes for Use in Multi-Gb/s Optical Data Links

Neutron and pion irradiation and annealing data from semiconductor lasers and photodiodes for use in 10 Gb/s datalinks are presented. These components are found to be generally more radiation resistant than their older counterparts. Radiation damage in lasers has been modeled to allow extrapolation of the results obtained to the final application.

The Versatile Transceiver: towards production readiness

Detectors involved in the upgrade programme of the LHC will need high-speed optical links to transfer readout and control data. The link front-end will be based on a radiation tolerant opto-electronic module, the Versatile Transceiver (VTRx), developed under the Versatile Link project. In this contribution we present a test system and protocol to be used to verify the compliance of the VTRx modules to the specifications, and a Versatile Link demonstrator based on the VTRx and the Gigabit Link Interface Board. Finally, we introduce the Small Footprint VTRx which is being designed for the CMS Tracker upgrade.

The GBLD: a radiation tolerant laser driver for high energy physics applications

The GigaBit Laser Driver (GBLD) is a radiation tolerant ASIC which is part of the GigaBit Transceiver (GBT) chipset. It is aimed to drive both edge emitting and VCSEL laser diodes at a data rate in excess of 5 Gb/s. The GBLD can provide a modulation current up to 24 mA and a bias current up to 43 mA. Pre- and de-emphasis functions are implemented to compensate for high external capacitive loads and asymmetric laser response. The chip is designed in a 130 nm CMOS technology and is powered by a single 2.5 V supply.

Single-Event Upsets in Photoreceivers for Multi-Gb/s SLHC Data Transmission

A 63 MeV proton beam was used to perform a single event upset (SEU) test on a candidate component for a future high luminosity large hadron collider (HL-LHC) high speed optical. An in-lab error injector was used to show that 1-0 bit errors are caused by the amplifiers response to the large signal caused by a single event transient (SET) in the photodiode.

Radiation hardness assurance and reliability testing of InGaAs photodiodes for optical control links for the CMS experiment

A radiation hard 80 Mbit/s digital optical link system with 7200 fiber channels is being produced for the CMS Experiment at CERN. A series of tests including radiation damage and thermally accelerated aging have been made to qualify and assure the radiation hardness and reliability of InGaAs photodiodes intended for use in this system.

Radiation hardness qualification of InGaAsP/InP 1310 nm lasers for the CMS Tracker optical links

The series of validation tests for radiation hardness qualification of lasers for use in 46000 optical links of the CMS Tracker detector at CERN, Geneva, Switzerland, are presented. These tests included accelerated radiation damage, annealing, and aging studies, simulating the effect of doses and fluences, up to 2/spl times/10/sup 14/ particles/cm/sup 2/ and 100 kGy, accumulated over a ten-year operating lifetime. The worst-case damage effect, in lasers operating closest to the beam-collision point, is expected to be a threshold current increase of under 6 mA. The lasers tested therefore qualify as being sufficiently radiation hard. The qualification tests also form the basis of future radiation hardness assurance of lasers during final production. An advance validation test of lasers from candidate wafers is defined that will confirm the radiation hardness of lasers before a large number of transmitters are assembled from these wafers.

Modal Dispersion Mitigation in Standard Single-Mode Fibers at 850 nm With Fiber Mode Filters

We investigate the possibility of using a fiber which supports only the fundamental LP01 mode at 850 nm as a mode filter to overcome modal dispersion in standard single-mode fiber links that employ either multitransverse or single-transverse-mode vertical-cavity surface-emitting lasers. The individual power penalties due to modal noise and modal crosstalk effects in the link are investigated.

Modeling TID Effects in Mach-Zehnder Interferometer Silicon Modulator for HL-LHC Data Transmission Applications

High-speed Mach-Zehnder interferometer silicon modulators were exposed to a total ionizing dose of 1.3 MGy, levels comparable to the worst radiation levels for a tracking detector after 10 years of operation at the High-Luminosity LHC, show a sensitivity to ionizing radiation after exposure to a dose of a few hundred kGy. A physical model to describe the effect of ionizing radiation on the modulators has been developed and is used to predict whether a more radiation-hard modulator can be designed to survive the harshest radiation environments expected at the HL-LHC.

Modelling radiation-effects and annealing in semiconductor lasers for use in future particle physics experiments

Optical link components used in future particle physics experiments will typically be exposed to intense radiation fields during the lifetime of the experiment and the qualification of these components in terms of radiation tolerance is thus required. We have created a model that describes the degradation of the L-I characteristic of a semiconductor laser undergoing irradiation with the annealing processes taken into account. This model can be used to predict the behaviour of a laser being irradiated with the different particle fluxes at different locations inside a particle physics experiment. The robustness of the model has been checked against the experimental data obtained during high-fluence (in excess of 1015 particles/cm2) neutron and pion irradiation testing in 2009 and 2010.