Maximizing the Bandwidth Efficiency of the CMS Tracker Analog Optical Links

The feasibility of achieving faster data transmission using advanced digital modulation techniques over the current CMS Tracker analog optical link is explored. The spectral efficiency of Quadrature Amplitude Modulation -Orthogonal Frequency Division Multiplexing (QAM-OFDM) makes it an attractive option for a future implementation of the readout link. An analytical method for estimating the data-rate that can be achieved using OFDM over the current optical links is described and the first theoretical results are presented

Potential Upgrade of the CMS Tracker Analog Readout Optical Links Using Bandwidth Efficient Digital Modulation

The potential application of advanced digital communication schemes in a future upgrade of the CMS Tracker readout optical links is currently being investigated at CERN. We show experimentally that multi-Gbit/s data rates are possible over the current 40 MSamples/s analog optical links by employing techniques similar to those used in ADSL. The concept involves using one or more digitally-modulated sinusoidal carriers in order to make efficient use of the available bandwidth.Comment: Presented at LECC 2006, Valencia, Spain. 5 pages, 11 figures

Feasibility of Using Bandwidth Efficient Modulation to Upgrade the CMS Tracker Readout Optical Links

Plans to upgrade the LHC after approximately 10 years of operation are currently being considered at CERN. A tenfold increase in luminosity delivered to the experiments is envisaged in the so-called Super LHC (SLHC). This will undoubtedly give rise to significantly larger data volumes from the detectors, requiring faster data readout. The possibility of upgrading the CMS Tracker analog readout optical links using a bandwidth efficient digital modulation scheme for deployment in the SLHC has been extensively explored at CERN. Previous theoretical and experimental studies determined the achievable data rate using a system based on Quadrature Amplitude Modulation (QAM) to be ~3-4Gbit/s (assuming no error correction is used and for an error rate of ~10-9). In this note we attempt to quantify the feasibility of such an upgrade in terms of hardware implementation complexity, applicability to the high energy physics (HEP) environment, technological feasibility and R&D effort required.Comment: CERN CMS Note. 16 pages, 10 figure

Neutron, Proton and Gamma Radiation Effects in Candidate InGaAs p-i-n Photodiodes for the CMS Tracker Optical Links

InGaAs p-i-n photodiodes will be used in the CMS tracker to receive the digital timing and control signals transmitted from the Front End Controller ( FEC) boards by 1^10nm wavelength lasers. These devices should be sufficiently rad-hard to survive the fluences/doses encountered in the tracker during a ten year operational period. Candidate p-i-n diodes have been irradiated, in a fully packaged, fibre-pigtailed form, with up to 10^15neutrons/cm2 ( <En>=6MeV), 4x10^14 protons/cm2 ( Ep=24GeV) and 100kGy 60Co photons. Displacement damage from the neutron and proton irradiation caused the leakage current to increase by 6-7 orders of magnitude and the responsivity to decrease by 90% after ~10^14 p/cm2 or 10^15 n/cm2. Gamma damage was almost negligible in comparison. If the current prototype p-i-n photodiodes are used in the tracker, they should be situated at least 50cm from the beam axis where the hadron fluence is less than 10^14/cm2

Response of the APV readout chip to laser-simulated, highly ionizing interactions

Heavily Ionizing Particles are know to cause sizable dead-time in the front end APV chip of the CMS Silicon Strip Tracker. To better understand this behavior, the effects of Highly Ionizing Particles in the CMS Silicon Strip Tracker were simulated using a 1060 nm laser. Calibrated laser pulses allow one to determine the energy threshold at which the dead-time becomes significant as well as the time evolution of the chip response. Various APV settings and supply line resistor values were investigated. Results agree with test beam data as well as previous laboratory measurements in confirming that settings can be found for which the dead-time is as low as 100ns for up to 50 MeV deposited energy

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 46 000 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 multiplied by 10**1**4 particles/cm**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. 19 Refs

A Method for the Static Characterisation of the CMS Tracker Analogue Optical Links

Analogue optical links are being developed for the CMS-Tracker. The large envisaged number of physical channels ( over 50.000) imposes semi-automated test procedures and efficient evaluation criteria to compare different link solutions, to optimise their performance, and to confirm their compliance with specifications when commissioning the system. In addition, self-triggered calibration schemes need to be developed to maintain the readout chain accuracy during the detector lifetime ( 10 years). In this paper we present a method for the static characterisation of the CMS analogue optical links, relying on an automated setup for gain, rms-noise and linearity measurements, and on a software program for off line processing of the test data. We propose a set of evaluation criteria and describe a compact representation of the results in the operational parameter space ( working point, operating range). This representation allows to quantify and compare the performance of links based on different components, as well as to develop and simulate practical testing and calibration procedures

Neutron damage studies of semiconductor lasers for the CMS tracker optical data links

The raw data from the silicon and MSGC tracking detectors in the future CMS Experiment at the LHC will be acquired via a 60000 channel, 100m long, analogue optical link. The use of directly modulated lasers is being investigated as a possible solution for the CMS optical link. Prototype lasers and monolithic laser arrays have been obtained from several manufacturers and the issues to be investigated include device performance, radiation hardness, reliability, packaging and projected cost. The test of radiation hardness precludes further investigations therefore this paper focuses on the performance of lasers and laser arrays before, during, and after irradiation with 6MeV neutrons

Effect of Neutron Irradiation of MQW Lasers to 10^15n/cm2

1300nm edge-emitting multi-quantum-well lasers are the baseline choice for the optical transmitter in the CMS tracker optical links. The radiation environment is expected to be ~10Mrad and ~10^14( neutron-equivalent)/cm^2 over ten years. Lasers from four manufacturers have been irradiated in naked die form with neutron fluences of ~2x10^14n/cm^2. One laser type was also irradiated in a fully packaged, fibre-pigtailed form up to ~10^15n/cm^2. Neutron damage caused an increase in laser threshold current and a decrease in output efficiency, but little change in signal - to - noise ratio, linearity, and emission wavelength spectrum