D. Charlton, J.D.Dowell, R.J.Homer, P. Jovanovic, I.R.Kenyon,
G.Mahout * H.R.Shaylor, J.A.Wilson. School of Physics and Astronomy, University of Birmingham
I.M. Gregor, 1. Mandic, R.B. Nickerson, R.Wastie, A.R. Weidberg. Physics Department, University 
S.Galagedera, M.C.Morrissey, J.Troska, D.J.White, CLRC Rutherford Appleton Laboratory 
A.Rudge,CERN
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Optical links will be used for the readout of the ATLAS SemiConductor Tracker and Pixel detectors. The Timing, Trigger and Control (TTC) Data for each module will be distributed from the off-detector electronics to each module by optical fibre. The data will also be read out by optical links. The binary transmission system is based on radiation hard VCSELs and Epitaxial Silicon PIN diodes operating at a wavelength X of 850 nm. The readout is done by low mass, non-magnetic optopackages each consisting of 2 VCSELs and I Pin diode. Radiation hard ASICs have been developed to drive the VCSELs (VDC chip) and to recover the 40 MHZ clock and the TTC data from the PIN diode signal (DORIC4). Each subpart of the package has been independently tested:

1.	The VDC and DORIC4 use bipolar npn transistors in AMS 0.8 pm BiCmos technology. The radiation hardness of the latter has been tested on 20 chips with neutrons up to the level needed for the SCT detector (I MeV 3. 1014 n.cm-1) with no deterioration of the signal. The effect of ionising radiation up to IOMrad is under study but the previous chip version (DORIC3) has already given good results.

2.	Several VCSELs from different manufacturers were irradiated. The MlTEL VCSELs have shown good recovery after a short annealing period for a neutron fluence about 1011n.cm-1. The typical light emitted by the VCSELs is a power of I mW for a lOmA current. In order to test their reliability over 10 years, elevated temperatures were used to perform an accelerated aging test on a large sample of VCSELs. The results show a very good reliability over the LHC operation time.

3.	The epitaxial PIN diode receivers have followed the same radiation hardness studies. Up to 96 Pin diodes were tested and their responsivity has dropped by only 30% with a value of 0.3 A/W at the highest radiation dose level. A total darkcurrent of less than 60 nA at room temperature is negligible at the -151C operational temperature of the Inner Detector. However, the radiation damage on the carrier will require a bias of more than 5V at the pixel level to optimize the responsivity. No PIN diodes have failed after an accelerated ageing test of 120 equivalent LHC years and there was no degradation in the responsivity or the risetime.

The design of the optopackage will be presented. The results of the system test, including Bit Error Test, will be given. Test of Single Event Upset have also been performed under a beta source of 4.3 107CM-2 s- I and neutrons higher than 7 MeV with fluence of 3.107 n.cm-2 S-1. No BER problems were observed after several hours of testing. To complete the test of the ATLAS environment, studies were done in a magnetic field up to 6T showing no loss in the signal and risetime with different orientations of the package.

Packaged arrays of 4 way PIN diodes and VCSELs, suitable for the offdetector opto-electronics have been successfully tested.

In conclusion, these completed studies show that the optical package developed for the ATLAS inner detector readout can successfully cope with its environment.
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A full study of the optical readout package for the ATLAS SCT/Pixel detector data transmission is presented. Radiation hardness studies of VCSEL emitters, Epitaxial Silicon PIN diodes receivers and their associated chips have been carried out with fluences higher than 1015n.CM-2 1 MeV neutron equivalent and total ionising doses of 10 Mrad. The reliability was assessed by testing a large number of devices and accelerated ageing tests were also pursued over a period equivalent to more than the LHC operation time. Bit Errors Rate tests, Single Event Upset and magnetic field studies up to 6T have also been done on a new optical package design with positive results.
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