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Opto-electronics

Opto-electronics. Why use opto-electronics General advantages HEP experiments Elements of system Emitters Fibres Receivers LHC examples. Advantages of Opto-electronics. General Much bigger bandwidth than Cu cables (bandwidth of a links is speed * distance). HEP experiments

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Opto-electronics

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  1. Opto-electronics • Why use opto-electronics • General advantages • HEP experiments • Elements of system • Emitters • Fibres • Receivers • LHC examples T. Weidberg

  2. Advantages of Opto-electronics • General • Much bigger bandwidth than Cu cables (bandwidth of a links is speed * distance). • HEP experiments • Fibres have lower mass and lower Z than Cu cables  smaller contribution to the r.l. of the detector. • Electrical isolation of the two ends of the link. T. Weidberg

  3. Opto-electronic System Receiver + amp. Emitter + driver Repeater fibre T. Weidberg

  4. Coding Schemes • Analogue: optical signal proportional to signal. • Digital: digitise data and send binary signals. • Non Return to Zero • Bi-Phase Mark • Others… 0 1 0 1 0 0 1 0 T. Weidberg

  5. Emitters • Old emitters were usually LEDs - power ~ 10 mW, linewidth ~ 50 nm • Newer emitters are semiconductor lasers • power ~ few mW, linewidth ~ nm. •  figures for edge emitters - advantages of VCSELs  figure. T. Weidberg

  6. SemiConductor Lasers Simple homojucntion laser Very high thresholds. Hetrojunction lasers. Confinement of carriers and wave  lower thresholds. T. Weidberg

  7. VCSELs • Very radiation hard • 850 nm matched to rad-hard Si PIN diodes. • Cheap to test and produce. • Easy to couple into fibres. • Easy to drive. • Low thresholds (~4 mA). T. Weidberg

  8. Fibres • Types of fibres ( figures) • Step Index Multi-mode (SIMM) • Graded Index Multi Mode (GIMM) • Monomode MM • Pros and Cons • Dispersion ( figures) • Launch power T. Weidberg

  9. SIMM Fibres • Simplest fibre: Step Index Multi-mode fibre. • Light trapped by total internal reflection. • Maximum angle • Problem is large modal dispersion T. Weidberg

  10. GRIN fibres Adjust refractive index profile to minimise modal dispersion. Best way to minimise dispersion is with single mode fibre T. Weidberg

  11. Fibre Dispersion and Attenuation Dispersion is a minimum ~ 1.3 mm Attenuation is minimum ~1.5 mm T. Weidberg

  12. Receivers • Receivers are usually PIN diodes. • Active region is low doped intrinsic  low depletion voltages. • Types of PIN Si l ~ 850 nm GaAs l: < ~ 900 nm InGaAs l: < ~1500 nm T. Weidberg

  13. ATLAS SCT/Pixel links • Low mass, low Z package ( figure). • Very rad-hard • Spike F doped, pure silica core SIMM fibre • VCSELs: very rad-hard. Stimulated emission  short carrier lifetimes  less sensitive to non-radiative processes (caused by radiation induced defects). Show rapid annealing after irradiation. • Epitaxial Si PIN diodes. Thin active layer  fully depleted at low bias voltage (< 10V) even after radiation damage. T. Weidberg

  14. 2 VCSEL+1 PIN Opto-package T. Weidberg

  15. VCSEL Array MT-12 connector 12 way ribbon fibre T. Weidberg

  16. Liquid Argon Calorimeter Readout T. Weidberg

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