1. Detector lecturesT. Weidberg1 Opto-electronics Why use opto-electronics –General advantages –HEP experiments Elements of system –Emitters –Fibres –Receivers LHC examples

2. Detector lecturesT. Weidberg2 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.

3. Detector lecturesT. Weidberg3 Opto-electronic System Emitter + driver fibre Repeater Receiver + amp.

4. Detector lecturesT. Weidberg4 Coding Schemes Analogue: optical signal proportional to signal. Digital: digitise data and send binary signals. –Non Return to Zero –Bi-Phase Mark –Others… 010 00 1 10

5. Detector lecturesT. Weidberg5 Emitters Old emitters were usually LEDs - power ~ 10  W, linewidth ~ 50 nm Newer emitters are semiconductor lasers -power ~ few mW, linewidth ~ nm. -  figures for edge emitters - advantages of VCSELs  figure.

6. Detector lecturesT. Weidberg6 SemiConductor Lasers Simple homojucntion laser Very high thresholds. Hetrojunction lasers. Confinement of carriers and wave  lower thresholds.

7. Detector lecturesT. Weidberg7 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).

8. Detector lecturesT. Weidberg8 Fibres Types of fibres (  figures) –Step Index Multi-mode (SIMM) –Graded Index Multi Mode (GIMM) –Monomode MM Pros and Cons –Dispersion (  figures) –Launch power

9. Detector lecturesT. Weidberg9 SIMM Fibres Simplest fibre: Step Index Multi-mode fibre. Light trapped by total internal reflection. Maximum angle Problem is large modal dispersion

10. Detector lecturesT. Weidberg10 GRIN fibres Adjust refractive index profile to minimise modal dispersion. Best way to minimise dispersion is with single mode fibre

11. Detector lecturesT. Weidberg11 Fibre Dispersion and Attenuation Dispersion is a minimum ~ 1.3  m Attenuation is minimum ~1.5  m

12. Detector lecturesT. Weidberg12 Receivers Receivers are usually PIN diodes. Active region is low doped intrinsic  low depletion voltages. Types of PIN Si ~ 850 nm GaAs : < ~ 900 nm InGaAs : < ~1500 nm

13. Detector lecturesT. Weidberg13 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.

14. Detector lecturesT. Weidberg14 2 VCSEL+1 PIN Opto-package

15. Detector lecturesT. Weidberg15 VCSEL Array MT-12 connector 12 way ribbon fibre

16. Detector lecturesT. Weidberg16 Liquid Argon Calorimeter Readout