1. Tutorial on optical fibres F. Reynaud IRCOM Limoges Équipe optique F. Reynaud IRCOM Limoges Équipe optique Cargèse sept 2002

2. optical fibre structure 1) Generalities Cargèse sept 2002 Silica fibres typical refractive index : 1,45 – 1,50 Refractive index difference Core diameter : 5 à 50 µmCladding diameter : 125 à 500 µm Refractive index profil

3. optical fibre manufacturing Cargèse sept 2002 1) preform manufacturing 2) Drawing process (Modified Chemical Vapour Deposition). PCVD (Plasma Chemical Vapour Deposition) OVPO (Outside Vapour Phase Oxydation 1) Generalities

4. 2) Propagation in optical fibres Cargèse sept 2002 Geometrical optics Snell Decartes law : i 1 > i lim Possibility to trap light beams in an high refractive index area surrounded by a low refractive index area

5. Cargèse sept 2002 Wave theory 2) Propagation in optical fibres First example planar mirror guide Propagation without losses: Intensity = 0 on mirrors a = n i with n = integer Two directions interference between two plane waves For each n one propagation mode

6. Cargèse sept 2002 2) Propagation in optical fibres Propagation without losses: Intensity =0 close to the core/cladding interface a+ 2  = n i with n = integer Two directions interference between two plane waves Second example Planar dielectric waveguide Wave theory One mode n One angle  n solution of the equation

7. Cargèse sept 2002 2) Propagation in optical fibres Second example Planar dielectric waveguide Wave theory Limited number of mode If only one>>>monomode  0    solutions

8. Cargèse sept 2002 2) Propagation in optical fibres Wave theory 3 D interference

9. Cargèse sept 2002 2) Propagation in optical fibres Properties of the modal structure Decomposition of any optical field on the mode basis Wave theory Same transverse field distribution at the input and output Propagation = phase shift  n is the propagation constant Propagation = phase shift

10. Cargèse sept 2002 2) Propagation in optical fibres  depends upon Dispersion Mode in a multimode fibre Modal or intermodal dispersion

11. Cargèse sept 2002 2) Propagation in optical fibres Dispersion Wavelength dependent  Chromatic or intramodal dispersion -10 -5 0 5 10 15 20 25 12001300140015001600 Wavelength (nm) Chromatic dispersion (ps/nm.km) G.652 (0.08 ps/nm 2.km) G.653 EDFA bandwidth G.655

12. 3) Determination of the mode number Diffraction properties Basic rules General case Multimode beam Monomode beam Cargèse sept 2002

13. 3) Determination of the mode number Core diameter /a Numerical aperture NA Number of spots or speckles Number of modes Case of an optical fibre

14. Cargèse sept 2002 3) Determination of the mode number One speckle diameter surface Fibre core Number of degrees of freedom diameter surface a Warning: N is wavelength dependent

15. Cargèse sept 2002 3) Determination of the mode number Two examples n 2 =1.450 a=8µm Monomode fibre n 1 =1.455 a=50µm n 2 =1.450 n 1 =1.462 Multimode fibre Warning: N is wavelength dependent @  = 1.3µm

16. 4) Characterisation of optical fibres Cargèse sept 2002 Numerical aperture Refractive index distribution n( radius ) radius

17. Cargèse sept 2002 4) Characterisation of optical fibres Fibre losses 1000 1200 1300 1400 1500 1600 1.0 Loss (dB/km) 0.1 0.5 0.2 Wavelength (nm) Transmission fibre loss (silica) I2I2 I1I1 Second step Detector Fibre length d Launching assembly =0

18. 5) Optical fibre implementation Cargèse sept 2002 Connectors Plug with a ceramic ferule FCPC E2000 body Loss as function of The transverse position error

19. Cargèse sept 2002 5) Optical fibre implementation couplers Fusion splicing polishing Glued From 2 to 2 From 2 to 8

20. Cargèse sept 2002 principal use>> optical fibre telecommunications 6) Application of optical fibers Very high bit rate 1 Tbit/sec Very low losses The solution for long distance signal propagation

21. Cargèse sept 2002 Optical fibre sensors Temperature Pressure Rotation Chemical concentration 6) Application of optical fibers

22. Possibility to built interferometers Mach Zehnder configuration Cargèse sept 2002 6) Application of optical fibers See next lecture

23. Cargèse sept 2002 7) Material and new optical fibers UV 0.3µm Visible Near IR 2µm Far IR 10µm

24. Cargèse sept 2002 DGD Slow PSP Fast PSP 7) Material and new optical fibers Polarisation preserving fibers Highly birefringent fibres core cladding Stress area Propagation

25. Cargèse sept 2002 7) Material and new optical fibres structure Photonic crystal fibres Monomode over a very large spectral domain