1. The LaRC Fiber Draw Tower Presented by Stan DeHaven

2. Draw Tower Research FOSS (Fiber Optic Sensing System) strain sensors. Use Bragg grating in fiber core. Holey Fiber – Multi-core hollow fiber. Tens of Micron hole spacing. NUPERC activity. PCF (Photonic Crystal Fiber) – Micron scale hole spacing. NUPERC activity. Draw Tower Capabilities

3. Fiber Optic Strain Sensor (FOSS) Bragg Gratings

4. Bragg Grating Reflection Spectrum reflection(%) 0 0.1 0.1 nm wavelength(nm) b = center reflection wavelength of Bragg grating  b ) -1 = center reflection wavenumber

5. Bragg Grating as 2nd Reflector in an Interferometer reflector 1 7 % Bragg grating < 0.1 % output power  b ) -1 decreasing wavenumber (increasing wavelength) L  w = -(2nL) -1 L = -(2n  w) -1

6. Multiple Gratings, Multiple Interferometers reflector 1 7 % Bragg gratings output L 1 L 2 L 3 decreasing wavenumber (increasing wavelength) power  w 1 = -(2nL 1 ) -1  w 2 = -(2nL 2 ) -1  w 3 = -(2nL 3 ) -1 (cm) -1

7. FFT To Separate Gratings power (cm) -1 FFT power cm L 1 L 2 L 3

8. Typical Laser Sweep time wavelength

9. FOSS Required Configuration reflector (distance 0) Bragg gratings L 1 L 2 L 3 L ref reference signal data signal Electronics: reference signal data signal A/D c data signal sampled according to reference length fringes

10. FFT To Separate Gratings power (cm) -1 FFT sampled set with  w=-(2nL ref ) -1 spacing between samples number of samples = N sam power cm L 1 L 2 L 3 “Spatial” set with ((N sam -1)  w) -1 between points

11. FFT -1 To Find Grating Spectra power cm L 1 L 2 L 3 “Spatial” set with  spat=((N sam -1)  w) -1 point spacing FFT -1 power (cm) -1  b ) -1 “Spectral” set with  spec=((N spec -1)  spat) -1 point spacing

12. Bragg Grating Reflection Spectrum reflection(%) 0 0.1 0.1 nm wavelength(nm) b = center reflection wavelength of Bragg grating  b ) -1 = center reflection wavenumber

13. FOSS Draw Tower Operation

14. Draw Tower Preform in Furnace

15. Bragg Grating Optics

16. Draw Tower View

17. Excimer Laser (248 nm, 500mJ)

18. Fundamentals of Photonic Crystals - What are photonic crystals? - Theory of Photonic Crystals Photonic Crystal Fibers (PCF) Fabrication of PCF Advantages and Challenges Photonic Crystals & Fibers

19. Photonic Crystals & fibers What are photonic crystals? Features of a photonic crystal: Made of low-loss periodic dielectric medium Optical analog to the electrical semiconductors Able to localize light in specified areas by preventing light from propagating in certain directions – optical bandgap.

20. Theory of photonic crystals

21. Theory of photonic crystals, con’t

23. In 2D photonic crystal structures it is possible to confine light within a cavity. Photonic band gaps appear in the plane of periodicity and in 2D we can achieve linear localization. By introducing a defect, i.e. removing one column, we may obtain a peak in the density of states localized in the photonic band gap – similar to semiconductors. The defect mode cannot penetrate the crystal in the xy- plane because of the band gap but extends in the z- direction

24. Photonic crystal fibers By making a suitable geometry of the periodic dielectric medium, a phonic crystal can be used as an optical fiber.

25. PCF Fabrication PCF Preform Construction PCF Drawing -similar to drawing capillary tubes

26. Preform Construction Tubes are packed in a hexagonal shape with hollow, solid, birefringent, doped or tubular core elements.

27. Multi-Core Preform

28. Drawing PCF Preform of packed tubes is drawn in a draw tower furnace Single tube drawing characteristicsPreform drawing down in furnace

29. SEM Image of Multicore Fiber

30. Multi-core Drop with drawn fiber

31. Advantages: PCF with high-index core is more flexible than conventional fiber: - Possible to make very large core area to send high power - Possible to make core very small compared to conventional fibers. Designer wavelengths possible. Air-guiding PCF (hollow core of fiber): - Possible to send high power - No entrance or exit reflectance Challenges: PCF is difficult to fabricate PCF is limited to specific frequencies

32. Draw Tower Capabilities Graphite Furnace Multiple heat zone furnace elements Fiber diameter feedback control IR and UV thermal fiber coating capability Excimer Laser Ability to write gratings while drawing fiber for increased fiber strength