The La RC Fiber Draw Tower Presented by

The La. RC Fiber Draw Tower Presented by Stan De. Haven

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

Fiber Optic Strain Sensor (FOSS) Bragg Gratings

Bragg Grating Reflection Spectrum lb = center reflection wavelength of Bragg grating (lb)-1 = center reflection wavenumber reflection(%) 0. 1 0 0. 1 nm wavelength(nm)

Bragg Grating as 2 nd Reflector in an Interferometer L output reflector 1 7% Bragg grating < 0. 1 % power Dw = -(2 n. L)-1 L = -(2 n. Dw)-1 (lb) -1 decreasing wavenumber (increasing wavelength)

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

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

wavelength Typical Laser Sweep time

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

FFT To Separate Gratings power sampled set with Dw=-(2 n. Lref)-1 spacing between samples number of samples = Nsam (cm)-1 FFT power “Spatial” set with ((Nsam-1)Dw)-1 between points cm L 1 L 2 L 3

-1 FFT To Find Grating Spectra power “Spatial” set with Dspat=((Nsam-1)Dw)-1 point spacing L 1 L 2 L 3 cm FFT-1 power “Spectral” set with Dspec=((Nspec-1)Dspat)-1 point spacing (lb)-1 (cm)-1

Bragg Grating Reflection Spectrum lb = center reflection wavelength of Bragg grating (lb)-1 = center reflection wavenumber reflection(%) 0. 1 0 0. 1 nm wavelength(nm)

FOSS Draw Tower Operation

Draw Tower Preform in Furnace

Bragg Grating Optics

Draw Tower View

Excimer Laser (248 nm, 500 m. J)

Photonic Crystals & Fibers • 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 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.

Theory of photonic crystals

Theory of photonic crystals, con’t

In 2 D photonic crystal structures it is possible to confine light within a cavity. Photonic band gaps appear in the plane of periodicity and in 2 D 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 xyplane because of the band gap but extends in the zdirection

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

PCF Fabrication • PCF Preform Construction • PCF Drawing -similar to drawing capillary tubes

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

Multi-Core Preform

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

SEM Image of Multicore Fiber

Multi-core Drop with drawn fiber

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

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