Fiber Accelerating Structures. By Andrew P. Hammond. What technology is needed for the next powerful linear accelerator to be built at SLAC?. Advanced Accelerator Research Division. Photonic bandgap (PBG) fiber for 1 mm telecommunications with a central defect. Basic Theory.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
By Andrew P. Hammond
What technology is needed for the next powerful linear accelerator to be built at SLAC?
Advanced Accelerator Research Division
Photonic bandgap (PBG) fiber for 1 mm telecommunications with a central defect
A photonic band gap (PBG) is a periodic arrangement of dielectric material that precludes certain wave length from propagating.
In a 1D PBG it is a periodic symmetric structure. When solved using the Maxwell equation lead to constructive and destructive interference for certain wavelengths.
In a 2D PBG fiber it is confined linearly.
Steven G. Johnson. Photonic Crystals, Periodic surprises in Electromagnetism. (2003)
From: http://ab-initio.mit.edu/photons/tutorial/, Retrieved 8/12/09
In a PBG Fiber a defect can be added that allows certain wavelength to propagate near it despite being in the band gap.
There are two major types of propagation in a defect, core and surface modes.
The program used to model the PBG fibers that I tested is called CUDOS, made by the University Sydney.
Assumes an infinite fiber with light of a certain wavelength moving down it.
Does not track movement of particular light source.
For an optical fiber to be used as an accelerator, it must over come the basic difficulties of: Laser Coupling, Accelerator Structure, and Alignment.
To potentially solve these difficulties:
1. The simple fiber accelerator parameters were optimized,
2. A double defect was examined,
3. A perturbed lattice was looked at.
I studied how the longitudinal Electric field shifted when basic parameters were shifted.
Pitch can’t be shifted independently
As radius of normal cylinder decrease so does field
As defect radius of defect increases field decreases
Possible to increase defect max by decreasing normal cylinder size
The E-field of the two maximum modes, defect size and field ratio, properties are:
The largest defect size has a uniformity in the defect of 3.2%.
The maximum field fiber has a uniformity of 9.8%.
At higher wavelengths, past ~2.5µm, the refractive index fluctuates a large amount as various absorption peaks are hit. This changes the PBG, so a new structure is needed.
Examined fiber structure at λ=16 µm, where n=1.484.
This wavelength needs a larger defect to support the mode. (Expected defect for radius = 10.52 µm).
Based on previous papers, I expect the higher the refractive index a lower pitch and lower normal radius will be needed.
The 16 micron fiber case shows an increased defect is necessary from a scaled up version to create an accelerating structure.
The higher gradient case has a uniformity of 17.4%.
The higher defect radius has a uniformity of 4.5%.
A double defect might serve to couple laser into another defect. It might also help offset the low electron bunch number.
Basic fiber parameters of large defect 2 micron case.
Observe partial coupling for separation of 5 and 7 cylinders. Despite the losses from lack of coverage, there is some coupling.
Past that the memory constraints perturb and remove mode.
Lower and the PBG is offset by values to close to one another.
In order to create stronger electric fields in the defect and eliminate hot E field spots, it is possible to perturb the lattice and maintain a uniform field.
 Eric Colby, Gary Lum, Tomas Plettner, and James Spencer. Gamma radiation studies on optical materials. IEEE Transactions on Nuclear Science, 49 (6), 2002.
* John D. Joannopoulos, Robert D. Meade, and Joshua N. Winn. Photonic Crystals, Molding the Flow of Light. Princeton University Press, 1995.
 R. Kitamura, L. Pilon, and M Jonasz. Optical constants of fused quartz from extreme ultraviolet to far infrared at near room temperatures. Applied Optics, 46 (33). (8118-8133),2007.
* Robert J. Noble. Dispersion information for photonic fiber modes from CUDOS simulations. ARDB Note 04, SLAC, 2005.
* Robert J. Noble, Eric R. Colby, Benjamin Cowan, Christopher M. Sears, Robert H Siemann, and James E. Spencer. Designing photonic bandgap fibers for particle acceleration. In Particle Accelerator Conference, PAC 07, SLAC-PUB-12571, June 2007.
 Burak Temelkuran, Shandon D. Hart, Gilles Benoit, John D. Joannopoulos, and Yoel Flink. Wavelength-scalable hollow optical fibres with large photonic bandgaps for co2 laser transmission. Nature, 420, 2002. 1