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Fiber Array Fabrication Techniques (view source)
Revision as of 21:24, 17 October 2008
, 21:24, 17 October 2008→Cleaving and Polishing Techniques
=== Cleaving and Polishing Techniques ===
=== Cleaving and Polishing Techniques ===
==== Using Hand Tools ====
<u>Note:</u> This process assumes that the uncut scintillators and waveguides are in segments or spools of more then 3 meters long. Please read each step completely before you begin this process.
* [[Using Hand Tools]]
'''Step 1: Cleaving'''
* [[Using Fly Cutter]]
# Technique 1
#* Place the fiber in the apparatus as shown in ''Work Stand Assembly'' under ''Cleaving''. Take the hobby knife and place it on the fiber (again look under ''Work Stand Assembly'' for the proper placement of the blade) and gently tap the butt end of the knife until the fiber is cut cleanly. Remove the fiber and inspect the freshly cleaved end. Look for any major breaks in the outer cladding (use magnifying glass if necessary). I will be posting pictures (as they become available) as to what is acceptable and unacceptable breaking in the cladding.
#* If the ends of the cleaved scintillators have major breaks in the outer cladding, then the best course of action it to toss out the unusable segment, properly polish the end attached to the spool and repeat Step 1. If the ends of the cleaved scintillators are borderline acceptable proceed to Step 2.
#* For the waveguides, it is best to give yourself an extra 1/2 cm of fiber in case the cleaved end has major breaks in the outer cladding.
# Technique 2
#* If you want to ensure that the outer cladding will not be disturbed during the polishing process you will need to remove the outer cladding for a short (about 0.5 mm) length of the fiber. This is a relatively easy process; it just takes some time, a lot of patience, and a microscope. To begin with, set up a cutting guide such that you can make a small cut perpendicular to the length of the fiber. If possible try and design your cutting guide such that it also lines up the cuts for all of the sides. I used a simple piece of paper wrapped around the fiber.
#* Using the hobby knife, make a shallow cut along your cutting guide. You do not have to cut all the way through the outer cladding, just most of the way. Try not to cut the inner fiber. To ensure that you do not, you might want to practice on some scraps of fiber. Take a piece of scrap fiber and begin cutting the outer cladding. The inner fiber feels much softer than the outer cladding. The only way to learn how to tell the difference is to slowly cut through the test fiber and feel the change in resistance. [[Image:Stripped Cladding.JPG|thumb|Fiber with Cladding Striped]]
#* Now that each side of the fiber is cut, start removing the cladding. To do this, it is easiest to use a second hobby knife. Place the second hobby knife along the cut in the fiber and place the initial hobby knife at the end of the fiber between the cladding and the fiber and use it to pry up the cladding. If you did it right the cladding should come up and break along the cut that you made. The fiber after the cladding is removed, is shown in the microscope picture to the right. (Note: don't worry about scratching the inner fiber; it will all be polished away anyway.)
#* Finally, during polishing, make sure to buff the fiber almost all the way down to where the cladding begins.
'''Step 2'''
* <u>Scintillators:</u> The segments cut using the ''Work Stand Assembly'' have an extra millimeter or so in length made by design so that by the end of the polishing process the segment will be of the proper length of 2 cm. That being said, if the fiber is borderline unacceptable, it can still be used provided that enough of the cladding is still intact to leave a sufficient length, once the defective part has been removed by polishing.
* <u>Waveguides:</u> Preparation of the ends of the clear waveguide fibers for gluing is the same as for the scintillating fibers, except that there is somewhat more freedom in the exact length of the finished fiber. If you allot 5 mm extra length when you cut the fiber from the spool then it should be possible to recover through polishing from several failed attempts to produce properly finished ends.
'''Step 3: Polishing'''
* Arrange the fiber in the apparatus as shown in ''Work Stand Assembly'' under ''Polishing''. If the end to be polished is significantly longer then the desired length (i.e. 0.2 cm or more), begin with the coarse emery board . If total length is less than 0.2 cm of desired length, begin with the much less coarse nail buffs (pictures of the nail buffs will be posted).
**<u>Note:</u> It seems that the color of the nail buffs signifies how fine or coarse the buff is. So if you cannot find the exact nail buffs that I used, just try to match the color of each and you should be fine.
* Using the emery board is a bit tricky and needs special care. Gently grind down the end of the fiber with the board, do not push too hard or to soft. The strokes should be at a steady pace but not too fast or to slow. Considering one up and one down stroke as one complete cycle, the speed should be around 1 revolution per second. I know that these directions are a little obscure, so the best way to figure out just how fast and how much pressure to apply is to use a scrap fiber and practice for yourself. The reason that you do not want to go too fast or apply too much pressure is that excessive grinding speed or pressure results in stripping the outer cladding around the fiber. After the fiber is polished down with the emery board, it is best to remove it from the apparatus and inspect it for major breaks in the outer cladding. The initial grinding process should take about 30 seconds depending on how much you need to shave off.
* Use the nail buffs on the fiber in the order of Black, White, Gray. I used 3 different ones because they came in a set, but if you just use the first (black) and last(gray) I think you should be fine. With these you do not have to be as cautious as with the emery boards, but still some care needs to be taken. Basically follow the same instructions as for the emery board. When you feel, through the buff, the fiber become smooth, it is time to switch to the next buff. Be sure not to over polish the fiber because it will result in rounded-off ends. If the ends are rounded, the epoxy will not adhere properly to the fiber.
* Here are pictures of what the fiber should look like after each step [[Fiber Pictures]]
==== Using Fly Cutter ====
[[Image:Fibersinangleclamp.JPG|thumb|right]]
The Fly Cutter is a milling tool used to shave away layers of a flat surface. For our purposes, the fly cutter is used to cut several fibers at the same time leaving the fiber's ends with a flat and even surface. We designed a "angle clamp" to bundle the fibers together so that we can cut a 5x5 set of fibers with the fly cutter. In the picture to the right, we see the fibers bundled in the angle clamp, the angle clamp itself is attached to a metal piece used to mount the angle clamp in the fly cutter machine. With the fibers secured in the angle clamp, we set the bundle through a few test runs with the fly cutter to determine how fast the blade needs to spin the cut the fibers properly. A rotation speed of 1500 rpms was deemed to produce the best results. In the picture below, we see the fibers after being cut by the fly cutter. Notice the fiber's ends have many small scratches in them but I am confident that those scratches will easily be removed with just a quick polish.
[[Image:Scratches_afterflycut.jpg|center|400 px]]
Something that was expected to happen was flaying or stripping of the outer most fiber's cladding. The picture on the right shows a close up view of the outer fibers, on the left a zoomed out view of the same fibers. The cladding is not damaged on all the outer fibers but it is stripped on the majority. All though there was noticeable damage to the cladding, I was surprised to see how well the cladding faired.
{| cellpadding="3" style="text-align:center; margin: 1em auto 1em auto"
|-
| [[Image:Fiberbundle_stripped.jpg|left|300 px]] || || [[Image:Fiberbundle_stripped_zoomout.jpg|right|300 px]]
|-
|}
The machinists who cut the bundled fibers gave warning about a consequence of using the fly cutter. That is, the interior fibers would become slightly recessed. After a brief test it was determined that the fibers were not recessed significantly enough to be measured by our equipment (i.e the recession would be less then 0.0001 mm off from the plane. Therefore, any recession will not affect any part of the Tagger construction or performance.
[[Image:Recessed_inner_afterflycut.jpg|center|400 px]]
=== Transmission Testing ===
=== Transmission Testing ===