Optical Transit

Which of the following optical observations would be the least affected by the “seeing”?

A.Observing a star as it rises from an observatory in Chile

B.Observing a star as it sets from an observatory in Arizona

C.Observing a star as it transits from an observatory in Hawaii

D.Observing a star as it rises with a space telescope

I'm sure that we can see both C and D. And I'm pretty sure we can see A, since Chile is near the equator and we can see the stars rise and set there, correct? so would B be the answer to the question "Which of the following optical observations would be the least affected by the “seeing”?"

Least means the minimum, not the maximum.
Both A and B would be maximum affected as stars would be on either east or west horizon, and light path is through the thickest air, approaching 200 miles.
C not so much as A or B, because transit on a line that passes overhead, is not on the horizon, and air is only 25 miles thick at minimum there, but could be up to 200 miles if star near south horizon.
D. would be minimum or least affected, as there is no air in light path to the space telescope.
D is your answer.

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Titan's Transit of the Crab Nebula, animation of

How Do Fiber Optic Cleavers Precisely Cut Optical Fibers in a Flash?

:: What is optical fiber cleaving?

Simply put, optical fiber cleaving is the art of cutting glass optical fibers at a perfect 90° angle with a mirror like surface. This isn't as easy as it sounds.

Why do we need to cut the fiber at a perfect 90° angle at all? Well, this is required when we want to fuse two optical fibers together. Optical fiber fusion splicing always requires that the fiber tips have a smooth end face that is perpendicular to the fiber axis. The cleave quality is very important in determining the fusion splicing loss. This is especially true for specialty fibers such as erbium-doped fibers and dispersion-compensating fibers.

:: How do fiber optic cleavers achieve this?

The basic idea of optical fiber cleaving is first to scratch the fiber with a very hard diamond edge scribing tool, which induces a sufficiently large surface crack, then the fiber cleaver applies a tensile stress to the fiber which causes the crack to expand rapidly across the fiber cross section. Some other fiber cleavers apply the tensile stress first and then scratch the fiber with the diamond edge scribing tool.

:: How does the fiber cross section surface look like after fiber cleaving?

After cleaving, the fiber cross section typically consists of three regions: the mirror region, the mist region and the hackle region. The mirror region is first produced while the crack propagates across the fiber. We want the mirror region to be as large as possible. A perfect fiber cleaving will be 100% mirror region which will result in minimum fusion splicing loss.

But in reality, as the crack propagates more, multiple crack fronts are produced close to the end of the cleave and that region is called the hackle region. The hackle region is a rough surface area which will cause bad fusion splicing. We never want hackle region to exist.

Mist region is the transition area between the mirror region and the hackle region.

:: Factors that affect the fiber cleaving quality

There are two major factors which mainly determines a fiber cleaving's quality: the size of the initial crack and the applied tensile stress. In these two factors, the applied tensile stress plays a major part.

Ideally, the tensile stress should be low enough so the crack propagates and mirror region occupies the entire cross section of the fiber. When there are unacceptable amount of hackle region, in almost 100% cases, you should first adjust your fiber cleaver's tensile stress.

But on the other hand, too low tensile stress can cause problems of its own. The main problem is an angled fiber cleave instead of a perpendicular 90% cut. Angled fiber cleave is the other culprit causing bad fusion splicing in addition to cleaves with too much hackle region.

Another problem caused by too low tensile stress is that a large initial crack is required to make a cut. This large initial crack itself may be a reason for bad splicing.

Even the best fiber optic cleavers cannot guarantee a high quality cleave 100% of the time. Two other major problem with fiber cleaving is fiber lip and fiber chip. Fiber lip is a protruding piece of glass at the periphery of a fiber tip. If the lip is longer than a few microns than it exhibits a serious problem for a good fusion splicing. 99% of the time you should re-cleave your fiber once you see a fiber lip on the tip.

Fiber chip is the opposite of a fiber lip. Fiber chip means the a small piece of glass missing from the periphery of the cleaved fiber tip. Even though smaller chips usually do not cause any bad fusion splicing, larger ones can be a serious problem. Larger fiber chip causes surface tension to shear the molten glass at the fiber tip and thus distort the fusion splice geometry.

:: High precision fiber cleaver manufacturers

A vast variety of fiber optic cleavers are commercially available now ranging from high precision cleavers for manufacturing floor and laboratory use to low cost field fiber cleavers for field splicing applications. Major supplies include AFL Fujikura, Fitel, Tyco/AMP, Sumitomo, Corning Cable Systems and more.

About the Author

Colin Yao is an expert on fiber optic communication technologies and products. Learn even more about
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