Photo: Speckle pattern from multimode fiber

Speckle pattern from multimode fiber

This picture is formed when you project laser light from a cleaved end of multimode fiber onto a screen. Light propogating in many different fiber modes interfere, producing a random interference pattern. The pattern is extremely sensitive to any influence to the fiber — vibration, a lightest touch, heat from your hand held over the fiber but not touching it — and then rapidly changes, just like an image in a kaleidoscope. One can make fiber-optic sensors based on this effect, and even a guard system. Demonstration of this pattern was the most popular one on the Open Day 1999 for school children at the Department of Physical Electronics.

There is another fine pattern superimposed to the large one. It is especially well visible on the big picture and can be mistaken for film grain. That is fine speckle pattern resulting from lighting rough screen surface (a sheet of paper in this case) with coherent light.

I should note that this photo is not an accurate representation of the real pattern, because the latter had a very large contrast range and its maxima completely saturated the red photosensitive layer of the film on this shot.

This picture illustrates List of Firms directory and is included in Picture Collection (ref. nr. a8-31) on Photo Pages

Taken in October 1999.
Fujichrome Sensia II 100 film, Canon EOS 500N, EF 75-300 1:4-5.6 II lens at 180mm, no filter, f/8 15sec, partial metering: central part of pattern -1 (sounds like it should be terribly underexposed, but it even has burned out highlights - metering is way off with laser light?); tripod. Scanned on Nikon LS30 scanner.

Vadim Makarov