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Tech
Focus:
A
look at new technologies shaping the world of laser displays
CG
Tools for Laser Artists
How
I Learned to Love Fiber Optics
Fiber
Optics: Technical Primer
Evaluating
New Catweazle Scanners by MediaLas
Tips
and Tricks on Making Fiber Optics
Work Magic for Your Laser Show
By
Tim Walsh, Laser Spectacles, http://www.laserspectacles.com
Because
I use fiberoptics in just about all my laser shows, viewers typically
think that they are seeing multiple lasers instead of just one.
Using optical fibers for remote beam delivery can be just like
getting lasers for free! It allows me to position scanners almost
anywhere I want them, as long as I can feed them light from a
hair-thin cable made of optical fiber.
My philosophy of lasers is a little bit of laser light is 100%
better than no laser light at all! Thus, even if sending laser
light through a fiber loses some optical power over a distance,
enough light will still be there to recreate the magic of a laser
beam. You should not let a slight loss of power dissuade you
from the advantages of using a fiber optics beam delivery system
(see Peter Mayer’s article for exact figures on light loss).
I have heard laserists and lighting designers say, “But
the focused beam of the fiber optic is not as good as the real
laser beam.” This may be technically true, but in my experience,
as long as nobody knows that they are looking at a fiber beam,
they cannot tell the difference.
Better
Beam Control
Actually, putting the laser beam through a good quality fiber
system can give a laserist control over the final shaping of
the beam. And through your choice of the type and diameter of
fiber you use, and the focal length of the lenses used for coupling
and collimating, you, as the laserist, have control over the
beam profile and the divergence of your laser beam.When the beam
exits the fiber, the colors are perfectly collinear, more so
than a raw laser beam exiting a PCAOM. In my experience, a step
index fiber gives a very flat beam profile, with the optical
power evenly spread over the laser “dot.” A properly
coupled graded index fiber can give a beam profile very similar
to a TEM00 laser beam—with most of the beam’s optical
power concentrated in the center of the laser “dot,”
and gradually tapering off at the edges. However, the step index
fiber is more forgiving of slight inaccuracies in coupling. I
recommend that first time users begin with step index fiber.
This
brings me to a word of warning: there is an art to using lasers
in fiberoptics. It is possible to mis-focus a beam into the fiber,
and then the amount of power coming out of the end of the fiber
will be greatly reduced. If you use fibers, don’t be satisfied
with your coupling technique unless the fiber exit beam has the
same quality as the beam going in. It is possible!
And, if you notice a significant drop in brightness from a fiber
head during or before a show, you should investigate immediately.
The lost power has got to go somewhere (if not out the end of
the fiber), and quite possibly something is going to burn.
To
avoid problems from the beginning, make the coupling beam path
from the laser into the fiber as short and direct as possible.
If you use a PCAOM for color modulation, place the fiber coupler
immediately after the PCAOM for best results. Try to avoid using
an actuator to switch the beam into the fiber—it can drift
slightly over time, leading to unreliable results, no matter
what the quality of your fiber coupler. Try to use a direct beam
path into the fiber, and use the actuator to shutter the beam
instead.
A trick
to use to get the input coupler focused onto a dot on the end
of the fiber is to turn the optics around, and use the input
coupler as the output coupler temporarily for focusing purposes.
By focusing the beam out the input coupler at infinity, and then
replacing the input coupler where it is intended to be, your
focal point will be close if not perfect.
But not all fiber systems are manufactured in such a way that
will allow you to easily do this. Whichever approach you take,
be sure to practice it far in advance of your show—this
is not something you can experiment with the night before your
show opens. You also will want to stock at least one spare fiber
with a connector mounted on it, just in case your system becomes
misaligned and the fiber input face is damaged by a poorly focused
beam.
Try
fiber optic beam delivery and your shows–like mine–may
never be the same again!
Tim
Walsh, Laser Spectacles, http://www.laserspectacles.com |
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