Download Business Unit Fiber Optics Business Unit Fiber Optics Fiberoptic

Business Unit
Fiber Optics
TECHNICAL DATA SHEET
Transfer to third party only by authority of LEONI Fiber Optics, Inc. - All rights reserved.
Created and published under restrictions of changes.
Fiberoptic Collimators and Focus Guides (Output Devices)
Description:
Applications:
LEONI’s collimators and Focus Guides are rugged and versatile
devices that greatly simplify the modification of optical fiber
outputs.
•
The components are designed to accept industry standard
fiberoptic connectors or standard cylindrical ferrules. While all
components come pre-set from the factory to meet the rquired specifications, they can be user adjusted to provide some degree •
of optimization as necessary.
Any application requiring collimated or focused optical
energy
o Sensing
o LIDAR
o Spectroscopy
o Medical
o General research
Source to fiber coupling
Features:
Collimators are specified to yield a particular minimum divergence based upon a fiber size and Numerical Aperture. Focus
Guides are specified to yield a particular spot size at a specified
working distance.
All optical components are available with BK-7 or Fused Silica
optics and with or without AR coating. These may also be used
in “reverse” as input couplers.
•
•
•
•
•
•
•
•
•
•
Collimate or focus the output of an optical fiber
Accepts connectorized or ferrule terminated optical fibers
Factory pre-set but user adjustable
Rugged barrel design for easy handling and mounting
Standard barrel diameters from 0.25” to 2.25”
Custom sizes readily available
Many Numerical Apertures can be accommodated
Accepts fiber or bundle diameters from singlemode to
1500μm
UV, VIS and NIR wavelengths
AR coated optics available
LEONI Fiber Optics, Inc.
(757) 258-4805
www.leonifo.com
[email protected] 1
Creator: C. Hall
LFFOC rev 0
Appr. auth.:
Business Unit
Fiber Optics
Transfer to third party only by authority of LEONI Fiber Optics, Inc. - All rights reserved.
Created and published under restrictions of changes.
TECHNICAL DATA SHEET
Collimation:
A common necessity with optical fiber is to modify the output of the fiber and the most common desire among all the ways you might modify
the output is to create a “collimated” beam. It is crucial to understand that fibers are not point sources as they have some finite size, and that
fibers are typically not low angular field sources, as they have substantial Numerical Apertures (or low f/#s), in comparison to what most optical
system what to see.
As a result, while these devices are commonly called collimators, they are in fact, simply “divergence reducers”, or perhaps “quasi-collimators”.
The law of Optical Invariance establishes that the product of the object aperture (size) multiplied by its angular field (NA or f/#), must equal the
product of the image aperture multiplied by its angular field.
Note: This is also all true for image formation vs collimation, since collimation is essentially image formation where the working distance is
infinity (or at least something quite far in comparison to the other sizes involved).
Example:
If you have a single fiber with a core diameter (“size”) of 100um (0.1mm) and an NA of 0.22 and you want to “collimate” the output into a 10mm
diameter beam. What is the divergence of that beam and what lens is needed?
The size multiplied by the NA will be a constant for this system:
SIZEfiber X NAfiber = SIZEoutput X NAoutput
In other words, for our initial conditions, 0.1mm times 0.22 will equal 10mm times the output divergence NA, or,
(0.1 X 0.22) / 10 = NAoutput
In this example, the output NA will be 0.0022 or, since NA = Sin ß, where ß in the half angle in degrees, we get ß = 0.13 degrees. We may
convert this to radians to get 2.2mRad divergence. Again, this represents the half angle.
You will notice that since the output beam diameter is 100X the fiber diameter, and the NA of the output beam is 1/100th the fiber NA. This is
the “best” collimation that can be achieved with these parameters. If your output beam was twice as large (20mm) then the calculated divergence would be cut in half. If the output beam was half as large (5mm) then the calculated divergence would be doubled. The Law of Optical
Invariance is a physical limitation and cannot be circumvented with a “special” lense, or lense combination.
To choose a lens that will work with the parameters identified above. We need a lens with a clear aperture of at least 10mm and a focal length
such that, when the fiber is placed at (or very near) the focal length, all the emitted energy within the fiber’s NA, is within that 10mm clear
aperture. Within commonly available lenses, this means you need a lens with a diameter of 12mm or greater. The desired focal length of the
lens is determined by the equation:
f = ((B/2) –r)/NA, where f is the focal length of the lens; B is the desired Beam Diameter; r is the radius of the fiber; and NA is the Numerical
Aperture of the fiber.
In this example the focal length of the lens should be 22.5. Fortunately, an 18mm diameter x 22.5mm FL lens is an off-the-shelf lens and will
work nicely for this. Placing the fiber output very near the focal point of this lens will result in the 10mm diameter beam with the calculated
divergence above.
Discussion:
The example above is why RoMack uses terms like “Quasi-Collimated” or “Reduced Divergence”. We are trying not to mislead anyone into believing they are going to get a perfectly collimated beam out of their fiber or bundle of fibers. There is always some divergence…. even with laser
beams! With some basic mathematics, and perhaps the thin lense formula. it can be seen that these same equations apply for couplers or even
focusing or imaging devices.
While single lens calculations and Optical Invariance are relatively simple, the implementation and usage can be confusing. RoMack application engineers are always ready to assist you in determining whether or not your optical system is feasible and selecting and optimizing the
necessary optical components.
LEONI Fiber Optics, Inc.
(757) 258-4805
www.leonifo.com
[email protected] 2
Creator: C. Hall
LFFOC rev 0
Appr. auth.: