Introduction |
Collimators are required to transform naturally diverging light-emission from an optical fiber to a
parallel beam of light. Most fiber-optic collimators available are designed for thin fibers with low NA.
High NA fibers such as Polymer Optical Fibers (POF) and Hard Polymer cladding fibers with an NA
above 0.38 cannot be collimated efficiently by most of these standard products without a great
reduction in output power (see Appendix for a discussion why special high NA collimators are
required).
The Prizmatix FCM
collimators are designed to work with High NA fibers and provide an
efficient solution to this problem.
Please see Prizmatix’s wide range of Fiber-Coupled LED light sources .
Collimator
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Features
- Optimal performance using NA Aspheric Lenses
- High NA suited for High NA Polymer Optical Fibers (POF)
- Reciprocal SMA, FC or fiber connection
- Compact
Applications
- Spot illumination
- Component test and inspection
- Can be used in reverse direction as
a free-space to fiber coupler
Specifications:
- FCM1-06 - 0.63 NA
- FCM1-05 – 0.53 NA
- FCM05-05 – 0.53 NA
Fiber Connector: SMA or FC
Material: Black anodized aluminium
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(A) Light output from fiber NA=0.5
(B,C) Same fiber with Collimator
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The following table inbdicates the far field divergence angle
of Prizmatix Collimators for High NA fibers:
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FCM05-05 beam diameter 1/2" |
Fiber Core Size |
Full Emission Cone |
D |
α |
α |
[µm] |
[mRad] |
[Deg] |
200 |
20 |
1.14 |
500 |
50 |
2.86 |
1000 |
100 |
5.73 |
1500 |
150 |
8.58 |
2000 |
200 |
11.46 |
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FCM1-05 beam diameter 1" |
Fiber Core Size |
Full Emission Cone |
D |
α |
α |
[μm] |
[mRad] |
[Deg] |
200 |
10 |
0.57 |
500 |
25 |
1.43 |
1000 |
50 |
2.86 |
1500 |
75 |
4.29 |
2000 |
100 |
5.729 |
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FCM1-06 beam diameter 1" |
Fiber Core Size |
Full Emission Cone |
D |
α |
α |
[μm] |
[mRad] |
[Deg] |
200 |
12 |
0.69 |
500 |
30 |
1.72 |
1000 |
60 |
3.44 |
1500 |
90 |
5.16 |
2000 |
120 |
6.88 |
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Dimensions |
Dimensions are in mm |
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Appendix: Why special High NA collimators are required?
Light emits from multimode fibers as a wide cone of light.
The divergence angle θmax is dictated by the reflection between
the fiber's core and cladding, according to their refractive index,
and is usually represented as the fiber's Numerical Aperture (NA).
The general relation in air is: NA= sin(θmax/2)
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Fig. A1: Optical fiber emission cone of light
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The following table compares the full emission
angle (2θmax) of common NA fibers:
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Typical Fiber Type |
NA |
Full Emission Cone |
α[RAD] |
α[Deg] |
Silica Fiber |
0.22 |
0.44 |
25.4 |
Polymer Optical Fiber (POF) |
0.5 |
1.05 |
60.0 |
Polymer Optical Fiber (POF) |
0.6 |
1.29 |
73.7 |
Polymer Optical Fiber (POF) |
0.63 |
1.36 |
78.1 |
Liquid Light Guide (Prizmatix LLG-3 or LLG-5) |
0.6 |
1.29 |
73.7 |
Prizmatix Optogenetics-Fiber-200 |
0.66 |
1.44 |
82.6 |
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In collimator the fiber is placed at the focus of the collimator lens
so the output rays will be parallel to the optical axis.
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Fig.A2: Collimator design |
Standard collimators are designed for low NA fibers
(like NA 0.22) therefore when high NA fiber is connected
to such collimator the highly divergent rays will be lost
(Fig. A3 (A)) resulting in significant power loses.
Alternatively if high NA fiber will be connected to
high NA collimator the collimator lens NA is matched to
the NA of the fiber resulting in good power throughput (Fig.A3 (B)).
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Fig.A3: (A) High NA fiber connected to low NA Collimator Lens,
(B) High NA fiber connected to high NA Collimator Lens |
The core diameter of the optical fiber will have significant
effect on the far field divergence angle of the collimator
output beam. As was shown above in collimator the optical
fiber is placed at focal point of the lens. Fig. A4 shows
the effect of non-infinitesimal radiant Object placed at focal point
of the lens. As size of the Object (d) increasing
the output beam divergence angle is increasing as well according to:
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α[rad] = d/f
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Fig.A4: |
Effect of non-infinitesimal radiant Object placed
at focal point of the lens. According to paraxial
approximation: Rays divergent from focal point (in green)
will travel parallel to optical axis after the lens,
Rays traveling parallel to optical axis (in blue) will
pass through the focal point on the right side,
Rays passing through center of the lens (in red)
will continue without refraction. The non-infinitesimal
size of the object will cause the output rays to divergent at full angle α
Multimode high NA fibers are in most cases too large
to be considered a point source. Hence, the beam leaving
the collimator will not be of constant diameter, but slightly
expanding. Smaller fibers will yield a small divergence angle,
whereas large core fibers will generate a larger divergence angle.
In order to reduce the output beam divergence of the collimator,
longer focal length lenses are required along with maintaining
high NA. If we need to satisfy these two requirements and still
to reduce the beam divergence we will need to increase the lens
diameter and consequently we will have an increase of output
beam diameter as shown in Fig. A5
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Fig. A5 |
In order to reduce divergence angle of the collimator output beam,
larger size lens with same NA as the optical fiber is required.
This will result in increase of the output beam diameter.
(A) Small size lens, (B) Large size lens.
Both lenses have same NA.
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