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Collimator for High NA Fibers



Introduction


  Collimators are required to generate a parallel beam of light out of the naturally diverging light emission from an optical fiber. Most fiber optic collimators available are designed for a low NA and thin fibers.

  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 of most these standard products, without a great reduction of output power.

  Prizmatix Collimator is designed to work with High NA fibers (up to 0.53) therefore provides efficient solution to this problem.

Features

  • Optimal performance using Aspheric Lenses
  • High NA suited for High NA Polymer Optical Fibers (POF)
  • Reciprocal SMA, FC or ST fiber connection
  • Compact

Applications

  • Spot illumination
  • Component test and inspection
  • Can be used in reverse direction as a free-space to fiber coupler

Specifications:



Lens NA: 0.53 suites for most high NA fibers

Fiber Connector:  SMA or FC

Material: Black anodized aluminium

Diameter: 0.70" (17.8mm)

Length: 1.11" (28.2mm)

Collimator output

Output of Free Space POF fiber NA=0.5 (A)
Same fiber with Prizmatix collimator (B, C)

Collimator output  
Why you need a collimator?

  Light emits from multimode fibers as a wide cone of light. The opening angle θmax is dictated by the internal total reflection in the fiber, and is usually represented as the Numerical Aperture (NA) of the fiber.

  The general relation in air is: NA= sin(θmax).

  The following table compares the full emission angle (2θmax) of common NA fibers:


Collimator emission cone

Typical Fiber Type Fiber Example NA Full Emission Cone
  α[RAD] α[Deg]
SILICA Optical Fiber Polymicro Tech. Deep UV fiber
FDA600660760
0.22 0.44 25.4
Hard Polymer Clad Multimode Fiber Thorlabs BFL37-1000 0.37 0.76 43.4
Hard Polymer Clad Multimode Fiber Thorlabs APCH1500 0.39 0.80 45.9
Hard Polymer Clad Multimode Fiber Thorlabs BFH48-600 0.48 1.00 57.4
Polymer Optical Fiber (POF) Mitsubishi Super ESKA SH4001 0.50 1.05 60.0
Liquid Light Guide EXFO 0.60 1.29 73.7


Collimator performance

  Multimode high NA fibers are too large to be considered as a point source. Hence, the beam leaving the collimator will not be of constant diameter, but slightly expanding.

  Roughly, beam divergence angle after the collimator changes with the diameter of the fiber.

  Smaller fibers will yield small divergence angle, whereas large core fibers will generate a larger divergence angle.

  The following table indicates the pivot angle of the emission cone of Prizmatix Collimator for High NA fibers:

Fiber Core Size Full Emission Cone
D [μm] α[RAD] α[Deg]
200 0.02 1.1
500 0.05 2.7
750 0.07 4.1
1000 0.10 5.5
1500 0.14 8.2
2000 0.19 10.9
Collimator emission cone


© Prizmatix, Israel