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Mid-IR Fiber Optics UV & VIS/NIR Fibers Optical Assemblies Resources OptoKnowledge Main Site

Optical assemblies for coupling into Mid-IR hollow fibers

Standard Products

Focal length / Coating

Connectors / Mounts

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AR Coating

OptoKnowledge selects lens materials and AR coatings for three different wavelength ranges. Note: these ranges are related to, but not identical to the designation of the fiber internal dielectric coatings. In cases where the back reflections from even AR coated lenses pose a concern, we also offer optical assemblies that utilize off-axis-parabolic (OAP) mirrors; however, these assemblies are more difficult to align.

AR Coating Transmission

Focal length

In general, coupling light into hollow core fibers is relatively simple, given the relatively large core. However, both transmission and beam quality can be adversely affected if the proper focal length optic is not used. In general, the beam should enter straight into the fiber with a relatively gradual focus. Optimal coupling into the lowest order mode occurs when the ratio of the focused spot size to the fiber ID, 2ωo / (ID) = 0.64.

Focal Length FIll for Hollow Core Fibers
Focal Beam Waist Table

The calculation for optimal focus assumes an ideal collimated Gaussian input beam, a non-ideal beam will have a larger focused spot. For this reason, we recommend selecting a focal length that is either equal to or less than the optimal focal length. Example recommendations are provided in the table for the case where the input laser beam has a diameter (D = 4 mm) and the fiber internal diameter is (ID = 300 Ám).

Focal Length Calculator

Wavelength: Ám

Laserbeam Diameter: mm

Fiber ID: Ám

Optimal Focal Length: mm

Focal Beam Waist Table
[1] Rick K. Nubling, James A. Harrington, "Launch conditions and mode coupling in hollow-glass waveguides," Optical Engineering 37(9), (1998).

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