Fiber Coupling

Perfect for FC/PC patch fibers

Optimized laser fiber coupling and fiber collimation

asphericon’s adjustable fiber collimators / fiber couplers ensure perfect alignment of FC/PC patch fibers in your laser set-up. Combine collimators – available from stock for NAs up to 0.275 – with BeamTuning or other beam shaping elements to obtain any desired output beam while maintaining a diffraction-limited wavefront. The sophisticated optical design enables simple fiber coupling, alignment, and wavefront adjustment with minimal adjustment.

NEW: Looking for a solution to easily alter the effective focal length of your fiber collimator while effortlessly connecting optical fibers to your system? Discover a|VariColl, our latest fiber collimator/fiber coupler, which is ideal for illuminating beam-shaping elements thanks to the separate adjustment of divergence and beam diameter.


The a|AspheriColl is an adjustable fiber collimator/fiber coupler for perfect alignment of FC/PC patch fibers. Combine the collimator, available from stock for NAs up to 0.275, with BeamTuning or other beam shaping elements to obtain any desired output beam while maintaining a diffraction-limited wavefront. The optical design of the a|AspheriColl allows easy fiber coupling, alignment as well as adjustment of the wavelength without much adjustment effort. Due to larger output beam diameters, the fiber collimator can operate without additional elements and impresses with its compact design. The a|AspheriColl 355 nm covers the wavelength range from 350 to 405 nm and thus also enables diffraction-limited collimation of laser beams in the UV range.

Specifications & Technical dimensions [mm]

  • Fiber collimator covering for NA’s up to 0.275
  • Focal length f = 20 mm, with Øe= 11,5 mm
  • Optimized for wavelength range 350 nm – 1600 nm
  • Easy wavelength adjustment
  • Perfectly aligned lateral position
  • Completely diffraction-limited performance (Strehl > 0.95) when used with FC/PC patch fibers
  • Thanks to matching adapters also usable for APC fibers
  • No truncation effects compared to other available fiber couplers/fiber optic collimators
  • Thanks to bigger output beam diameters, no additional expansion might be needed (shorter system length)

Output beam diameter

The diameter of the collimated output beam generated by an a|AspheriColl depends on the NA of the fiber from the laser source. This is a function of the wavelength.

The basic diameter is set as shown in the following graph. Pre-aligned for the wavelengths [nm] 355, 532, 632, 780 and 1064, the a|AspheriColl collimates output beams from single mode fibers with NA’s up to 0.275.

Optical performance

The map on the right shows the measured wavefront of an a|AspheriColl at 632nm. The diameter of the collimated output beam, which depends on the fiber’s numerical aperture (NA) and mode field diameter (MFD), is already in a usable range. The fiber collimator is already perfectly aligned to the design wavelength. If needed, it can also be adjusted in a certain wavelength range. Due to its outer diameter of 30 mm the a|AspheriColl fits into any standard holder (e.g. from OWIS). By simply pluging in the fiber, the a|AspheriColl is ready to use.

Wavelength range

Covered range of wavelengths for fiber optic coupling/fiber collimation with the a|AspheriColl for the design wavelengths [nm] 355, 532, 632, 780, 1064.

Looking for a solution for fiber coupling?


Discover asphericon’s latest fiber collimator, the a|VariColl. As well as coupling and collimating your optical fiber, it also enables you to enlarge or reduce your input beam, creating perfect input conditions for all subsequent beam shaping optics. The adjustable effective focal length allows compensation for manufacturing deviations in fiber NA (numerical aperture). Thanks to high-precision optics and a sophisticated optical design, beam size and divergence can be effortlessly modified independently of each other. Available in design wavelengths of 532, 632, 780, and 1,064 nm, the a|VariColl is distinguished by a compact design that allows the tiniest adjustments to output beam diameter and divergence.

Specifications & Technical dimensions [mm]

  • Effective focus length: 47–99 mm
  • Fiber collimator for NAs from 0.055 to 0.12
  • Available in four design wavelengths (532 nm, 632 nm, 780 nm, 1064 nm)
  • Wide spectral range: 500–1,200 nm
  • Generation of collimated diffraction-limited beams up to 11 mm 1/e² with RMS wavefront error < 50 mλ
  • Adjustable beam diameter with constant divergence within the design wavelength
  • Precise adjustment of divergence also possible
  • Perfect for illumination of a|TopShape, a|AiryShape, and a|SqAiryShape, as the separate adjustment of divergence and beam diameter allows optimal input conditions
  • Laser induced damage threshold: 12 J/cm², 100 Hz, 6 ns, 532 nm

Wavelength range

Covered wavelength range of the a|VariColl fiber collimator for the design wavelengths [nm] 532, 632, 780, 1064.


The a|VariColl was developed to compensate for variations in the numerical aperture (NA) of fibers due to manufacturing. For NAs in the range of 0.055 to 0.12, an output beam with a maximum 1/e² diameter of 11 mm can be achieved in diffraction-limited quality. For NAs below 0.12, smaller diffraction-limited diameters are also possible (see diagram).

Optical performance

Are you looking for a solution to smoothly change the EFL of your fiber collimator while easily connecting the patch fiber to your setup? The diagram shows the measured wavefront and intensity profile of the a|VariColl 532 nm. One of the key features of the a|VariColl is that a collimated beam remains collimated, no matter what beam diameter you choose. The a|VariColl generates a diffraction-limited wavefront and is thus perfectly suited for the use of beam-shaping optics, for example from asphericon’s BeamTuning range (a|TopShape, a|AiryShape, a|SqAiryShape). In particular, the separate adjustment options for divergence and beam diameter create optimal input beam conditions.

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