Compact fiber collimator

Fiber collimator reduces the divergence angle of the light output from an optical fiber. Fiber collimators are used to match the beam divergence from a fiber with the optical setup. Another application is coupling light into the fiber from free space. To achieve efficient coupling light has to be focused on the fiber facet, creating the focal spot with the same size as the fiber mode, which could be as small as 3 µm for visible light. Such small focal spot makes the alignment difficult. Fiber collimator increases the beam size, simplifying the alignment.

Diffractive collimator schematic
Schematic of the diffractive fiber collimator

Fiber collimator specification:

Wavelength, nmBeam diameter, µmDivergence full angle, degreesFiberConnector
405 – 155010 – 1000.15 – 6Single modeFC/PC, FC/APC

Conventional fiber collimators use GRIN lenses, attached to the fiber using a mechanical housing. This requires an alignment and assembly of several components. Instead, we use a 3D diffractive lens, imprinted in the polymer very close to the fiber edge. Free form diffractive element acts as a perfect aspheric lens, preserving the diffraction limited beam quality. The space between the fiber edge and the diffractive lens is filled with a transparent polymer, making the whole assembly essentially a monolithic single piece component. No mechanical housing is required, making the collimator extremely compact. In fact, using a naked eye, one cannot tell the difference between a bare fiber and fiber with the collimator.

Besides the stability, the fiber nanoimprint technology allows for a precise control of the distance between the fiber and the lens. This makes possible to have small beam diameters (10-100 µm), enabling the control of a divergence angle, rather than a simple collimation. Relatively small beam diameter after the collimator is an advantage for fiber coupling applications. Indeed, having large beam diameter makes the spatial alignment easy, but the angular alignment becomes much more challenging! The small beam diameter of ~50µm achieves the compromise between lateral and angular alignment tolerance.

SEM image of the diffractive fiber collimator
SEM image of the diffractive lens of a fiber collimator

 

Applications:

  • Fiber coupling
  • Divergence angle control
  • Collimation

Advantages of the diffractive fiber collimator:

  • No alignment required
  • Monolithic design
  • Highly reproducible
  • Extremely compact size

Contact us to order fiber collimators or to customize them for your application!