Lensed Fiber Arrays

Lensed fiber arrays project light into free space. The lens design allows certain combinations of working distance and the mode field diameter that occurs at the ‘waist’ of the beam. The achievable working distance and mode field diameters depend upon the wavelength and the type of fiber used. The working distance is measured from the top of the lenses and can be up to 100 μm for both focused and collimated beams. The lenses protrude from the fiber array by a maximum of 250 μm.

Note: we can also offer lensed fiber arrays with periscopic mirrors suitable for wafer level testing.

Lensed or tapered fibers are traditionally manufactured using a subtractive process, i.e. grinding, melting or etching.  The resulting shapes are limited by the basic process parameters of these techniques. Our lenses, on the other hand, are created using an additive process of high-precision 3D printing using Dip-in Laser Lithography (DiLL) and Two-Photon Polymerization (2PP). This offers much more control over the shape of the lens, allowing aspherical shapes to correct for various aberrations and asymmetric shapes for adapting the beam profile.

An additional advantage of our 3D-printed lenses is that they are created when the fibers are already secured in an array. This avoids length deviations between the individual fibers.

Both lensed fiber arrays (LFAs) and the PHIX spot size converters (SSCs) can tailor the mode field diameter to improve the coupling of light between fiber arrays and photonic integrated circuits (PICs). There are also some significant differences.

LFAs are suitable for free space operation, for example allowing contactless measurements to be performed. Our SSCs, on the other hand, require a permanent adhesion to the PIC using epoxy. This improves the thermal stability of the optical coupling.

SSCs enable low-loss coupling to PICs due to their lithographically defined waveguides. LFAs face some challenges for coupling to low mode field diameter waveguides, because the placement accuracy of the microlenses is limited by the fiber placement accuracy.

This additive manufacturing process for creating microlenses allows them to be printed on the top surfaces of photonic integrated circuits (PICs) as well. For example, a microlens array can be used to focus or collimate light coming from a grating on the chip.

In order to further improve mode field conversions between fiber arrays and PICs, a process for printing microlenses on the chip facets is currently being developed. These lenses perform mode field conversions on the chip itself, so that much more lenient placement tolerances exist in the free space between the components. This way, the losses due to variations in core concentricity and cladding diameter of the optical fibers can be greatly reduced.