1. The number and type of fibers (base material);
2. Their spacing and (for 2D) the type of lattice used;
3. The core diameter and numerical aperture, or other methods of specifying the refractive index distribution, which determine other detailed design of the mode structure;
4. Polarization processing; in the case of polarization-maintaining fiber, there is also the direction of the fast axis or the slow axis relative to the array;
5. Non-vertical polished fiber end face angle;
6. Fiber core positioning accuracy;
7. Use end caps, mode converters, etc.;
8. Package type.
Due to the large number of variable parameters, optical fiber arrays usually need to be made into custom optical devices tailored to specific applications.
The fiber array is mostly made of quartz fiber, which can be applied to various spectral regions from near-infrared to ultraviolet. However, they can also be made from certain specialty fibers. Both single-mode fiber and multi-mode fiber are used, depending on the application. In some cases, polarization-maintaining fibers are used.
In some cases, the fiber array is formed by arranging a plurality of optical fibers in the original size, for example, having a standard cladding diameter of 125 μm. If the fiber coating is omitted or removed (as usual), this will result in the smallest possible core spacing of the same order of magnitude (assuming the fiber core is centered and multi-core fiber is not used).
For some applications, such as coupling to photonic integrated circuits, smaller optical fibers and smaller core spacing are required. In this case, it is possible to directly use correspondingly smaller fibers or use tapered fibers to produce by drawing the fibers while heating them to the glass softening temperature.
Sometimes, it is necessary to apply an additional mode size converter to a waveguide mode of relatively small size. In other cases, coreless end caps of different shapes (such as rectangular or circular cross-sections) are used.