One- or two-dimensional arrays of optical fibers are known as fiber arrays, fiber-optic arrays, or fiber array units. Instead of being formed over the entire fiber length, such an array frequently only exists for the very end of a bundle of fibers. Such an array's function typically involves coupling light from a source array to the fibers or from the fibers to another component, like a set of planar waveguides on a photonic integrated circuit. The following explanations cover various other applications.
Individual fibers are frequently inserted into V-grooves created on a solid surface to create a linear fiber array. A precise array of holes in a glass, polymer, or metal plate, for instance, could be used to position fibers in a two-dimensional array. A straightforward square lattice is the most typical type of 2D matrix, though other types are also possible. Although more complex and irregular patterns are possible, a simple and very regular structure is formed almost always. Fiber arrays, for instance, can contain several groups of fibers, i. e. and some of the fibers are spaced apart more widely. Fiber bundles, on the other hand, are really asymmetrical structures. Additionally, the fibers may form an irregular bundle in some places while forming a completely regular array at the end, which would serve as the interface.
The fiber spacing is frequently kept to a minimum, but in some cases, fiber arrays with noticeably larger spacing are used for specific applications.
Fibers Used. The majority of fibers used in fiber arrays are silica fibers, which can be used in a range of spectral ranges, from the near-infrared to the ultraviolet. They can, however, also be made from specific specialty fibers. Depending on the application, single-mode and multimode fibers are both employed. There are instances where polarization-maintaining fibers (e. g. of the PANDA type) are employed.
Packaging. Making sure that the fiber ends are perfectly aligned in all dimensions is crucial when making fiber arrays. Additionally, the input or output end frequently needs to be packaged so that the entire fiber array can be handled easily and safely. For instance, the end of a fiber array could be a block of optical glass material that is shaped appropriately and may have alignment-helping features, much like a fiber connector. One may also surround an array with a metal flange, especially for 2D arrays.
The coupling losses are greatly reduced by applying an anti-reflection coating, which can also be used with bare fiber ends.
Cleaving and Splicing. Cleaving each involved fiber individually is not desirable for volume manufacturing. As a result, processes based on lasers that can cleave entire arrays have been created.
The ends of the fibers are typically cleaved perpendicularly, but occasionally they need to be polished at an angle relative to the fiber axis. After rigidly embedding the fibers in a glass structure, they are typically polished together rather than individually.
Fusion splicing can also be used to assemble entire fiber arrays, as opposed to just single fibers . Such procedures have been developed, such as softening fiber ends with CO2 lasers. For multimode fibers, at least, the resulting splice losses can be quite minimal.
Coupling to a Lens Array. It is frequently collimated with a lens array (or microlens array), especially when the output of the fibers is sent into empty space. Naturally, the fiber spacing must then precisely match the lens spacing, and accurate alignment is essential because it greatly affects the direction and level of collimation of the resulting beam.
There are many different uses for fiber arrays.
Coupling to photonic integrated circuits. It is necessary to interface photonic integrated circuits and similar optoelectronic devices with the outside world, primarily using fiber optics. The number of inputs and outputs is frequently quite large; various signals are guided in various waveguides on the circuit, and those reaching the chip's edge require coupling to optical fibers. Naturally, this results in the use of fiber arrays.
Due to their small size, waveguides and fiber cores must be positioned very precisely in relation to one another. Only active alignment, i.e., can accomplish that. e. with the transmission being measured during the alignment process, frequently under automatic control.
Data and telecom applications. To distribute a data signal to several outputs, it is frequently necessary to split the signal. Cable TV is a common example, where the same collection of TV shows is distributed to various audiences. Planar waveguide circuits, whose outputs must be coupled to fibers, are frequently used for signal splitting (often following a fiber amplifier). Thus, coupling the fibers to the splitter is best accomplished using a fiber array.
In wavelength division multiplexing, where each fiber of a linear array may be associated with a different center wavelength, and fiber-optic switches for network routing, similar issues are also present.
In optical fiber communications, data can be transmitted at astronomical bit rates and possibly in both directions at once. The use of multiple fibers is however occasionally required. Then, using interfaces (fiber connectors) based on fiber arrays is desirable to simplify connections. One makes sure that no fibers are unintentionally exchanged while establishing a connection for all pertinent fibers in a single connecting process.
The flexible routing of data signals using 1D or 2D fiber arrays in conjunction with microlens arrays and movable mirror arrays made with MEMS technology is another application in the telecom sector. Such small devices can be made to function as quick and flexible optical cross connect switches.
These technologies are useful not only for telecom providers, but also in a wide range of other industries, including fiber-optic sensing, infrastructure monitoring, and factory automation.
Coupling to Laser Diode Arrays/VCSEL Arrays. A standard array of laser emitters is present in laser diode arrays, also known as diode bars. A fiber array and such a device can be coupled so that each image's radiation enters a different fiber. For VCSEL arrays, similar methods can be used.
Beam Combining. Spectral beam combining works especially well with linear fiber arrays. A diffraction grating could be used to combine the beams from each fiber in the array to create one fiber laser, for instance.
Each wavelength slot in the emitter array on the left has a single fiber. The output has a complete superposition of all wavelength components.
With a 2D fiber array and an appropriate lens array for collimating the light, coherent beam combining is also feasible [8, 9]. Here, the single-frequency, phase-stabilized output of a fiber amplifier is fed to each fiber. For the output to have a high beam quality, all the components must be placed very precisely.