In many cases, it is necessary to align an optical fiber with another optical fiber or with a device that is optoelectronic such as a laser diode, a light-emitting diode, or a modulator. This can involve either carefully aligning the device and placing it in contact with the optical fiber, or it can require the use of a lens that allows the coupling over an air gap. In comparison, typically the size of the optical fiber moe is very much larger than the size of the mode is a silicon optical chi or laser diode. In this case, a lensed fiber or tapered fiber is used to match the fiber optical mode field distribution to that of the other element. The lens which is on the other end of the optical fiber can be formed by performing processes like laser cutting, polishing, or fusion splicing. Nowadays, the process of laser line beam splitter manufacturing is done by many optics manufacturing companies which makes it easier to maufacture and design polarizer optics.
It’s process
In a lab environment, a bare fiber end is combined with the help of a fiber launch system, which sued a microscopic objective lens to focus the light on a fine or very small point. A micro-precision table (precision translation stage) is used to move the optical fiber, lens, or device which helps in order to optimize the coupling efficiency. Fibers with the connectors which are present on the other end make this whole process much simpler: inside a pre-aligned fiberoptic collimator the connector is simply plugged in, which consists of a lens that is either adjustable or it is precisely positioned with respect to the fiber. In order to achieve the best injection efficiency in a single-mode fiber, the beam direction, position, size, and deviation must all be optimized. If good beams are used, a coupling efficiency of up to 70-90% can be achieved.
If the single-mode fibers are properly polished, then the emitted beams are able to achieve an almost perfect Gaussian shape — if the good lens is used, it can be achieved even in the far-field. The size o the ens should be large enough n order to support the full numerical aperture of the fiber, and it must not add aberrations in the beam. For this, lenses that are aspheric in nature are used.
