Single core fiber collimator is precisely positioned by pigtail and self focusing lens. It can convert the transmitted light in the fiber into collimating light (parallel light), or coupling the external parallel (nearly parallel) light into the single-mode fiber.
Single core fiber collimator can collimate a beam, expand it, and also focus the beam into a spot of a certain size, allowing the beam to pass through a particular optical element more easily or to be coupled more efficiently. As shown in Figure 1, the beam directly coming out of the fiber has a larger divergence Angle than the beam passing through the collimator, which will lead to more loss of light energy, so it is not conducive to transmission and coupling. Using Single core fiber collimator at both ends obviously improves its efficiency.
The basic structure of Single core fiber collimator is shown in Figure 2:
The components of Single core fiber collimator are marked in Figure 2. The types of fibers can be selected according to the requirements and application scenarios, including various single-mode and multi-mode fibers, polarization-maintaining fibers, and the number of fibers can be single fiber, double fiber, and four-fiber. Packaging can use glass tube, but also can use stainless steel tube, gold-plated tube and other materials for packaging.
There is also an air gap between the Pigtail and the lens, which is very important and sensitive to Single core fiber collimator as a whole. For Single core fiber collimator with fixed material parameters, the size of the air gap can be adjusted by using precise instruments to adjust the parameters of the final outgoing beam. That is to say, by adjusting it, you can achieve the"kaleidoscope"of the beam.
Glue is also a very key link, glue first plays the role of bonding and fixing. Secondly, it is also necessary that there will be no significant expansion or contraction at high and low temperatures, because this will lead to the change of air gap, affect the parameters of the whole Single core fiber collimator , and even make the optical path offset, causing greater loss.
See Figure 3. For this reason, the G-lens collimator allows certain optical components to be glued directly to the surface, making the module more compact than C-lens does.
Next, we take a look at the important parameters of Single core fiber collimator, as shown in FIG. 4. The first is the working distance (WD). The working distance is generally twice the distance between the Single core fiber collimator end face and the waist beam position of the beam. Spot diameter refers to the spot size of the beam at the waist beam position, which is the smallest spot in the whole beam. The focusing function of the beam can be realized by reducing the spot diameter.
For Single core fiber collimator, since the beam propagated in it is a Gaussian beam, technicians can analyze the performance of the Single core fiber collimator by constructing the q parameter of the beam, combining the size of the air gap shown in FIG. 2 and the optical parameter matrix of the lens, and then using the computer to calculate the working distance and spot diameter in FIG.