In free-space optical passive devices such as optical isolators, optical circulators, optical switches and so on, the end faces of the input and output optical fibers must be separated by a certain distance, so that some optical elements can be inserted into the optical path to realize the device functions.
However, the Gaussian beam output by the optical fiber that is actually a near-Gaussian beam, which can be approximately dealt by a Gaussian beam, has a very small waist radius, thus the divergence angle is comparatively bigger, so the direct coupling loss between the two optical fibers is extremely sensitive to its spacing. When the distance between the two fiber ends is about 2mm, the coupling loss is as high as 25dB, and it increases sharply with the increase of the distance.
In order to add elements between two optical fibers, we must increase the distance between the end faces of two optical fibers while maintaining high coupling efficiency. The fiber collimator has such a function that it collimates the light output from the optical fiber into a light beam with a large waist spot and a small divergence angle, so as to increase the tolerance of the axial spacing.
However, how to choose a suitable fiber collimator? The following points should be noted.
1. Optical fiber model of the fiber collimator: The optical fiber model needs to be matched with matching systems such as light emitting system and receiving system.
2. Mechanical dimension of optical fiber collimator: the mechanical dimension needs to be consistent with the supporting system.
3. Working distance of optical fiber collimators: According to actual application requirements, it is very important to determine the distance between two optical fiber collimators. Once the spacing is determined, it is difficult to change.
For example, if a pair of optical fiber collimators with a working distance of 10mm are manufactured, without changing the configuration of the optical fiber collimators. In fact, it is difficult to change, the optical fiber collimators are usually fixed with glue or solder. If they are used for other working distances, the loss will obviously change.
4. The spot quality of optical fiber collimator: spot size, roundness, M2, etc., which needs to be determined according to actual requirements, for example, the spot size can't be less than the element diaphragm size, etc.
5. For the double fiber collimator, there is another very important parameter, that is, crossing angle and crossing distance.
Definition of crossing angle and crossing length: the crossing angle is determined by the curvature of the lens and the distance between two optical fibers, and the crossing length is determined by the focal length of the lens. Make sure you know the said definition when purchasing.
6. There are many options for the lens of fiber collimator.
For example, there are spherical lenses, plane lenses (self-focusing lenses), aspheric lenses and so on. That can meet different application environment.
As an advanced technology enterprise, Zhongshan Meisu Technology Co., Ltd. has a number of patented technologies. All the rich experience and expertise in ultra-precision assembly enable us to provide fiber array subassemblies and other optical equipment for different fields such as optical communication, biochemical sensing and laser imaging. If you have any needs, please feel free to contact us.