Optical fibers are joined either by fusion/mechanical splice, which is a permanent joint, or by connectors, which can be disengaged repeatedly. Optical connectors are used mostly at joints that need to be switched for optical service operation and maintenance reasons, while permanent joints are in use mostly in other applications.
When joining optical fibers, the opposed cores must be properly aligned. Optical fiber connector/splice loss occurs mostly in the following manner.
Mechanisms of Light Loss at Optical Fiber Joint
(1) Poor concentricity
Poor concentricity of joined optical fibers causes a connector/splice loss. In the case of general purpose single-mode fibers, the value of connector/ splice loss is calculated roughly as the square of the amount of misalignment multiplied by 0.2. (For example, if the light source wavelength is 1310 nm, misalignment by 1 µm results in approximately 0.2 dB of loss.)
(2) Axial run-out
A connector/splice loss occurs due to an axial run-out between the light axes of optical fibers to be joined. For example, it is necessary to avoid an increased angle at fiber cut end when using an optical fiber cleaver before fusion splicing, since such an angle can result in splicing of optical fibers with run-out.
(3) Gap
An end gap between optical fibers causes a connector/splice loss. For example, if optical fiber end faces are not correctly butt-joined in mechanical splicing, a splice loss.
(4) Reflection
An end gap between optical fibers results in 0.6 dB of return loss at the maximum due to the change in refractive index from the optical fiber to the air. Cleaning optical fiber ends is important for optical connectors. In addition, the whole optical connector ends should be cleaned because loss can also occur due to dirt between optical connector ends.
