The maximum power that a fiber can handle will always be limited by the lowest limit of any of these damage mechanisms. A fiber component, such as a bare fiber, patch cable, or fused coupler, may have multiple potential avenues for damage (e.g., connectors, fiber end faces, and the device itself). These mechanisms include damage that occurs at the air / glass interface (when free-space coupling or when using connectors) and in the optical fiber itself. The following tutorial details damage mechanisms relevant to unterminated (bare) fiber, terminated optical fiber, and other fiber components from laser light sources.
Laser-Induced Damage in Silica Optical Fibers Preparation and Handling of Optical Fibers
The MFD in the near field can be determined from this far-field measurement using the Hankel Transform. The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. the sine of the aperture half-angle (or the numerical aperture for an SM fiber). As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture the data can then be plotted as power vs. An aperture is placed in the far field of the fiber output, and the intensity is measured. The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). The light can be approximated as a Gaussian power distribution as shown to the right, where the MFD is the diameter at which the optical power is reduced to 1/e 2 from its peak level. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. The mode field diameter (MFD) is one measure of the beam width of light propagating in a single mode fiber. The right image shows the standard intensity profile of the beam propagated through the fiber with the MFD and core diameter called out. The left image shows the intensity profile of the beam propagated through the fiber overlaid on the fiber itself.
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