Fiber loss--Scattering loss

In the night, with flashlights in the air exposure, you can see a bunch of light beam. People have to see the night sky thick beam searchlight issue. Why, then, we will see these light beam it? This is because there are many smoke, dust and other tiny particles floating in the atmosphere, the light shines on these particles, resulting in a scattering, it fired up in all directions. This phenomenon was first discovered by Rayleigh, so the people of this scattering called "Rayleigh scattering."

Scattering is how is it? The original composition of the material molecules, atoms, electrons and other small particles are some of the natural frequency of vibration, and can release the corresponding wavelength and the frequency of light. Particle vibration frequency determined by the particle size. Larger particles, the lower the frequency, the release of the longer wavelength of light; the smaller the particle, the higher the frequency, the release of the shorter wavelengths of light. This vibration frequency is called the natural vibration frequency of the particle. However, this vibration is not self-generated, it needs some energy. Once the particle has a certain wavelength of light exposure, and exposure to light with the frequency of natural vibration frequency of the same particle, it will cause resonance. The electronic particle will begin to vibrate with that frequency, the result is that the particles scatter the light in all directions, the energy of the incident light is absorbed and converted into particle energy, particle energy re-turn injection in the form of light energy to go. Therefore, the external observation of the people, to see if the light hit the particles after flying out in all directions.

Fired in all directions so that light scattering, part of which the scattered light along the optical propagation in the opposite direction and reflected back in the incident-side optical fiber can receive this part of the scattered light. Makes part of the scattering of light by the loss of light energy, which is that people do not want. However, this phenomenon can also be used by us, because if we are sending the received light intensity of this part of the analysis, you can check out this fibers break, the size of defects and wear and tear. In this way, through human ingenuity, put a bad thing into something good.