Basis of Fiber Loss and Calculation

Attenuation/loss of data

Transmitting light through an optical fiber is prone to some losses. Does not matter how adequate everything fits in the system, there will be some loss at any point. Suppose transmitting light via fiber cable from point A to point B, where Point A is the sender and B is the receiver. The distance between them is X km. Data is transmitted in the form of light reflecting inside the core. While traveling, there is some loss of light or some property loss. So, data is not the same as it was before. If we are sending ‘m’ dB of data from A, we are receiving like ‘m/2’ dB, and this loss is inevitable. Light is distorted even in the core that has been made of reflective glass. This happens in the energy transfer module. Even when electricity is passed via cable. There is some heat generated by electric electrons striking with the transmitting material's electron. Same with the fiber and signal amplitude gets decremented and some data is lost which is called fiber attenuation. 

What causes fiber attenuation?

There are four baselines that attenuation depends on. They are Dispersion Loss, Absorption Loss, Scattering Loss, and Bending Loss. Let us go through them shortly.

  1. Dispersion: The passing light through an optical fiber follows certain measurements. Some light wave travels at a longer wavelength and some travels at a shorter length. If we call short length A and it travels at a wavelength of λ1, Longer wavelength bending B with λ2 angle. They both transmit to the endpoint, but their travel time is different. This causes some loss. This pulse broadening method is called Dispersion. The more different the wavelengths are in the light; the more dispersion is created. There are two kinds of dispersion loss. They are intramodal and intermodal also known as IsI. Multimode optical fibers are used to pass led light through because it is not diameter is greater. And because the diameter is greater, it can accept more lights of different wavelengths. Lasers transmit monochromatic light and easily usable in single-mode fibers. So, less dispersion is created.
  2. Absorption: Absorption loss is just like it is suggested in the name. When lights are passed through a fiber, multiple wavelengths are created. When the waves strike glass core molecules inside the fiber, heat is generated. And this is the practical rule of physics. Energy is transferred from one form to another and some energy is lost at the time of this transfer in the form of heat. Transmitting from point A to B happens nonetheless, but data gets lost in this way. This is the fundamental of absorption loss. There are also two types of absorption loss in attenuation. One is intrinsic absorption and the other is extrinsic absorption. When the glass core absorbs the energy, it is called intrinsic absorption. The refractive index is made of some impurity on purpose. So, when this impurity absorbs the light and generates heat in the form of data loss is called extrinsic absorption.
  3. Scattering: Scattering is the direct loss of data for the medium inside the fiber that blocks the light in some way to lose some of its dimension. Suppose skydiving from an airplane with a hat on top of the head. Now after the jump, the hat falls off due to the air blocking as the falling speed is greater. And it was intended to happen. The same process is the scattering loss. While traveling, the light gets scattered inside the fiber and produces a loss. There are two types of loss in scattering. They are linear and non-linear. Forward direction scattering is called linear scattering and bi-directional is tagged as non-linear scattering.
  4. Bending: Bending loss happens when a length of fiber is being bent and inside various wavelengths of light create a radius of curvature. When it happens outside the fiber, we can call it ‘R’ and when it happens inside, we may call it ‘r’. And light is being reflected. At the time of transmitting, the radius of curvature is created. This causes bending loss. There are two types of bending loss. One is macro bending, and another is micro bending. And for example's sake, we can easily implement R>r. So, these are the reasons behind loss in fiber.

Calculation

As we said before, loss of light inside the fiber is a must whether it’s a multimode or single-mode fiber. This does not necessarily mean all of it happens inside the fiber. There is also a loss in the connector. It happens due to the connector pairs match with the connector loss allowance. Also, the number of splices pair with splice loss allowance. It is measured in dB. So, the total link lost is the combined loss of fiber attenuation, connector loss, and splice loss. There is also a calculation of the power budget. Power loss is calculated for the sake of ensuring if the loss is happening in the fiber. Helps resolve some issues quickly by knowing where exactly the issue is. The receiver power budget or PR and the transmitter power budget or PT has a difference and explained as PB.  So,PB = PR- PT.

This is the Basis of Fiber Loss and Calculation. Proper measurement and calculations are done periodically to have a minimum loss in the transmit process.