For measuring fiber loss over a distance, the appropriate tool to use is?

The appropriate tool for measuring fiber loss over a distance is the Optical Time Domain Reflectometer (OTDR). An OTDR provides a graphical representation of the fiber's performance by sending a pulse of light down the fiber and measuring the time it takes for reflections to return. It can identify and quantify various losses along the length of the fiber, such as splice losses and attenuation.

Using the OTDR allows technicians to not just measure loss but also locate faults and irregularities in the fiber, making it an essential tool in fiber optic testing and maintenance. This capability is important for ensuring the integrity of the fiber optic link, especially in longer distances, where losses can accumulate and need precise identification.

While an inspection microscope is useful for examining connectors and end faces for cleanliness, and a visual fiber tracer helps to verify the path of the fiber, and a light source and power meter measure loss at a specific point, none of these tools provide the comprehensive loss measurement over distance that the OTDR offers. Therefore, in the context of assessing fiber loss along the entire length of a fiber optic cable, the OTDR stands out as the most suitable instrument.