Akin to water flowing from a small pipe into a large pipe, gainers are essentially perceived increases in optical power that occur at splice points due to variations in fiber characteristics, including core diameter, numerical apertures, mode field diameters and backscatter. Akin to water flowing from a small pipe into a large pipe, gainers are essentially perceived increases in optical power that occur at splice points due to variations in fiber characteristics, including core diameter, numerical apertures, mode field diameters and backscatter. ssive elements including WDM muxes and demuxes. OTDRs are sophisticated instruments, and as such the reflected signal is subjected to algorithmic digital processing, and events are analyzed, interpreted an insertion loss (IL) of typically 0. Since. Have you ever seen the optical illusion where two lines are drawn side by side, one with arrow points and one with inverted arrow points (Figure 1)? The line with the inverted arrow points looks longer, even though the two lines are the same length. There is a common optical test that can also be. Optical fiber and fiber optic cables are used as a means to transport optical energy and information over short or long distances. The gain is seen in the fiber trace following the splice which is higher than the fiber trace before.