What does optical return loss (ORL) define?

Optical return loss (ORL) measures how much light is reflected back towards the source from any point along a fiber optic cable. It effectively quantifies the return of light due to Fresnel reflections at various interfaces and from Rayleigh backscatter within the fiber.

When light is transmitted through an optical fiber, some of it can be reflected back towards the source instead of passing through to the end of the fiber. ORL expresses this as a ratio, typically in decibels (dB), where a higher ORL indicates better performance, meaning less light is reflected back.

The other options address different aspects of fiber optics: the total power loss of the fiber pertains to overall attenuation, while the ratio of signal power to noise power is often described as signal-to-noise ratio (SNR), and minimum reflectance of the fiber does not capture the comprehensive nature of ORL. Thus, the defining characteristic of ORL being tied to Fresnel reflections and Rayleigh backscatter is what makes the first choice the correct answer.