Optical Return Loss vs. Optical Insertion Loss Explained

This page explains the difference between Optical Return Loss and Optical Insertion Loss in fiber optic systems.

Optical Return Loss (ORL)

Optical Return Loss is the ratio of reflected power to the incident power from any point in a fiber optic system or fiber link. Essentially, it quantifies how much of the light injected into the fiber is reflected back towards the source. A higher ORL is generally desirable, as it indicates less reflection. Excessive reflections can degrade signal quality.

It’s expressed mathematically as:

Optical Return Loss (ORL): $10 * Log (P_i / P_r)$

Where:

• $P_i$ = Incident Power
• $P_r$ = Reflected Power

ORL is typically measured in dB (decibels).

Optical Insertion Loss

Optical Insertion Loss, sometimes called attenuation, is the loss of optical signal power that occurs when the signal passes through an optical device or any portion of a fiber cable. In simpler terms, it tells you how much weaker the signal becomes after traveling through a specific component or length of fiber. A lower insertion loss is generally better, as it means more of the original signal power is making it through.

It’s calculated as:

Optical Insertion Loss = Power Input to the device (in dB) - Power Output from the device (in dB).

The measurement involves feeding optical input power into the optical device or fiber cable and then measuring the optical output power. The difference between these two values represents the insertion loss.