Insertion Loss

definition:
The power loss caused by inserting a certain device.

If a certain optical component is inserted into the device, it may cause some loss in the device or on the optical surface. For example:

• Fiber optic connector is a mechanical or fusion joint used to connect two optical fibers, rather than using only one continuous fiber. Due to mismatches in effective mode area or similar effects, optical losses may occur on non ideal surfaces.
• Placing a Faraday isolator behind the output of the laser is to eliminate back reflection. In non ideal anti reflection coatings of isolators, some power is lost, usually due to parasitic absorption or dispersion.

Insertion loss is usually characterized by decibels, which is the ratio of output power to input power taken as the logarithm of 10 and then multiplied by 10 For example, the insertion loss of fiber optic connectors is around 0.5 dB. High quality fusion joints can reduce this value to 0.02 dB.

For high-power devices, it is usually not desirable to have significant insertion loss. On the one hand, there is power loss, and on the other hand, strong thermal effects may occur due to the absorbed light.