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Insertion Loss

Author: the photonics expert Dr. Rüdiger Paschotta

Definition: power losses due to insertion of a device

Categories: article belongs to category general optics general optics, article belongs to category fiber optics and waveguides fiber optics and waveguides

Units: %, [[decibel|dB]]

DOI: 10.61835/yma Cite the article: BibTex plain text HTML Link to this page LinkedIn

If an optical device is inserted into a setup, some of the optical power may be lost in the device or at optical interfaces. Some examples:

A fiber connector, a mechanical splice or a fusion splice may be used to connect two fibers, instead of having a single continuous fiber. Some of the optical power will be lost due to non-perfect interfaces, not exactly matching effective mode areas or similar factors.
The larger amount of insertion loss may be intentionally inserted in the form of a fiber-optic attenuator.
A Faraday isolator is inserted after the output of a laser in order to prevent it against back-reflections. Some power is lost at imperfect anti-reflection coatings of the isolator and possibly by parasitic absorption or scattering in the optical elements.

The insertion loss (or attenuation) is usually specified in decibels, calculated as 10 times the logarithm of base 10 of the ratio of input and output powers. For fiber connectors, for example, it is often of the order of 0.5 dB. High-quality fusion splices may reach values like 0.02 dB.

For high-power devices, a high insertion loss is often unwanted not only due to the power loss but also because of possibly strong heating effects resulting from absorbed light.

A convenient method for measuring insertion loss is optical time-domain reflectometry. With that, the insertion loss of multiple optical elements along a fiber can be measured separately.

Optical Loss Testers

For use mainly in optical fiber communications, there are optical loss testers with which insertion losses can be quite conveniently measured.

More to Learn

Encyclopedia articles:

Suppliers

The RP Photonics Buyer's Guide contains 104 suppliers for fiber couplers. Among them:

Focuslight Technologies

Focuslight Technologies has fiber couplers which allow one to couple the light from a single emitter or from multiple emitters into a single fiber with only one lens element. They consist of a monolithic glass block with two opposite crossed cylindrical surfaces and mounting surfaces. The light of the fast and slow axes is collimated by one cylindrical lens to produce an almost symmetrical focus.

AMS Technologies

AMS Technologies provides a broad variety of fiber couplers for single mode (SM), multi mode (MM) and polarization maintaining (PM) fibers for various applications:

SM couplers & combiners, also in low-loss fused fiber technology
module-style SM couplers & combiners in small or 19-inch-cases
fused MM couplers & combiners
Fused bidirectional MM fiber optic star couplers
PM couplers & combiners with customizable coupling ratio and/or wavelength
fused PM couplers & combiners
PM couplers based on bow-tie fibers
high-power MM N×1 pump combiners for high-power fiber laser applications
MM power combiners, also with signal feedthrough
high temperature couplers for up to +250 °C
sub-zero PM couplers operating from −55 °C
fused dual-clad fiber (FDCF) couplers

DK Photonics

DK Photonics uses a unique fusing technique and polarization-maintaining fibers to fabricate the polarization maintaining fused coupler (PMC). The coupling ratio can be selected according to the customer’s request. It features low excess loss, small size and high polarization extinction ratio. PMC is widely used for optical sensors and optical gyros.

TOPTICA Photonics

TOPTICA´s COOL patent pending fiber coupling concept is new, because it does not use any mechanical micro adjustable parts, which normally are the first to move due to thermal or mechanical influences.All major optical components are solidly mounted and the optical micro alignment is unsusceptible to mechanical and thermal distortions or translations.

CSRayzer Optical Technology

CSRAYZER’s polarization-maintaining filter or fused coupler series products are used to split inputs from a polarization-maintaining optical fiber according to the given coupling ratio. They are widely used in fiber lasers, optical fiber amplifiers, optical fiber communications and fiber sensors, having compact dimensions, low insertion loss, low polarization dependent loss and high stability, and the ability to work under different temperature conditions.

Schäfter + Kirchhoff

High precision fiber couplers (fiber port) optimized for high pointing stability and long-term stability. Efficient coupling of collimated laser radiation into single-mode and PM fiber cables. Available as 60SMS and 60SMF version.

Questions and Comments from Users

2021-07-27

Is there a significant difference between SMF insertion loss and MMF insertion loss? If so, which one is usually higher?

The author's answer:

Multimode fibers often have higher propagation losses than single-mode fibers. That, however, would not usually be called an insertion loss; that term is more commonly used for specific devices or splices.

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