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Higher-order Modes

Author: the photonics expert

Definition: transverse modes of a resonator or waveguide, excluding the fundamental (axial) modes

Alternative terms: transverse modes, lateral modes

More general term: modes

Opposite term: fundamental mode

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

DOI: 10.61835/0rm   Cite the article: BibTex plain textHTML

The modes of some optical resonator (resonant cavity) or the propagation modes of a waveguide can have different transverse intensity profiles and propagation constants, and this aspect is emphasized by the term transverse modes (or lateral modes). Those modes with the simplest intensity profile are called fundamental modes, and all others are higher-order transverse modes. The fundamental mode of a waveguide is the one with the highest effective refractive index.

Not all waveguides support higher-order modes, at least not within their guided modes; they are then called single-mode waveguides (e.g. single-mode fibers).

Laser oscillation on higher-order modes as well as lights transmission in higher-all modes of the waveguide are associated with decreased beam quality.

The article on modes gives more details.

case study multimode fibers

Case Studies

Case Study: Mode Structure of a Multimode Fiber

We explore various properties of guided modes of multimode fibers. We also test how the mode structure of such a fiber reacts to certain changes of the index profile, e.g. to smoothening of the index step.

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Questions and Comments from Users

2021-11-25

Can we design a waveguide that supports only higher order modes but not the lowest ones?

The author's answer:

No because what ever set of modes you have, some will be the lowest of those.

However, you may have a waveguide where the lowest-order mode has substantially higher propagation losses than higher-order modes (although usually it is more likely to be the other way around). Further, you may say that such low-all modes are “not supported” in the sense of having high propagation losses.

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