---
title: "Fiber Coupling Efficiency calculator — AperiOptic"
description: "Mode-overlap coupling between Gaussian beam and fiber MFD. Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/fiber-coupling-efficiency"
---

# Fiber Coupling Efficiency calculator

Mode-overlap coupling between Gaussian beam and fiber MFD.

Category: [Fiber Optics](https://aperioptic.com/calculators)

Formula: `η = (2·w·w₀/(w² + w₀²))²`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| Beam waist | `w` | µm | 5 |
| Fiber MFD | `MFD` | µm | 10.4 |

## Result with the default inputs

- Efficiency: 99.8463 %
- Loss: 0.0067 dB

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/fiber-coupling-efficiency?w=5`](https://aperioptic.com/calculators/fiber-coupling-efficiency?w=5). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Optical fiber](https://en.wikipedia.org/wiki/Optical_fiber)

[All optics calculators](https://aperioptic.com/calculators)

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The interactive page: https://aperioptic.com/calculators/fiber-coupling-efficiency (AperiOptic runs in the browser; free, no account). Every page of the site as Markdown: https://aperioptic.com/llms.txt