Enter fiber and sweep inputs
Use core radius or core diameter. If you enter both, the radius value takes priority.
Formula used
Numerical aperture: NA = √(n₁² − n₂²)
Normalized frequency: V = (2πaNA) / λ
Marcuse mode radius approximation: w / a = 0.65 + 1.619 / V3/2 + 2.879 / V6
Mode field diameter: MFD = 2w
Effective area: Aeff = πw²
Approximate cutoff wavelength: λc = (2πaNA) / 2.405
Keep the core radius and wavelength in matching units. This approximation works best for weakly guiding, step-index, single-mode style fiber analysis.
How to use this calculator
- Enter the operating wavelength in nanometers.
- Provide the core radius, or fill the optional core diameter field.
- Enter core and cladding refractive indices, or type a manual numerical aperture.
- Set the wavelength sweep range for the Plotly trend graph.
- Press the calculate button to show the result above the form.
- Use the CSV or PDF buttons to export the current calculation summary.
Example data table
| Wavelength (nm) | Core radius (µm) | NA | V-number | MFD (µm) | Effective area (µm²) |
|---|---|---|---|---|---|
| 850 | 3.20 | 0.1200 | 2.8385 | 6.3619 | 31.7878 |
| 1,310 | 4.10 | 0.1400 | 2.7531 | 8.2904 | 53.9816 |
| 1,550 | 4.50 | 0.1300 | 2.3714 | 9.9858 | 78.3169 |
These rows use the same Marcuse approximation implemented in the calculator.
FAQs
Mode field diameter describes the effective width of the optical power distribution in a fiber’s guided fundamental mode. It is usually larger than the physical core because the field extends into the cladding.
As wavelength increases, the optical field becomes less tightly confined for the same fiber geometry and aperture. That usually increases mode radius and mode field diameter.
Use the override when the manufacturer already provides numerical aperture, or when you want to compare scenarios quickly without changing refractive indices.
The V-number measures how strongly the mode is confined. Lower values indicate weaker confinement. A value below about 2.405 usually indicates single-mode guidance for a step-index fiber.
It is best for weakly guiding, step-index, single-mode style fibers. Specialty fibers, strongly guiding structures, or exact design verification may need numerical simulation instead.
Effective area helps estimate nonlinear performance, optical intensity, and coupling behavior. Larger effective area generally lowers intensity for the same launched power.
That can be normal in single-mode fibers. The guided field does not stop exactly at the core boundary, so part of the optical energy exists in the cladding region.
The cutoff wavelength is the approximate boundary where higher-order modes stop propagating in an ideal step-index fiber. It helps judge whether the selected wavelength is comfortably single-mode.