Bragg Grating Calculator

1. Enter n_eff and the grating period with the correct unit.
2. Keep m = 1 unless you intentionally use higher orders.
3. If modeling sensing, add temperature change and or strain.
4. Adjust advanced coefficients for your fiber or packaging.
5. Press Submit to view results above the form.
6. Use CSV or PDF buttons to export the latest output.

Operational ranges for grating period and index

Telecom gratings often use Lambda between 520 and 550 nm with n_eff near 1.44 to 1.47, producing reflections around 1500 to 1600 nm. Shorter periods shift responses toward 800 to 1100 nm, while longer periods push beyond 1600 nm for sensing and filtering.

Interpreting diffraction order in practical designs

Order m scales wavelength inversely. Keeping m = 1 maximizes reflected wavelength for a given structure. Using m = 2 halves the Bragg wavelength, which is useful for compact laboratory demonstrations or specialized sources, but it can reduce usable bandwidth and complicate component selection.

Temperature driven drift and typical coefficients

For silica, dn/dT is commonly around 8e-6 to 10e-6 per degC, while thermal expansion alpha is near 0.55e-6 per degC. At 1550 nm, the combined temperature sensitivity is frequently about 8 to 14 pm per degC, depending on n_eff and packaging constraints.

Strain response and the strain optic constant

The strain term uses (1 - p_e). With p_e around 0.22, (1 - p_e) is about 0.78. Near 1550 nm this can correspond to roughly 1.0 to 1.3 pm per microstrain, helping convert measured wavelength shifts into axial strain in structural monitoring.

Quality checks using cross comparison and exports

Engineers often verify that computed lambdaB matches expected spectral regions before committing to fabrication. Exported CSV results support traceability, while a PDF snapshot is useful for design reviews. Comparing multiple runs with small parameter changes highlights which input dominates drift and supports tolerance budgeting.

Common application scenarios and measurable outcomes

In sensing, wavelength shift is mapped to temperature, strain, or both, typically with compensation strategies. In filtering, designers target a reflection peak at a specified wavelength with controlled sensitivity to environment. This calculator reports initial and shifted wavelengths plus sensitivities, enabling quick feasibility checks before detailed optical simulation.

1) What does the calculator compute first?

It computes the initial Bragg wavelength using n_eff, grating period, and diffraction order. It then applies temperature and strain terms to estimate the shifted wavelength and sensitivities.

2) Which unit should I use for the grating period?

Use nm for most fiber Bragg gratings. Use um or mm only if your structure is physically larger. The calculator converts the period internally for consistent wavelength computation.

3) Why do my temperature results look high or low?

Temperature sensitivity depends on dn/dT, alpha, and n_eff. Packaging materials can change effective expansion and stress transfer. Replace defaults with measured coefficients for your assembly.

4) How should I enter strain?

Microstrain is common in structural testing. Enter microstrain directly and keep the unit set to microstrain. If you have unitless strain, switch the unit to strain and enter the raw value.

5) Is the graph a full spectral simulator?

No. The plot is an illustrative Gaussian peak centered at the computed wavelengths. It helps visualize direction and magnitude of shift, not exact reflectivity, bandwidth, or sidelobe behavior.

6) What is a good workflow for design verification?

Run baseline inputs, then vary one parameter at a time, exporting results for documentation. Use the reported sensitivities to estimate drift under expected temperature and strain ranges.