Measure wavelength spread, frequency spread, and bandwidth accurately. Review Q factor, resolving power, and coherence. Built for engineers evaluating lasers, filters, and sources daily.
Choose a mode, enter engineering values, and calculate spectral width, coherence, and resolution metrics.
| Case | Input Basis | Center Wavelength | Bandwidth | Approx. Frequency Width | Q Factor |
|---|---|---|---|---|---|
| DWDM optical channel | 1520 nm to 1570 nm | 1545 nm | 50 nm | 6.28 THz | 30.90 |
| Narrow laser source | 1549.95 nm to 1550.05 nm | 1550 nm | 0.10 nm | 12.48 GHz | 15,500 |
| Instrument specification | 1550 nm with R = 10,000 | 1550 nm | 0.155 nm | 19.34 GHz | 10,000 |
Wavelength bandwidth: Δλ = λmax − λmin
Center wavelength: λ0 = (λmin + λmax) / 2
Frequency from wavelength: f = c / λ
Exact frequency bandwidth: Δf = fhigh − flow
Approximate conversion: Δf ≈ cΔλ / λ02
Fractional bandwidth: FBW = (Δf / f0) × 100
Quality factor: Q = f0 / Δf = λ0 / Δλ
Coherence length: Lc = cτc / n, with τc = k / Δf
Here, c is the speed of light, n is refractive index, and k depends on line shape: Gaussian 0.44, Lorentzian 1/π, Rectangular 0.886.
Spectral bandwidth describes the spread of wavelengths or frequencies occupied by a source, signal, filter, or instrument response. Wider bandwidth generally means lower spectral selectivity and shorter coherence time.
The exact value comes from endpoint frequency conversion. The approximate value uses Δf ≈ cΔλ/λ² and is very useful for narrowband cases. Comparing both highlights when approximation error may matter.
Use wavelength mode when optical specifications are given as lower and upper wavelengths, such as filter passbands, laser tuning ranges, emission windows, or instrument spectral spans.
Resolving power is the ratio of center wavelength to wavelength bandwidth. Higher resolving power indicates finer discrimination between nearby spectral features and typically corresponds to narrower passbands.
Q factor compares the center frequency to the bandwidth. A larger Q means a narrower band relative to its center frequency, which often indicates sharper resonance or stronger selectivity.
Different spectral shapes transform differently into the time domain. Gaussian, Lorentzian, and rectangular profiles use different factors, so the same bandwidth does not always produce the same coherence time.
Refractive index adjusts coherence length inside a medium. Light travels more slowly in glass, fiber, or other materials, so the effective coherence length becomes shorter than in air or vacuum.
Yes. It works well for laser linewidth estimates, optical filter passbands, spectroscopy instruments, wavelength-division systems, and other engineering tasks involving spectral spread and selectivity.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.