Optical Bandwidth Calculator

Calculation mode

Center wavelength (nm)

Spectral efficiency (bits/s/Hz)

Start wavelength (nm)

End wavelength (nm)

Laser linewidth or FWHM (nm)

Guard band (%)

Filter roll-off (%)

Usable utilization (%)

Example data table

Scenario	Center λ (nm)	Span	Spacing	Efficiency	Usable rate
C-band narrow laser	1550	2.4 nm	100 GHz	2.5 bits/s/Hz	~318.8 Gbps
Dense channel set	1550	40 channels	50 GHz	3.0 bits/s/Hz	~4.59 Tbps
Wide modulation band	1310	300 GHz	75 GHz	1.8 bits/s/Hz	~413.1 Gbps

These rows are illustrative. Real systems also depend on dispersion, OSNR, modulation format, filtering, and forward error correction.

Formula used

1) Wavelength to frequency bandwidth
Δf ≈ c × Δλ / λ²

2) Effective occupied bandwidth
Effective bandwidth = Raw bandwidth × (1 + roll-off) × (1 + guard band)

3) Usable bandwidth
Usable bandwidth = Raw bandwidth × utilization

4) Estimated throughput
Throughput = Usable bandwidth × spectral efficiency

5) Channelized band estimate
Aggregate band ≈ channel count × channel spacing

Here, c is the speed of light, λ is center wavelength, Δλ is wavelength span, and bandwidth values are converted between Hz, GHz, and THz as needed.

How to use this calculator

Select a mode based on available measurements.
Enter center wavelength and either wavelength span, frequency band, or channel details.
Set spectral efficiency, guard band, roll-off, and expected utilization.
Press the calculate button to display results above the form.
Review raw bandwidth, effective occupied band, usable bandwidth, and estimated payload rate.
Export the displayed results using the CSV or PDF buttons.

FAQs

What does optical bandwidth mean here?

It represents the spectral width available for carrying optical information. The calculator converts wavelength or channel spacing into usable frequency bandwidth and payload estimates.

Why convert wavelength span into frequency?

Optical communication capacity is commonly evaluated in hertz. Converting nanometer span into gigahertz or terahertz makes rate estimation and channel planning easier.

What is spectral efficiency?

Spectral efficiency tells how many bits can be transmitted per second for each hertz of usable optical bandwidth. Higher order modulation usually increases this value.

Why include guard band and roll-off?

These factors reflect practical spectral overhead. Filters, isolation margins, and pulse shaping reduce how much of the raw optical band becomes usable payload capacity.

Is the result exact for real fiber systems?

No. Real links depend on noise, nonlinear effects, dispersion, coding, and receiver design. The calculator gives a strong planning estimate, not a laboratory guarantee.

Can I use this for DWDM planning?

Yes. The channel mode is useful for dense wavelength systems because it estimates occupied optical band, aggregate payload, and the impact of spacing choices.

Which mode should I choose?

Use wavelength mode for spectral width in nanometers, frequency mode for known gigahertz values, and channel mode when planning based on channel count and spacing.