What is the bandwidth-distance product?

The bandwidth-distance product (BDP) characterizes a fiber's capacity, expressed in MHz·km or GHz·km. It means a fiber rated at 500 MHz·km can carry 500 MHz over 1 km, or 250 MHz over 2 km. Multimode fiber datasheets list BDP directly; single-mode fiber is dispersion-specified instead.

How does modal dispersion limit multimode fiber bandwidth?

In multimode fiber, different propagation modes travel at slightly different speeds, causing a light pulse to spread over time. The effective bandwidth drops roughly as BDP / length. Graded-index multimode fiber (OM3, OM4) minimizes this by shaping the refractive index profile.

What is chromatic dispersion and how does it limit single-mode fiber?

Chromatic dispersion occurs because different wavelengths of light travel at different speeds. The dispersion coefficient D (ps/nm·km) combined with the source spectral width Δλ (nm) gives a pulse spread of D × Δλ × L (ps). Narrower spectral sources (e.g., DFB lasers) drastically reduce this penalty.

What is the rise-time budget?

The rise-time budget adds up all pulse-spreading contributions in a link (transmitter, fiber, receiver). The total system rise time must be less than 70% of the bit period (for NRZ) to maintain adequate eye opening. This tool computes the fiber's rise-time contribution from its bandwidth.

What are typical BDP values for common multimode fiber types?

OM1 (62.5 µm): 200 MHz·km at 850 nm. OM2 (50 µm): 500 MHz·km. OM3: 2,000 MHz·km (VCSEL-optimized EMB). OM4: 4,700 MHz·km EMB. OM5: 4,700 MHz·km at 850 nm with wideband support.

Fiber Optic Bandwidth Calculator

Name: Fiber Optic Bandwidth Calculator
Availability: InStock
Author: Nham Vu

Enter fiber length, modal bandwidth, and dispersion values to compute bandwidth-distance product, dispersion-limited bandwidth, and rise-time budget.

Fiber Parameters

Fiber Type

Fiber Length (km)

Enter distance in kilometers

Modal Bandwidth-Distance Product (MHz·km)

OM3: 2000 · OM4: 4700 · OM2: 500 · OM1: 200

Concatenation Exponent γ

Typically 0.7 for installed multimode links (TIA-568)

Enter fiber parameters and click Calculate to see results.

Formulas Used

1 Effective BW = BDP / L^γ (L in km, BDP in MHz·km)

2 Pulse spread σ = 1 / (2 π × BW_eff)

3 Fiber rise time t_r = 0.35 / BW_eff (Gaussian approximation)

4 NRZ budget = 0.7 / bit rate (70% of bit period)

Summary

Enter fiber length, modal bandwidth, and dispersion values to compute bandwidth-distance product, dispersion-limited bandwidth, and rise-time budget.

How it works

Select fiber type: multimode (bandwidth limited by modal dispersion) or single-mode (limited by chromatic dispersion).
Enter the fiber length in kilometers.
For multimode fiber, enter the modal bandwidth-distance product (MHz·km) from the datasheet.
For single-mode fiber, enter the chromatic dispersion coefficient (ps/nm·km) and spectral width (nm) of the source.
Click Calculate to get the effective bandwidth, bandwidth-distance product, and rise-time budget.
Review the rise-time budget to confirm your system meets the target bit rate.

Use cases

Verify that a multimode fiber link supports a target Ethernet speed (1G, 10G, 40G).
Estimate chromatic dispersion penalty for a single-mode DWDM span.
Compute fiber rise-time contribution in a link budget for high-speed digital transmission.
Compare OM3 vs. OM4 multimode fiber performance over a given distance.
Determine the maximum link length before dispersion exceeds the system rise-time budget.
Support coursework calculations in optical communications or fiber-optics engineering.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu