Effective modal bandwidth is a multimode-fiber bandwidth parameter that must be read with its stated wavelength and test basis. The MHz·km unit expresses a bandwidth-length product; it is not an Ethernet data rate or a standalone reach guarantee. The OM3 and OM4 reference products here list effective modal bandwidth at 850 nm, while the OM1 table lists overfilled modal bandwidth. Keep those types separate when comparing figures. To select a fiber for a data center link, combine the appropriate fiber specification with the actual transceiver interface, channel length and loss budget. Request clarification when a datasheet gives only a bandwidth number without identifying its type or wavelength, rather than assuming it matches another supplier’s entry.
Do not drop the bandwidth type
Overfilled modal bandwidth and effective modal bandwidth describe different specification contexts. The OM1 product on this site lists overfilled bandwidth at stated wavelengths. Its missing effective modal bandwidth entry is not a zero and should not be relabeled for a cleaner comparison table.
The OM3 and OM4 reference entries identify effective modal bandwidth at 850 nm. Keep the full parameter label with the value whenever it is copied into a procurement sheet or technical discussion.
Use the source values in their proper scope
The source literature used for OM3-300 lists at least 2,000 MHz·km at 850 nm; the OM4 source lists at least 4,700 MHz·km for the corresponding effective modal bandwidth entry. These are supplier reference limits, not measurements of an available batch.
A higher reference value is one difference between the products. The complete comparison still includes geometry, attenuation, coating and the offered specification. Ask which product grade and document revision the quotation follows.
Why bandwidth alone does not establish Ethernet reach
The intended optical interface and complete channel requirements determine how the fiber specification is used in a network design. Channel length, connections and their loss allowances remain part of the review. Dividing a MHz·km value by a nominal data rate does not establish a supported Ethernet distance.
Start with the required interface, then confirm the fiber category and channel conditions applicable to it. For coated-fiber procurement, keep that system requirement connected to the supplier specification without claiming that bare-fiber data proves the performance of a completed cable assembly.
| Reference product | Parameter to read | Wavelength context |
|---|---|---|
| OM1 | Overfilled modal bandwidth | 850 nm and 1300 nm entries |
| OM3 | Effective modal bandwidth | 850 nm entry |
| OM4 | Effective modal bandwidth | 850 nm entry |
| Completed network | Interface and full channel requirements | Check the intended optical equipment |
Frequently asked questions
Is MHz·km the same as a network data rate?
No. It is a bandwidth-length specification unit. It does not directly state Ethernet rate or supported channel distance.
Can OM1 bandwidth be compared as if it were EMB?
Do not relabel an overfilled modal bandwidth value as effective modal bandwidth. Keep the stated type and wavelength.
Does OM4 remove the need to check connector loss?
No. The complete channel loss budget and optical-interface requirements still need to be met.
Sources & reference context
This guide is published by OpticFiberHub and summarizes the supplier literature identified below with editorial purchasing guidance. Product values describe the source grade, not a measured result or a conformity guarantee for a new order.
- OM1 reference specifications — YOFC OM1 (62.5/125 μm) Multimode Fibre — reference specifications. Original product reference.
- OM3 reference specifications — Jiangsu Nanfang Optical Fiber Product Manual, pages 13–14.
- OM4 reference specifications — Jiangsu Nanfang Optical Fiber Product Manual, pages 15–16.
Quality & technical resources explains source selection, translated documents and the limits of historical batch records. Request the current specification and applicable records for the actual offered material.
Further terminology reference: The Fiber Optic Association: optical fiber fundamentals.
