Optical transceivers are among the most frequently ordered — and most frequently mis-specified — components in networking procurement. This guide covers form factors, reach, wavelength, fiber type, and the OEM compatibility question that every buyer must navigate.
1. Form Factor Cheat Sheet
| Form Factor | Max Speed | Typical Reach | Primary Use |
|---|---|---|---|
| SFP | 1 Gbps | 550 m (SX) / 10 km (LX) | Enterprise switches, industrial Ethernet, factory automation |
| SFP+ | 10 Gbps | 300 m (SR) / 10 km (LR) | Data center ToR, campus backbone, metro access |
| SFP28 | 25 Gbps | 100 m (SR) / 10 km (LR) | 5G fronthaul, 25G server access, enterprise upgrade path |
| QSFP+ | 40 Gbps | 100 m (SR4) / 10 km (LR4) | Legacy data center (being phased out in favor of 100G) |
| QSFP28 | 100 Gbps | 100 m (SR4) / 2 km (CWDM4) / 10 km (LR4) | Data center spine/leaf, DCI, metro |
| QSFP-DD | 400 Gbps | 100 m (SR8) / 2 km (DR4) / 10 km (LR4) | Hyperscale data center, AI/ML clusters |
SFP28 is backward-compatible with SFP+ cages — a 25G SFP28 transceiver will physically fit in an SFP+ port (though it will operate at the port's maximum speed, typically 10G unless the switch supports 25G). QSFP-DD is backward-compatible with QSFP28 cages at reduced speed.
2. Reach and Fiber Type: Don't Get This Wrong
| Code | Reach | Fiber | Wavelength | Connector |
|---|---|---|---|---|
| SR / SR4 / SR8 | 100–300 m | MMF (OM3/OM4) | 850 nm VCSEL | MPO / MTP (parallel) or LC (SR) |
| LR / LR4 | 10 km | SMF (OS2) | 1310 nm / CWDM | LC duplex |
| CWDM4 | 2 km | SMF (OS2) | 4× CWDM (1271–1331 nm) | LC duplex |
| ER / ER4 | 40 km | SMF (OS2) | 1310 nm / LAN-WDM | LC duplex |
Common mistake: Ordering an LR (single-mode) module for a multi-mode fiber plant. The 1310 nm laser in an LR module will not couple efficiently into 50 µm or 62.5 µm multi-mode fiber — you'll get no link or severe packet loss. Always match module type to installed fiber.
3. The OEM Compatibility Question
Major switch and router OEMs (Cisco, Juniper, Arista, HPE, etc.) encode an identifier in their transceiver firmware. The switch reads this identifier on insertion and may refuse to bring up the link if the code doesn't match its expected vendor string.
Compatible (third-party) transceivers address this by being pre-programmed with the target OEM's identifier code. A properly coded compatible transceiver is functionally and electrically identical to the OEM-branded equivalent — same laser, same receiver, same MSA compliance — with an OEM-compatible identifier in firmware.
Key points for buyers:
Always specify the target platform. "Cisco compatible" is not enough — specify the switch model and IOS/IOS-XR/Junos version. Some platforms (notably Cisco Catalyst and Nexus) use different encoding schemes.
Request DOM/DDM support. Digital Optical Monitoring provides real-time temperature, voltage, TX bias, TX power, and RX power readings — essential for troubleshooting and preventive maintenance.
Insist on pre-shipment testing. ADD Components tests every optical transceiver on the customer's specified platform (or an equivalent) before shipping. A module that codes correctly in the programmer may still fail in-situ due to firmware revision mismatches.
MSA compliance is the baseline. Multi-Source Agreement standards define the mechanical, electrical, and optical parameters. Any module claiming MSA compliance should interoperate with any MSA-compliant host port — compatibility coding notwithstanding.
4. Quick Selection Guide
| Your Application | Recommended Module |
|---|---|
| 10G server access, ToR switch uplinks, <300 m | SFP+ 10G SR (850 nm, MMF) |
| 10G campus/metro backbone, >300 m | SFP+ 10G LR (1310 nm, SMF, 10 km) |
| 25G server access, 5G fronthaul, <100 m | SFP28 25G SR (850 nm, MMF) |
| 25G enterprise/carrier, >100 m | SFP28 25G LR (1310 nm, SMF, 10 km) |
| 100G data center leaf-spine, <100 m | QSFP28 100G SR4 (850 nm, MMF, MPO) |
| 100G intra-data center, <2 km, duplex fiber | QSFP28 100G CWDM4 (SMF, LC duplex) |
| 100G DCI / metro, up to 10 km | QSFP28 100G LR4 (SMF, LC duplex) |
| 400G hyperscale, <100 m | QSFP-DD 400G SR8 (850 nm, MMF, MPO-16) |
| 1G industrial / factory automation | SFP 1G SX (MMF, 550 m) or LX (SMF, 10 km), industrial temp (–40 to +85 °C) |
For optical transceiver availability, platform compatibility verification, and volume pricing, contact sales@add-components.com or WhatsApp. Specify your platform (switch/router model and OS version), required reach, and quantity — we'll confirm compatibility and ship pre-coded modules from stock.