Optical transceivers are small, but choosing the wrong one can stop a network project in its tracks. A module that doesn’t match the switch, the fiber type or the link distance simply won’t work. This guide walks you through the five questions you need to answer before buying an SFP, SFP+ or QSFP transceiver.
1. What speed does the port support?
The form factor of the module is defined by the port on your switch, router or server. These are the most common options:
- SFP: 1 Gbps (also 100 Mbps in older equipment).
- SFP+: 10 Gbps. Most SFP+ ports also accept 1G SFP modules.
- SFP28: 25 Gbps, common in modern data center servers.
- QSFP+: 40 Gbps, built from four 10G lanes.
- QSFP28: 100 Gbps, built from four 25G lanes.
Check the equipment datasheet: the port type and supported speeds are always listed there.
2. Single-mode or multimode fiber?
The transceiver must match the fiber already installed (or planned). Multimode modules (usually 850 nm, labeled SR or SX) are designed for short links inside a building or data center. Single-mode modules (1310 nm or 1550 nm, labeled LR, LX, ER or ZR) are designed for long distances between buildings, campuses or cities. If you are not sure which fiber you have, check the cable jacket: yellow usually means single-mode, while aqua, violet or orange usually means multimode.
3. How long is the link?
Each module is rated for a maximum distance. As a general reference for 10G:
- SR (850 nm, multimode): up to 300 m on OM3 and 400 m on OM4.
- LR (1310 nm, single-mode): up to 10 km.
- ER (1550 nm, single-mode): up to 40 km.
- ZR (1550 nm, single-mode): 80 km and beyond.
For 1G, the equivalents are SX (550 m on multimode), LX (10 to 20 km) and EX/ZX for longer links. Always choose a module rated for a distance equal to or greater than your real link, and keep in mind that connectors and splices add loss along the way.
4. Duplex or BiDi?
Standard transceivers use two fibers: one to transmit and one to receive, with a duplex LC connector. BiDi transceivers transmit and receive over a single fiber using two different wavelengths, which halves fiber usage. They must always be installed in matched pairs (an “upstream” and a “downstream” module).
5. Is it compatible with your equipment brand?
Many switches and routers only accept modules that are coded for their platform. A compatible transceiver is programmed so the equipment recognizes it as a supported module, delivering the same performance at a fraction of the cost of the original-brand part. At Broadstick, we code our transceivers for the brand you require, including Cisco, MikroTik, Huawei, HP/Aruba, Dell, Ubiquiti, Fortinet, Juniper and many more.
What about short connections inside the rack?
For links of just a few meters between switches and servers in the same rack, a Direct Attach Cable (DAC) is usually the most economical option. It combines two modules and a copper cable in a single assembly. For slightly longer runs, Active Optical Cables (AOC) offer the same convenience with lighter, thinner cables. If you need to connect to an RJ45 copper port, SFP and SFP+ RJ45 modules are also available.
Quick checklist
- Port type and speed (SFP, SFP+, SFP28, QSFP+, QSFP28).
- Fiber type (single-mode or multimode).
- Link distance, with some margin.
- Duplex or BiDi.
- Equipment brand and model for compatibility coding.
Need help choosing?
Browse our full range of optical transceivers, from 1G to 100G, or contact our team with your equipment model and link distance. We will recommend the right module for your network.