Optical transceiver standards can be quite a confusing subject to discuss, not helped by the fact many of the “standards” are not actually ratified sets of specifications at all and are simply rough guidelines that vendors generally adopt, albeit sometimes not to the exact same levels as each other. A prime example of this are the longer range SFP standards such as 1000BASE-EX and -ZX which can vary wildly between vendors, sometimes with reach variations as much as 20km between different sources.
Knowing which type of module to buy for your individual applications is important. You don’t want to buy an underspecified LX module when you need to cover 25km, likewise you don’t want to pay a premium for an EX module to cover a 500m run. Here we discuss the various standards, their official and not-so-official ranges, to help you identify the correct modules for your next project.
Gigabit SFP / GBIC
Generally distances quoted are based on typical loss figures, and presumed 50/125 (OM2) fibre for multimode and 9/125 (OS1) for singlemode. There can be variations for better or worse depending on fibre type (for example distances are shorter when using 62.5/125 (OM1) fibre, but normally longer using OM3 or OM4). Number and quality of splices and connectors can have an impact too – if in doubt it is always advisable to run a loss test over the fibre link before purchasing any equipment to ensure the optical budget is within range of the SFP specification.
| Name | Standard | Fibre | Distance | Notes | |
|---|---|---|---|---|---|
| 1000BASE-SX | Yes, 802.3z | Multimode | 550m | ||
| 1000BASE-LX | Yes, 802.3z | Multi & Singlemode | 550m / 5km | Often referred to as -LRM, sold as longer range multimode module for older fibre types such a OM1. | |
| 1000BASE-LX10 aka -LH | Yes, 802.3ah | Singlemode | 10km | Generally -LH is the preferred name, although it is not the official standard. Either way the specification is the same. | |
| 1000BASE-EX | No | Singlemode | 40km | Using 1310nm, potential distances can be slightly longer dependant on fibre loss and launch power. Sometimes advertised as 30km for safety’s sake, and occasionally as long as 60km by less scrupulous vendors. | |
| 1000BASE-ZX | No | Singlemode | 70km | Using 1550nm – similar to EX, these are sometimes advertised anywhere between 60km and 80km. | |
| 1000BASE-EZX | No | Singlemode | 120km | Not even non-standard but industry accepted in the eyes of IEEE. High powered 1550nm modules with lengths up to 120km available from some specialist sources. Highly dependent on fibre type and link loss to achieve anything close to 120km. | |
| 1000BASE-BX | Yes, 802.3ah and No | Singlemode | 10 – 80km | Officially single strand, bi-directional (BiDi) optics are rated to 10km. There are some variations including BX40 and BX80 which, similar to -EX and -ZX, are not ratified by industry accepted. 40km and 80km respectively. |
10Gigabit SFP+ / XFP / XENPAK / X2
10G standards are fairly similar to Gigabit, and in fact a lot more are fully ratified – possibly taking heed of the industry demands to gather a group of defined specifications for a wider range of applications and products. Distances expressed are based on 50/125 (OM3) laser optimised multimode and 9/125 (OS2) singlemode fibre. Possibly more importantly than with Gigabit, link loss and splice/connector quality has a bearing on link lengths – so much so, the process of cleaning connectors is part of the IEEE standard for optical testing.
| Name | Standard | Fibre | Distance | Notes | |
|---|---|---|---|---|---|
| 10GBASE-SR | Yes, 802.3ae | Multimode | 300m | Also available as -USR, lower cost ultra-short range modules covering approx. half the distance but this is vendor specific. | |
| 10GBASE-LX4 | Yes, 802.3ae | Multi & Singlemode | 300m / 10km | A 4 lane WDM, single strand (BiDi) solution. Very expensive, and the adoption rate is low. | |
| 10GBASE-LRM | Yes, 802.3aq | Multimode | 220m | Similar to 1000BASE-LX – a 1310nm wavelength module designed for multimode fibre, essentially enabling a reasonable distance on older, non-laser optimised fibre such as OM2. | |
| 10GBASE-LR | Yes, 802.3ae | Singlemode | 10km | ||
| 10GBASE-ER | Yes, 802.3ae | Singlemode | 40km | ||
| 10GBASE-ZR | No | Singlemode | 80km | Not an official standard, but industry recognised. Essentially uses the same 1550nm specification of -ER but with a higher powered launch and higher performance receive sensitivity to increase range. |
That covers the common types of Gigabit and 10G optics and should provide a solution to the vast majority of applications. I specifically haven’t covered less common single fibre solutions such as CWDM/DWDM as there are a whole other set of standards for these, which once again are often interpreted differently between vendors. These applications are far more specialist though and usually require careful planning and design.
Advance modules follow the standards set by IEEE where applicable. In instances where there is no fixed standard, for example on longer reach singlemode optics, we generally design our modules to match or exceed the specifications of the highest specified vendor modules in the market. We can then encode to support a wide range of vendor’s equipment, safe in the knowledge we are more-often-than-not exceeding the specification defined by the vendor.
