SFP 10G SR optical transceiver: the ultimate FAQ guide

What is 10G SFP+ optical module?

10G optical modules have gone through the development from 300Pin, XENPAK, X2, XFP, and finally achieved the same size as SFP form factor to transmit 10G signals, which is SFP+. The 10G SFP+ optical module is a new generation of 10G optical module, which can meet the fibre channel 8.5G and Ethernet 10G applications according to ANSI T11 protocol. The 10G SFP+ optical module is about 30% smaller than the earlier XFP optical module and looks the same as the common 1G SFP module. The 10G SFP+ optical transceiver only retains the basic electrical, optical and optoelectronic conversion functions and reduces the signal control functions such as SerDes, CDR, EDC and MAC in the original XFP design, thus simplifying the design of the 10G module and resulting in lower power consumption. The SFP+ transceiver has significant advantages such as high density, low power consumption, and lower system construction cost, and is widely used in the field of 10 Gigabit Ethernet fiber optic data communication, and is the mainstream product of 10 Gigabit module.

What is SFP 10G SR optical module?
SFP 10G SR optical transceiver is compatible with SFP Multi-Source Agreement and SFF-8472 digital diagnostics functions. It is an optical transceiver in a hot-pluggable SFP+ form factor, and the "SR" stands for Short Range, which means it can be used with multimode fiber(MMF) for data transmission distance up to 300m. The SFP 10G SR transceiver consists of three sections: a VCSEL laser transmitter, a PIN photodiode integrated with a trans-impedance preamplifier (TIA) and MCU control unit.

SFP 10G SR vs. SFP 10G LR: what’s the difference?
The 10Gbase-SR and 10Gbase-LR are two different 10 Gigabit Ethernet specifications. The "SR" in SFP 10G SR stands for short range. The specification supports short wavelength (850nm) on multimode fiber (MMF) with coding mode of 64B/66B, and the effective transmission distance is 2 ~ 300m. To support 300m transmission, it needs to adopt optimized 50μm wire diameter OM3 fiber (optimized multimode 3). Because it uses low-cost solid-state laser components and the working wavelength is only 850nm, it is also the cheapest among all the 10G modules. However, SFP 10G SR transceiver is very sensitive to fiber type and is limited by short distance.

The "LR" in 10Gbase-LR refers to "long range". The specification supports long wavelength (1310nm) on single-mode optical fiber (SMF) with coding mode of 64B/66B. The effective transmission distance is 2m to 10km. The SFP 10G LR optical module meets this specification and has the characteristics of miniaturization, low power consumption and long transmission distance.

To sum up, the difference between SFP 10G LR transceiver and SFP 10G SR transceiver mainly lies in the different transmission distance: the SFP 10G SR multimode optical module is used for transmission distance within 300m, while the SFP 10G LR single-mode optical module is used for transmission distance of 300m to 10km.

SFP 10G SR vs. SFP 10G LRM

Both SFP 10G SR module and SFP 10G LRM module support multimode transmission. When SFP 10G SR transceiver is matched with OM3 optical fiber jumper, the maximum transmission distance is 300m; when used with OM4 optical fiber jumper, its transmission distance can reach 400m. While the maximum transmission distance is 200m when the SFP 10G LRM optical module is used with OM3 and OM4 optical fiber jumpers. So how to choose between the two? Generally, when the transmission distance is less than 300m, it is recommended to select SFP 10G SR optical transceiver. However, if there are other special requirements for transmission, such as modal bandwidth of 500 MHz-km, then it is recommended to choose SFP-10G-LRM optical module. At present, many users still use OM1 and OM2 optical fiber jumpers. When SFP 10G SR optical module is used with OM1/OM2 optical fiber jumpers, it can only transmit 33m, and when SFP 10G LRM optical module is used with OM1/OM2 optical fiber jumpers, it can transmit 220m. Therefore, the application scope of SFP 10G LRM transceiver is larger than that of SFP 10G SR transceiver.

It should be noted that in order to ensure that the SFP 10G LRM optical module passes FDDI (Fiber Distributed Data Interface) level, it should be coupled via multimode conversion fiber patch cables when using OM1 and OM2 fibers, while mode conditioning patch cables are not required when using OM3 and OM4 fiber patch cables. It is recommended to measure the optical power before inserting the fiber into the optical module, when the received optical power is greater than 0.5dBm, a 5dB fiber attenuator should be inserted at the transmitting end of the optical module on both sides of the link.

10G SFP+ DAC vs. 10G SFP+ transceiver vs. 10GBase-T module
10GBASE-T RJ45 modules are usually wired using Cat6a or Cat7 network cables with a maximum transmission distance of 100m at Gigabit rates and up to 30-80m at 10G rates. In data centers, where hundreds of cables are required, using cheap network cables can save a lot of costs. In addition, 10GBASE-T modules can maximize the use of existing copper structure wiring, which also saves a lot of expenses.

The 10G SFP+ transceiver meets the standard of Multi-Sourcing Agreement (MSA), and provides the cost effective solution for 10G optical data communication. It supports both duplex and simplex LC optics interfaces. The 10G SFP+ transceiver consists of 10Gbit/s DFB/EML optical transmitter and PIN receiver, which allow 300m~120km 10G Ethernet and 10G fiber channel applications. However, the maintenance cost of its fiber optic cabling is relatively high.

The SFP+ DAC (Direct Attach Cable) is the least expensive of the three products, with the only drawback that the transmission distance is very limited—up to 10 meters, and is more suitable for cabling connections within and between racks. If transmission distance is not a factor that must be considered, SFP+ DAC has lower power consumption and lower latency, making it a more ideal cabling solution for data centers.

Is 10G SFP+ backwards compatible with 1G SFP?

SFP and SFP+ modules look exactly the same. And as they have the same size, your SFP transceiver will fit seamlessly into an SFP+ switch port and vice versa. However, the connection won’t work as you expect it to. If you plug an SFP device into an SFP+ port, the speed will be locked at 1 Gbps. Plugging an SFP+ module into an SFP port delivers no results at all, as the 10G transceiver can never auto-negotiate to 1Gbps.