SFP Module Types: Single-Mode vs Multimode SFP
What is SFP Module?
SFP module is a hot-pluggable transceiver with a small form factor for high-density data communications. It has an electrical interface on the one end that connects to the system equipment such as a network switch, and an optical interface on the other end that connects to the outer fiber optic cables. In the process, the optical module completes receiving and transmitting optical signals by signal conversion — optical-electrical-optical.
What is Single-mode vs Multimode SFP Module Type?
Single-mode vs multimode fiber describes the number of modes that can propagate through the fiber. SIngle-mode (SM) fiber can only propagate a single light mode at a time while multimode (MM) fiber can propagate multiple light modes. SIngle-mode SFP works with single-mode fiber, and multimode SFP works with multimode fiber.
What are the Differences Between Single-mode and Multimode SFP?
The major differences between single-mode SFP and multimode SFP are listed in the table below, more details are manifested in the following parts.
How to identify single-mode SFP vs multimode SFP at one sight? Remember the rule of thumb on manufacturer color coating.
The first method is to identify the Bale Clasp. In general, the bale Clasp on single-mode SFP is usually blue. Yet some are red, yellow, etc. The bale Clasp on multimode SFP is black.
Single-mode vs multimode SFP Transmitter Laser
Previously I mentioned that the SFP module has the function of receiving and transmitting the optical signal, which is due to the transmitter and receiver built into the optoelectronic device. The laser in the transmitter is the core part of the optical transceiver. It feeds electrical current into the semiconductor material to generate gains and finally launches laser via laser oscillation in the resonator.
The market has seen various transceiver Laser types, which varify in the semiconductor material and resonator structure. VCSEL and FP are usually used for transmission distance within 40km, and over 40km reach generally use DFP lasers. Other laser types: DML is used for lower speed 25G in medium 2-10km transmission. EML laser is applied in high-speed and long-distance applications.
Some of the examples of QSFPTEK single-mode SFP and multimode SFP with different Laser types are enlisted below:
• Cisco SFP-10G-SR Compatible 10GBASE-SR SFP+ uses a VCSEL Laser for max 300m transmission.
• Cisco GLC-LH-SM Compatible 1000BASE-LX/LH SFP is equipped with an FP Laser for up to 10km transmission.
• Cisco QSFP-40G-LR4 Compatible 40GBASE-LR4 QSFP+ is equipped with DFB Lasers for up to 10km transmission.
• Cisco QSFP-100G-ZR4-S Compatible 100GBASE-ZR4 QSFP28 is equipped with EML Lasers for up to 80km long-distance transmission.
Single-mode vs multimode SFP Transmission Distance
The core is the central and innermost layer of fiber. A size distinction exists between single-mode and multimode fiber cores. Multimode fiber has a wider fiber core, generally 50um for OM2/OM3/OM4/OM5 fiber and 62.5um for OM1 fiber. However, the core diameter in a single-mode fiber is quite small. 9um is common; 7um and 5um are also available.
Light passes through a thinner core with fewer reflections, which leads to a lower attenuation value. This means SMF against MMF can carry a higher bandwidth at a longer distance to maintain acceptable signal levels.
Accordingly, MM SFP is generally used for short-distance transmission while SM SFP is mostly applied in medium to long-range transmission environments. More specifically, a value is assigned on SFP to evaluate the max transmission distance within the signal stability range. MM SFP has the max reach option of 100m, 150m, 300m, 500m, etc. SMF SFP is common in 2km, 10km, 40km, 80km, 120km, etc.
Single-mode vs multimode SFP Wavelength
850nm is the typical central wavelength of MMF SFP, deployed in short-reach transmission. Single-mode fiber imposes more harsh requirements on the optics used. 1310nm and 1550nm are two common wavelengths on the SM SFP modules for long-haul transmission.
1310nm is a special wavelength, that adapts to both multimode and single-mode usage. Some SFPs using a wavelength of 1310nm support both multimode and single-mode fiber. For example, the GLC-LH-SM 1000BASE-LX/LH SFP with a wavelength of 1310nm supports up to 10km link over OS2 SMF or up to 500m links via OM3 MMF.
Single-mode vs multimode SFP Price
The harsh tolerance and higher performance of single-mode SFP determine its higher cost. The FP, DFB or even EML laser transmitter in SM SFP is much more expensive than the VCSEL laser in the MM SFP.
Some of the examples of QSFPTEK modules with different Laser, wavelength, transmission distance, and prices are enlisted below:
Single-mode SFP and multimode SFP are two SFP module types breakdown by the mode amount of light propagation through the fiber at a time. Multimode SFP is a transceiver that will work with multimode fiber while single-mode SFP is the module that will work with single-mode fiber. Single-mode vs multimode SFP can be identified by the color of Bale Clasp on SFP or the matching fiber sheath color. The physical characteristics between SFP module SMF and MMF SFP that matters are the Laser transmitter type. Multimode SFP with a cheaper VCSEL transmitter mainly uses a wavelength of 850nm for short-range transmission. Single-mode SFP with FP, DFB, or EML laser mostly uses 1310nm or 1550nm wavelength for long-haul transmission.
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