Definition

Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Typical multi mode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters. In fiber optics technology single mode fiber is one of two types of fiber currently in use. It is a single strand of glass fiber for a single ray (or mode) of light transmission. Single mode fiber is used for long distance transmission. Many customers may don’t know the meaning of multi mode and single mode fiber, here is more details.

• The key difference between SMF and MMF?
• Types
• Applications
• Conclusion

Multimode vs singlemoed total interal reflection

The key difference between SMF and MMF?

Distance:

Single Mode Fiber has a greater distance potential and can support runs between 2 meters and 10,000 meters. Multi-mode generally has a reach up to ~550 meters, whereas single mode has the potential to reach 10,000 meters (40,000 meters with ER)Single mode fiber -> lower power loss characteristic than multi-mode fiber, which means light can travel longer distances through it than it can through multi mode fiber. 

Costs:

The optics for SMF are twice the cost of MMF optics.BUT when installed as part of a project, the extra cost of SMF is negligible compared to MMF. The fragility and increased cost to produce single mode fiber makes it more expensive to use, which is why multi-mode is typically used when you don’t need the distance of single mode.

Speed:

Both single-mode and modern multi-mode fiber can handle 10G speeds.The distance requirement is critical Multi-mode which can get you 300-400 meters.Single-mode can get you 10km, 40km, 80km, and even farther – you just need to use the appropriate optic for the distance required. Prices go up accordingly.

Compatibility issues:

They are not compatible.You cannot mix multi-mode and single mode fiber between two endpoints.The optics are not compatible either.

How they work:

Multi-mode fiber (MMF) – uses a much bigger core and usually uses a longer wavelength of light. Because of this, the optics used in MMF have a higher capability to gather light from the laser. In practical terms, this means the optics are cheaper.Single-mode fiber (SMF) has much tighter tolerances for optics used. The core is smaller and the laser wavelength is narrower. This means that SMF has the capability for higher bandwidth and much longer distances in transmission. Single-mode fiber has a smaller core (9 micron), resulting in less light diffraction over distance than multi-mode fiber (50, 62.5 micron).

Types:

Multi-mode fibers are described by their core and cladding diameters. Thus, 62.5/125 µm multi-mode fiber has a core size of 62.5 micrometres (µm) and a cladding diameter of 125 µm.In addition, multi-mode fibers are described using a system of classification determined by the ISO 11801 standard — OM1, OM2, and OM3 — which is based on the modal bandwidth of the multi-mode fiber. OM4 (defined in TIA-492-AAAD) was finalized in August 2009, and was published by the end of 2009 by the TIA. OM4 cable will support 125m links at 40 and 100 Gbit/s. The letters "OM" stand for optical multi-mode.

Multi-mode Fiber Types:

Single-mode Fiber Types:

There are several designations used to describe various types of SM fiber that are often confusing. Here are the ones in common use today.

ITU Standards

Applications

Conclusion:

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Outer Appearance Identification - Single-Mode vs Multimode SFP Color Coding

Single-mode SFP vs multimode SFP is color-coded with different Bale Clasp. Though the color-coding rule is not total conformity for different vendors, generally the Bale Clasp of multimode SFP is black, and fiber patch cables used with multimode SFP  are usually orange (OM1/OM2), aqua green (OM3/OM4), green (OM5).

Fig 1: Black color-coded Bale Clasp 1G SFP are multimode SFP, and used with OM1/OM2 multimode fiber patch cables in orange, OM3, OM4 in aqua green, or OM5 in green.

The most common color of single-mode SFP Bale Clasp is blue, there are also some in yellow, red, etc. Fiber optic jumpers used with single-mode optical modules are generally yellow.

Fig 2: Blue/Yellow/Red color-coded Bale Clasp 1G SFP are single-mode SFP, and are often used with single-mode fiber patch cables in yellow.

Inner Component Identification - Single-Mode vs Multimode SFP Transmitter

The optical module is mainly composed of three parts: optoelectronic device, functional circuit, and optical interface. The transmitter and receiver are two parts of the optoelectronic device, of which the transmitter is the core component of SFP modules.

In the market, VCSEL lasers are the most commonly used multimode optical modules transmitter for short-range optical fiber transmission. And FP (Fabry-Perot) or DFB（Distributed Feedback）lasers are usually utilized in single-mode optical modules for medium to long-distance transmission. VSCEL lasers own the advantages in the production process for they can be tested the whole manufacturing process. The difference between FP and DFB lasers is mainly in semiconductor materials and resonant cavity structures. 

DFB has a higher production cost and is designed for high-speed and long-range transmission.

Here are examples of QSFPTEK manufactured SFP modules with different transmitters for different transmission applications.

• Cisco SFP-10G-SRCompatible 10GBASE-SR SFP+ is equipped with a VCSELtransmitter for max 300m short-distance transmission.

• Cisco GLC-LH-SMCompatible 1000BASE-LX/LH SFP is equipped with an FP transmitter for up to 10km long-distance transmission.

• Cisco QSFP-40G-LR4Compatible 40GBASE-LR4 QSFP+ is equipped with DFB transmitters for up to 10km long-distance transmission.

• Cisco QSFP-100G-ZR4-SCompatible 100GBASE-ZR4 QSFP28 is equipped with EML transmitters for up to 80km long-distance transmission.

The Difference Between Multimode and Single-Mode Fibers

The way in which these two fiber types transmit light eventually led to their separate names. Generally designed for systems of moderate to long distance (e.g., metro, access and long-haul networks), single-mode optical fibers have a small core size (< 10 µm) that permits only one mode or ray of light to be transmitted. This tiny core requires precision alignment to inject light from the transceiver into the core, significantly driving up transceiver costs.

In comparison, multimode optical fibers have larger cores that guide many modes simultaneously. The larger core makes it much easier to capture light from a transceiver, allowing source costs to be controlled. Similarly, multimode connectors cost less than single-mode connectors as a result of the more stringent alignment requirements of single-mode optical fiber. Single-mode connections require greater care and skill to terminate, which is why componentsare often pre-terminated at the factory. On the other hand, multimode connections can be easily performed in the field, offering installation flexibility, cost savings and peace of mind.

For these reasons, multimode optical fiber systems continue to be the most cost-effective fiber choice for enterprise and data center applications up to the 500 – 600 meter range.

Beyond the reach of multimode optical fibers, it becomes necessary to use single-mode optical fiber. However, when assessing single-mode optical fibers, be sure to consider newer options. A bend-insensitive, full-spectrum single-mode optical fiber provides more transceiver options, greater bandwidth and is less sensitive to handling of the cables and patch cords than is conventional single-mode optical fiber.

Which Multimode Fiber Type and Why?

At one time, the network designer or end user who specified multimode optical fiber for short reach systems had to choose from two fiber types defined by their core size, namely, 50 micron (µm) or 62.5 µm. Now, that choice is slightly different: choose from OM3, OM4, or the new OM5 grade of 50 µm multimode optical fibers. Today, 62.5 µm OM1 multimode optical fiber is virtually obsolete and is relegated for use with extensions or repairs of legacy, low bandwidth systems. In fact, 62.5 µm OM1 fiber supports only 33 meters at 10G and is not even recognized as an option for faster speeds.

50 µm multimode optical fibers were first deployed in the 1970s for both short and long reach applications. But as data rates increased, 50 µm fiber’s reach became limited with the LED light sources used at the time. To resolve this, 62.5 µm multimode optical fiber was developed and introduced in the 1980s. With its larger core, 62.5 µm optical fiber coupled more signal power than 50 µm optical fiber, allowing for longer reach (2 kms) at 10 Mb/s to support campus applications. That was the only time when 62.5 µm fiber offered an advantage over 50 µm optical fiber.

With the advent of gigabit (1 Gb/s) speeds and the introduction of the 850 nm VCSEL laser light source in the mid-1990s, we saw a shift back to 50 µm optical fiber, with its inherently higher bandwidth. Today, 50 µm laser-optimized multimode (OM3, OM4, and OM5) optical fibers offer significant bandwidth and reach advantages for short reach applications, while preserving the low system cost advantages of multimode optical fiber.

What is the advantage of multi mode fiber?Multimode fiber optic cable has a larger core, typically 50 or 62.5 microns that enables multiple light modes to be propagated. Because of this, more data can pass through the multimode fiber core at a given time. The maximum transmission distance for MMF cable is around 550m at the speed of 10Git/s.

Single-mode fiber optic cable has several distinct advantages, especially for long-distance, high-performance data networking and telecommunications:

1. Higher Bandwidth and Longer Distances: Single-mode fiber provides a higher transmission rate and can carry signals at much greater distances than multi-mode fiber. This is because single-mode fiber has a smaller core (usually about 9 micrometers in diameter), which minimizes the dispersion of light signals and allows data to travel further without degradation.

2. Less Signal Attenuation: Due to its smaller core and the way light travels through it (mostly in a straight line), single-mode fiber experiences less signal loss or attenuation over long distances. This makes it ideal for applications that require data to be transmitted over long distances without the need for signal repeaters.

3. Higher Data Rates: Single-mode fiber is capable of supporting extremely high data rates, up to tens of Gbps, making it suitable for high-bandwidth applications such as Internet backbones, cable television, and university campus networks.

4. No Modal Dispersion: Modal dispersion, a common issue in multi-mode fibers where different modes of light arrive at the end of the fiber at different times, is not a problem in single-mode fibers. This results in higher-quality signal transmission.

5. Compatibility with Advanced Technologies: Single-mode fiber is well-suited for newer, advanced technologies like Dense Wavelength Division Multiplexing (DWDM) and Coarse Wavelength Division Multiplexing (CWDM), which can greatly increase the bandwidth capacity of the fiber by transmitting multiple signals at different wavelengths simultaneously.

6. Future-Proofing: As network speeds and demands increase, single-mode fiber's ability to accommodate higher bandwidths and faster speeds makes it a more future-proof investment compared to multi-mode fiber.

7. Scalability: Single-mode fiber is more scalable for future applications and technologies. Its capacity to support higher bandwidths and longer distances makes it easier to upgrade as network needs evolve.

However, it's important to note that single-mode fiber optic cables and associated equipment (like transceivers and patch panels) can be more expensive than their multi-mode counterparts. This makes single-mode fiber a more suitable choice for situations where its specific advantages are required, such as long-distance communication links or high-speed data transmission networks.