Although single-mode fiber (SM) and multimode fiber (MM) cable types are widely used in various applications, their differences can still be confusing. This article will take you to understand single-mode and multimode fiber from these aspects and choose the appropriate fiber optic cable.
What is Single-mode Fiber?
Compared with multimode fiber, single-mode fiber optic cable has a smaller core diameter (8-10 microns) and can propagate in the wavelength range of 1310nm and 1550nm. This limits the optical signal to only one path or mode, hence the name “Single-mode.” So the signal can travel longer distances without bouncing off edges, causing distortion or attenuation. Single-mode fiber is the best choice for long-distance data transmission, such as 100 kilometers (60 miles), due to the small signal attenuation caused by a single optical mode.
Single-mode Fiber Types: OS1 and OS2
The single-mode fiber type can be divided into OS1 and OS2 fiber, which are SM fiber specifications. OS1 and OS2 are standard single-mode optic cables, using 1310nm and 1550nm wavelengths, respectively, and the maximum attenuation is 1dB/km and 0.4dB/km.
Note: These two cables have different characteristics and are suitable for other applications. OS2 SM Fiber can’t be connected with OS1 SM Fiber, which may result in poor signal performance.
OS1 and OS2, What’s the Difference?
① OS1 SM cables comply with ITU-T G.652 specifications, including ITU-T G.652A and ITU-T G.652B standards (regular), ITU-T G.652C, and G.652D standards (low-peak).
② OS2 SM cables only comply with the ITU-T G.652C or ITU-T G.652D standards specifically for low-water peak fibers. These low-water peak fibers are commonly used in CWDM (Coarse Wavelength Division Multiplexing) applications. A new standard, G657A1, publishes bend-insensitive SM fibers for an optimized balance of performance and cost, and some OS2 SM fibers comply with this standard.
2. Cable Structure
① OS1 is embedded in a heavy polymer jacket and tight buffered. Ensures maximum protection of the fiber optic core and keeps it secure. Designed for indoor applications such as campuses or data centers.
② OS2 is primarily of loose tube construction and is more suitable for outdoor situations (e.g., street, underground, and buried). When deployed in some harsh environments, more robust cable construction is required. The OS2 SMF helix is placed in a semi-rigid tube that can be stretched to a certain extent without damaging the core.
① OS1 has a maximum attenuation of 1.0db/km at 1310nm and 1550nm, and a maximum transmission distance of 10 km.
② The value of OS2 at 1310nm and 1550nm is 0.4db/km, and the maximum transmission distance can reach 200 km. Both OS1 and OS2 single-mode fiber allows speeds from 1 to 10GbE and varying transmission distances. Additionally, OS2 can be used for 40G/100G Ethernet connections.
The following diagram will clearly show the difference between OS1 and OS2.
OS1 vs. OS2, How to Select?
When choosing OS1 and OS2 single-mode fiber, be aware of long-distance transmission, and then select the appropriate cable according to your link length requirements.
① OS1 is suitable for indoor network infrastructure, mainly deployed in internal building/campus networks and internal wiring in telecom switches and data centers. OS2 is better suited for outdoor and general-purpose loose tube solutions, which include outdoor equipment and most backhaul networks.
② OS1 used to be the only single-mode fiber standard. The maximum link length of campus cabling was about 10 km, which could no longer meet people’s growing demand for link length. OS2 is more suitable for long-distance transmission, with better performance and less loss. Ideal for connecting 1G/10G/40G/100G Ethernet connections for long-distance high-performance requirements. Therefore, more and more suppliers tend to provide solutions with OS2 SMF cables for modern network applications.
What is Multimode Fiber?
Multimode optical fiber is a common type of optical fiber. Its working wavelength is 850nm/1300nm. It supports hundreds of transmission modes. It has the advantages of high bandwidth and low cost and is suitable for short-distance optical fiber transmission (such as computer rooms, buildings, and campuses) ). The multimode fiber’s refractive index is divided into steps and graded.
How Many Types of Multimode Fiber?
As we all know, multimode fiber is usually divided into OM1, OM2, OM3, OM4, and OM5 fiber types. For more information, refer to the following: What are the Differences Between OM1, OM2, OM3, OM4, and OM5?
What is the Difference Between Single-mode and Multimode Fiber?
1. Core Diameter
① Although the cladding diameter of the multimode fiber and the single-mode fiber is the same, and the diameter is 125 μm, the core diameter of the single-mode fiber is much smaller than that of the multimode fiber. Even when others are available, their typical core diameter is 9 µm. Multimode fiber typically has a core diameter of 50 µm and 62.5 µm, which gives it a higher “light-spotting” capability and simplifies connections.
② Multimode fiber attenuates more than single-mode fiber because of its larger core diameter. Single-mode fiber optic cables have a skinny core, so light passing through them is not reflected too often, keeping attenuation to a minimum.
2. Wavelength & Light Source
Multimode fibers generally use LEDs (light-emitting diodes) or vertical-cavity surface-emitting lasers (VCSEL) as light sources because LED light sources can generate many modes of light (the light is more dispersed). Single-mode fibers generally use lasers or laser diodes as light sources because The laser light source can produce a single mode of light, which has the advantages of high brightness and power. The commonly used single-mode fiber wavelengths are 1310nm and 1550nm.
The bandwidth of multimode fiber is limited by its optical mode, and the maximum current bandwidth is 28000MHz*km of OM5 fiber. The bandwidth of single-mode fiber is theoretically unlimited because it only allows one light mode to pass through at a time.
4. Single-mode vs. Multimode Fiber Distance
The transmission distance of single-mode fiber is longer, which is suitable for long-distance transmission. The transmission distance of multimode fiber is relatively short, which is ideal for short-distance transmission, and OM3/OM4/OM5 multimode fiber can support high-speed data transmission. Because multimode fiber has a large core diameter and supports multimode light, its fiber distance is limited by modal dispersion, a common phenomenon in multimode step-index fibers. Single-mode fiber is not. This is the essential difference between them. In addition, OS2 single-mode fiber can support longer distances on 40G and 100G links, which are not listed in the table.
5. Different Costs
Singlemode fiber optic components and equipment are more expensive than multimode fiber optics. Multimode fiber can support multiple light modes, and its price is higher than single-mode fiber. However, in terms of equipment, single-mode fiber equipment is more expensive than multimode fiber equipment because it usually uses solid-state laser diodes.
What are the Advantages of Single-mode Fiber?
① Single-mode fiber distance: Single-mode fiber supports longer distances than multimode fiber because of its lower attenuation. For example, MMF can generally reach hundreds of meters, while SMF can reach 200 kilometers.
② Bandwidth capacity: Single-mode fiber optic cables provide higher bandwidth than multimode fiber optic cables.
③ Data dispersion: SMF only transmits one mode of light and will not cause modal dispersion.
④ Single-mode fiber speed: Single-mode fiber has no modal dispersion, modal noise, and other effects of multimode transmission. As a result, it can transmit signals at higher speeds and up to 50 times longer distances than multimode fiber.
What are the Advantages of Multimode Fiber?
① For LAN or MAN, both can be realized. However, single-mode optical fibers are afraid of bending and have high requirements for splicing, and additional losses are likely to occur. So, using single-mode fibers will increase the difficulty of wiring and maintenance management. If multimode fibers are used, there will be no such problems.
② The use of SMF has higher requirements for cleaning, while MMF can be plugged in after wiping.
③ The cost of single-mode laser transceivers for multimode fibers is lower than that of single-mode fibers, and the power consumption of multimode lasers is lower than that of single-mode lasers.
How to Choose Between Single-mode Fiber and Multimode Fiber?
SMF and MMF have their advantages in cost and application. When selecting single-mode and multimode fiber optic cables, the first factor to consider is the fiber distance you need. For example, in data centers, multimode fiber optic cables are sufficient for transmission distances of 300-400 meters. And in applications requiring distances of up to several kilometers, single-mode fiber is the best choice. And in applications where single-mode and multimode fiber can be used, other factors such as cost and future upgrade requirements should also be considered in your selection.
The comparison of single-mode and multimode fibers shows that the single-mode fiber cabling system is suitable for long-distance data transmission applications and is widely deployed in operator networks, metropolitan area networks, and passive optical networks. Multimode fiber cabling systems have short transmission distances and are widely deployed in enterprises, data centers, and local area networks. No matter which one you choose, it is an important task for every network designer to choose the one that best suits your network needs based on the total cost of fiber.
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