SMF and MMF? How to Choose?

Ⅰ. Introduction

Fiber optic communication technology plays an important role in modern information transmission. Single-mode fiber (SMF) and multi-mode fiber (MMF) are the two main types of  fiber optic cable. In this article, we will compare SMF and MMF from core structure, transmission modes, advantages and disadvantages, and classification. Finally, at the end of the article, we will ultimately recommend the most suitable applications for each fiber type.

Ⅱ. Principle of Fiber Optic Communication

This section will introduce the principle briefly, you can find detailed introduction in another article.

The main structure of an optical fiber has three layers, namely, Core, Cladding, and Coating. The optical signal is transmitted through the core, and then achieves its total internal reflection by the refractive index difference between the Core and Cladding.

In a curved optical fiber, the path of the optical signal seems curved, but actually continuously moving forward in a zigzag manner, between core and cladding.

Ⅲ. Core Structure and Transmission Modes of SMF and MMF

SMF. The core diameter of SMF is small, so making optical signals transmit only along the central path of the fiber.

MMF. MMF’s core diameter is larger, allowing optical signals to propagate along multiple paths within the fiber simultaneously.

Ⅳ. SMF vs MMF

Compared to SMF, MMF encounters more serious signal attenuation and distortion during transmission. On the one hand, due to the different transmission speeds in various paths, the time they reach the receiver may be different. That is the dispersion issue, causing signal distortion during transmission. On the other hand, the limitation in optical materials disables the signal reflectivity in core reaches 100%. Therefore, the signal transmitted in MMF is continuously attenuated.

However, MMF also has its advantages. The main benefits of MMF are lower cost, easier installation and maintenance. Although the transmission distance, bandwidth, and speed can not be as high as SMF, it is a cost-effective and practical choice for most short to medium-distance applications with moderate bandwidth requirements.

Ⅴ. How to choose between SMF and MMF?

• Distance

When considering long-distance transmission, SMF is more suitable for applications such as city-to-city communication, international connections, and data center interconnections. In contrast, MMF works better for short to medium distances, typically ranging from a few hundred meters to two kilometers.

The signal attenuation and distortion encountered during transmission cause the signal quality to degrade continuously in MMF, which is why MMF is only suitable for short to medium-distance signal transmission. On the other hand, SMF almost eliminates issues like splitting or delay during transmission, allowing for long-distance transmission.

• Bandwidth and Speed

Regarding high bandwidth and ultra-fast data transmission, SMF is ideal for telecom networks, high-capacity data communication, as well as high-performance computing (HPC). Besides, for short-distance, high-bandwidth applications, MMF performs well and is commonly used in LANs and internal data center connections.

Because of its higher signal stability and lower dispersion, SMF can handle higher data rates and greater bandwidth. Meanwhile, signal quality continuously decreases in MMF, limiting its bandwidth and transmission speed.

• Cost

For budget-conscious, short-distance applications, MMF performs better, such as LANs, small businesses, or offices. SMF is more expensive so it’s better for environments that require stable and high-performance networks, such as telecom backbones and high-performance computing(HPC).

Compared to MMF, SMF requires higher manufacturing precision, resulting in a higher production cost, along with higher light source and installation costs.

• Connection Method

MMF has been more widely used in applications with short wiring distances and flexible usage, such as LANs and internal data centers. SMF, however, is better for large-scale wiring, such as long-distance, telecom networks, and international communication. Despite the connection method of SMF is more complex, the stability and low loss requirements make it a preferred choice in mentioned scenarios.

The smaller core diameter of SMF requires high precision during installation, unsuitable for quick connections and frequent disconnections. MMF is easier to install and connect, with higher tolerance and lower precision requirements, so suitable for rapid deployment.

• Upgrade

SMF is better for long-term, high-efficiency, and scalable network environments, such as telecom networks, international connections, and backbone networks. MMF, on the other hand, is ideal for applications with relatively stable network demands, especially short-distance applications, like LANs and small data centers. In these applications, requirements of bandwidth are unlikely to increase significantly in the coming years, so the need for MMF upgrades is low, and current performance is sufficient to meet the demands.

With the development of society, the demands for information transmission rates and capacities will continue to rise. SMF supports higher-speed data transmission and can integrate with WDM better. The connection can better improve the data transfer efficiency, making SMF better suitable to future network upgrades.

Ⅵ. Classification of SMF(OS1 vs OS2) and MMF(OM1 vs OM2 vs OM3 vs OM4 vs OM5)

• SMF: OS1 vs OS2

OS1 and OS2 are two common fiber categories of SMF. The choice between OS1 and OS2 mainly depends on the environmental conditions, transmission distance, and bandwidth requirements of the application.

• OS1 is used for indoor fiber cabling with lower bandwidth and speed, suitable for fiber connections within buildings. Additionally, OS1 is suitable for stable and controlled environments where its performance is sufficient.
• OS2 is more suitable for long-distance and high-performance fiber connections, offering higher bandwidth, better for long-distance and harsh environments. OS2 is more stretch-resistant and bend-resistant, and can be used in outdoor installations, such as outdoor cabling and telecom tower connections.

• MMF: OM1 vs OM2 vs OM3 vs OM4 vs OM5

MMF has several types, including OM1, OM2, OM3, OM4, and OM5. They mainly differ in core diameter, bandwidth, maximum applicable speed, and maximum transmission distance.

The table below represents the basic information of OM1-OM5 when using optical signal under a  850nm wavelength.

The following content is a comparison of suitable applications for OM1 – OM5.

• Traditional LAN, especially networks below 1Gbps. Telephone communications and video surveillance. Legacy fiber infrastructure and its upgrades.
• Small to medium-sized business LANs, internal data center connections, especially those who have no plan to large-scale upgrades.
• Suitable for 10 Gbps Ethernet applications. Widely used in data centers, for high-bandwidth connections between switches and servers. Ideal for large-scale cloud computing services and high-performance computing (HPC).
• A common choice in high-speed data centers and enterprise networks. Supports high-bandwidth data exchange between switches and routers. Meets the high-performance data transmission needs of cloud computing environments and virtualization applications.
• Designed for future ultra-high-speed networks. Ideal for large-scale cloud computing, artificial intelligence (AI), and machine learning (ML) applications in high-performance computing (HPC). Also an ideal choice for deploying WDM systems.

When selecting MMF, the following guidelines can be used:

• Short distance, low bandwidth requirements: Choose OM1 or OM2.
• Medium distance, high bandwidth requirements: Choose OM3.
• Long distance, high bandwidth requirements: Choose OM4.
• Future expansion needs, ultra-high-speed transmission: Choose OM5.