Singlemode vs. Multimode Fiber Optics: Which is Better for You

Most of our customers are very well versed in the different types of fibers available to them, but those new to fiber optics ask us to explain the difference between single mode and multimode fiber optics.

Singlemode and multimode are two different types of fiber optic cables that are used for data transmission. While both types of cables use light to transmit data, there are significant differences in their design and performance. In this article, we will explore the differences between singlemode and multimode fiber optics.

Multimode fiber optic cables have a larger core diameter, typically 50 or 62.5 micrometers, which allows multiple modes or paths of light to be transmitted through the cable. Multimode fiber is primarily used for shorter distances, typically less than 2 kilometers, due to the high dispersion and attenuation that occurs over longer distances. Multimode fiber is commonly used in LANs, campus networks, and data centers where distances are short, and high bandwidth is required.

Singlemode fiber optic cables have a much smaller core diameter, typically 9 micrometers. This smaller core size allows only a single mode of light to be transmitted through the cable. Singlemode fiber is designed for long-distance data transmission, typically over distances greater than 10 kilometers. Singlemode fiber has much lower attenuation and dispersion than multimode fiber, making it suitable for longer distances and higher bandwidth applications. Singlemode fiber is commonly used in telecommunications networks, long-haul applications, and submarine communication systems.

The light source used to transmit data through fiber optic cables is also different for singlemode and multimode fiber. Singlemode fiber requires a laser light source, which produces a narrow beam of light that is precisely aligned with the fiber. Multimode fiber can be used with either a laser or an LED light source, which produces a broader beam of light that can be transmitted over multiple paths.

Singlemode light travels down a fiber optic cable by following a single path, known as the fundamental mode, which is aligned with the center of the fiber’s core. The core of a singlemode fiber is much smaller than that of a multimode fiber, typically only 9 micrometers in diameter, and is surrounded by a cladding layer that has a lower refractive index than the core. This design allows the light to be guided down the core without being scattered or reflected as it travels through the fiber.

The key factor that enables singlemode light to travel down the fiber without being scattered or reflected is the principle of total internal reflection. Total internal reflection occurs when light is traveling through a medium with a high refractive index, such as the core of a fiber optic cable, and reaches the boundary with a medium with a lower refractive index, such as the cladding layer. When the angle of incidence of the light is such that the refracted angle would be greater than 90 degrees, the light is reflected back into the core, rather than being refracted into the cladding layer.

This process allows the light to travel down the fiber in a straight line, following the fundamental mode of the fiber. The purity of the singlemode light path, combined with the low attenuation and dispersion characteristics of the fiber, enables it to transmit data over long distances with minimal loss or distortion.

Singlemode fibers are typically used in long-haul telecommunications and data transmission applications, where high bandwidth and low signal loss are critical. The use of singlemode fibers enables data to be transmitted over distances of tens of kilometers or more, with high signal integrity and low latency.

Multimode light travels down a fiber optic cable by taking multiple paths, known as modes, through the fiber’s core. The core of a multimode fiber is larger than that of a singlemode fiber, typically 50 or 62.5 micrometers in diameter, which allows for multiple paths of light to be transmitted through the fiber.

When light enters a multimode fiber, it is guided down the core of the fiber by the principle of total internal reflection, just like in a singlemode fiber. However, because the core is larger, the angle of incidence of the light can vary, which results in the light being reflected at different angles and taking multiple paths through the core. This causes the different modes of light to arrive at the end of the fiber at different times, which can result in distortion and signal loss, especially over longer distances.

The dispersion and attenuation of light in a multimode fiber are much higher than in a singlemode fiber, which limits the transmission distance and bandwidth capacity of the fiber. However, multimode fibers are often used for shorter distances and lower bandwidth applications, where their lower cost and simpler infrastructure make them an attractive option.

Multimode fibers can be used with either an LED or laser light source. LED light sources are commonly used in LANs, campus networks, and data centers, where distances are short and high bandwidth is required. Laser light sources are typically used for longer distances, such as in building-to-building or campus-to-campus links, where high bandwidth and lower signal loss are required.

In conclusion, the primary differences between singlemode and multimode fiber optics are the core diameter, transmission distance, and light source used. Multimode fiber is designed for shorter distances and can be used with LED or laser light sources, while singlemode fiber is designed for longer distances and requires a laser light source. When selecting a fiber optic cable for a particular application, it is essential to consider the distance over which the data must be transmitted, the bandwidth requirements, and the cost of the cable and associated equipment.