Fiber optics can transmit data faster and over longer distances than other technologies, making it the foundation of contemporary data transmission. As a result, fiber optics are extensively used in internet services, telecom, and enterprise data center networks.

Many critical decisions come into play in the installation of fiber optic cabling, opting for single mode or multimode being one of them. This choice will have major implications for your network’s bandwidth, distance, and budget. Hence, it is vital that you have a good understanding of the differences between these two variants of fiber optic glass.

The key difference between single-mode and multimode optical fiber cables is that in the former, light rays propagate solely through one path. On the other hand, multiple light rays propagate through the waveguide at the same time in multimode optical fiber. Single-mode fiber also has a comparatively smaller core diameter than multimode fiber. Before we dig more deeply into the differences between these fiber optic glass cables, let’s better understand them.

Single-mode optical fiber

If the fiber core is so small that only a light ray at a 0° incident angle can stably pass through the fiber length without much loss, it is known as single-mode optical fiber. The core-to-cladding diameter is 9 to 125 micrometers in this situation. Single-mode optical fiber is also known as mono-mode optical fiber or uni-mode optical fiber.

Optical fiber has three parts: core, cladding, and coating or buffer. The core single-mode optical fiber is tight at the center and comprises a single fiber strand. Emitted light from the source tends to travel through this specific section. Therefore, a sharp, focused light beam like a laser is required as the optical source for the small diameter of the core. Single-mode optical fiber is known to possess minimal signal distortion owing to the transmission of just a single light ray.

Multimode optical fiber

Several light rays propagate through the fiber at the same time in multimode optical fiber. However, every light ray reflects at a certain distinctive angle during transmission. In the case of multimode optical fiber, the core-to-cladding diameter is 50-62.5 to 125 micrometers. The diameter of the core is large enough to allow several light rays to transmit through it, and it uses an LED as its optical source. As the number of light reflections created as the light passes through the core increases in the case of multimode optical fiber, it creates the ability for more data to pass through at a given time.

Understanding the differences between single-mode and multimode optical fiber

Core Diameter

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The core diameter of single-mode fiber is way smaller than multimode fiber. While the former has a core diameter of 9 µm, the multimode fiber core diameter is typically between 50 µm and 62.5 µm. This allows multimode optical fiber cable to have greater “light gathering” ability and simplify connections. Due to the larger core diameter, its attenuation is greater than that of single-mode fiber. Single-mode cable has a very narrow fiber core. Therefore, the light passing through these optical cables is not reflected too often, keeping attenuation to a minimum.

Light source and wavelength

Budget-friendly light sources like VCSELs (vertical-cavity surface-emitting lasers) and LEDs (light-emitting diodes) that work at 850nm and 1300nm wavelengths are generally used in multimode fiber cables due to their large core size. On the other hand, single-mode fiber usually uses a laser or laser diode to produce light that is injected into the cable. The most frequently used single-mode fiber wavelengths are 1310 nm and 1550 nm.

Bandwidth

The bandwidth of multimode fiber is limited by its light mode. Conversely, theoretically, single-mode fiber has unlimited bandwidth as it allows just one light mode to pass through at a time. Therefore, it is a widely preferred choice in today’s fast-paced environment. Both of these optical fiber types function quite differently with regard to bandwidth. Single-mode optical fiber cable makes use of bright and strong light sources with lower attenuation. In the case of multimode optical fiber, the brightness is lower, and the attenuation is higher. Higher bandwidth and an uninterrupted experience are obviously demanded by most users, giving single-mode optical fiber an upper hand.

Color Sheath

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As per the standard definition under the Telecommunications Industry Association’s TIA-598-C Optical Fiber Cable Color Coding, single-mode cable is coated with a yellow outer sheath for non-military applications, and multimode fiber is coated with an orange or aqua jacket.

Transmission distance

Electronics and their light output capacity determine the transmission distance in fiber optical cables, and single-mode fiber proves to be superior in this regard as well by being capable of both short and long-distance transmission. Moreover, its transmission is not impacted by resolution quality or single bandwidth. Most of these can relay up to 10 km over a single-mode fiber cable. On the flip side, the maximum range of a multimode fiber cable tends to be between 300 and 550 meters due to its cable grading.

As multimode optical fiber supports more than one light mode and has a large core size, its fiber distance is limited by modal dispersion, which is a pretty common phenomenon in multimode step-index fiber. This does not happen with single-mode fiber.

Cost           

Expenses involved are one of the key factors to consider when making any kind of purchasing decision. Naturally, you would always want to go for the option that delivers the best possible results at an affordable price. Currently, single-mode fiber has a cost advantage over its multimode variants. While they have more intricate optical processors and stronger light sources, due to their efficiency in manufacturing, single-mode fiber cables are known to be priced lower compared to multimode cables. In fact, on average, they are able to achieve 30% savings over multimode fiber.

However, it is also vital to consider that most fiber systems use transceivers responsible for combining a transmitter and receiver into a single module of fiber optic technology to receive and send over an optical network. At the moment, the price of multimode transceivers is two to three times lower than that of single-mode transceivers.

Bottom line

As multiple modes or light paths travel down a multimode fiber optic cable, it can provide high bandwidth over a short distance. All light from a pulse travels at almost the same speed and arrives at around the same time in a single-mode fiber, and hence has no effect of modal dispersion as found in multimode fiber. It is able to support higher bandwidth levels with less signal loss over longer distances and is ideal for long-haul signal transmission applications ranging from remote offices to campuses. Due to their multiple light paths, however, multimode fiber cables are good for projects that need high bandwidth over a short distance range.    You need to ponder over your specific requirements and budget limitations to select the ideal fiber optic cable for your project.