What’s the Difference between Single & Multimode Fibre Optic Cable
Fibre optics can transmit data faster and over longer distances than other technologies, making it the foundation of contemporary data transmission. As a result, fibre optics are extensively used in internet services, telecom, and enterprise data center networks.
Many critical decisions come into play in the installation of fibre 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 fibre optic glass.
The key difference between single-mode and multimode optical fibre 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 fibre. Single-mode fibre also has a comparatively smaller core diameter than multimode fibre. Before we dig more deeply into the differences between these fibre optic glass cables, let’s better understand them.
Single-mode optical fibre
If the fibre core is so small that only a light ray at a 0° incident angle can stably pass through the fibre length without much loss, it is known as single-mode optical fibre. The core-to-cladding diameter is 9 to 125 micrometers in this situation. Single-mode optical fibre is also known as mono-mode optical fibre or uni-mode optical fibre.
Optical fibre has three parts: core, cladding, and coating or buffer. The core single-mode optical fibre is tight at the center and comprises a single fibre 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 fibre is known to possess minimal signal distortion owing to the transmission of just a single light ray.
Multimode optical fibre
Several light rays propagate through the fibre at the same time in multimode optical fibre. However, every light ray reflects at a certain distinctive angle during transmission. In the case of multimode optical fibre, 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 fibre, it creates the ability for more data to pass through at a given time.
Understanding the differences between single-mode and multimode optical fibre
The core diameter of single-mode fibre is way smaller than multimode fibre. While the former has a core diameter of 9 µm, the multimode fibre core diameter is typically between 50 µm and 62.5 µm. This allows multimode optical fibre 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 fibre. Single-mode cable has a very narrow fibre 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 fibre cables due to their large core size. On the other hand, single-mode fibre usually uses a laser or laser diode to produce light that is injected into the cable. The most frequently used single-mode fibre wavelengths are 1310 nm and 1550 nm.
The bandwidth of multimode fibre is limited by its light mode. Conversely, theoretically, single-mode fibre 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 fibre types function quite differently with regard to bandwidth. Single-mode optical fibre cable makes use of bright and strong light sources with lower attenuation. In the case of multimode optical fibre, 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 fibre an upper hand.
As per the standard definition under the Telecommunications Industry Association’s TIA-598-C Optical fibre Cable Color Coding, single-mode cable is coated with a yellow outer sheath for non-military applications, and multimode fibre is coated with an orange or aqua jacket.
Electronics and their light output capacity determine the transmission distance in fibre optical cables, and single-mode fibre 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 fibre cable. On the flip side, the maximum range of a multimode fibre cable tends to be between 300 and 550 meters due to its cable grading.
As multimode optical fibre supports more than one light mode and has a large core size, its fibre distance is limited by modal dispersion, which is a pretty common phenomenon in multimode step-index fibre. This does not happen with single-mode fibre.
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 fibre 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 fibre cables are known to be priced lower compared to multimode cables. In fact, on average, they are able to achieve 30% savings over multimode fibre.
However, it is also vital to consider that most fibre systems use transceivers responsible for combining a transmitter and receiver into a single module of fibre 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.
As multiple modes or light paths travel down a multimode fibre 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 fibre, and hence has no effect of modal dispersion as found in multimode fibre. 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 fibre 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 fibre optic cable for your project.