The fiber optic technology has been in our lives for a while now. It eases the communication and the transmission of information and it becomes more and more indispensable, especially in the business world. But do you know the difference between single-mode fiber and multi-mode fiber?
Single Mode fiber
Single Mode fiber is a single strand of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission. Single Mode Fiber with a relatively narrow diameter, through which only one mode will propagate typically 1310nm or 1550nm. It carries higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width.
Single-mode fiber gives you a higher transmission rate and up to 50 times more distance than multimode, but it also costs more.
Single-mode fiber has a much smaller core than multimode. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fiber cable type.
Multimode fiber
Multimode fiber is made of glass fibers, with a common diameter in the 50-to-100 micron range for the light carry component (the most common size is 62.5). POF (Plastic Optical Fiber) is a newer plastic-based cable which promises performance similar to glass cable on very short runs, but at a lower cost.
Multimode fiber gives you high bandwidth at high speeds over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable’s core typically 850 or 1300nm. Typical multimode fiber core diameters are 50, 62.5, and 100 micrometers. However, in long cable, multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission.
Difference in applications
Multiple modes/light paths travel down a multimode fiber cable, so it only offers high bandwidth over a short distance.
When run over longer distances, modal dispersion (distortion) becomes an issue. This is typically expressed in a fiber’s “effective modal bandwidth” characteristic, which is an inverse relation between fiber bandwidth and reach distance. As signaling bandwidth increases, the reach distance decreases – and vice versa – due to the modal dispersion effect.
In single-mode fiber, all light from a pulse travels at about the same speed and arrives at roughly the same time, eliminating the effects of modal dispersion found in multimode fiber. This supports higher bandwidth levels with less signal loss over longer distances. It’s ideal for long-haul signal transmission applications, such as across or between campuses, undersea or in remote offices. There are essentially no distance limitations.
Difference in distance
Generally, single-mode cables should be used over long distances (greater than 500 m), whereas multimode cables should be used over short distances (less than 500 m). Reason being – the larger core diameter in multimode fiber cables allows for a greater number of signals/ rays of light to travel through at a time. Thus, you’re most likely to find multimode cables in LAN backbones within individual buildings and single-mode cables in inter building connections or WANs (wide area networks).
Unlike single-mode fiber, there is a dispersion or degradation of the signal after a certain distance depending on the grade of multimode fiber type. These cables are graded from OM1-OM5 and each grade has a different bandwidth capacity. Typically, an OM1 grade cable will have an approximate recommended distance of 100ft/33 m, whereas an OM4 grade cable will have an approximate recommended distance of 1,312 ft/400 m.
How do I know what type of fiber I need?
This is based on transmission distance to be covered as well as the overall budget allowed. If the distance is less than a couple of miles, multimode fiber will work well and transmission system costs (transmitter and receiver) will be in admissible range. If the distance to be covered is more than 10–12 miles, single mode fiber is the choice.
Transmission systems designed for use with single mode fiber will typically cost more (due to the increased cost of the laser diode).
NOTE: In order to enhance the transmission capacity of optical fiber, Space Division Multiplexing (SDM) transmission systems with Multi-Core Fiber (MCF) are being implemented in the present scenario as Standard Single Mode Fibers (SSMF) based system’s spectral densities are approaching Shannon limits.
Multi-Core Fiber (MCF) is a fiber that can have multiple cores inside a single cladding. As MCF has multiple cores, it has greater transmission capacity as compared to SSMF.
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