Difference Between Single Mode and Multimode Fiber

Fiber Optic cable is a network cable containing multiple strands of glass fibers. It uses light pulses generated by small lasers or light-emitting diodes to carry communication signals, provides higher bandwidth and transmits data, and is designed for long-distance, high-performance data networking, and telecommunications.

Structure of fiber optic cable

The fiber optical cable is composed of Sinterklaas core and several layers of protective materials:

●  Jacket: protect inner components

●  Buffer: Used to encapsulate one or more optical fibers, providing protection from physical damage.

●  Cladding: The glass or plastic shield around the core. The cladding prevents light from escaping the core, effectively keeping the signal moving down the glass.

●  Core: A cylinder of glass or plastic and light traveling in the core.

Difference Between Fiber Optic Cable vs Copper Cable

◆  Transmission Rate: Comparing the speed of data transmission, fiber optic cables are more than a hundred times faster than the transmission speed of electrons on copper conductors, at present, copper cable reach up to 40 Gbps, while OM5 optical fiber can reach 100 Gbps.

◆  Transmission distance：Both fiber optic cable and copper fibers are experienced signal losses over long distances, but this attenuation is much greater with copper. Over 100 meters, it is estimated that the optical fiber will only lose 3% of the signal strength, while within the same distance, the copper cable will lose 94% of the signal strength.

◆   EMI - Copper wires generate electromagnetic interference fields, which can cause signal errors in other cables. on the other hand, Fiber optic cabling is resistant to electromagnetic interference, making it ideal for industrial environments.

◆   Electrical Isolation - Because fiber optic cables do not carry electricity, there is no need for transmitters and receivers to the ground.

◆   Appearance - Fiber optic cables are about a quarter the diameter and a tenth the weight of copper cables, making them easier to install and promoting better air circulation in the cabinet.

There are two basic modes of fiber optic cabling: single mode and multi-mode.

Single mode cables have a small diameter 9micron core allowing one pathway of light, Multimode cables have two different large diameter core sizes 50 and 62.5micron allowing multiple pathways of light.

Single mode cables have theoretically unlimited bandwidth whereas multimode cables have a limited bandwidth. it's more suitable for long-distance applications, while multimode cables are better suited for short distance applications.

Single mode and multimode cables are available in Duplex and Simplex

Duplex fiber optic cables consist of two fibers, usually in a side-by-side style.they are used in applications that require simultaneous bi-directional data transfer, such as Fiber Media Converters, Industrial Ethernet Switches.

Simplex fiber optic cables consist of a single strand of glass plastic fiber and an outer sheath. They are used in applications that require one-way data transfer.  Single mode fiber optic is typically used in applications such as telephone signals, cable TV, RS232/422/485 to Fiber Converter.

Single mode optical fiber (SMF) is designed to carry light with a single mode, which means that light wave travels straight down the center of the core without bouncing off the edges.

Single mode fibers have a small core size (usually 9 μm) that permits only one mode or ray of light to be transmitted in the range from 1260nm to 1625nm, Unlike multi-mode, single-mode doesn’t have different light paths that reflect light off the cladding but instead has a single light beam, so there is almost no light reflection when light passes through the single mode fiber core. This will lower fiber attenuation and create the ability for the signal to travel further.  

Here are some features of single-mode fiber:

●  SMF core diameter is about 9μm. The cladding diameter of SMF is 125μm.

●  The source of optical signals in SMF is a Laser or laser diodes.

●  The typically optical wavelengths of SMF is 1310nm and 1550nm.

●  In theory, SMF offers unlimited bandwidth because it provides a single light transmission mode at a time.

●  The color-coding or sheath color for an SMF is yellow for non-military applications.

●  The small core size helps to reduce dispersion and allows longer transmission distances to be achieved.

●  High transfer rates use for long distances such as WAN connection.

Two types of Single Mode Optical Fiber

OS1: OS1 is the first type of SMF compliant with ITU-T G.652A/B/C/D. the optical fiber core diameter is about 8 to 9μm. OS1 cabling is tight-buffered construction, which is widely used for indoor applications, such as campus or data center, the indoor fiber has greater loss per kilometer than OS2 outdoor fiber. the maximum attenuation for OS1 is 1.0 db/km, and maximum transmission distance can reach to 2km.

OS2: OS2 is a comparatively better type of SMF. It is compliant with ITU-T G.652C and G.652D, explicitly applier to the low-water-peak fibers, and these low-water-peak fiber are usually used for CWDM (Coarse Wavelength Division Multiplexing),It features the same diameter of 8 to 9μm, but OS2 cabling is loose-tube design, the signal suffers a negligible attenuation of 0.4dB/km. Due to lower attenuation, the signal strength remains consistent throughout the transmission. the maximum transmission distance of OS2 single mode fiber can reach over 10 km, so this type of SMF is preferred for long-distance and outdoor optical fiber installations such as street, seabed.

All of these differences between OS1 and OS2 discussed above are listed in the table below.

Single-mode fibers can also be classified according to industry standards:

◆  Standard singlemode fiber (G.652)

◆  Cutoff shifted fiber (G.654)

◆  Low water peak fiber (G.652)

◆  Dispersion shifted fiber (G.653)

◆  Non-zero dispersion shifted fiber (G.655)

◆  Bend-insensitive fiber (G.657)

If you want to use for the indoor application and distance is under 2km,then OS1 is a better choice, and it’s much cheaper than OS2 to save your cost, however, if used for outdoor applications, and the distance is over 10km, then you should choose OS2. The OS2 single mode fiber optic cables are ideal for connecting 1G/10G/40G/100G Ethernet connections, meeting the requirements of high performance with long distances.

Multi-mode fiber uses a large diameter glass core size of either 50um or 62.5um which provides multiple modes or pathways for light to travel. The multiple modes allow more light (mainly data) to travel through the cable.

Multimode optical fiber is designed to use VCSEL lasers to transmit light in the 800nm-1300nm wavelength range. However, at longer distances, the light will start to experience dispersion (distortion in light) which can limit data transmissions through unclear, incomplete signal on the receiver end.

Due to distance limitations, multimode optic fibers have been widely used in many short-distance applications of less than 1000m, deployed for applications inside buildings or between sites of close proximity like campus networks, data centers, municipal complexes, Local Area Networks (LAN), and so on.

Features of Multi-Mode Optical Fiber:

●  Larger core diameter, usually 50~100 Micrometers (62.5 most common), the cladding diameter remains 125μm.

●  The source of optical signals in MMF are either light-emitting diode (LEDs) or vertical-cavity surface-emitting lasers (VCSELs).

●  The typically optical wavelengths of SMF is 850nm and 1300nm.

●  The bandwidth of MMF is limited due to modal dispersion. the theoretical value of MMF bandwidth is 28000MHz*km.

●  The color-coding or sheath color for an MMF is an orange or aqua jacket.

●  Due to higher attenuation via dispersion, the MMFs are suitable for short-distance fiber optic transmission. However,by using suitable fiber optic connectors, the transmission distance can be extended.

●  MMF supports 100Gbit/sec transmission speed. The general, practical data transmission rate of MMF is 100Mbit/sec up to 2km and 10Gbit/sec up to 550 meters.

●  Widely used cable in LAN networks today

●  Easier to terminate

●  Transmitters and receivers are more economical

How Many Types of Multimode Fiber?

Multimode fiber optic cables can be classified into OM1 fiber, OM2 fiber, OM3 fiber, OM4 fiber and OM5 fiber, details as below:

OM1 Fiber

OM1 fibers usually have an orange jacket and a core size of 62.5 μm. and is most commonly used in 100M Ethernet applications, usually using LED light source.

OM2 Fiber

OM2 fiber is also equipped with an orange jacket and uses a LED light source but with a smaller core size of 50 μm. It supports up to 10 Gigabit Ethernet up to 82 meters but is more commonly used in 1 Gigabit Ethernet applications.

OM3 Fiber

OM3 fiber comes with an aqua color jacket. Like the OM2, its core size is 50 μm, but the cable is optimized for laser-based equipment. OM3 supports 10 Gigabit Ethernet up to 300 meters. In addition, OM3 can support 40 Gigabit and 100 Gigabit Ethernet up to 100 meters, but the most commonly used is 10 Gigabit Ethernet.

OM4 Fiber

OM4 fiber is fully backwards compatible with OM3 fiber and shares the same unique aqua jacket. OM4 is specifically developed for VSCEL laser transmission. Compared with OM3’s 300M, it allows up to 550m of 10 Gig/s link distances. And it can run 40/100GB up to 150 meters using MPO connectors.

OM5 Fiber

OM5 fiber, also known as WBMMF (wideband multimode fiber), is the latest type of multimode fiber, and it is backwards compatible with OM4. Its core size is the same as OM2, OM3, and OM4. The color of OM5 fiber jacket is lime green. It is designed and specified to support at least four WDM channels at a minimum speed of 28Gbps per channel through the 850-953 nm window.

Note:  OM1 has a core of 62.5μm, while OM2,OM3,OM4 all have a core of 50μm, so OM1 can’t be used as a patch cable in a system involving OM2,OM3,OM4, and it will not work with connectors rated for OM2,OM3,OM4.

Difference between OM1 vs OM2 vs OM3 vs OM4 vs OM5

The mainly difference lies in diameter, jacket color, optical source and bandwidth, which is shown as follows:

As we all know, single mode means that the fiber can propagate one type of light mode at a time. and multimode means the fiber can propagate multiple modes. The main differences between single mode and multimode fiber mainly lies in fiber core diameter, Light Propagation, Optical source, bandwidth, Jacket color, and cost.

Core Diameter

The core diameter of multimode fiber is much larger, usually 50 or 62.5μm, while a single mode fiber has a core diameter between 8 and 10μm. it’s important to note that there is no way to distinguish between single mode and multimode optical fibers with the naked eye, because the cladding diameter of single mode and multimode fiber are both 125 μm.

Light Propagation

The light propagation is different between single mode and multimode fibers. multimode fiber including step index and grade index. On the other hand, single mode fiber only support "step index. the light propagation of single mode fiber during signal transmission is less than that of multimode fiber.

Optical source

Single mode cables use a laser as light source, which can generate high power, precisely controlled light with wavelength of 1310nm and 1550nm. While multimode fiber usually use low-cost light sources, such as LEDs(light-emitting diodes) and VCSELs (vertical cavity surface-emitting laser) that operate at 850nm and 1300nm wavelengths.

Bandwidth

The bandwidth of a single mode fiber is theoretically unlimited ,because it only allows one light mode to pass through at a time.

Multiple modes/light paths travel down a multimode fiber cable, it only offers high bandwidth over a short distance, when running at longer distances, modal dispersion (distortion) becomes an issue, As the signaling bandwidth increases, the range of the distance decreases, and vice versa.

Jacket Color

Jacket color is often used to distinguish multimode cables from single mode ones. according to TIA-598C standard, for non-military applications, single mode cable is coated with yellow outer sheath, and multimode fiber is coated with orange or aqua jacket.

Cost

The cost of Multimode cable and single-mode cables are roughly the same. But the whole multimode fibre systems are much cheaper than single-mode fibre systems and considered more cost-effective in the right application. This is because single mode fibers normally use solid-state laser diodes that are much more expensive than LED or VCSEL components. Multimode transceivers are usually two times cheaper than single-mode transceivers.