Tag Archives: single-mode fiber

40G Deployment: The Cost Difference Between SMF and MMF


40G network are now being extensively adopted within LANs and data centers. 100G is still predominantly in the carrier network, but could soon extend its stretch to your local network. There exists much confusion as to whether to choose single-mode fiber (SMF) or multimode fiber (MMF) for deploying 40G bandwidth, and how to get fully prepared for scaling to higher-speed 100G. If you are hesitating to make the choice, you may find this article helpful.

40G Cost: Difference Between SMF and MMF

Multimode Fiber (MMF): Cost-effective With Higher Tolerance to Dirt

Cost-effectiveness: Multimode fiber (MMF) has been evolving to handle the escalating speed: OM3 has been superseded by OM4 and OM5 is there ready to use. MMF has a wider array of short distance transceivers that are easier to get. One of the liable argument that in favor of using MMF is that multimode optics use less power than single-mode ones, but only in condition that you have tens of thousands of racks. In essence, MMF still has its position under certain circumstances, like cabling within the same rack, in Fiber Channel and for backbone cabling in some new construction buildings.

smf mmf

Tolerance to Dirt: Multimode fiber tends to have a lot more tolerance to dirty connections than single-mode fiber. It can handle very dirty couples or connectors to ensure reliable and consistent link performance. Besides, it is easy to terminate, and more accommodating bend radius. So MMF is preferred by links that change frequently or are less than permanent.

smf mmf

Single-mode Fiber (SMF): Higher Capability and Better Future-proofing

Speed capability: Capacities are really vital for network growth. SMF does so with relatively larger capability than that of MMF. The gap between SMF and MMF cabling is much wider for high-density, high-speed networks. If you want to go further with SMF, say scaling to 100G or beyond, you simply need to upgrade the optics. Unlike using MMF, in which you have to upgrade the glass (OM3 to OM4 to OM5), the labor cost concerning this cannot be underestimated. The capacity for scaling of SMF alone makes it worth the cost. You can use single-mode for almost everything, no need for media conversion. SMF offers enough bandwidth to last a long time, making it possible to upgrade 100 Gbps to Tbps with CWDM/DWDM.

smf mmf

Future proofing: Despite the fact that SM optical transceivers usually cost higher than MM optics, SMF cabling is cheaper and can support much longer distance and reliable performance. Not to mention that bandwidth on SMF keeps going up and up on the same old glass. The good news is that the cost of SMF is dropping in recent years, and it is redesigning to run with less power, thus advocators of SMF think that it is pretty much the only rational choice for infrastructure cabling and the sure winner for today and tomorrow.

SMF and MMF: A Simple Comparison of Cost

There is no doubt that SMF is a better investment in the long run, but MMF still has a long way to go in data center interconnections. In fact the price difference of SMF optics and MMF optics can be minimized if you choose the right solution. Assuming to connect two 40G devices at 70 m away, let’s see the cost of SMF and MMF in the following chart.

Module Connector Type SMF or MMF Price 2 Connections 4 Connections 6 Connections
40GBASE-SR4 MPO12 MMF, OM4 $49.00 $564.48 $1128.96 $1693.44
40GBASE-BiDi LC MMF, OM4 $300.00 $1534.24 $2734.24 $3934.24
40GBASE-LR4 LC SMF, OS2 $340.00 $1,609.84 $2,969.84 $4,329.84
80 Gbit 160 Gbit 240 Gbit



Choosing the right fiber for your network application is a critical decision. Understanding your system requirements in order to select the appropriate fiber will maximize the value and performance of your cabling system. Be sure to select the right cable on the basis of aspects including link length, performance, and of course costs. FS provides a broad range of 40G optical transceivers and fiber patch cables with superior quality and fair price. For more details, please visit www.fs.com.

Common Mistakes in Fiber Optic Network Installation

When install a fiber optic network, people may make some common mistakes, which were usually overlooked. In this article, I will list the most common ones. Hope to give you some guidance for your optical network installation.

1. Single Strand Fiber Device Must Be Used in Pairs

You will never buy two left shoes, but people often make a similar mistake when they’re working with Single Strand Fiber (SSF). Single strand fiber technology allows for the use of two independent wavelengths, such as 1310 and 1550 nm, on the same piece of cable. The most common single strand fiber device is Bi-Directional (BiDi) transceiver. Two BiDi transceiver must be matched correctly. One unit must be a 1310nm-TX/1550nm-RX transceiver (transmitting at 1310 nm, receiving at 1550 nm) and the other must be a 1550nm-TX/1310nm-RX transceiver (transmitting at 1550 nm, receiving at 1310 nm). The 1550nm-TX/1310nm-RX transceiver is more expensive than the 1310nm-TX/1550nm-RX transceiver, due to the cost of their more powerful lasers. So network engineers may hope to save money by installing a pair of 1310nm-TX/1550nm-RX transceivers. But, like mismatched shoes, it doesn’t work.


2. Don’t Use Single-Mode Fiber over Multimode Fiber

Some people may want to make use of legacy cabling or equipment from an older fiber installation to save cost. But keep in mind that single-mode and multimode fiber are usually incompatible. Multimode fiber uses cable with a relatively large core size, typically 62.5 microns (om2, om3 and om4), and 50 microns (om1) still used in some installations. The larger core size simplifies connections and allows for the use of less powerful, less expensive light sources.  But the light therefore tends to bounce around inside the core, which increases the modal dispersion. That limits multimode’s useful range to about 2 km. Single-mode fiber combines powerful lasers and cabling with a narrow core size of 9/125 microns to keep the light focused.  It has a range of up to 120 km, but it is also more expensive. If you tried to use single-mode fiber over a multimode fiber run.  The core size of the fiber cable would be far too large.  You’d get dropped packets and CRC errors.


3. Understand All kinds of Fiber connectors First

Fiber optic transceivers use a variety of connectors, so make clear their differences before you begin ordering products for a fiber installation is necessary. SC (stick and click) is a square connector. ST (stick and twist) is a round, bayonet-type. LC, or the “Lucent Connector”, was developed by Lucent Technologies to address complaints that ST and SC were too bulky and too easy to dislodge. LC connectors look like a compact version of the SC connector. SFP (small form‐factor pluggable) transceivers usually use LC connector.  Less common connectors include MT-RJ and E2000.


4.Connector Links and Splice Times Also Affect 

Although single-mode fiber suffers from less signal loss per km than multimode, all fiber performance is affected by connectors and splices. The signal loss at a single connector or splice may seem insignificant. But as connectors and splices become more numerous signal loss will steadily increase. Typical loss factors would include 0.75 dB per connector, 1 dB per splice, 0.4 dB attenuation per km for single-mode fiber and 3.5 dB attenuation per km for multimode fiber.  Add a 3 dB margin for safety. The more splices and connectors you have in a segment, the greater the loss on the line.

5. Don’t Use APC connector with UPC Connector

Fiber connections may use Angle Polished Connectors (APC) or Ultra Polished Connectors (UPC), and they are not interchangeable. There are physical differences in the ferules at the end of the terminated fiber within the cable (shown in the figure below).  An APC ferrule end-face is polished at an 8° angle, while the UPC is polished at a 0° angle. If the angles are different, some of the light will fail to propagate, becoming connector or splice loss. UPC connectors are common in Ethernet network equipment like media converters, serial devices and fiber‐based switches. APC connectors are typical for FTTX and PON connections.  ISPs are increasingly using APC.


6. Don’t Connect SFP to SFP+ Transceivers

Small Form Pluggable (SFP) transceivers are more expensive than fixed transceivers.  But they are hot swappable and their small form factor gives them additional flexibility. They’ll work with cages designed for any fiber type and their prices are steadily dropping.  So they have become very popular. Standard SFPs typically support speeds of 100 Mbps or 1 Gbps. XFP and SFP+ support 10 Gbps connections. SFP+ is smaller than XFP and allows for greater port density.  Though the size of SFP and SFP+ is the same, you can’t connect SFP+ to a device (SFP) that only supports 1 Gbps.

Related Article: Optical Module Maintenance Methods and Installation Tips

What Kind of Single-mode Fiber Should You Choose?

As we all know, multimode fiber is usually divided into OM1, OM2, OM3 and OM4. Then how about single-mode fiber? In fact, the types of single-mode fiber seem much more complex than multimode fiber. There are two primary sources of specification of single-mode optical fiber. One is the ITU-T G.65x series, and the other is IEC 60793-2-50 (published as BS EN 60793-2-50). Rather than refer to both ITU-T and IEC terminology, I’ll only stick to the simpler ITU-T G.65x in this article. There are 19 different single-mode optical fiber specifications defined by the ITU-T.

Name Type
ITU-T G.652 ITU-T G.652.A, ITU-T G.652.B, ITU-T G.652.C, ITU-T G.652.D
ITU-T G.653 ITU-T G.653.A, ITU-T G.653.B
ITU-T G.654 ITU-T G.654.A, ITU-T G.654.B, ITU-T G.654.C
ITU-T G.655 ITU-T G.655.A, ITU-T G.655.B, ITU-T G.655.C, ITU-T G.655.D, ITU-T G.655.E
ITU-T G.656 ITU-T G.656
ITU-T G.657 ITU-T G.657.A, ITU-T G.657.B, ITU-T G.657.C, ITU-T G.657.D

Each type has its own area of application and the evolution of these optical fiber specifications reflects the evolution of transmission system technology from the earliest installation of single-mode optical fiber through to the present day. Choosing the right one for your project can be vital in terms of performance, cost, reliability and safety. In this post, I may explain a bit more about the differences between the specifications of the G.65x series of single-mode optical fiber families. Hope to help you make the right decision.

The ITU-T G.652 fiber is also known as standard SMF (single-mode fiber) and is the most commonly deployed fiber. It comes in four variants (A, B, C, D). A and B have a water peak. C and D eliminate the water peak for full spectrum operation. The G.652.A and G.652.B fibers are designed to have a zero-dispersion wavelength near 1310 nm, therefore they are optimized for operation in the 1310-nm band. They can also operate in the 1550-nm band, but it is not optimized for this region due to the high dispersion. These optical fibers are usually used within LAN, MAN and access network systems. The more recent variants (G.652.C and G.652.D) feature a reduced water peak that allows them to be used in the wavelength region between 1310 nm and 1550 nm supporting Coarse Wavelength Division Multiplexed (CWDM) transmission.


G.653 fiber was developed to address this conflict between best bandwidth at one wavelength and lowest loss at another. It uses a more complex structure in the core region and a very small core area, and the wavelength of zero chromatic dispersion was shifted up to 1550 nm to coincide with the lowest losses in the fiber. Therefore, G.653 fiber is also called dispersion-shifted fiber (DSF). G.653 has a reduced core size, which is optimized for long-haul single-mode transmission systems using erbium-doped fiber amplifiers (EDFA). However, its high power concentration in the fiber core may generate nonlinear effects. One of the most troublesome, four-wave mixing (FWM), occurs in a Dense Wavelength Division Multiplexed (CWDM) system with zero chromatic dispersion, causing unacceptable crosstalk and interference between channels.


The G.654 specifications entitled “characteristics of a cut-off shifted single-mode optical fiber and cable.” It uses a larger core size made from pure silica to achieve the same long-haul performance with low attenuation in the 1550-nm band. It usually also has high chromatic dispersion at 1550 nm, but is not designed to operate at 1310 nm at all. G.654 fiber can handle higher power levels between 1500 nm and 1600 nm, which is mainly designed for extended long-haul undersea applications.

G.655 is known as non-zero dispersion-shifted fiber (NZDSF). It has a small, controlled amount of chromatic dispersion in the C-band (1530-1560 nm), where amplifiers work best, and has a larger core area than G.653 fiber. NZDSF fiber overcomes problems associated with four-wave mixing and other nonlinear effects by moving the zero-dispersion wavelength outside the 1550-nm operating window. There are two types of NZDSF, known as (-D)NZDSF and (+D)NZDSF. They have respectively a negative and positive slope versus wavelength. Following picture depicts the dispersion properties of the four main single-mode fiber types. The typical chromatic dispersion of a G.652 compliant fiber is 17ps/nm/km. G.655 fibers were mainly used to support long-haul systems that use DWDM transmission.


As well as fibers that work well across a range of wavelengths, some are designed to work best at specific wavelengths. This is the G.656, which is also called Medium Dispersion Fiber (MDF). It is designed for local access and long haul fiber that performs well at 1460 nm and 1625 nm. This kind of fiber was developed to support long-haul systems that use CWDM and DWDM transmission over the specified wavelength range. And at the same time, it allow the easier deployment of CWDM in metropolitan areas, and increase the capacity of fiber in DWDM systems.

G.657G.657 optical fibers are intended to be compatible with the G.652 optical fibers but have differing bend sensitivity performance. It is designed to allow fibers to bend, without affecting performance. This is achieved through an optical trench that reflects stray light back into the core, rather than it being lost in the cladding, enabling greater bending of the fiber. As we all know, in cable TV and FTTH industries, it is hard to control bend radius in the field. G.657 is the latest standard for FTTH applications, and, along with G.652 is the most commonly used in last drop fiber networks.

From the passage above, we know that different kind of single-mode fiber has different application. Since G.657 is compatible with the G.652, some planners and installers are usually likely to come across them. In fact, G657 has a larger bend radius than G.652, which is especially suitable for FTTH applications. And due to problems of G.643 being used in WDM system, it is now rarely deployed, being superseded by G.655. G.654 is mainly used in subsea application. According to this passage, I hope you have a clear understanding about these single-mode fibers, which may help you make the right decision.

SMF or MMF? Which Is the Right Choice for Data Center Cabling?

Selecting the right cabling plant for data center connectivity is critically important. The wrong decision could leave a data center incapable of supporting future growth, requiring an extremely costly cable plant upgrade to move to higher speeds. In the past, due to high cost of single-mode fiber (SMF), multimode fiber (MMF) has been widely and successfully deployed in data center for many years. However, as technologies have evolved, the difference in price between SMF and MMF transceivers has been largely negated. With cost no longer the dominant decision criterion, operators can make architectural decisions based on performance. Under these circumstances, should we choose SMF or MMF? This article may give you some advice.

MMF Can’t Reach the High Bandwidth-Distance Needs
MMF datacenterBased on fiber construction MMF has different classifications types that are used to determine what optical signal rates are supported over what distances. Many data center operators who deployed MMF OM1/OM2 fiber a few years ago are now realizing that the older MMF does not support higher transmit rates like 40GbE and 100GbE. As a result, some MMF users have been forced to add later-generation OM3 and OM4 fiber to support standards-based 40GbE and 100GbE interfaces. However, MMF’s physical limitations mean that as data traffic grows and interconnectivity speeds increase, the distance between connections must decrease. The only alternative in an MMF world is to deploy more fibers in parallel to support more traffic. Therefore, while MMF cabling has been widely and successfully deployed for generations, its limitations now become even more serious. Operators must weigh unexpected cabling costs against a network incapable of supporting new services.

SMF Maybe a Viable Alternative
Previously, organizations were reluctant to implement SMF inside the data center due to the cost of the pluggable optics required, especially compared to MMF. However, newer silicon technologies and manufacturing innovations are driving down the cost of SMF pluggable optics. Transceivers with Fabry-Perot edge emitting lasers (single-mode) are now comparable in price and power dissipation to VCSEL (multimode) transceivers. Besides, Where MMF cable plants introduce a capacity-reach tradeoff, SMF eliminates network bandwidth constraints. This allows operators to take advantage of higher-bit-rate interfaces and wave division multiplexing (WDM) technology to increase by three orders of magnitude the amount of traffic that the fiber plant can support over longer distances. All these factors make SMF a more viable option for high-speed deployments in data centers.

SMF datacenter

Comparison Between SMF and MMF
10GbE has become the predominant interconnectivity interface in large data centers, with 40GbE and 100GbE playing roles in some high-bandwidth applications. Put simply, the necessity for fiber cabling that supports higher bit rates over extended distances is here today. With that in mind, the most significant difference between SMF and MMF is that SMF provides a higher spectral efficiency than MMF, which means it supports more traffic over a single fiber using more channels at higher speeds. This is in stark contrast to MMF, where cabling support for higher bit rates is limited by its large core size. This effectively limits the distance higher speed signals can travel over MMF fiber. In fact, in most cases, currently deployed MMF cabling is unable to support higher speeds over the same distance as lower-speed signals.

Name Interface FP (SMF) VCSEL (MMF)
Link Budget (dB)
4 to 6 2
Reach (in meters) (Higher value is better)
10GbE 1300 300
40GbE 1300 150
100GbE 1300 <100

As operators consider their cabling options, the tradeoff between capacity and reach is important. Network operators must assess the extent to which they believe their data centers are going to grow. For environments where users, applications, and corresponding workload are all increasing, single-mode fiber offers the best future proofing for performance and scalability. And because of fundamental changes in how transceivers are manufactured, those benefits can be attained at prices comparable to SMF’s lower performing alternative.


Understanding Wavelengths in Fiber Optics

The light we are most familiar with is surely the light we can see. Our eyes are sensitive to light whose wavelength is in the range of about 400 nm to 700 nm, from the violet to the red. But for fiber optics with glass fibers, we use light in the infrared region which has wavelengths longer than visible light. Because the attenuation of the fiber is less at longer wavelengths. This text may mainly tell you what the common wavelengths used in fiber optics are and why they are used.


Wavelengths Definition

In fact, light is defined by its wavelength. It is a member of the frequency spectrum, and each frequency (sometimes also called color) of light has a wavelength associated with it. Wavelength and frequency are related. Generally, the radiation of shorter wavelengths are identified by their wavelengths, while the longer wavelengths are identified by their frequency.

Common Wavelengths in Fiber Optics

Wavelengths typically range from 800 nm to 1600 nm, but by far the most common wavelengths actually used in fiber optics are 850 nm, 1300 nm, and 1550 nm. Multimode fiber is designed to operate at 850 nm and 1300 nm, while single-mode fiber is optimized for 1310 nm and 1550 nm. The difference between 1300 nm and 1310 nm is simply a matter of convention. Both lasers and LEDs are used to transmit light through optical fiber. Lasers are usually used for 1310nm or 1550nm single-mode applications. LEDs are used for 850nm or 1300nm multimode applications.


Why Those Common Wavelengths?

As mentioned above, the most common wavelengths used in fiber optics are 850 nm, 1300 nm and 1550 nm. But why do we use these three wavelengths? Because the attenuation of the fiber is much less at those wavelengths. Therefore, they best match the transmission properties of available light sources with the transmission qualities of optical fiber. The attenuation of glass optical fiber is caused by two factors: absorption and scattering. Absorption occurs in several specific wavelengths called water bands due to the absorption by minute amounts of water vapor in the glass. Scattering is caused by light bouncing off atoms or molecules in the glass.

It is strongly a function of wavelength, with longer wavelengths having much lower scattering. From the chart below, we can obviously see that there are three low-lying areas of absorption, and an ever-decreasing amount of scattering as wavelengths increase. As you can see, all three popular wavelengths have almost zero absorption.



After reading this passage, you may know some basic knowledge of wavelengths in fiber optics. Since the attenuation of the wavelengths at 850 nm, 1300 nm, and 1550 nm are relatively less, they are the most three common wavelengths used in fiber optic communication. Fiberstore offer all kinds multimode and single-mode fiber optic transceivers which operate on 850 nm and 1310 nm respectively very well. For more information, please visit fs.com.

Related Article: From O to L: the Evolution of Optical Wavelength Bands

Do You Know About Mode Conditioning Patch Cord?

The great demand for increased bandwidth has prompted the release of the 802.3z standard (IEEE) for Gigabit Ethernet over optical fiber. As we all know, 1000BASE-LX transceiver modules can only operate on single-mode fibers. However, this may pose a problem if an existing fiber network utilizes multimode fibers. When a single-mode fiber is launched into a multimode fiber, a phenomenon known as Differential Mode Delay (DMD) will appear. This effect can cause multiple signals to be generated which may confuse the receiver and produce errors. To solve this problem, a mode conditioning patch cord is needed. In this article, some knowledge of mode conditioning patch cords will be introduced.

What Is a Mode Conditioning Patch Cord?

A mode conditioning patch cord is a duplex multimode cord that has a small length of single-mode fiber at the start of the transmission length. The basic principle behind the cord is that you launch your laser into the small section of single-mode fiber, then the other end of the single-mode fiber is coupled to multimode section of the cable with the core offset from the center of the multimode fiber (see diagram below).

mode conditioning patch cord

This offset point creates a launch that is similar to typical multimode LED launches. By using an offset between the single-mode fiber and the multimode fiber, mode conditioning patch cords eliminate DMD and the resulting multiple signals allowing use of 1000BASE-LX over existing multimode fiber cable systems. Therefore, these mode conditioning patch cords allow customers an upgrade of their hardware technology without the costly upgrade of their fiber plant.

Some Tips When Using Mode Conditioning Patch Cord

After learning about some knowledge of mode conditioning patch cords, but do you know how to use it? Then some tips when using mode conditioning cables will be presented.

    • Mode conditioning patch cords are usually used in pairs. Which means that you will need a mode conditioning patch cord at each end to connect the equipment to the cable plant. So these patch cords are usually ordered in numbers. You may see someone only order one patch cord, then it is usually because they keep it as a spare.
    • If your 1000BASE-LX transceiver module is equipped with SC or LC connectors, please be sure to connect the yellow leg (single-mode) of the cable to the transmit side, and the orange leg (multimode) to the receive side of the equipment. The swap of transmit and receive can only be done at the cable plant side. See diagram below.

mode conditioning patch cord

  • Mode conditioning patch cords can only convert single-mode to multimode. If you want to convert multimode to single-mode, then a media converter will be required.
  • Besides, mode conditioning patch cables are used in the 1300nm or 1310nm optical wavelength window, and should not be used for 850nm short wavelength window such as 1000Base-SX.


From the text, we know that mode conditioning patch cords really significantly improve the data signal quality and increase the transmission distance. But when using it, there are also some tips must be kept in mind. Fiberstore offer mode conditioning patch cords in all varieties and combinations of SC, ST, MT-RJ and LC fiber optic connectors. All of the Fiberstore’s mode conditioning patch cords are at high quality and low price. For more information, please visit fs.com.

Difference Between OS1 and OS2 Single Mode Fiber Cable

As we all know, multimode fiber is usually divided into OM1, OM2, OM3 and OM4. Then how about single mode fiber? In general, single mode fiber is categorised into OS1 and OS2. OS1 and OS2 are cabled single mode optical fibre specifications. In fact, there are many differences between OS1 and OS2 single mode fiber. This text will make a comparison between them and then give you a guide on how to choose the right one for your applications.

OS1 single mode fibers are compliant with ITU-T G.652A or ITU-T G.652B standards. Besides, the low-water-peak fibers defined by ITU-T G.652C and G.652D also come under OS1 single mode fibers. That is to say OS1 is compliant with specifications of ITU-T G.652. However, OS2 single mode fibers are only compliant with ITU-T G.652C or ITU-T G.652D standards, which means OS2 is explicitly applied to the low-water-peak fibers. These low-water-peak fibers are usually used for CWDM (Coarse Wavelength Division Multiplexing) applications.

OS1 and OS2 Single Mode FibreBesides the standards, the main difference between OS1 and OS2 single mode fibers is the cable construction. Typically, OS1 cabling is tight-buffered construction, which is usually used for indoor applications, such as campus or data centre. Yet OS2 cabling is loose-tube design. Cable with this construction is appropriate for outdoor cases like street, underground and burial. For this reason, OS1 indoor fibre has greater loss per kilometre than OS2 outdoor fibre. In general, the maximum attenuation for OS1 is 1.0 db/km and for OS2 is 0.4db/km. As a result, the maximum transmission distance of OS1 single mode fiber is 2 km but the maximum transmission distance of OS2 single mode fiber can reach 5 km and is up to 10 km. Then for all these reasons, OS1 is much cheaper than OS2. There is point need to pay attention to is that both OS1 and OS2 single mode fibers over their distance will allow speeds of 1 to 10 gigabit Ethernet. All of these differences between OS1 and OS2 discussed above are listed in the table below. You can get a clear understanding from it.

Name OS1 OS2
Standards ITU-T G.652A/B/C/D ITU-T G.652C/D
Construction Tight buffered Loose tube
Application Indoor Outdoor
Attenuation 1.0db/km 0.4db/km
Distance 2 km 10 km
Price Low High

Learning about the differences between OS1 and OS2 single mode fiber cable, then which cable should you choose? First, if you want to use for indoor application, OS1 is better for you. However, if used for outdoor application, you should choose OS2. Second, there is no benefit to be gained in using OS2 cable if under 2 km. OS2 is best for distance over 2 km. Finally, you should note that OS1 is much cheaper than OS2. In order to save cost, if the OS1 is enough for your application there is no need to use OS2. Fiberstore offers OS1 and OS2 single mode fiber patch cable as well as all kinds of multimode fiber patch cable. It is your optimal selection.

Related Article: What are OM1, OM2, OM3 and OM4 multimode fiber?

What’s the Difference: Single Mode vs Multimode Fiber

fiber cable diagAn optical fiber is a flexible, transparent fiber made of extruded glass or plastic, slightly thicker than a human hair. Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than wire cables. Optical fibers typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total internal reflection which causes the fiber to act as a waveguide.

In general, there are two kinds of optical fiber: fibers that support many propagation paths or transverse modes are called multimode fibers (MMF), while those that support a single mode are called single mode fibers (SMF). Single mode vs multimode fiber: what’s difference between them? Reading this text will help you get the answer.

Single Mode vs Multimode Fiber: What’s single mode optical fiber?

In fiber-optic communication, a single mode optical fiber (SMF) is an optical fiber designed to carry light only directly down the fibre – the transverse mode. For single mode optical fiber, no matter it operates at 100 Mbit/s or 1 Gbit/s date rates , the transmission distance can reach to at least 5 km. Typically, it is used for long-distance signal transmission.

single mode fiber

Single Mode vs Multimode Fiber: What’s multimode optical fiber?

Multimode optical fiber (MMF) is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Typical transmission speed and distance limits are 100 Mbit/s for distances up to 2 km (100BASE-FX), 1 Gbit/s up to 1000m, and 10 Gbit/s up to 550 m. There are two kinds of multimode indexes: step index and graded index.

multimode fiber

What’s difference between single mode optical fiber and multimode?

  • Core diameter

The main difference between multimode and single mode fiber is that the former has much larger core diameter, typically has a core diameter of 50 or 62.5 µm and a cladding diameter of 125 µm. While a typical single mode fiber has a core diameter between 8 and 10 µm and a cladding diameter of 125 µm.

Single Mode vs Multimode Fiber

  • Optical source
    Both lasers and LEDs are used as light sources. Laser light sources are significantly more expensive than LED light sources however they produce a light that can be precisely controlled and which has a high power. Because the LED light sources produce a more dispersed light source (many modes of light) these light sources are used with multimode
    cable. While a laser source is used (which produces close to a single mode of light) with single mode cable.

Single Mode vs Multimode Fiber

  • Bandwidth
    Since multimode fiber has a larger core-size than single mode fiber, it supports more than one propagation mode. Besides, like multimode fibers, single-mode fibers do exhibit modal dispersion resulting from multiple spatial modes, but the modal dispersion of single mode fiber is less than multi-mode fiber. For these reasons, single mode fibers can have a higher bandwidth than multi-mode fibers.
  • Jacket color
    Jacket color is sometimes used to distinguish multimode cables from single mode ones. The standard TIA-598C recommends, for non-military applications, the use of a yellow jacket for single mode fiber, and orange or aqua for multimode fiber, depending on type. Some vendors use violet to distinguish higher performance OM4 communications fiber from other types.

Single Mode vs Multimode Fiber

  • Modal dispersion
    The LED light sources sometimes used with multimode fiber produce a range of wavelengths and these each propagate at different speeds. This will lead to much modal dispersion, which is a limit to the useful length for multimode fiber optic cable. In contrast, the lasers used to drive single mode fibers produce coherent light of a single wavelength. Hence its modal dispersion is much less than multimode fiber. Due to the modal dispersion, multimode fiber has higher pulse spreading rates than single mode fiber, limiting multimode fiber’s information transmission capacity.

Single Mode vs Multimode Fiber

  • Price
    For multimode fiber can support multiple light mode, the price of it is higher than single-mode fiber. But in terms of the equipment, because single mode fiber normally uses solid-state laser diodes, therefore, the equipment for single mode fiber is more expensive than equipment for multimode fiber. And for this reason , the cost of using multimode fiber is much less than using single-mode fiber instead.

Single Mode vs Multimode Fiber: What kind of optical fiber should I choose?
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 the $500 to $800 range. If the distance to be covered is more than 3-5 miles, single mode fiber is the choice. Transmission systems designed for use with this fiber will typically cost more than $1000 due to the increased cost of the laser diode.

Optical Mode Conditioners We Need to Know

Networking applications such as ATM have traditionally used different adapter cards to support multimode and single-mode fiber. Gigabit Ethernet standard (IEEE 802.3z) is the first industry standard to propose the use of both fiber types with the same adapter card.

Parallel Sysplex links were originally offered as either 50 Mbyte/s data rates over multimode fiber or 100 Mbyte/s data rates over single-mode fiber. With the announcement of more recent servers, support for multimode fiber has been withdrawn as a standard feature and is now available only on special request. There is a need to support 100Mbyte/s adapter cards over installed multimode fiber to facilitate migration of those customers who have been using the 50 Mbyte/s option.

In order to address these concerns, special fiber optic adapter cable have been developed, known as Mode Conditioning Patch Cable (MCP), This cable contains both single-mode and multimode fibers, and should be inserted on both ends of a link to interface between a single-mode adapters card and a multimode cable plant. The MCPs for parallel sysplex link, Gigabit Ethernet, Fiber Channel, and many other applications are available today.

mode conditioning fiber

Next, let us describe the technical issues associated with this approach. The bandwidth of fiber optic cables are typically measured using over-filled launch condition, which result in equal optical power being launched into all fiber modes. This is also known as a mode scramble launch, and is approximately equivalent to the conditions achieved when using Lambertian source such as an LED. By contrast, laser source being more highly collimated tend to produce an under-filled launch condition; this can result in either larger or smaller effective bandwidth relative to an overfilled launch, and is sensitive to small changes in the fiber’s refractive index profile. As discover in recent gigabit link tests, bandwidth measured using over-filled launch conditions is not always a good indication of link performance for laser applications over multimode fiber.

singlemode fiber

Because of the bandwidth limitations of multimode optical fiber, future multi-gigabit fiber optic interconnects will be based on single mode fiber cable. For this reasons, most new fiber installations include at least some single mode fiber in the cable infrastructure. However, many applications continue to use multimode fiber optic extensively; a recent survey of building premise cable installers reported that most LAN infrastructures currently installed are composed of about 90% multimode fiber. As the fiber cable plant is upgraded to support higher data rates on single-mode fiber, we must also provide a migration path that continues to reuse the installed multimode cable plant for as long as single mode fiber optic cable affects many important datacom applications:

I/O applications currently using multimode fiber for ESCON will need to migrate the cable plant to single-mode fiber in order to take full advantage of the higher bandwidth of FICON links. Future FICON enhancements that extend this protocol to multi-gigabit data rates will also require single-mode fiber.

Networking applications such as ATM have traditionally used different adapter cards to support multimode and single-mode fiber. Gigabit Ethernet standard (IEEE 802.3z) is the first industry standard to propose the use of both fiber types with the same adapter card.

Parallel Sysplex links were originally offered as either 50 Mbyte/s data rates over multimode fiber or 100 Mbyte/s data rates over single-mode fiber. With the announcement of more recent servers, support for multimode fiber has been withdrawn as a standard feature and is now available only on special request. There is a need to support 100Mbyte/s adapter cards over installed multimode fiber to facilitate migration of those customers who have been using the 50 Mbyte/s option.

In order to address these concerns, special fiber optic adapter cable have been developed, known as mode conditioning patch cable (MCP), This cable contains both single-mode and multimode fibers, and should be inserted on both ends of a link to interface between a single-mode adapters card and a multimode cable plant. The MCPs for parallel sysplex link, Gigabit Ethernet, Fiber Channel, and many other applications are available today.

The bandwidth of Fiber Patch Cables are typically measured using over-filled launch condition, which result in equal optical power being launched into all fiber modes. This is also known as a mode scramble launch, and is approximately equivalent to the conditions achieved when using Lambertian source such as an LED. By contrast, laser source being more highly collimated tend to produce an under-filled launch condition; this can result in either larger or smaller effective bandwidth relative to an overfilled launch, and is sensitive to small changes in the fiber’s refractive index profile. As discover in recent gigabit link tests, bandwidth measured using over-filled launch conditions is not always a good indication of link performance for laser applications over multimode fiber. when a fast rise time laser pulse is applied to multimode fiber, significant pulse broadening occurs due to the difference in propagation times of different modes within the fiber. This pulse broadening is known as differential mode delay and mode-specific attenuation in the fiber, and the launch conditions of the test. DWD is made worse by the excitation of relatively few modes groups and a high percentage of modal power concentrated in lower order modes. The impact of DWD increase with link length. There is, unfortunately, not a simple relationship between the industry specified over-fill launch measured bandwidths of the fiber and the effective bandwidth due to DWD.

The radial overfill launch method was developed as a way to establish consistent and repeatable modal bandwidth measurement of a given fiber couple with a given source. A radial over-fill launch is obtained when a laser spot is projected onto the core of the multimode fiber, symmetric about the core center with the optic axis of the source and fiber aligned; the laser spot must be larger than the fiber core, and the laser divergence angle must be less than the fiber’s numerical aperture. When these conditions are satisfied, the worst case modal bandwidth of the link is taken to be the worse case of the over-fill and radial over-fill launch bandwidth and the DWD limited bandwidth of a fiber; thus, high speed laser links implemented over multimode fiber optic cable will likely experience bandwidth values closer to the radial over-fill launch method rather than the more commonly specified over-fill launch method.

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