MTP/MPO trunk cables are terminated with the MTP/MPO connectors (as shown in the following figure). Trunk cables are available with 12, 24, 48 and 72 fibers. MTP/MPO trunk cables are designed for data center applications. The plug and play solutions uses micro core cable to maximize bend radius and minimize cable weight and size. Besides, MTP/MPO trunk cables also have the following advantages:

• Saving installation time–With the special plug and play design, MTP/MPO trunk cables can be incorporated and immediately plugged in. It greatly helps reduce the installation time.
• Decreasing cable volume–MTP/MPO trunk cables have very small diameters, which decrease the cable volume and improve the air-conditioning conditions in data centers.
• High quality–MTP/MPO trunk cables are factory pre-terminated, tested and packed along with the test reports. These reports serve as long-term documentation and quality control.

MPO/MTP harness cable (as shown in the following figure) is also called MPO/MTP breakout cable or MPO/MTP fan-out cable. This cable has a single MTP connector on one end that breaks out into 6 or 12 connectors (LC, SC, ST, etc.). It’s available in 4, 6, 8, or 12 fiber ribbon configurations with lengths about 10, 20, 30 meters and other customized lengths. MPO/MTP harness cable is designed for high density applications with required high performance. It’s good to optimize network performance. Other benefits are shown as below:

• Saving space–The active equipment and backbone cable is good for saving space.
• Easy deployment–Factory terminated system saves installation and network reconfiguration time.
• Reliability–High standard components are used in the manufacturing process to guarantee the product quality.

MPO/MTP cassette modules provide secure transition between MPO/MTP and LC or SC discrete connectors. They are used to interconnect MPO/MTP backbones with LC or SC patching. MPO/MTP Cassettes are designed to reduce installation time and cost for an optical network infrastructure in the premises environment. The modular system allows for rapid deployment of high density data center infrastructure

as well as improved troubleshooting and reconfiguration during moves, addons, and changes. Aside from that, it has other advantages:

• MPO/MTP interface–MPO/MTP components feature superior optical and mechanical properties.
• Optimized performance–Low insertion losses and power penalties in tight power budget, high-speed network environments.
• High density–12 or 24 fiber cassettes can be mounted in 1U scaling up to 72 or in 3U scaling up to 336 discrete LC connectors.

The above shows that the MPO/MTP system is a good solution for data center requirements. This high density, scalable system is designed to enable thousands of connections.

FTTH is a reliable and efficient technology which holds many advantages such as high bandwidth, low cost, fast speed and so on. This is why it is so popular with people and develops so rapidly. Now, let’s take a look at its advantages in the following.

• The most important benefit to FTTH is that it delivers high bandwidth and is a reliable and efficient technology. In a network, bandwidth is the ability to carry information. The more bandwidth, the more information can be carried in a given amount of time. Experts from FTTH Council say that FTTH is the only technology to meet consumers’ high bandwidth demands.
• Even though FTTH can provide the greatly enhanced bandwidth, the cost is not very high. According to the FTTH Council, cable companies spent $84 billion to pass almost 100 million households a decade ago with lower bandwidth and lower reliability. But it costs much less in today’s dollars to wire these households with FTTH technology.
• FTTH can provide faster connection speeds and larger carrying capacity than twisted pair conductors. For example, a single copper pair conductor can only carry six phone calls, while a single Fiber pair can carry more than 2.5 million phone calls simultaneously. More and more companies from different business areas are installing it in thousands of locations all over the world.
• FTTH is also the only technology that can handle the futuristic internet uses when 3D “holographic” high-definition television and games (products already in use in industry, and on the drawing boards at big consumer electronics firms) will be in everyday use in households around the world. Think 20 to 30 Gigabits per second in a decade. No current technologies can reach this purpose.
• The FTTH broadband connection will bring about the creation of new products as they open new possibilities for data transmission rate. Just as some items that now may seem very common were not even on the drawing board 5 or 10 years ago, such as mobile video, iPods, HDTV, telemedicine, remote pet monitoring and thousands of other products. FTTH broadband connections will inspire new products and services and could open entire new sectors in the business world, experts at the FTTH Council say.
• FTTH broadband connections will also allow consumers to “bundle” their communications services. For example, a consumer could receive telephone, video, audio, television and just about any other kind of digital data stream using a simple FTTH broadband connection. This arrangement would more cost-effective and simpler than receiving those services via different lines.

As the demand for broadband capacity continues to grow, it’s likely governments and private developers will do more to bring FTTH broadband connections to more homes. According to a report, Asian countries tend to outpace the rest of the world in FTTH market penetration. Because governments of Asia Pacific countries have made FTTH broadband connections an important strategic consideration in building their infrastructure. South Korea, one of Asian countries, is a world leader with more than 31 percent of its households boasting FTTH broadband connections. Other countries like Japan, the United States, and some western countries are also building their FTTH broadband connections network largely. It’s an inevitable trend that FTTH will continue to grow worldwide.

Fiber optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information.

First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks. Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers have reached internet speeds of over 100 petabits per second using fiber-optic communication.

Fiber's advantages has led to its use as the backbone of all of today's communications, telecom, Internet, CATV, etc. - even wireless, where towers are connected on fiber and antennas are using fiber up the towers.

Optical Fiber - The Better Solution

This photo from the infancy of fiber optics (to the right) was used to illustrate that one tiny optical fiber could carry more communications signals than a giant copper cable. Today one single mode fiber could carry the same amount of communications as 1000 of those old copper cables!

Fiber offers thousands of times more bandwidth than copper cables and can go more than 1000 times further before needing repeaters - both of which contribute to the immense economic advantage of fiber optics over copper. You can do a similar analysis for using wireless transmission also, but wireless is limited by the available wireless spectrum which is overcrowded because of everyone's desire to use more mobile devices.

How Fiber Optic Communication Works

The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal.

Fiber (or fibre) consists of a strand of pure glass a little larger than a human hair. Fiber optic cable employs photons and pulsing laser light for the transmission of digital signals. Photons pass through the glass with negligible resistance. As light passes through the cable, its rays bounce off the cladding in different ways as shown below. The optic core of fiber optic cable is pure silicon dioxide. The electronic 1s and 0s of computers are converted to optically coded 1s and 0s. A light-emitting diode on one end of the cable then flashes those signals down the cable. At the other end, a simple photodetector collects the light and converts it back to electrical signals for transmission over copper cable networks.

Step index multimode was the first fiber design but is too slow for most uses, due to the dispersion caused by the different path lengths of the various modes. Step index fiber is rare - only POF uses a step index design today.

Graded index multimode fiber uses variations in the composition of the glass in the core to compensate for the different path lengths of the modes. It offers hundreds of times more bandwidth than step index fiber - up to about 2 gigahertz.

Singlemode fiber shrinks the core down so small that the light can only travel in one ray. This increases the bandwidth to almost infinity - but it's practically limited to about 100,000 gigahertz - that's still a lot!

 

Optic Fiber Cable Construction

 

Optical fiber consists of a core and a cladding layer, selected for total internal reflection due to the difference in the refractive index between the two. In practical fibers, the cladding is usually coated with a layer of acrylate polymer or polyimide. This coating protects the fiber from damage but does not contribute to its optical waveguide properties.

Individual coated fibers (or fibers formed into ribbons or bundles) then have a tough resin buffer layer and/or core tube(s) extruded around them to form the cable core. Several layers of protective sheathing, depending on the application, are added to form the cable.

Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber bundle imaging applications.

A “dopant” is added to the core to actually make it less pure than the cladding. This changes the way the core transmits light. Because the cladding has different light properties than the core, it tends to keep the light within the core. Because of these properties, fiber optic cable can be bent around corners and can be extended over distances of up to 100 miles.

A typical laser transmitter can be pulsed billions of times per second. In addition, a single strand of glass can carry light in a number of wavelengths (colors), meaning that the data-carrying capacity of fiber optic cable is potentially thousands of times greater than copper cable.

 

Types Of Fiber Optic Cable

• Plastic cable, which works only over a few meters, is inexpensive and works with inexpensive components.
• Plastic-coated silica cable offers better performance than plastic cable at a little more cost.
• Single-index monomode fiber cable is used to span extremely long distances. The core is small and provides high bandwidth at long distances. Lasers are used to generate the light signal for single-mode cable. This cable is the most expensive and hardest to handle, but it has the highest bandwidths and distance ratings.
• Step-Index multimode cable has a relatively large diameter core with high dispersion characteristics. The cable is designed for the LAN environment and light is typically generated with a LED (light-emitting diode).
• Graded-index multimode cable has multiple layers of glass that contain dispersions enough to provide increases in cable distances.

Cable specifications list the core and cladding diameters as fractional numbers. For example, the minimum recommended cable type for FDDI (Fiber Distributed Data Interface) is 62.5/125 micron multimode fiber optic cable.That means the core is 62.5 microns and the core with surrounding cladding is a total of 125 microns.

• The core specifications for step-index and graded-index multimode cables range from 50 to 1,000 microns.
• The cladding diameter for step mode cables ranges from 125 to 1,050 microns.
• The core diameter for single-mode step cable is 4 to 10 microns, and the cladding diameter is from 75 to 125 microns.

 

Indoor Vs. Outdoor Optic Fiber Cable Applications

Fiber optic cable consists of the core, the cladding and the coating. The core is a cylindrical rod of dielectric material. Dielectric material conducts no electricity. Light propagates mainly along the core of the fiber. The core is generally made of glass. The core is described as having a radius of (a) and an index of refraction n1. The core is surrounded by a layer of material called the cladding. Even though light will propagate along the fiber core without the layer of cladding material, the cladding does perform some necessary functions. (The basic structure of an optical fiber is shown in the following figure.)

The size of the optical fiber is commonly referred to by the outer diameter of its core, cladding and coating. Example: 50/125/250 indicates a fiber with a core of 50 microns, cladding of 125 microns, and a coating of 250 microns. The coating is always removed when joining or connecting fibers. A micron (µm) is equal to one-millionth of a meter. 25 microns are equal to 0.0025 cm. (A sheet of paper is approximately 25 microns thick).

Besides the basics, Fiber optic cables can be classified by other ways.

To solve the problem, mode conditioning patch cable was developed as a solution for network applications where Gigabit Ethernet hubs with laser based transmitters are deployed. Mode conditioning patch cable is the mean to achieve the drive distance of installed fiber plant beyond its original intended applications. It allows customer upgrading their hardware technology without the cost of upgrading fiber plant. In addition, mode conditioning patch cable significantly improves data signal quality while increasing the transmission distance.

What is Mode Conditioning Patch Cable?

Mode Conditioning Patch Cable, or Mode Conditioning Patchcord (MCP), is a duplex multimode patch cable that has a small length of single mode fiber at the start of the transmission length. Designed to "condition" the laser launch and obtain an effective bandwidth closer to that measured by the overfilled launch method, the MCP allows for laser transmitters to operate at gigabit rates over multimode fiber without being limited by DMD. The point is to excite a large number of modes in the fiber, weighted in the mode groups that are highly excited by overfill launch conditions, and to avoid exciting widely separated mode groups with similar power levels. This is achieved by launching the laser light into a single mode fiber, then coupling it into a multimode fiber that is off-center relative to the single mode fiber core. This is shown beside.

Tips: Different offsets are required for 50µm and 62.5µm multimode fibers. Engineers have found that an offset of 17~23 µm can achieve an effective modal bandwidth equivalent to the overfill launch method for 62.5µm multimode fibers. And an offset of 10~16 µm is good for 50µm multimode fibers.

The basic principle behind the cable is to launch laser into the small section of single mode fiber. The other end of single mode fiber is coupled to the multimode section of the cable with the offset from the center of the multimode fiber. This patch cable is required with transceivers (e.g.1000BASE-LX/LH, 10GBASE-LX4 and 10GBASE-LRM) that use both single mode and multimode fibers. When launching into multimode fiber, the transceiver can generate multiple signals that causes DMD which can severly limit transmission distances. The MCP removes these multiple signals, eliminating problems at the receiver end. Here is a figure that shows an MCP and how it is typically connected to a transceiver module. When required, it is inserted between a transceiver module and the multimode cable plant.

Requirements for Using MCPs in Laser-Based Transmissions

Gigabit Ethernet

The requirement for MCP is specified only for 1000BASE-LX/LH transceivers transmitting in the 1300nm window and in applications over multimode fiber. MCP should never be used in 1000BASE-SX links in the 850nm window. MCP is required for 1000BASE-LX/LH applications over FDDI-grade, OM1, and OM2 fiber types. MCP should never be used for applications over OM3, also known as "laser-optimized fiber".

10-Gigabit Ethernet

The requirement for MCP is specified only for 10GBASE-LX4 and 10GBASE-LRM transceivers transmitting in the 1300nm window and in applications over multimode fiber. MCP should never be used in 10GBASE-SR links in the 850nm window. MCP is required for 10GBASE-LX4 and 10GBASE-LRM applications over FDDI-grade, OM1, and OM2 fiber types. MCP should never be used for applications over OM3, also known as "laser-optimized fiber."

Notes for the Installation of MCPs

When using 1000BASE-LX/LH, 10GBASE-LX4 and 10GBASE-LRM transceivers with legacy 62.5µm or 50µm multimode fiber, you must install MCP between the transceiver and the multimode fiber cable on both ends of the link. The MCP is required for all links over FDDI-grade, OM1 and OM2 fiber types, and should never be used for applications over OM3 and more recent fiber types.

Note: It is not recommended using 1000BASE-LX/LH, 10GBASE-LX4 and 10GBASE-LRM transceivers with multimode fiber and no patch cable for very short link distances (tens of meters). The result could be an elevated Bit Error Rate (BER) and receiver damage.

Types of Fiber Optic Loopbacks

Fiber optic loopbacks can be with various jacket types, cable diameters, connector terminations and cable lengths. Traditional fiber optic loopbacks, i.e.  Fiber Optic Loopback Cables, can be regarded to be two fiber optic connectors on the same piece of simplex fiber optic patch cable put together, thus it forms a loop. Classified by the connector types, two most commonly used fiber optic loopback cables are SC and LC type, while there are also FC, MTRJ, and MTP etc types.

Besides the traditional fiber optic loopbacks, there are also molded fiber optic loopbacks (or fiber optic loopback plugs), i.e. Fiber Optic Loopback Modules, with compact design. Unlike the traditional fiber optic loopback cables with visible cable parts, fiber optic loopback module has its cables and fibers well protected inside the housing. It integrates every part into one single body, which help save space and make it easier to operate as well as offer better protection to the whole product. By incorporating a rigid connector shell for fiber protection with an easy to use, ergonomic package, the fiber optic loopback module is designed for durability and performance. Molded fiber optic loopbacks are also mainly available in SC and LC types, which are easy to use for fiber optic test purpose in the lab experiments or manufacturing environment.

Just like fiber optic patch cables, fiber optic loopbacks can also be classified by fiber types:  singlemode and multimode. The fiber types can be 9/125µm single mode fiber, 50/125µm multimode fiber, or 62.5/125µm multimode fiber. Typically single mode SC and LC loopbacks are blue, and typical multimode LC and SC loopbacks are beige. The color also goes with the practice of fiber optic patch cables.

Applications of Fiber Optic Loopback

A tipical application of fiber optic loopback is to check fiber optic transceiver by loopback test. Loopback test means a hardware or software method, a loopback test, feeds a received signal or data back to the sender. It is utilized as an aid in debugging physical connection problems.

Loopback test is the easiest way to ensure the transceiver is working faultlessly. On fiber optic transceiver manufacturing floors and in R&D labs, a fiber optic loopback is used to verify the transceiver whether it is working perfectly as designed. Basically what the loopback does is directly routing the laser signal from the transmitter port back to the receiver port. Then the transmitted pattern is compared with the received pattern to make sure they are identical and have no error.

What is Fiber Optic Connector?

Fiber Optic Connector, or optical fiber connector, is removable activities between optical fiber and optical fiber connection device. It is to put the fiber of two surface precision docking, so that the optical output of optical energy to maximize the fiber optic coupler in receiving optical fiber, and optical link due to the intervention and to minimize the effects on the system, this is the basic requirement of fiber optic connector. To a certain extent, fiber optic connector also affects the fiber optic transmission reliability and the performance of the system.

Key Features of Fiber Optic Connectors

Structure of Fiber Optic Connectores

Optical fiber to fiber optic interconnection can be made by a joint, a permanent connection, or a connector, and is different from the plug in it can be to disconnect and reconnect. Fiber optic connector types are as various as the applications for which they were developed. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters. But all connectors have the same four basic components.

Ferrule: The fiber is installed in a long, thin cylinder, the ferrule, which act as a fiber alignment mechanism. The ferrule is bored through the center at a diameter that is slightly larger than the diameter of the fiber cladding. The end of the fiber is located at the end of the ferrule. Ferrules are typically made of metal or ceramic, but they may also be constructed of plastic.

Connector Body: Also known as the connector housing, the body holds the ferrule. It is usually constructed of metal or plastic and includes one or more assembled pieces which hold the fiber in place. The details of these connector body assemblies vary among connectors, but the welding and/or crimping is commonly used to attach strength members and cable jackets to the connector body. The ferrule extends past the connector body to slip into the couping device.

Cable: The cable is attached to the connector body. It acts as the point of entry for the fiber. Often, a strain relief boot is added over the junction between the cable and the connector body, providing extra stength to the junction.

Coupling Device: Most fiber optic connectors do not use the male-female configuration common to electronic connectors. Instead, a coupling device such as an alignment sleeve is used to mate the connectors. Similar devices may be installed in fiber optic transmitters and receivers to allow these devices to be mated via a connector. These devices are also known as feed-through bulkhead adapters.

Types of Fiber Optic Connectors

According to the different classification methods, fiber optic connectors can be divided into different types. According to the different transmission media, fiber connectors can be divided into single-mode and multimode fiber optic connectors. According to the different structures, fiber connectors can be divided into various types like ST, SC, FC, LC, MT-RJ, MPO/MTP, MU, DIN, E2000, SMA, BICONIC, D4, etc. According to the pin end surface of the connector, they can be divided into PC, UPC and APC. According to the number of fiber cores, fiber connectors can be divided into single-core and multi-core fiber optic connectors. In all, about 100 fiber optic connectors have been introduced to the marketplace, but only a few represent the majority of the market. Here is a rundown of the connectors that have been the leaders of the industry.

ST Connector: ST is probably still the most popular connector for multimode networks, widely used in the optical distribution frame (ODF), like most buildings and campuses. It has a bayonet mount and a long cylindrical 2.5 mm ceramic (usually) or polymer ferrule to hold the fiber. Most ferrules are ceramic, but some are metal or plastic. ST connectors are constructed with a metal housing and are nickel-plated, can be inserted into and removed from a fiber-optic cable both quickly and easily. They have ceramic ferrules and are rated for 500 mating cycles. From a design perspective, it is recommended to use a loss margin of 0.5 dB or the vendor recommendation for ST connectors.

SC Connector: This is a kind optical fiber connector developed by Japan's NTT. SC is a snap-in connector with a 2.5 mm ferrule that is widely used for it's excellent performance. Its shell is rectangular, adopted by the pin type and the structure of the coupling sleeve size. The end face of the pin is used more PC or APC model grinding method, fastening way is to use the plug pin bolt type, do not need to rotate. SC connector latches with a simple push-pull motion. SC connectors provide for accurate alignment via their ceramic ferrules. Typical matched SC connectors are rated for 1000 mating cycles. SC connector features with low price, involve loss small ripple, high compressive strength and high density installation.

FC Connector: FC connector was originally developed by NTT, Japan. FC is short for FERRULE CONNECTOR. It also uses a 2.5 mm ferrule, its external strengthening way is to use metal sleeve, fastening way as the turnbuckle. FC connectors offer extremely precise positioning of the fiber-optic cable with respect to the transmitter's optical source emitter and the receiver's optical detector. FC connectors feature a position locatable notch and a threaded receptacle. FC connectors are constructed with a metal housing and are nickel-plated. They have ceramic ferrules and are rated for 500 mating cycles. This kind of connector is simple in structure, convenient operation.

LC Connector: LC type connector is a famous BELL developed by the institute of research, using convenient operation modular jack (RJ) latch mechanism is made. The pin and the size of the sleeve is adopted by the general SC, FC, half size is 1.25 mm. It can improve the density of optical fiber connector in the optical fiber distribution frame. Otherwise, it's a standard ceramic ferrule connector, easily terminated with any adhesive. LC connector features with good performance and is highly favored for single mode.

MT-RJ Connector: MT-RJ is a duplex connector used with single-mode and multimode fiber optic cables. It uses pins for alignment and has male and female versions. MT-RJ connectors are constructed with a plastic housing and provide for accurate alignment via their metal guide pins and plastic ferrules. MT-RJ connectors are rated for 1000 mating cycles. The typical insertion loss for matched MT-RJ connectors is 0.25 dB for SMF and 0.35 dB for MMF.

MPO/MTP Connector The MPO Connector is the industry acronym for "Multi-fiber Push On", with push-on insertion release mechanism, provides consistent and repeatable interconnections and available with 4, 8, 12, or 24 fibers. MTP® is a trademark of US Conec for MPO connector. The MTP/MPO is a connector manufactured specifically for a multifiber ribbon cable. The MTP/MPO single-mode connectors have an angled ferrule allowing for minimal back reflection, whereas the multimode connector ferrule is commonly flat. The ribbon cable is flat and appropriately named due to its flat ribbon-like structure, which houses fibers side by side in a jacket.

MU Connector: MU connector looks like a miniature SC with a 1.25 mm ferrule, with a simple push-pull design and compact miniature body. It is used for for compact multiple optical connectors and self-retentive mechanism for backplane applications. The connectors are composed of plastic housing. MU connectors are the optical connectors which miniaturized and were advanced the density application and performance. The table below illustrates some types of above connectors and lists some specifications. Each connector type has strong points.

DIN Connector: DIN is an abbreviation for Deutsches Institut für Normung or German Institute for Standardization, which is a German manufacturing industry standards group. DIN connector encompasses several types of cables that plug into an interface to connect devices. It is round, with pins arranged in a circular pattern. Typically, a full-sized DIN connector has three to 14 pins with a diameter of 13.2 millimeters. This type of connector was used widely for PC keyboards, MIDI instruments, and other specialized equipment.

E2000 Connector: E2000 fiber optic connector has a push-pull coupling mechanism, with an automatic metal shutter in the connector as dust and laser beam protection. One-piece design for easy and quick termination, used for high safety and high power applications. E2000 connector available for Singlemode PC, APC and Multimode PC. The E2000 Connector is one of the few fiber optic connectors featuring a spring-loaded shutter which fully protects the ferrule from dust and scratches. The shutter closes automatically when the connector is disengaged, locking out impurities which could later lead to network failure, and locking in potentially harmful laser beams.

Obsolete Connectors

SMA Connector: Amphenol developed the SMA from the "Subminiature A" hence SMA, microwave connector. The model 905 had a machined ferrule exactly 1/8 inch in diameter that mated in a machined adapter. When the adapters were not precise enough for better fibers, a necked-down ferrule that mated with a Delrin adapter for better insertion loss performance. These connectors are still in use on some military and industrial systems.

BICONIC Connector: This is the Biconic, the yellow body indicating a SM version (MMs were usually black). Developed by a team led by Jack Cook at Bell Labs in Murray Hill, NJ, the Biconic was molded from a glass-filled plastic that was almost as hard as ceramic. It started with the fiber being molded into the ferrule. This lasted until the company could get a 125 micron/5mil pin insert into the plastic mold, at which point the fiber was glued into the ferule with epoxy. When singlemode versions first appeared, the ferrules were ground to center the fiber core in the ferrule to reduce loss. Since it was not keyed and could rotate in the mating adapters, it had an airgap between the ferrules when mated, meaning loss was never less than 0.3 dB due to fresnel reflection. Usually MM Biconics had losses of 0.5-1 dB and SM 0.7 dB or higher.

D4 Connector: D4 connector was probably the first connector to use ceramic or hybrid ceramic/stainless steel ferrules. It's keyed and spring loaded, the ferrule has a 2.0mm diameter ferrule. D4 connectors have a high-performance threading mounting system and a keyed body for repeatability and intermateability.

Color Codes

Since the earliest days of fiber optics, orange, black or gray are multimode and yellow is singlemode. However, the advent of metallic connectors like the FC and ST made color coding difficult, so colored boots were often used. The TIA 568 color code for connector bodies and/or boots is Beige for multimode fiber, Blue for singlemode fiber, and Green for APC (angled) connectors.

With an increase in the amount of cable found in residential, commercial and industrial applications in recent years, there is a greater fuel load in the event of a fire. Wire and cable manufacturers responded by developing materials that had a high resistance to fire while maintaining performance. Low-smoke, zero-halogen compounds proved to be a key materials group that delivered enhanced fire protection performance. Today, LSZH cables are being used in applications beyond the traditional transit, shipboard, military and other confined-space applications. This tutorial is provided to help you learn more about the LSZH fiber optic cables.

What is LSZH Fiber Optic Cable?

LSZH Fiber Optic Cable is a kind of fiber optic cable of which the jacket and insulation material are made of special LSZH materials. When these cables come in contact with a flame very little smoke is produced making this product ideal for applications where many people are confined in a certain place (office buildings, train stations, airports, etc.). While a fire may be very harmful in a building, the smoke can cause more damage to people trying to locate exits and inhalation of smoke or gases.

Fiber optic cable insulation and jacket made from LSZH materials are free of halogenated materials like Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At), which are reported to be capable of being transformed into toxic and corrosive matter during combustion or decompositions in landfills.

The most prominent characteristic of LSZH fiber optic cable is safety. LSZH fiber optic cables are used in public spaces like train and subway stations, airports, hospitals, boats and commercial buildings, where toxic fumes would present a danger in the event of a fire. Similarly, low-smoke property is also helpful. More people in fires die from smoke inhalation than any other cause. Using LSZH fiber optic cables which release low smoke and zero halogenated materials in these places would be really important to the safty of people.

Applications of LSZH Fiber Optic Cables

There is no doubt that the amount of fiber optic cables installed in buildings has been increasing as data communication proliferated. Central office telecommunication facilities were some of the first places that LSZH cables became common due to the large relative fuel load represented by wire and cable.

Public Spaces like train stations, hospitals, school, high buidings and commercial centers where the pretection of people and equipment from toxic and corrosive gases is critical should apply LSZH fiber optic cable for the safty of people.

Data Centers contain large amounts of cables, and are usually enclosed spaces with cooling systems that can potentially disperse combustion byproducts through a large area. In industrial facilities, the relative fuel load of cables will not be at the same level. Other materials burning may also contribute greater amounts of dangerous gases that outweigh the effect of the cables. There have been notable fires where cables burning contributed to corrosion (the Hinsdale Central Office fire is a famous example), but in some instances, better fire response techniques could have prevented this damage.

Nuclear Industry is another area where LSZH cables have been and will be used in the future. Major cable manufacturers have been producing LSZH cables for nuclear facilities since the early 1990s. The expected construction of new nuclear plants in the U.S. in coming years will almost certainly involve some LSZH cable.

One of the most important things to understand about LSZH fiber optic cable is that no two products are the same and that there are many factors that will define the suitability of the final product to its application. In fact, research done by a major pulling lubricant supplier tested 27 LSZH compounds and found a huge variation in physical properties. So even using material that meets the base requirements of one of the many specifications available may not result in the best material for the application. Understanding the goals, results and limits of these tests are key to finding the right product. In any case, the trend to consider environmental concerns with a greater weight relative to performance has increased and it can be generally stated that there is an enlarging market for fiber optic cables that can be demonstrated to be environmentally friendly.

Conclusion

When selecting or designing a fiber optic cable for any application, the operating enviroments where the fiber optic cable will be used, whether extreme or not, must be considered along with availability, performance, and price, among other things. And when the safety of humans and the enviroment is a consideration, along with high-performance and capability, then LSZH fiber optic cables are what you must specify.

Warm Tips: When choosing LSZH fiber optic cables, factors such as the environment and price should be considered. An environmental factor such as the temperature of the installation could reduce the flexibility of the cable. Will the application be in an open area or confined? Will other flammable material be present? LSZH fiber optic cables also tend to be higher in cost. 

International Standards

Two main groups are working on international standards: International Electrotechnical Commission (IEC) and International Telecommunication Union (ITU).

IEC: The IEC is a global organization that prepares and publishes international standards for all electrical, electronic, and related technologies, which serve as a basis for national standardization.

National Standards

In addition to the international standards, countries or union of countries define their own standards in order to customize or fine tune the requirements to the specificity of their country.

European Telecommunications Standards Institute

The European Telecommunications Standards Institute (ETSI) defines telecommunications standards and is responsible for the standardization of Information and Communication Technologies (ICT) within Europe. These technologies include telecommunications, broadcasting, and their related technologies, such as intelligent transportation and medical electronics.

Telecommunication Industries Association / Electronic Industries Alliance

The Telecommunication Industries Association (TIA) provides additional recommendations for the United States. TIA is accredited by the American National Standards Institute (ANSI) to develop industry standards for a wide variety of telecommunications products. The committees and subcommittees define standards for fiber optics, user premises equipment, network equipment, wireless communications, and satellite communications.

NOTE: There are many other standard organizations that exist in other countries.

Fiber Optic Standards

Test and Measurement Standards

Instruction of the Diagram

Related Products

LC Connector

SC Connector & Quick-SC Connector

MU Connector

MPO Connector

Ferrule Polishing Options

Polishing Type	Connection	Feature	Connector
PC (Physical Contact)		Ferrule and faces are polished sphercally so as to ensure fiber-to-fiber contact. This polishing type of ferrule guarantees a return loss of 25dB.	SC, FC, LC and MU etc. attached to multi-mode fiber or single-mode fiber
UPC (Ultra Physical Contact)		An evolution of PC polishing, this method achieves a return loss of 40dB. It is possible to connect with a PC-polished connector. In that case, however, performance is guaranteed according to the level of PC polishing achieved.	SC, FC, LC and MU etc. attached to multi-mode fiber or single-mode fiber
APC (Angled Physical Contact)		APC is polished on an 8° angle. When compared with a normal PC connector, an APC connector exhibits better reflectance properties, because the angled polish reduces the amount of light reflected at the connector interface.	SC, ST, FC, LC and MU etc. only attached to single-mode fiber

The MCP patch cord is required with -LX or  longwave Gigabit Ethernet Transceivers that use both single mode and multimode fibers. When launching into multimode fiber, the transceiver can generate multiple signals that causes Differential Mode Delay (DMD) which can severly limit transmission distances. A mode conditioning cable removes these multiple signals, eliminating problems at the receiver end.

Using mode conditioning patch cable is not difficult, but there are also some notes that we should keep in mind. Here are some frequently-asked questions about mode conditioning patch cable for you.

1. When & Where is Mode Conditioning Patch Cable Needed?

2. How does Mode Conditioning Patch Cable Work?

Answer: Mode conditioning patch cable launches the laser at a precise offset from the center of the multimode fiber. This causes the laser to spread across the diameter of the fiber core, reducing the effect known as Differential Mode Delay (DMD) which occurs when the laser couples onto only a small number of available modes in multimode fiber.

3. Why should Mode Conditioning Patch Cable be ordered in Pairs?

Answer: Mode conditioning patch cables are normally used in pairs. That means that one at each end to connect the equipment to the cable plant. So then these cables are usually ordered in even numbers. The usual reason why someone may order one cable is so they may keep it as a spare.

4. How should Mode Conditioning Patch Cable be Connected?

Answer: If Gigabit 1000BASE-LX switch is equipped with SC or LC connectors, the yellow leg (single mode) of the cable should be connected to the transmit side, and the orange leg (multimode) to the receive side of the equipment.

5. Do all Multimode Fiber Types Require Mode Conditioning?

Answer: Some manufacturers of the newer "high end" multimode fibers claim that that their premium line cables will not require mode conditioning.

6. When holding the yellow Single Mode Cable up to a Light, the Light does not Come Through on the Other Side. Does This Indicate that it is a Defective Cable?

Answer: The core of the single mode cable is so small than it does not gather enough light for it to be visible without a microscope on the other side. This is a normal condition for any single mode cable.

7. Can Mode Conditioning Patch Cable be used to Convert Single Mode to Multimode or Vice Versa?

Answer: No. Conversions of multimode and single mode require Fiber to Fiber Media Converters.

As light passes through a point in space, the direction and amplitude of the vibrating electric field traces out a path in time. A polarized lightwave signal is represented by electric and magnetic field vectors that lie at right angles to one another in a transverse plane (a plane perpendicular to the direction of travel). Polarization is defined in terms of the pattern traced out in the transverse plane by the electric field vector as a function of time.

Polarization can be classified as linear, elliptical or circular, in them the linear polarization is the simplest. Whichever polarization can be a problem in the fiber optic transmission.

More and more telecommunication and fiber optic measuring systems refer to devices that analyse the interference of two optical waves. The information given by the interferences cannot be used unless the combined amplitude is stable in time, which means, that the waves are in the same state of polarization. In those cases it is necessary to use fibers that transmit a stable state of polarization. And polarization-maintaining fiber was developed to this problem. (The polarization-maintaining fiber will be called PM fiber for short in the following contents.)

What Is PM Fiber?

The polarization of light propagating in the fiber gradually changes in an uncontrolled (and wavelength-dependent) way, which also depends on any bending of the fiber and on its temperature. Specialised fibers are required to achieve optical performances, which are affected by the polarization of the light travelling through the fiber. Many systems such as fiber interferometers and sensors, fiber laser and electro-optic modulators, also suffer from Polarization-Dependent Loss (PDL) that can affect system performance. This problem can be fixed by using a specialty fiber so called PM Fiber.

Principle of PM Fiber

Provided that the polarization of light launched into the fiber is aligned with one of the birefringent axes, this polarization state will be preserved even if the fiber is bent. The physical principle behind this can be understood in terms of coherent mode coupling. The propagation constants of the two polarization modes are different due to the strong birefringence, so that the relative phase of such copropagating modes rapidly drifts away. Therefore, any disturbance along the fiber can effectively couple both modes only if it has a significant spatial Fourier component with a wavenumber which matches the difference of the propagation constants of the two polarization modes. If this difference is large enough, the usual disturbances in the fiber are too slowly varying to do effective mode coupling. Therefore, the principle of PM fiber is to make the difference large enough.

In the most common optical fiber telecommunications applications, PM fiber is used to guide light in a linearly polarised state from one place to another. To achieve this result, several conditions must be met. Input light must be highly polarised to avoid launching both slow and fast axis modes, a condition in which the output polarization state is unpredictable.

The electric field of the input light must be accurately aligned with a principal axis (the slow axis by industry convention) of the fiber for the same reason. If the PM fiber path cable consists of segments of fiber joined by fiber optic connectors or splices, rotational alignment of the mating fibers is critical. In addition, connectors must have been installed on the PM fibers in such a way that internal stresses do not cause the electric field to be projected onto the unintended axis of the fiber.

Types of PM Fibers

Circular PM Fibers

It is possible to introduce circular-birefringence in a fiber so that the two orthogonally polarized modes of the fiber—the so called Circular PM fiber—are clockwise and counter-clockwise circularly polarized. The most common way to achieve circular-birefringence in a round (axially symmetrical) fiber is to twist it to produce a difference between the propagation constants of the clockwise and counterclockwise circularly polarized fundamental modes. Thus, these two circular polarization modes are decoupled. Also, it is possible to conceive externally applied stress whose direction varies azimuthally along the fiber length causing circular-birefringence in the fiber. If a fiber is twisted, a torsional stress is introduced and leads to optical-activity in proportion to the twist.

Circular-birefringence can also be obtained by making the core of a fiber follows a helical path inside the cladding. This makes the propagating light, constrained to move along a helical path, experience an optical rotation. The birefringence achieved is only due to geometrical effects. Such fibers can operate as a single mode, and suffer high losses at high order modes.

Circular PM fiber with Helical-core finds applications in sensing electric current through Faraday effect. The fibers have been fabricated from composite rod and tube preforms, where the helix is formed by spinning the preform during the fiber drawing process.

Linear PM Fibers

There are manily two types of linear PM fibers which are single-polarization type and birefringent fiber type. The single-polarization type is characterized by a large transmission loss difference between the two polarizations of the fundamental mode. And the birefringent fiber type is such that the propagation constants between the two polarizations of the fundamental mode are significantly different. Linear polarization may be maintained using various fiber designs which are reviewed next.

Linear PM Fibers With Side Pits and Side Tunnels

Side-pit fibers incorporate two pits of refractive index less than the cladding index, on each side of the central core. This type of fiber has a W-type index profile along the x-axis and a step-index profile along the y-axis. A side-tunnel fiber is a special case of side-pit structure. In these linear PM fibers, a geometrical anisotropy is introduced in the core to obtain a birefringent fibers.

Linear PM Fibers With Stress Applied Parts

An effective method of introducing high birefringence in optical fibers is through introducing an asymmetric stress with two-fold geometrical symmetry in the core of the fiber. The stress changes the refractive index of the core due to photoelastic effect, seen by the modes polarized along the principal axes of the fiber, and results in birefringence. The required stress is obtained by introducing two identical and isolated Stress Applied Parts (SAPs), positioned in the cladding region on opposite sides of the core. Therefore, no spurious mode is propagated through the SAPs, as long as the refractive index of the SAPs is less than or equal to that of the cladding.

The most common shapes used for the SAPs are: bow-tie shape and circular shape. These fibers are respectively referred to as Bow-tie Fiber and PANDA Fiber. The cross sections of these two types of fibers are shown in the figure below. The modal birefringence introduced by these fibers represents both geometrical and stress-induced birefringences. In the case of a circular-core fiber, the geometrical birefringence is negligibly small. It has been shown that placing the SAPs close to the core improves the birefringence of these fibers, but they must be placed sufficiently close to the core so that the fiber loss is not increased especially that SAPs are doped with materials other than silica. The PANDA fiber has been improved further to achieve high modal birefringence, very low-loss and low cross-talk.

PANDA Fiber (left) and Bow-tie Fiber (right). The built-in stress elements made from a different type of glass are shown with a darker gray tone.

Tips: At present the most popular PM fiber in the industry is the circular PANDA fiber. One advantage of PANDA fiber over most other PM fibers is that the fiber core size and numerical aperture is compatible with regular single mode fiber. This ensures minimum losses in devices using both types of fibers.

Linear PM Fibers With Elliptical Structures

The first proposal on practical low-loss single-polarization fiber was experimentally studied for three fiber structures: elliptical core, elliptical clad, and elliptical jacket fibers. Early research on elliptical-core fibers dealt with the computation of the polarization birefringence. In the first stage, propagation characteristics of rectangular dielectric waveguides were used to estimate birefringence of elliptical-core fibers. In the first experiment with PM fiber, a fiber having a dumbbell-shaped core was fabricated. The beat length can be reduced by increasing the core-cladding refractive index difference. However, the index difference cannot be increased too much due to practical limitations. Increasing the index difference increases the transmission loss, and splicing would become difficult because the core radius must be reduced. Typical values of birefringence for the elliptical core fiber are higher than elliptical clad fiber. However, losses were higher in the elliptical core than losses in the elliptical clad fibers.

Linear PM Fibers With Refractive Index Modulation

One way to increase the bandwidth of single-polarization fiber, which separates the cutoff wavelength of the two orthogonal fundamental modes, is by selecting a refractive-index profile which allows only one polarization state to be in cutoff. High birefringence was achieved by introducing an azimuthal modulation of the refractive index of the inner cladding in a three-layer elliptical fiber. A perturbation approach was employed to analyze the three-layer elliptical fiber, assuming a rectangular-core waveguide as the reference structure. Examination of birefringence in three-layer elliptical fibers demonstrated that a proper azimuthal modulation of the inner cladding index can increase the birefringence and extend the wavelength range for single-polarization operation.

A refractive index profile is called Butterfly profile. It is an asymmetric W profile, consisting of a uniform core, surrounded by a cladding in which the profile has a maximum value of ncl and varies both radially and azimuthally, with maximum depression along the x-axis. This profile has two attributes to realize a single-mode single-polarization operation. First, the profile is not symmetric, which makes the propagation constants of the two orthogonal fundamental modes dissimilar, and secondly, the depression within the cladding ensures that each mode has a cutoff wavelength. The butterfly fiber is weakly guiding, thus modal fields and propagation constants can be determined from solutions of the scalar wave equation. The solutions involve trigonometric and Mathieu functions describing the transverse coordinates dependence in the core and cladding of the fiber. These functions are not orthogonal to one another which requires an infinite set of each to describe the modal fields in the different regions and satisfy the boundary conditions. The geometrical birefringence plots generated vs. the normalized frequency V showed that increasing the asymmetry through the depth of the refractive index depression along the x-axis increases the maximum value of the birefringence and the value of V at which this occurs. The peak value of birefringence is a characteristic of noncircular fibers. The modal birefringence can be increased by introducing anisotropy in the fiber which can be described by attributing different refractive-index profiles to the two polarizations of a mode. The geometric birefringence is smaller than the anisptropic birefringence. However, the depression in the cladding of the butterfly profile gives the two polarizations of fundamental mode cutoff wavelengths, which are separated by a wavelength window in which single-polarization single-mode operation is possible.

Applications of PM Fibers

PM fibers are applied in devices where the polarization state cannot be allowed to drift, e.g. as a result of temperature changes. Examples are fiber interferometers and certain fiber lasers. A disadvantage of using such fibers is that usually an exact alignment of the polarization direction is required, which makes production more cumbersome. Also, propagation losses are higher than for standard fiber, and not all kinds of fibers are easily obtained in polarization-preserving form.

PM fibers are used in special applications, such as in fiber optic sensing, interferometry and quantum key distribution. They are also commonly used in telecommunications for the connection between a source laser and a modulator, since the modulator requires polarized light as input. They are rarely used for long-distance transmission, because PM fiber is expensive and has higher attenuation than single mode fiber.

Requirments for Using PM Fibers

Termination: When PM fibers are terminated with fiber connectors, it is very important that the stress rods line up with the connector, usually in line with the connector key.

Splicing: PM fiber also requires a great deal of care when it is spliced. Not only the X, Y and Z alignment have to be perfect when the fiber is melted together, the rotational alignment must also be perfect, so that the stress rods align exactly.

Another requirement is that the launch conditions at the optical fiber end face must be consistent with the direction of the transverse major axis of the fiber cross section.

Traditionally, a fiber optic link requires two fibers for full duplex communications. It is very important to ensure that the equipment on the link are connected properly at each end. However, when the link contains two or more fibers, maintain the correct polarity across a fiber network become more complex, especially when using multi-fiber MPO components for high data rate transmission. Luckily, pre-terminated MPO components adopt humanized design for polarity maintenance and the TIA 568 standard provides three methods for configuring systems to ensure that proper connections are made. This article will introduce polarity in MPO system and 40/100GbE polarization connectivity solutions in details.

Polarity in MPO Components

To maintain the correct polarity in MPO systems, the property of the components of MPO systems should be understood firstly. This part will introduce the basic components that are used in MPO system.

MPO Connector: To understand the polarity in 40/100 GbE transmission, the key of MPO technology—MPO connector should be first introduced. MPO connector usually has 12 fibers. 24 fibers, 36 fibers and 72 fibers are also available. Each MTP connector has a key on one of the flat side added by the body. When the key sits on the bottom, this is called key down. When the key sits on the top, this is referred to as the key up position. In this orientation, each of the fiber holes in the connector is numbered in sequence from left to right and is referred as fiber position, or P1, P2, etc. A white dot is additionally marked on one side of the connector to denote where the position 1 is. (shown in the following picture) The orientation of this key also determines the MTP cable's polarity.

MPO Adapter: MPO (male) connectors are mated to MPO(female) connectors using a MPO adapter. As each MPO connector has a key, there are 2 types of MPO adapters:

MPO Cables: MPO trunk cable with two MPO connectors (male/female) on both side of the cable serves as a permanent link connecting the MPO modules to each other, which is available with 12, 24, 48, 72 fibers.

MPO harness cable, which is terminated with a male/female connector on the MPO side and several duplex LC/SC connectors on the other side, provides a transition from multi-fiber cables to individual fibers or duplex connectors.

MPO Cassette: Modular MPO cassette is enclosed unit that usually contains 12 or 24-fiber factory terminated fan-outs inside. It enables the user to take the fibers brought by a trunk cable and distribute them to a duplex cable with a MPO connector (at the rear) to the more common LC or SC interface (on the front side). The following is a MTP cassette with 6 duplex LC interface and a MTP connector.

Three Cables for Three Polarization Methods

The three methods for proper polarity defined by TIA 568 standard are named as Method A, Method B and Method C. To match these standards, three type of MPO truck cables with different structures named Type A, Type B and Type C are being used for the three different connectivity methods respectively. In this part, the three different cables will be introduced firstly and then the three connectivity methods.

MPO Trunk Cable Type A: Type A cable also known as straight cable, is a straight through cable with a key up MPO connector on one end and a key down MPO connector on the opposite end. This makes the fibers at each end of the cable have the same fiber position. For example, the fiber located at position 1 (P1) of the connector on one side will arrive at P1 at the other connector. The fiber sequence of a 12 fiber MPO Type A cable is showed as the following:

MPO Trunk Cable Type B: Type B cable (reversed cable) uses key up connector on both ends of the cable. This type of array mating results in an inversion, which means the fiber positions are reversed at each end. The fiber at P1 at one end is mated with fiber at P12 at the opposing end. The following picture shows the fiber sequences of a 12 fiber Type B cable.

MPO Trunk Cable Type C: Type C cable (pairs flipped cable) looks like Type A cable with one key up connector and one key down connector on each side. However, in Type C each adjacent pair of fibers at one end are flipped at the other end. For example, the fiber at position 1 on one end is shifted to position 2 at the other end of the cable. The fiber at position 2 at one end is shifted to position 1 at the opposite end etc. The fiber sequence of Type C cable is demonstrated in the following picture.

Three Connectivity Methods

Different polarity methods use different types of MTP trunk cables. However, all the methods should use duplex patch cable to achieve the fiber circuit. The TIA standard also defines two types of duplex fiber patch cables terminated with LC or SC connectors to complete an end-to-end fiber duplex connection: A-to-A type patch cable—a cross version and A-to-B type patch cable—a straight-through version.

The following part illustrates how the components in MPO system are used together to maintain the proper polarization connectivity, which are defined by TIA standards.

Method A: the connectivity Method A is shown in the following picture. A type-A trunk cable connects a MPO module on each side of the link. In Method A, two types of patch cords are used to correct the polarity. The patch cable on the left is standard duplex A-to-B type, while on the right a duplex A-to-A type patch cable is employed.

Method B: in Connectivity Method B, a Type B truck cable is used to connect the two modules on each side of the link. As mentioned, the fiber positions of Type B cable are reversed at each end. Therefore standard A-to-B type duplex patch cables are used on both sided.

Method C: the pair-reversed trunk cable is used in Method C connectivity to connect the MPO modules one each side of the link. Patch cords at both ends are the standard duplex A-to-B type.

Upgrade to 40/100GbE With Correct Polarity

The using of MPO/MTP connectors for 40/100G transmission is achieved with multimode fiber by transmitting multiple parallel 10G transmissions that will then be recombined when received. This method has been standardized. The following is to offer 40G transmission solution and 100G respectively.

40G Transmission Connectivity

The 40G transmission usually uses 12-fiber MPO/MTP connectors. There are eight lanes within twelve total positions being employed for transmitting and receiving signals. Looking at the end face of the MPO/MTP connector with the key on top, the four leftmost positions are used to transmit, the four rightmost positions are used to receive, the four in the center are unused. The following picture shows the optical lane assignments. (Tx stands for Transmit, Rx stands for Receive) This approach would transmit 40G using for parallel 10G lanes in each direction according to 40GBase-SR4.

100G Transmission Connectivity

The 100G transmission over multimode requires a total of 20 fibers, 10 for transmitting and 10 for receiving. There are three options which is introduced as following:

The first method is to use a 24-fiber MPO/MTP connector with the top center 10 positions allocated for receiving and the bottom 10 position allocated for transmitting,as shown in the following figure. This method is recommended by IEEE.

The second option is to use two 12-fiber MPO/MTP connectors side by side. The 10 positions in the center of the connector on the left are used for transmitting and the center 10 positions of the left are used for receiving.

The third way of 100G transmission also uses two 12-fiber MPO/MTP connectors, but it uses the stacked layout as showed in the following figure. The ten center positions of the top connector are used for receiving and the ten center position of the bottom are used for transmitting.

Understand Polarity in 40/100G

Any transmit position should be connected to its own receive position. Here's an analogy to illustrate: Think of ball players. You have pitchers & catchers. For 10G transmission, Pitcher 1 needs to throw to Catcher 1, Pitcher 2 to Catcher 2 and so on. (showed on the left side of the following picture) For 40/100G, any pitcher can throw to any catcher.(showed on the right side of the following picture)

But if you've got two catchers looking at each other as showed in the following picture, there isn't a whole lot happening.

Conclusion

Network designer using MPO/MTP components to satisfy the increasing requirement for higher transmission speed, during which one of the big problems—polarity, can be solved by selecting the right types of MPO cables, MPO connectors, MPO cassette and patch cables. Consider the polarity method to be used and selecting the correct MPO/MTP components to support that methods, the proper solution for 40/100G transmission would be achieved with high density and flexibility and reliability.