Most Popular Articles

• Ethernet Passive Optical Network Tutorial

  Feb 8, 2016 by Articles / 997 Views

  EPON is a PON-based network that carries data traffic encapsulated in Ethernet frames. Unlike other PON technologies which are based on the ATM standard, it uses a standard 8b/10b line coding and operates at standard Ethernet speed. This lets you utilize the economies-of-scale of Ethernet, and provides simple, easy-to-manage connectivity to Ethernet-based, IP equipment, both at the customer premises and at the central office.

  EPON Network Structure

  A typical EPON system is composed of OLT, ONU, and ODN (Figure 1).

  

  Figure 1. EPON Network Structure

  The OLT（Optical Line Terminal）resides in the Central Office (CO) and connects the optical network to the metropolitan-area network or wide-area network, also known as the backbone or long-haul network. OLT is both a switch or router and a multi-service platform which provides EPON-oriented optical interfaces. Besides the network assembling and access functions, OLT could also perform bandwidth assignments, network security and management configurations according to the customers’ different QoS/SLA requirements.

  The ONU（Optical Network Unit）is located either at the end-user location or at the curb and provides optical interfaces which are connected to the OLT and service interfaces at users’ side such as voice, data and video.

  The ODN（Optical Distributed Network）is an optical distribution network and is mainly composed of one or more passive optical splitters which connects the OLT and ONU. Its function is to split downstream signal from one fiber into several fibers and combine optical upstream signals from multiple fibers into one. Optical splitter is a simple device which needs no power and could work in an all-weather environment. The typical splitters have a splitting ratio of 2, 4, 8, 16 or 32 and be connected to each other. The longest distance the ODN could cover is 20 km.

  EPON Downlink and Uplink Technology

  In an EPON the process of transmitting data downstream from the OLT to multiple ONUs is fundamentally different from transmitting data upstream from multiple ONUs to the OLT.

  In the downstream direction, Ethernet frames transmitted by the OLT pass through a 1:N passive splitter and reach each ONU. N is typically between 4 and 64. This behavior is similar to a shared-medium network. Because Ethernet is broadcast by nature, in the downstream direction (from network to user), it fits perfectly with the Ethernet PON architecture: packets are broadcast by the OLT and extracted by their destination ONU based on the media-access control (MAC) address (Figure 2).

  
  Figure 2. Downstream Traffic in EPON

  In the upstream direction, due to the directional properties of a passive optical combiner, data frames from any ONU will only reach the OLT, and not other ONUs. In that sense, in the upstream direction, the behavior of EPON is similar to that of a point-to-point architecture. However, unlike in a true point-to-point network, in EPON data frames from different ONUs transmitted simultaneously still may collide. Thus, in the upstream direction (from users to 13 network) the ONUs need to employ some arbitration mechanism to avoid data collisions and fairly share the fiber-channel capacity (Figure 3).

  
  Figure 3. Upstream Traffic in EPON

  EPON and ADSL Comparison

  The requirement of bandwidth is increasing crazily with the incoming of digital age. Therefore the current high speed copper cable ADSL (Asymmetric Digital Subscriber Line) cannot meet our needs longer. The bandwidth of ADSL is limited to only a few megabit per second and the upstream and downstream bandwidth are not equal either. However, optical fiber has larger bandwidth and superior transmission capability which reaches gigabit per second. Hence, optical fiber used in access network is the future trend. And since Ethernet is low cost, uncomplicated widely-used in current network, and its application is very popular nowadays. So it is not hard to see that it is feasible and economical to combine them together. EPON technology combines a mature Ethernet technology and high-bandwidth PON technology, which is an ideal access method to achieve integrated services. In the future, highbandwidth business will surely drive up existing EPON which has the rate of 1.25Gbps in both the downstream and upstream directions.

  EPON Technical Advantages

  EPONs are simpler, more efficient, and less expensive than alternate multiservice access solutions. Key advantages of EPONs include the following:

  Higher bandwidth: up to 1.25 Gbps symmetric Ethernet bandwidthLower costs: lower up-front capital equipment and ongoing operational costsMore revenue: broad range of flexible service offerings means higher revenues

   

  With the growing of EPON technology, interaction standards and EPON devices, EPON has entered the large scale application phase driven by the huge market demands. EPON is fit for the access market which is at the end of the fibers and which has a certain density and these markets include FTTH, FTTP, FTTB, FTTN etc.

  EPON becomes a very economical and effective broadband access solution because of its predominance in equipment investment and also the operations, maintenance and etc. It could be said that the EPON technology has become the developing direction of access network’s technologies in the future as an ideal solution for FTTH.

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• MPO/MTP Solutions for High Density Applications

  Feb 6, 2016 by Articles / 994 Views

  As the bandwidth demands grow rapidly, data centers have to achieve ultra-high density in cabling to accommodate all connections. MPO/MTP technology with multi-fiber connectors offers ideal conditions for high-performance data networks in data centers. This article will introduce information about MPO/MTP solutions, such as MPO/MTP trunk cable, MPO/MTP harness cable and MPO/MTP cassettes.

  MTP/MPO Trunk Cable

  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

  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

  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.

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• Compact Optical Splitter Module for PON Architecture FTTH Deployment

  Feb 8, 2016 by Articles / 967 Views

   

  Passive Optical Network (PON) system has expanded extensively as an optical network in the construction of Fiber To The Home (FTTH) economically. To allow multiple users to share an optical fiber in a PON, the Optical Splitter that branches an optical signal is indispensable. Recently, plug-and-play structures that make use of modules and connectors are desired to simplify the installation construction of optical splitters. Moreover, because the splitter module is installed in the outside plant, high reliability that can endure harsh environmental conditions is a critical requirement. In addition, compactness and cost savings are also important considerations. Therefore, we have developed it by economically using a superior flame-retardant plasticresin for the module case. We have confirmed that the optical splitter modules have excellent optical characteristics and sufficient reliability.

  
  

  1. Introduction of Optical Splitter Modules

  PON system has expanded extensively as an optical network in the construction of FTTH economically. As shown in Fig. 1, PON architecture allows a signal transmitted over a single optical fiber from the telephone exchange office to be shared with multiple users, hence achieving cost reduction per subscriber. Planar Lightwave Circuit (PLC) splitter, an optical splitter is a key to realize the branching of optical signal in the telecommunication network, and currently has a maximum of 32 split ratio capability.

  

  Installation of optical splitter is simplified with the application of latch-on or snap method that can expedite the process with quick plug-in action. This plug-and-play method is commonly applied at the interconnection points in the FTTH network (This method enables field installation of optical components without any special tools or skills in managing bare optical fibers). To effectively deploy with such simple techniques and modular designs, connectorized components are essential to be integrated in the structure design of optical splitters. In addition, flexibility of network is achieved with the application of module terminated with connector cord, which allows easy reconfiguration of the network. Furthermore, in the FTTH PON architecture, the function of Fiber Distribution Hub (FDH) is to house optical splitter outdoor, therefore the FDH is critical in ensuring high reliability against environmental factors. Due to the space constraint in the FDH, down-sizing of optical splitter module design is done. The pervasive FTTH deployment worldwide has been called for an imminent need to develop low-cost solutions. The newly developed small sized and lightweight optical splitter is made from retardant plastic resin with sturdiness comparable to the conventional metal packaging in withstanding outdoor environmental conditions, but at a fraction of its original cost. This article illustrates the development of 1×16, 1×32 and 2×32 Wavelength Division Multiplexing (WDM) optical splitter module. The characteristics and reliability evaluation will also be discussed in this article.

  2. Structure of Optical Splitter Modules

  2.1. PLC-Type Splitter

  As shown in Fig. 2, the optical fiber is being branched to 32 outputs through a 1×32 PLC-type optical splitter. PLC chip is a silica glass embedded with optical wave circuit. The circuit pattern is designed to branch a single input into multiple output channels. Optical fiber is adhered to PLC chip with resin curedby ultraviolet exposure; this interface conforms to Telcordia GR-1209 and GR-1221 test conditions, hence good reliability is ensured. Furthermore, inorder to actualize the size reduction, bend insensitive Single Mode Fiber (SMF) has been introduced into this module.

  

  2.2. Flame Retardant Plastic Package

  The structure of optical splitter module developed is shown in Fig. 3. Bend insensitive fiber with bending radius of 15 mm is applied to the optical splitter module to achieve a considerable size reduction of the packed module. The overall dimension of L118mm×D87 mm×H13 mm is 3/5 of the size of the conventional optical module utilizing SMF of bending radius 30 mm. In addition, as a flame retardant plastic resin has replaced metallic materialin the splitter packaging, the weight decreases to 1/3 of the conventional metallic packaging version.

  

  Figure 4 illustrates the internal configuration of the optical splitter module. The splitter module is terminated with optical connector pigtails. The 2 mm fiber cords are fixed onto the cable retainer with adhesive.This structure is designed to withstand tensile strength of maximum 68.6 N. Moreover, as the optical cord has a similar structure to the loose tube cables, allowing the optical fiber free movement within the cord effects the expansion and contraction of the optical cord that will not exert any external tension onto the fiber.

  

  The structure of strain relief boot is shown in Fig.5. The boot is designed to control the bending radius to a minimum of optical fiber limit, i.e., 15 mm. This prevents an increase in attenuation brought upon by fiber bend. The flexible boot developed has taken factors like hardness, thickness and the quantity of cord per boot into the design considerations to control the bending radius to a minimum of 15 mm when a loadis applied at 90° bend to the optical cord perpendicularly.

  

  3. OPTICAL PERFORMANCE AND CHARACTERISTIC

  3.1. Functionality of FDH

  Figure 6 captures the appearance of FDH system in configuration with optical splitter module load. The hub, optical connector, and optical adapters are all mounted onto a panel to enable ease of operation with a latch mechanism. The pigtail is elegantly managed in a U-shape through the mandrel. This plug-and-play method makes installation extremely simple and efficient.

  

  3.2. Fundamental Optical Characteristics

  The 1×16 and 1×32 splitter modules were fabricated to be mountable onto the above described fiber distribution hub. The vacant port (a port which is not in service) present in the FDH will result in back reflections of the optical signal. To prevent return loss from the end face of vacant port, SC connector is polished to an Angled Physical Contact (APC) interface. Data below tabulates the optical characteristics of the optical splitter module, inclusive of the connector pigtails.

  The histograms shown in Figs. 7 and 8 illustratethe insertion loss performance of 1×16 and 1×32 optical splitter module respectively. At operating wavelength 1310 nm, the average insertion loss of 1×16 splitter stands at 13.23 dB while that of 1×32 splitter is 16.33 dB. Similarly, at 1550 nm operation wavelength, the insertion loss of 1×16 and 1×32 splitter module is 13.10 dB and 16.22 dB respectively. In addition, the standard deviation of 1×16 splitter is 0.29 dB while 1×32 splitter yields a standard deviation of 0.34dB. At the same time, this value decreases to 0.23 dB for 1×16 splitter and 0.28 dB for the 1×32 splitter at wavelength 1550 nm.

  

  The performances of other optical characteristics apart from insertion loss are shown in Table 1. These results show consistent good performances, as exhibited in the insertion loss histogram, in characteristics including uniformity, return loss and PDL values.

  

  3.3. Temperature dependent loss

  History from past experimental results has shown that components terminated with optical pigtail cord are susceptible to insertion loss fluctuation with temperature change. To isolate the effects of cordage expansion/contraction on the optical fiber within, the optical cord is designed to allow free movement of optical fiber, thus eliminating the external stress fromthe expansion/contraction of the cord. Figure 9 depicts the insertion loss variation of the 1×32 optical splitter module during temperature cycling from −40 °C to +85 °C. The average, minimum, and maximum values obtained from the 32 output ports are illustrated in the graph shown in Fig. 9. From the graph, the maximum loss deviation between the ports with maximum and minimum insertion loss is 0.17 dB. This result has an evident exceptional stability of the optical splitter module that is developed.

  

  3.4. Wavelength dependent loss

  The wavelength dependent loss of the 1×32 optical splitter module is shown in Fig. 10. The performances of insertion losses over wavelengths from 1260 nm to 1680 nm are measured. Again, the average loss from 32 ports and minimum and maximum wavelength dependent losses are illustrated in the graph. The average deviation is 0.36 dB while the maximum deviation from all the 32 ports is 0.86 dB.

  

  This proves that the splitter module has shown resilience in insertion loss variation over a broad spectrum of wavelength.

  A variety of optical devices are stored in this optical splitter module, making it multifunctional. An example is the 2×32 WDM optical splitter module shown in Fig. 11 and the structure of its cable retainer in Fig.12. A WDM filter was built in front of a 1×32 splitter module, enabling the structure to have multiple wavelengths.

  

  Figure 13 shows the wavelength dependent loss of the 2×32 WDM optical splitter module. With the WDM filter, the wavelength ranging from 1530nm to1570nm are transmitted from the B port, and the other wavelength ranges are transmitted from the A port. The wavelength dependent loss of A port and B port are split evenly among the 32 fibers, hence excellent loss performance is obtained in each port.

  

  4. Reliability of Optical Splitter Modules

  The reliability of 1×32 splitter module is evaluated in accordance to test procedures stipulated in the Telcordia GR-1209 and GR-1221. The test conditions and the results of the 1×32 splitter module measured at 1550 nm are shown in Table 2. The average, maximum, and minimum values of 32 output ports measured are recorded in Table 2. The results of side pulltest and cable retention test are maximum in-situ datamonitored during load application onto the cable cord. On the other hand, the recorded data of damp heat, temperature cycling, mechanical shock, vibration, and water immersion shows the variation of insertion loss before and after the test conditions. From the results, it is confirmed about the reliability of 1×32 splitter module.

  

  The results of high temperature and humidity test are depicted in Fig. 14. The optical splitter samples underwent a total of 2000 hours of storage at 85 °C and of 85% relative humidity. Insertion loss data at 100 hrs, 168 hrs, 500 hrs, 1000 hrs, and 2000 hrs juncture were measured. The average insertion loss of the 32 ports, maximum and minimum insertion loss measured at 1550 nm are displayed in the graph. From the graph in Fig. 14, it is concluded that there is very minimal loss variation even after 2000 hrs. The optical splitter module has shown good stability when exposed to high temperature and humidity conditions.

  

  Furthermore, to meet the flame retardant requirements for optical components and accessories, we have applied frame retardant plastic material of 1.5 mm thickness complying to UL-94 V-0. On the same note, the jacket of optical fiber cord is made of grade V-0 flame retardant PVC.

  5. Conclusion

  A compact and economical optical splitter that boasts of superior optical performance and reliability against stringent environmental conditions suited for outdoor installation has been successfully developed. This plug-and-play design for installation of the above optical splitter has enabled simple and speedy installation, at the same time provided added flexibility for future network reconfigurations, thus making this optical splitter module the perfect solution for PON architecture FTTH deployment.

   

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• Optics and Cables Selection for Storage Area Network (SAN)

  Feb 7, 2016 by Articles / 942 Views

  Optics and cables are the most important infrastructures of network connectivity. In a storage area network (SAN), switches are used between servers and storage devices. This means that you should make connection with optics and cables between the server and switch, storage and switch as well as the switch and switch. Of course, according to different application environments, you should choose different optics and cables in order to get the best performance. Furthermore, you may need to consider the future expansion of your network. Thus, an economical and effective solution of optics and cables are very necessary.

  Key Factors Influencing Your Decision

  Firstly, there are some key factors which will influence your decision. Thus, you must make sure that what your network really requires. As we mentioned above, an SAN has server, storage device and switches. So, what should we consider in every section of the network?

  1. Server
  Bandwidth: Depending on the application load requirements, customers typically decide whether they want 1GbE, 10GbE, or 40GbE. In some cases, the decision may also be dictated by the type of traffic, e.g. DCB (Data center bridging) requires 10GbE or higher.Cost: Servers claim the highest share of devices deployed in any data center. Choosing a lower cost connectivity option results in a much lower initial deployment cost.Power: In any high density server deployment, a connectivity option which consumes lower power results in much lower OpEx.Distance: Servers are typically connected to a switch over a very short distance, i.e. typically within the same rack or, in some cases, within the same row.Cabling Flexibility: Some customer prefer to make their own copper cables due to variable distance requirement. This requirement limits the choice of connectivity to copper cables only.

   

  2. Storage
  Reliability: Typical storage traffic is very sensitive to loss. Even a minor loss of traffic may result in major impact on application performance.Qualification: Storage vendor qualification or recommendation plays an important role in this decision due to reasons such as customer support, peace of mind, etc.Latency: Any time spent in transition is time taken away from data processing. Reducing transition time results in much faster application performance. The result may have a direct impact on customers' bottom line, e.g. faster processing of online orders.

   

  3. Switch
  Bandwidth: On server facing ports, servers typically dictate the per port bandwidth requirement. However, per port bandwidth requirement for the network facing (switch-to-switch) ports denpends on multiple factors including amount of traffic generated by the servers, oversubscription ratios, fiber limitations, ect.Distance: An inter-switch or switch to router connection could range from a few inches to tens of kilometers. Generally, the price of optics increases as the distance increases.Latency: The network topology and application traffic profile (East-west, HPC (High Performance Computing), computer cluster, etc.) and influence the minimun latency that can be tolerated in the network.

   

  • Server to Switch Connectivity Solution

  

  • Storage to Switch Connectivity Solution

   

   

  • Switch to Switch Connectivity Solution

   

  

   COMPUFOX Solutions

  COMPUFOX  offers a comprehensive solution of optics and cables which supports your network from 1GbE to 100GbE. We have a great selection of 1000BASE-T/SX/LX SFP, BiDi SFP, 10GBASE-SR/LR SFP+, DWDM SFP+, whole series 40G QSFP+ optics and cables, as well as the 100G CFP2 and CFP4, etc. which help you solve the cost issue in fiber project. Especially the 40G QSFP+ optics, with the passive optic design, they can be compatible with all the equipment of all major brands. In addition, most of them are ready stock. See Links below:

  • CFP
  • CWDM
  • DWDM
  • GBIC
  • QSFP+
  • SFP+
  • SFP
  • X2
  • XENPAK
  • XFP
  • QSFP+ Cables
  • QSFP+ to 4 SFP+ Cables
  • QSFP+ to 4 XFP Cables
  • QSFP+ to 4 LC Cables
  • QSFP+ to CX4 Cables
  • SFP Cables
  • SFP+ Cables
  • SFP+ to XFP Cables

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• Polarity and MPO Technology in 40/100GbE Transmission

  Feb 5, 2016 by Articles / 938 Views

  It have been proved that reducing cable diameters and increasing connection densities offered by fiber links would be extremely valuable during installation in constrained space, like data center, large enterprise equipment rooms, central office, etc. With the market turning to 40/100G transmission, to reduce congestion during cabling and make it easier to organize equipment cable runs, the network designers turns to MPO/MTP technology and components for today's duplex fiber transmission. Then, network designers face another challenge which is how to assure the proper polarity of these array connections using MPO/MTP components from end-to-end.

  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:

  Type A—key-up to key-down. Here the key is up on one side and down on the other. The two connectors are connected turned 180° in relation to each other.Type B—key-up to key-up. Here both keys are up. The two connectors are connected while in the same position in relation to each other.

   

  

   

  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.

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