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  • OTDR (Optical Time Domain Reflectometer) Dead Zone Tutorial

     

    OTDR (Optical Time Domain Reflectometer) is a familiar fiber test instrument for technicians or installers to characterize an optical fiber. To understand the specifications which may affect the performance of OTDR can help users get maximum performance from their OTDRs. This tutorial will introduce one of the key specifications—Dead Zone.

    What Is a Dead Zone?

    The OTDR dead zone refers to the distance (or time) where the OTDR cannot detect or precisely localize any event or artifact on the fiber link. It is always prominent at the very beginning of a trace or at any other high reflectance event.

    OTDR_Trace
    Why makes a Dead Zone occur?

    OTDR dead zone is caused by a Fresnel reflection (mainly caused by air gap at OTDR connection) and the subsequent recovery time of the OTDR detector. When a strong reflection occurs, the power received by the photodiode can be more than 4,000 times higher than the backscattered power, which causes detector inside of OTDR to become saturated with reflected light. Thus, it needs time to recover from its saturated condition. During the recovering time, it can not detect the backscattered signal accurately which results in corresponding dead zone on OTDR trace. This is like when your eyes need to recover from looking at the bright sun or the flash of a camera. In general, the higher the reflectance, the longer the dead zone is. Additionally, dead zone is also influenced by the pulse width. A longer pulse width can increase the dynamic range which results in a longer dead zone.

    OTDR connection
    Event Dead Zones & Attenuation Dead Zone

    In general, dead zones on an OTDR trace can be divided into event dead zone and attenuation dead zone.

    OTDR_dead_zone
    Event Dead Zone

    The event dead zone is the minimum distance between the beginning of one reflective event and the point where a consecutive reflective event can be detected. According to the Telcordia definition, event dead zone is the location where the falling edge of the first reflection is 1.5 dB down from the top of the first reflection.

    EDZ
    Attenuation Dead Zone

    The attenuation dead zone is the minimum distance after which a consecutive non-reflective event can be detected and measured. According to the Telcordia definition, it is the location where the signal is within 0.5 dB above or below the backscatter line that follows the first pulse. Thus, the attenuation dead zone specification is always larger than the event dead zone specification.

    ADZ

    Note: In general, to avoid problems caused by the dead zone, a launch cable of sufficient length is always used when testing cables which allows the OTDR trace to settle down after the test pulse is sent into the fiber so that users can analyze the beginning of the cable they are testing.

    The Importance of Dead Zones

    OTDR_testThere is always at least one dead zone in every fiber—where it is connected to the OTDR. The existence of dead zones is an important drawback for OTDR, specially in short-haul applications with a large number of fiber optic components. Thus, it is important to minimize the effects of dead zones wherever possible.

    As mentioned above, dead zones can be reduced by using a lower pulse width, but it will decrease the dynamic range. Thus, it is important to select the right pulse width for the link under test when characterizing a network or a fiber. In general, short pulse width, short dead zone and low power are used for premises fiber testing and troubleshooting to test short links where events are closely spaced, while a long pulse width, long dead zone and high power are used for long-haul fiber testing and communication to reach further distances for longer networks or high-loss networks.

    The shortest-possible event dead zone allows the OTDR to detect closely spaced events in the link. For instance, testing fibers in premises networks (particularly in data centers) requires an OTDR with short event dead zones since the patch cords of the fiber link are often very short. If the dead zones are too long, some connectors may be missed and will not be identified by the technicians, which makes it harder to locate a potential problem.

    Short attenuation dead zones enable the OTDR not only to detect a consecutive event but also to return the loss of closely spaced events. For instance, the loss of a short patch cord within a network can now be known, which helps technicians to have a clear picture of what is actually inside the link.

    Summary

    OTDR is one of the most versatile and widely used fiber optic test equipment which offers users a quick, accurate way to measure insertion loss and shows the overview of the whole system you test. Dead zone, with two general types, is an important specification of OTDR. It is necessary for users to understand dead zone and select the right configuration in order to get maximum OTDR performance during test. In addition, OTDRs of different brands are designed with different minimum dead zone parameters since manufacturers use different testing conditions to measure the dead zones. Users should choose the suitable one according to the requirements and pay particular attention to the pulse width and the reflection value.

     

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  • Fiber Media Converter Tutorial

    Fiber media converter is a cost-effective solution to overcome the bandwidth and distance limitations of traditional network cable. It dramatically increases the bandwidth and transmission distance of the local area network (LAN) by allowing the use of fiber and integrating new equipment into existing cabling infrastructure. To better understand it, this article will give an overview of fiber media converter.

    What is Fiber Media Converter?

    Fiber media converter is a transfer media that connects two dissimilar media types. Generally, it is a device that converts electrical signal used in copper unshielded twisted paired (UTP) network cabling into light waves used in fiber optic cabling, and vice versa. This kind of fiber media converter is called copper-to-fiber media converter that provides a simple way to introduce fiber into a LAN without tearing out the existing copper wiring or making changes to copper-based switches. Furthermore, there is another kind of fiber media converter that supports fiber-to-fiber conversion, which provides connections between dual-fiber and single-fiber or between multimode fiber and single-mode fiber. Fiber-to-fiber media converters also provide a cost-effective solution for wavelength conversion in Wavelength Division Multiplexing (WDM) applications, which are also known as transponders.

    Types of Fiber Media Converters

    There are a wide variety of fiber media converters available in the market. According to different criteria, fiber media converters may be classified into different types.

    Managed VS Unmanaged

    The managed fiber media converter has the functions of networking monitoring, fault detection and remote management. It helps the network administrator to easily monitor and manage the network. An unmanaged fiber media converter, however, allows for simple communication with other devices and does not have the monitoring and management functions that managed fiber media converter has.

    Platform: Stand-Alone VS Modular Chassis-Based

    According to the platform type, fiber media converters can be divided into stand-alone fiber media converter and modular chassis-based fiber media converter. Stand-alone fiber media converters are designed to be used in where a single or limited number of converter(s) need(s) to be quickly implemented. Modular chassis-based fiber media converters, however, are used in high-density applications that multiple points of copper and/or fiber integration are essential.

    Copper-to-Fiber Media Converter VS Fiber-to-Fiber Media Converter

    According to media types, fiber media converters may be classified into copper-to-fiber media converter and fiber-to-fiber media converter.

    Copper-to-Fiber Media Converter

    Copper-to-fiber media converters are the key to integrating fiber into a copper infrastructure. According to different applications, copper-to-fiber media converters may be further divided into Ethernet copper-to-fiber media converters, video-to-fiber media converters and serial-to-fiber media converters.

    Fs copper-to-fiber-media-converter.jpg

    Ethernet Copper-to-Fiber Media Converter

    This kind of fiber media converter supports the IEEE 802.3 standard and provides connectivity for Ethernet, fast Ethernet, Gigabit and 10 Gigabit Ethernet devices. SC to RJ45 media converters, SFP to RJ45 media converters, PoE media converters, mini media converters and industrial media converters are all among this type.

    Fs ethernet-copper-to-fiber-media-converter.jpg

    The SC to RJ45 media converter comes with RJ45 and SC ports, which is designed to be used with fiber cable preterminated with the SC-type connector.The SFP to RJ45 media converter comes with RJ45 and pluggable fiber optics ports, which allows for flexible network configurations using SFP transceivers. PoE media converters can transparently connect copper to fiber while providing Power-over-Ethernet (PoE) to standards-based PoE compliant devices such as IP cameras, VoIP phones and wireless access points. Mini media converter is a miniature-sized copper-to-fiber converter. It is ideal for bringing fiber to the desktop and for mobile applications where light weight, compact size and low power are required.Industrial media converters are compact and robust devices designed to convert Gigabit Ethernet or Fast Ethernet networks into Gigabit or Ethernet fiber optic networks.

     

    Video Copper-to-Fiber Media Converter

    Video copper-to-fiber media converter also called fiber optic multiplexer, which is used to transmit and receive signals such as video, audio, data and Ethernet. fiber optic multiplexers are devices that process two or more light signals through a single optical fiber (as shown in the following figure), increasing the amount of information that can be carried through a network. Since signals may be analog or digital, video copper-to-fiber can be further divided into converters transmitting analog signals and converters transmitting digital signals. As the name applies, converters transmitting analog signals give amplitude or frequency modulation of the electric signal and then convert it into optical signal. Demodulation will also be done at the receiving end. Converters transmitting digital signals, however, digitize and multiplex the video, audio and data signals, transforming multiple low-speed digital signals into one high-speed signal. This high speed signal will then be turned into optical signal transmitting on a fiber.

    Fs vedio-copper-to-fiber-media-converter.png

    In accordance with different applications, there are three commonly used video copper-to-fiber media converters: plesiochronous digital hierarchy (PDH) multiplexers, synchronous digital hierarchy (SDH) multiplexers and synchronous plesiochronous sigital hierarchy (SPDH) multiplexers. Using the PDH fiber transmission technologies, PDH multiplexers are E1 point-to-point optical transport equipment. And the general transmission capacity of this kind of multiplexer is 4E1,8E1 and 16E1. SDH multiplexers, having a large transmission capacity, are designed to support end-to-end provisioning and management of services across all segments of the optical network. SPDH multiplexers adopt both PDH and SDH technologies. It is a PDH transmission system that based on the PDH code speed adjustment principle at the same time, use as far as possible parts of the SDH network technology.

    Serial-to-Fiber Media Converter

    This kind of media converter provides fiber extension for serial protocol copper connections. It accepts serial data on one port in RS232, RS485 or other format and convert the serial data stream into a fiber optic signal to a matching unit at the other end of the fiber span.

    Fs serial-to-fiber-media-converter.jpg

    Fiber-to-Fiber Media Converter

    Fiber-to-fiber media converters are used to extend network distance by providing connectivity between multimode and single-mode fiber, between different “power” fiber sources and between dual fiber and single-fiber. Furthermore, they also support conversion from one wavelength to another. Mode converter and WDM OEO transponder are two common types of fiber-to-fiber media converters.

    Mode Converter

    A mode converter can be used to allow for an adiabatic transition between two optical modes. Other than cross-connecting different fiber types, mode converters can also re-generate optical signals, extending transmission distance and double fiber cable usage. It is usually applied in multi-mode to single-mode fiber conversion.

    Fs mode-converter.jpg

    WDM OEO Transponder

    When a fiber media converter is used in the WDM system, it is called WDM OEO transponder which converts the incoming signal from the end or client device to a WDM wavelength. WDM OEO transponders are often used for dual fiber to single fiber conversion and wavelength conversion.

    Networks may require conversion between dual and single-fiber, depending in the type of equipment and the fiber installed in the facility. The following figures shows the role of WDM transponder played in the fiber optic network.

    Fs wdm-oeo-transponder-dual-fiber-to-single-fiber-conversion.jpg

    WDM OEO transponders are capable of wavelength conversion by using small form-factor pluggable (SFP) transceivers that transmit different wavelengths, provide a cost-effective solution to convert from standard optical wavelengths (850nm, 1310nm and 1550nm) of legacy equipment to optical wavelengths specified for WDM networks.

    Fs wdm-oeo-transponder-wavelength-conversion.jpg

    Selection Guide of Fiber Media Converters

    A proper fiber media converter may provide a cost-effective solution for extending Ethernet transmission while reducing cable and labor cost. When selecting fiber media converters for your network, the following points should be taken into consideration:

    The chip of the fiber media converter shall work in both full-duplex and half-duplex systems. The reason is that some N-Way Switches and HUBs may use half-duplex mode operations, and serious collision and data loss may be caused if the fiber media converter only supports full-duplex operation. Connection test should be done between the fiber media converter and different optical fiber splices. Otherwise, data loss and unstable transmission may happen on account of incompatibility between different fiber media converters.To ensure the proper operation of the fiber media converter, temperature measurement is also necessary. This is because the fiber media converter may not work correctly in high-temperature environment. Thus, it is important to know exactly its working temperature.Safety device guarding against data loss shall be equipped in the fiber media converter.The fiber media converter shall meet the IEEE802.3 standards. If not, there must be a risk of incompatibility.
     
    For a selection of Compufox fiber media converters, please click on the link below:
     
     
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  • Fiber Optic Patch Panels Tutorial

    What Is Fiber Optic Patch Panel?

    Fiber optic patch panel, or fiber optic patch bay, is a common cable management facilities. It includes a series of connection points of electronic equipment and the mainly connections are fiber optic patch cables. The patch panel allows circuits to be easily arranged and rearranged by simply plugging and unplugging the path cables, or changing the circuit of select signals without the use of expensive dedicated switching equipment. It can be an opened box used to protect the bare fiber and the optical fiber cables, meanwhile it protects spaces for fusion splicing and components connections by fiber adapters. During the unused condition, all fiber optic connectors, fiber patch cables and adapters should be kept away from dust. Fiber optic patch panels help with the installation density of the fiber optic cabling and provide more convenient organization and management.

    A typical fiber optic patch panel has some jacket on the front side to receive short patch cables while on the back of the panel. There are either jacks or punch down blocks that receive the connections of longer and more permanent cables. The patch panels are often used to connect several computers by linking them via the panel, which enables the LAN to connect to the Internet or another WAN.

    Types of Fiber Optic Patch Panels

    According to the installation ways, there are mainly two types of fiber optic patch panels: wall-mounted patch panels and rack-mounted patch panels.

    Wall-Mounted Fiber Optic Patch Panel
    Wall-mounted fiber optic patch panels basically keep 12 different fibers separated from one another. If the amount of the fiber is more than 12, the extra fibers can be moved to a second panel or an engineer can use a panel that is designed to hold more fibers separately. The wall-mounted patch panels can be constructed to hold up to 144 fibers at once.

    Wall-mounted fiber optic patch panels use the inside fiber optic adapters panels, patch cables and pigtails to realize the function of optical fiber distribution. They are used for protective connections for the fiber cables and pigtails in fiber optic cabling and user terminal applications. The patch panels are installed on the indoor wall and terrace to provide a flexible fiber management system for transitional outside plant cable to inside cable and connector assemblies.

    wall mounted fiber optic patch panel

     

    Rack-Mounted Fiber Optic Patch Panel
    Rack-mounted fiber optic patch panels hold the fibers horizontally and are often designed to open like a drawer. The sliding-opened structure offers engineers an easy access to the optical fibers inside. The rack-mounted patch panels are optional with different kinds of fiber optic adapter ports and pre-installed inner trays and accessories. And fiber optic pigtails of different types are optional, such as SC, FC, ST, LC, E2000 etc. Also, rack-mounted patch panels can be customized by the quantity of optical fibers.

    Rack-mounted fiber patch panels are used to terminated and distributed optical fiber cables. They are convenient to organize and connect the fiber optic links. These patch panels are applied to many fiber optic products, such as DWDM MUX DEMUX, Rack Chassis Splitter, Optical Distribution Frame(ODF) etc. They are fully stable with no risk of movement and offer secure environment for fiber optic adapters, patch cables and pigtails.

    Rack-Mounted Fiber Optic Patch Panel

     

    According to different applications, fiber optic patch panels can be classified as following:

    Loaded Fiber Optic Patch Panel
    Loaded fiber optic patch panels are usually designed for fitting on a standard 19" rack and can provide the best protection for fiber optic applications. There are rubber grommets on the back of loaded fiber optic patch panels to protect the fiber cables from damage. Each loaded patch panel has fiber splice trays and cable routing spools. What's more, it includes zip ties, cable routing clamps and mounting screws, fiber splice sleeves and installation instructions. There is a special black textured which can be installed a sleek look in the server rack of these loaded fiber patch panels.

    Loaded Fiber Patch Panel

     

    Swing-Out Fiber Optic Patch Panel
    Swing-out fiber optic patch panels are lightweight and robust patch panels. They are designed for the installation of up to 48 standard optical fibers. These patch panels offer an economic alternative to metal fiber enclosures. The lower tray is designed to gain access to preformed fiber and splice management areas, at the same time, make it easy for installation and dressing of fiber optic cables. All common adapter panel/plate types, includes LC, SC, and ST can be changed with the front plates that can accommodate 6 or 12 duplex, or 12 simplex adapters each.

    Swing-Out Patch Panel

     

    Fixed Fiber Optic Patch Panel
    Fixed fiber optic patch panels are 19" rack-mountable for connecting up to 24 optical fibers. They are suitable for use with manufactured pigtails or field installation connectors. The installation size is adapted by using appropriate mounting brackets, while the chassis will not be changed. Fixed patch panels are easy to use and more artistic while they can also keep rugged design. These patch panels are easier to terminate, providing greater capacity and easier fiber cable managements. Generally, fixed rack-mounted patch panels do not slide out, but we do offer sliding patch panels for even quicker access to the fiber terminations.

    Fixed Fiber Optic Patch Panel

     

    Slide-Out Fiber Optic Patch Panel
    Slide out fiber optic patch panels fit with standard 19" or 23" racks and are designed to support both patching and splicing in one unit. Each slide-out patch panel has a slide-out master panel with an integrated tray stop to prevent over extension of fiber cables. The slide-out patch panel also has a two-piece top and swell latch door to allow for easy access to the adapter panels.

    Slide-Out Patch Panel

     

    High-Density Fiber Optic Patch Panel
    High-density fiber optic patch panels have been engineered to be able to significantly increase density for both patching and splicing. High-density patch panels maximize the amount of adapter panels per rack unit of height, so by utilizing LC quad style adapters you can effectively terminate up to 96 fibers per rack unit of space. There are several other features that make a high density fiber patch panel in an exceptionally nice product to work with. The sliding tray has locking positions to prevent over-extending the fibers. High-density patch panels also have a split top design which allows for easier cable management, and improved strain relief for the cable ingress.

    High Density Fiber Patch Panel

     

    Fiber Optic Patch and Splice Combos Patch Panel
    Fiber optic patch and splice combos patch panels fit with standard 19" or 23" racks and are designed to support both patching and splicing in one unit. Fiber patch and splice combos have to support termination panels in an upper slide-out shelf with a lower compartment for splice trays in a slide-out shelf. This allows for a full front access application. Blank panels are available to fill unused panel positions.

    Fiber Optic Patch and Splice Combos Patch Panel

     

    Signature Series Patch Panel
    The Signature Series fiber patch panel offers a solution in which you can adapt the fiber patch panel to many fiber adapter panels or fiber module footprints you want in a way that has never been offered before. This new fiber patch panel series is engineered to allow adaptation to a wide variety of fiber patching applications as well as fiber module installations, including a bulkhead that fits Corning adapter plates. You can now adjust to any of these scenarios with just a simple swap of the fiber bulkhead bracket. The unique master panel design allows for easy and secure routing of fiber without obstructions or compromising your bend radius.

    Signature Series Patch Panel

     

    LGX Fiber Optic Patch Panel
    LGX fiber optic patch panels are rack-mountable patch panels designed to support the storage of splice trays. They provide high-density fiber connectivity solutions. LGX patch panels have universal mounting hardware to hold fully terminated LGX cassettes. This maximizes the performance of networking space while saving valuable installation time.

    LGX Patch Panel Patch
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  • Compact Optical Splitter Module for PON Architecture FTTH Deployment

     

    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.

    PON system structure

    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.

    1x32 PLC Splitter

    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.

    1x32 splitter external structure

    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.

    1x32 splitter internal structure

    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.

    strain relief boot model

    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.

    installed splitter modules in FDH

    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.

    1x16 splitter insertion loss

    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.

    optical characteristics measurement

    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.

    1x32 splitter insertion loss temperature dependence

    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.

    1x32 splitter insertion loss wavelength dependence

    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.

    2x32 WDM splitter configuration

    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.

    2x32 WDM splitter insertion loss wavelength dependence

    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.

    1x32 splitter reliability test

    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.

    insertion loss variation of loss during damp heat test

    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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  • Ethernet Passive Optical Network Tutorial

    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).

    EPON Network Structure
    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).

    Downstream Traffic in EPON
    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).

    Upstream Traffic in EPON
    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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