Introduction of Fiber Optic Patch Cord

A fiber optic patch cord is a fiber optic cable capped at either end with connectors that allow it to be rapidly and conveniently connected to CATV, an optical switch or other telecommunication equipment. Its thick layer of protection is used to connect the optical transmitter, receiver, and the terminal box. Fiber optic patch cords are characterized by low insertion loss, high return loss, good repeatability, good interchange and excellent environmental adaptability.

Construction
A fiber optic patch cord is constructed from a core with a highrefractive index, surrounded by a coating with a low refractive index, that is strengthened by aramid yarns and surrounded by a protective jacket. Transparency of the core permits transmission of optic signals with little loss over great distances. The coating's low refractive index reflects light back into the core, minimizing signal loss. The protective aramid yarns and outer jacket minimizes physical damage to the core and coating.

Size
Ordinary cables measure 125 µm in diameter (a strand of human hair is about 100 µm ). The inner diameter measures 9 µm for single-mode cables, and 50/62.5 µm for multi-mode cables. The development of "reduced bend radius" fiber in the mid-2000s, enabled a trend towards smaller cables. Each unit of diameter reduction in a round cable produces a disproportionate corresponding reduction in the space the cable occupies.

Classification
Patch cords are classified by transmission medium (long or short distance), by connector construction and by construction of the connector's inserted core cover. They can be classified as followings.

1. Transmission medium
According to transmission medium, fiber optic patch cord can be classified as single-mode (as the first picture below) and multi-mode (as the second picture below). Single-mode fiber is generally yellow, with a blue connector, and a longer transmission distance. Multi-mode fiber is generally orange or gray, with a cream or black connector, and a shorter transmission distance.

2. Connector construction
Connector design standards include FC, SC, ST, LC, MTRJ, MPO, MU, SMA, FDDI, E2000, DIN4, and D4. Cables are classified by the connectors on either end of the cable. Some of the most common cable configurations include FC-FC, FC-SC, FC-LC, FC-ST, SC-SC, and SC-ST.

3. Inserted core cover
According to the construction of the connector's inserted core cover, fiber optic patch cord can be classified into APC, UPC, and PC configuration. A UPC inserted core cover is flat and is used in SARFT and early CATV. An APC connector's inserted core cover is oblique (about 30°, ±5°). Industry standard is a minimum of – 40dB for PC back reflection measurement and – 50dB for UPC back reflection measurement. If even less back reflection is required, an APC might be necessary. An APC connector has an 8ºangle cut into the ferrule. These connectors are identifiable by their green color. An APC polished connector has an industry standard minimum of – 60dB measurement. APC fiber ends have low back reflection even when disconnected.

Applications
Patch cables are widely used for connections to CATV (Cable Television), telecommunication networks, computer fiber networks and fiber test equipment. Applications include communication rooms, FTTH (Fiber to The Home), LAN (Local Area Network), FOS (Fiber Optic Sensor), fiber optic communication system, optical fiber connected and transmitted equipment, defense combat readiness, etc.

Fiber optic patch cord plays an important role in fiber communication industry, thus getting more knowledge of fiber optic parch cord is necessary for all people in this industry. This article helps us know better of fiber optic patch cord from construction, classification, size, applications and so on.

Introduction to Optical Fiber Cable

An optical fiber cable is a cable containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed. Optical fibers are widely used in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data rates) than wire cables. This article helps us know more of fiber cable from different aspects, such as design, reliability and quality, cable types and so on.

Design

In order to protect fiber from damage, there are different applications of optical fibers according to different environment. For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid, in a lightweight plastic cover to form a simple cable. For use in more strenuous environments, a much more robust cable construction is required. In addition, a critical concern in outdoor cabling is to protect the fiber from contamination by water. Finally, the cable may be armored to protect it from environmental hazards, such as construction work or gnawing animals.

Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, dual use as power lines, installation in conduit, lashing to aerial telephone poles, submarine installation, and insertion in paved streets.

Reliability and Quality

Optical fibers are very strong, but the strength is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing process. The initial fiber strength, as well as its change with time, must be considered relative to the stress imposed on the fiber during handling, cabling, and installation for a given set of environmental conditions. There are three basic scenarios that can lead to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigues, and zero-stress aging.

Cable Types

OFC: Optical fiber, conductive
OFN: Optical fiber, nonconductive
OFCG: Optical fiber, conductive, general use
OFNG: Optical fiber, nonconductive, general use
OFCP: Optical fiber, conductive, plenum
OFNP: Optical fiber, nonconductive, plenum
OFCR: Optical fiber, conductive, riser
OFNR: Optical fiber, nonconductive, riser
OPGW: Optical fiber composite overhead ground wire
ADSS: All-Dielectric Self-Supporting

Fiber Material

There are two main types of material used for optical fibers. These are glass and plastic. They offer widely different characteristics and therefore fibers made from the two different substances find uses in very different applications.

Color Coding

Individual fibers in a multi-fiber cable (as the picture below) are often distinguished from one another by color-coded jackets or buffers on each fiber. The identification scheme used by Corning Cable Systems is based on EIA/TIA-598, "Optical Fiber Cable Color Coding." EIA/TIA-598 defines identification schemes for fibers, buffered fibers, fiber units, and groups of fiber units within outside plant and premises optical fiber cables. This standard allows for fiber units to be identified by means of a printed legend. This method can be used for identification of fiber ribbons and fiber sub-units.

Capacity and Market

Modern fiber cables can contain up to a thousand fibers in a single cable, with potential bandwidth in the terabytes per second. In some cases, only a small fraction of the fibers in a cable may be actually "lit". So they have a big market in fiber optic industry. For example, companies can lease or sell the unused fiber to other providers who are looking for service in or through an area.

Fiber Optic Transceivers

Fiber optic transceivers consist of a transmitter on one end of a fiber and a receiver on the other end. The transmitter takes an electrical input and converts it to an optical output from a laser diode or LED. The light from the transmitter is coupled into the fiber with a connector and is transmitted through the fiber optic cable plant. The light from the end of the fiber is coupled to a receiver where a detector converts the light into an electrical signal which is then conditioned properly for use by the receiving equipment.

Sources For Fiber Optic Transmitters

The sources used for fiber optic transmitters need to meet several criteria: it has to be at the correct wavelength, be able to be modulated fast enough to transmit data and be efficiently coupled into fiber. Four types of sources are commonly used, LEDs, fabry-perot (FP) lasers, distributed feedback (DFB) lasers and vertical cavity surface-emitting lasers (VCSELs).

There are many differences between LEDs and lasers. Firstly, LEDs have much lower power outputs than lasers and their larger, diverging light output pattern makes them harder to couple into fibers, limiting them to use with multi-mode fibers, while lasers are on the contrary. Secondly, LEDs have much less bandwidth than lasers and are limited to systems operating up to about 250 MHz or around 200 Mb/s. Lasers have very high bandwidth capability, most being useful to well over 10 GHz or 10 Gb/s. Thirdly, because of their fabrication methods, LEDs and VCSELs are cheap to make. Lasers are more expensive. Fourthly, LEDs have a limited bandwidth while all types of lasers are very fast. Moreover, LEDs have a very broad spectral output, while lasers have a narrow spectral output that suffers very little chromatic dispersion.

The choice of these devices is determined mainly by speed and fiber compatibility issues. As many premises systems using multi-mode fiber have exceeded bit rates of 1 Gb/s, lasers (mostly VCSELs) have replaced LEDs. The output of the LED is very broad but lasers are very focused, and the sources will have very different modal fill in the fibers. The restricted launch of the VCSEL (or any laser) makes the effective bandwidth of the fiber higher, but laser-optimized fiber, usually OM3, is the choice for lasers.

Detectors For Fiber Optic Receivers

The electronics for a transmitter are simple. They convert an incoming pulse (voltage) into a precise current pulse to drive the source, while receivers use semiconductor detectors to convert optical signals to electrical signals. Silicon photodiodes are used for short wavelength links. Long wavelength systems usually use InGaAs detectors as they have lower noise than germanium which allows for more sensitive receivers.

Transceivers Packaging

As to the packaging, transceivers are usually packaged in industry standard packages like these XFP modules (as the picture below) for gigabit data links(L) and Xenpak (R). The XFP modules connect to a duplex LC connector on the optical end and a standard electrical interface on the other end. The Xenpak are for 10 gigabit networks but use SC duplex connection. Both are similar to media converters but are powered from the equipment they are built into.

From this article, we can know better of fiber optic transceivers from the following aspects: sources for fiber optic transmitters, detectors for fiber optic receivers, and transceivers packaging. As the rapid development of fiber optic communication industry, fiber optic transceivers are playing an increasingly important role in modern communication.

Introduction to Wavelength-division Multiplexing

Wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using differentwavelengths (i.e., colors) of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity. A WDM system uses a multiplexer at the transmitter to join the signals together, and a demultiplexer at the receiver to split them apart. With the right type of fiber it is possible to have a device that does both simultaneously, and can function as an optical add-drop multiplexer. WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fiber.

WDM systems are divided into different wavelength patterns: Coarse Wavelength Division Multiplexing (CWDM) and Dense Wavelength Division Multiplexing (DWDM).

CWDM is the technology of choice for cost efficiently short-haul transmission in telecoms or enterprise networks. CWDM typically has the capability to transport up to 16 channels (wavelengths) in the spectrum grid from 1270 nm to 1610 nm with a 20 nm channel spacing. Passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components such as bandpass filters and prisms.

While Dense Wavelength Division Multiplexing (DWDM) is designed for long-haul transmission where wavelengths are packed tightly together, providing a high-capacity solution in telecom networks. It’s effective for wavelengths between approximately 1525-1565 nm (C band), or 1570-1610 nm (L band). A basic DWDM system contains several main components: a DWDM terminal multiplexer, an intermediate line repeater, an intermediate optical terminal, an optical add-drop multiplexer, and a DWDM terminal demultiplexer.

As an additional optical transport layer, DWDM technology plays an important role in fiber optic communication field. Wavelength-converting transponders serve originally to translate the transmit wavelength of a client-layer signal into one of the DWDM system’s internal wavelengths in the 1,550nm band. In the mid-1990s, signal regeneration in transponders quickly evolved through 1R to 2R to 3R and into overhead-monitoring multi-bitrate 3R regenerators. We need wavelength converters, which is exactly what a transponder is. A transponder can be made up of two transceivers placed after each other: the first transceiver converting the 1550 nm optical signal to/from an electrical signal, and the second transceiver converting the electrical signal to/from an optical signal at the required wavelength. Transponders that don’t use an intermediate electrical signal are in development.

Since communication over a single wavelength is one-way (simplex communication), and most practical communication systems require two-way (duplex communication) communication, so two wavelengths will be required. As a result, at each end both a transmitter and a receiver will be required. A combination of a transmitter and a receiver is called a transceiver. It converts an electrical signal to and from an optical signal. There are usually transceiver types based on WDM technology: Coarse WDM (CWDM) Transceivers (as the picture below) and Dense WDM (DWDM) Transceivers.

From the above introduction, we can know better of what the WDM is, the main types of it and some main concepts related to WDM. WDM technology is now widely used in fiber optic communications.

Introduction to Fiber Optic Patch Cables

A fiber optic patch cord is a fiber optic cable capped at either end with connectors that allow it to be connected to telecommunication equipment. It has thick layer of protection which is used to connect the optical transmitter, receiver, and the terminal box.

Structure

A fiber patch cord refers to install connector plugs on both cable ends to implement the connection of optical path activities. One end with the plug is called pigtails. Fiber patch cords are similar to coaxial cable, but the former don't have mesh shields and the center is glass core for light propagation. In a multi-mode fiber, diameter of the core is 5µm ~ 65µm, which is roughly the thickness of a human hair. And the diameter of single-mode fiber core is 8µm ~ 10µm. In order to keep the fiber optic inside the core,the outside of the core is surrounded by a layer of glass envelope and the refractive index of it is lower than core.Then the outside is a thin plastic jacket to protect the envelope.

Classification

According to the different transmission media of fiber patch cord, they can be divided into common silicon-based single-mode optical fiber, multi-mode jumpers, as well as other patch cords such as the patch cord with plastic transmission medium.

Single mode fiber (as the picture below) is generally in yellow. The joint and protective case are blue. And the transmission distance is long.

Multi-mode fiber (as the picture below) is generally in orange, and some in gray. The joint and protective case are beige or black. And the transmission distance is shorter.

According to the connector structure, it can be divided into FC patch cord, SC patch cord, ST patch cord, LC patch cord, MTRJ patch cord, MPO patch cord, MU patch cord, SMA patch cord, FDDI patch cord, E2000 patch cord, DIN4 patch cord, D4 patch cords and many other forms. The common fiber patch cord can be divided into FC-FC, FC-SC, FC-LC, FC-ST, SC-SC, SC-ST and so on

Tips For Using

The sending and receiving wavelengths at both ends of the fiber patch cords in the transceiver module must be consistent with each other, which means both ends of the fiber must be the same wavelengths of transceiver module. A simple way to distinguish is that the color of the transceiver module must be consistent. In general case, short-wave optical module uses multi-mode fiber (orange fiber) and long wavelength module uses single-mode fiber (yellow fiber) to ensure the accuracy of data transmission.

Do not excessively bend and circle fibers, which will increase the light attenuation in the transmission process.

Fiber optic connectors must be protected with protective case after using. Because dust and oil will damage the fiber coupling.

If the fiber connector is dirty, it should be cleaned with a cotton swab and alcohol. Otherwise it will affect the quality of communication.

1,Before using, the ceramic ferrule and the end sides of fiber patch cords must be cleaned with alcohol and cotton.

2,When using, the fiber minimum bend radius is no shorter than 150mm.

3,Protecting the ferrule and ferrule end sides to prevent bumping and pollution. People should promptly wear the dust cap after disassembling.

4,Do not look into the fiber end sides during laser signals transmission.

5,Fiber patch cords must be replaced promptly after human factors or other force majeure factors.

6,Before installation, instructions must be carefully read. Installation and commissioning process must be with guidance of engineers of manufacturers or distributors.

7,If the fiber-optic network or system appears abnormal condition, troubleshooting method can be individually tested. You can do firstly the on-off test when testing or excluding the patch cords' fault. You can usually use visible laser pointer to do lighting judge for the entire fiber links, or further using the precision-grade optical fiber insertion loss return loss meter to test its targets. If the indicators are within the acceptable range, then the jumper indicating is normal, otherwise unqualified.

Features

1. Low insertion loss
2. Good repeatability
3. High return loss
4. Good mutual inserting performance
5. Excellent temperature stability
6. Good tensile strength properties

Application

Fiber Jumper products are widely applied to the communications room, fiber to the home, local area networks, fiber optic sensors, fiber optic communication systems, fiber optic transmission equipment connectors, defense readiness and so on. They are also applied to cable television, telecommunications networks, computer networks and fiber optical test equipment. They are mainly used in several ways specifically.

1. The optical fiber communication systems
2. Optical access network
3. Fiber optic data transmission
4. The optical fiber CATV
5. Local area network (LAN)
6. Test equipment
7. Fiber optic sensor

Selection Guide

According to the termination types, fiber patch cords can be divided to three types ST-ST, SC-SC, and ST-SC. There are mainly two kinds by category: single mode fiber and multi-mode fiber. Fiber patch cord's length specifications are 0.5m, 1m, 2m, 3m, 5m, 10m and so on. According to the outer sheath material of cable, it can be divided into ordinary types, common flame retardant, low smoke zero halogen (LZSH) and so on.

According to the fireproofing grade and fire-resistant material requirements of buildings, the entire cabling system should take appropriate measures. When laying cables or optical fiber cables in shafts of flammable regions and buildings, we should use flame retardant cable and fiber optic cable. In large public spaces we should use flame retardant, low smoke, low toxicity cable or fiber optic cable. Flame retardant wiring devices should be used in adjacent equipment or joint points.

The Difference Between FiberPatch Cord And Pigtail Fiber

Pigtail fiber is also called pigtail pigtail line, only one end connected to the head, while the other end is a cable core breakage. It is connected with other cable cores by welding and often appears in the fiber optic terminal box. It is used for connecting cable and fiber optic transceivers (also uses couplers, fiber jumpers, etc.)

The optical fiber connector is detachably (activity) connection device between the optical fibers. It makes the two end sides of the optical fiber dock precisely so that the light energy output by launching fiber can be coupled to the receiving fiber at the maximum. And at the same time,the effects on system will be minimized due to optical link's involvement, which is the basic demand of fiber optic connectors. To a certain degree, fiber optic connectors also affect the reliability and performance of the optical transmission system.

Polishing  Ways

After the symbol "/" means cross-sectional technology of fiber optic connectors, namely grinding way.

"PC" is widely used in the telecom operator's equipment. The joint cross section is flat. "PC" represents cross-sectional process of fiber connectors. PC is the most commonly used. In the broadcasting and early CATV, APC models are often used. The head of pigtail uses a belt angle (8 degrees) in end surface and the slope is generally hard to be seen, which can improve the quality of television signals. It's mainly because the TV signal is modulated by analog optics. When the joint coupling surface is vertical the reflecting light returns along the original path.Because of the uneven distribution of fiber index, it will again return to coupling surface. Although this time the energy is small the noise cannot be completely eliminated because of the analog signals, thus it means to superimpose a weak signal with time delay in the original clear signal. It is double image showed on the screen. Pigtail head with belt angle can make the reflecting light not return along the original path. Generally, the digital signals will not have this problem.

"SC" indicates that pigtail connector type is SC connector.The sidelight interface of transmission equipment is generally used with SC connector in industry. SC connector is made of engineering plastics. It can resist high temperature and cannot easily oxidized. ODF connector interface of sidelight is generally used FC. FC is with metal joint, but there will be no problem of high temperature of ODF, and in the meanwhile the pluggable times of metal interface are more than plastic interface, which leads to the fact that ODF pigtail is more frequently maintained than light board pigtail. Other common connector models are ST, DIN, and FDDI.

There is also a "UPC" technology. Its attenuation is smaller than the PC and it's generally used in equipment with special needs. The flange is generally FC/UPC. Foreign manufacturers just use FC/UPC in internal fiber jumper of ODF, which can improve the index of ODF equipment itself.

The Introduction of Common Optical Modules

The continuous expansion and rate improvement of the transmission capacity of communication network trunk has made optical fiber communication the main means of modern information networks. In today's optical communications networks, wide area network (WAN), metropolitan area network (MAN), local area network (LAN) and so on make a demand of the optical transceiver module which is one of the core optoelectronic devices because of the increasing types, which leads to the high demand and the increasingly high degree of complexity at an alarming pace. A sharp increase in optical transceiver modules leads to its diversity, so we need to improve the related technologies to meet the needs of this application.

What Is Optical Transceiver Module

The optical transceiver module is composed of the optoelectronic devices, functional circuits and optical interfaces and other components. The optoelectronic devices include the transmission and reception parts. The emitting portion is inputting a certain rate of signals. After processed by the internal driver chip, the semiconductor laser (LD) or a light emitting diode (LED) will emit a modulated optical signal in corresponding rate. In it's interior part, it has the light automatic power control circuit, which makes the optical signal power output stable. Receiving portion is the inputting a certain rate of the optical signal. After processed by a light detecting diode module, it will be transformed into an electrical signal. After the output of the preamplifier corresponding rate, the electrical signal will be typically PECL level. In the meanwhile, the input optical power will output an alarm signal when it's less than a certain value.

The Classification of Optical Transceiver Modules

According to the rate point there are 100Base (megabytes), 1000Base (Gigabit), and 10GE which are used in Ethernet. 155M, 622M, 2.5G, and 10G are used in SDH .

According to package points: 1×9, SFF, SFP, GBIC, XENPAK, XFP. Various packages shown in figure1-6.

1×9
It’s the welding type optical module, generally no higher than Gigabit speed. It mostly uses SC Interface.

SFF
SFF is welding small package optical modules. It’s generally no higher than Gigabit speed, mostly using the LC interfaces. Small package optical modules use advanced precision optics and integrated circuit technology. The size is only half of the ordinary duplex SC (1X9) fiber optic transceiver module, but in the same space it can be increased to double the number of ports of light. It can also increase the line port density, and lower system cost of per port. Moreover, because a small package SFF modules use the copper network similar MT-RJ interface, and the size is the same with common computer network, which is conducive to the existing copper-based network equipment's transition to higher speed fiber-optic network to meet the rapid growth of network bandwidth.

GBIC
GBIC is hot swappable gigabit interface of optical module and it uses SC interface. Giga bitrate interface converter is the abbreviation of GBIC. GBIC is an interface device that converts the gigabit optical signals to electrical signals. GBIC is designed for hot-swappable. GBIC is an international standard interchangeable products. Because of the flexibility of the GBIC Gigabit switch interface design, it accounts for a large market share.

SFP
SFP (as the picture below) package is the hot-plug small package module. Its highest data rates can reach up to 4G and it uses the LC interfaces. The module volume of SFP is half less than the GBIC, but SFP can be configured more than double ports on the same panel. SFP is the abbreviation of small-form-pluggable, which can be simply understood as an upgrade version of the GBIC. Other features of SFP and GBIC modules are basically the same. Some switch vendors call the SFP module as small GBIC (MINI-GBIC).

XENPAK
XENPAK is applied for gigabit Ethernet interfaces, using SC interface.

XFP
XFP 10G optical module in package can be used in gigabit Ethernet, SONET, and other systems. It uses LC interface

More Understanding of GBIC, SFP, SFP+, XFP

The first thing to know is GBIC (Giga Bitrate Interface Converter). It is a generic, low-cost Gigabit Ethernet stacking modules providing high-speed connectivity between Cisco switches, not only creating a stack of high-density port, but also achieving the server or Gigabit backbone connection for fast Ethernet to Gigabit Ethernet transition. GBIC module is divided into two categories, one is common cascade of GBIC module, the second is dedicated stacking GBIC module.

Secondly, small form factor pluggable (SFP) transceivers are optical modules, which can be simply understood as upgraded versions of GBIC. Compared with GBIC, the module volume of SFP module is reduced by half. SFP module can configure more than double the number of ports on the same panel. Since the SFP module is functionally consistent with GBIC, therefore, some switch vendors call it as small GBIC (Mini -GBIC). Because SFP can be directly inserted in the circuit board, it saves space and time in the package.

Gigabit network currently often uses the SFP + modules. SFP is small form-factor pluggable. The difference is that one is used in gigabit networks and the other supports the gigabit and fast. SFP+ is the latest pluggable fiber optic module for 10Gbps Ethernet and 8.5Gbps fiber channel (fiber channel) system.

SFP+ has a more compact package than the X2 and XFP form factor, and the power consumption is less than 1W. It also provides the mounting density higher than the current 10Gbps devices. A more novel design has made SFP+ have the same volume with the standard of SFP (Small Form Factor Pluggable) industry, and the latter for data rates is up to 4Gbps.

As the well-known XFP, it is 10 gigabit small form factor pluggable gigabit Ethernet optical transceiver module. XFP is a serial module for 10GbE field, and it is the optical module for next generation. But as to the ongoing discussions about whether directly use 10G or transmitted to 4G first and the introduction of 4G network standards and products, XFP seems to have taken some blows.

Difference Between SFP+, SFP and XFP

10G module has developed from 300Pin, XENPAK, X2, XFP, and ultimately realized 10G transmission signal of the same size as SFP, which is the SFP+. With its advantages of compact and low cost, SFP has met the equipment needs of high-density optical modules. From 2002 to 2010, it has replaced XFP and become the mainstream of 10G market.

Advantages of SFP+ optical module

1, SFP+ has a more compact package than the X2 and XFP form factor. And the size is the same as SFP.

2, It can be connected directly with the same type of XFP, X2, XENPAK.

3, The cost is lower than XFP, X2, XENPAK.

Differences between SFP+ and SFP

1, SFP and SFP+ are the same size.

2, SFP protocol specification: IEEE802.3, SFF-8472.

Difference between SFP + and XFP

1, SFP+ and XFP are both 10G fiber optical modules, and they can be communicated with other types of 10G modules.

2, SFP+ is smaller than the XFP from the size.

3, Because of the smaller volume of SFP+, it can transmit the signal modulation function, serial/deserializer, MAC, clock and data recovery (CDR), as well as electronic dispersion compensation (EDC) function to the motherboard card from the module.

4, XFP complies the XFP MSA agreement;

How Much Do You Know About PON?

Definition

PON (Passive Optical Network) is a telecommunication network that uses point-to-multipoint fiber to the end-points in which unpowered optical splitters are used to enable a single optical fiber to serve multiple end-points. A PON consists of an optical line terminal (OLT) at the service provider's central office and a number of optical network units (ONUs) or Optical Network Terminals (ONTs) near the end users.The optical distribution network (ODN) between the OLT and ONU contains fiber and passive optical splitters or couplers.

PON system mainly consists of the optical line terminal (OLT: Optical Line Terminal) in central office. And the optical distribution network (ODN: Optical Distribution Network) includs passive optical devices, the client's optical network unit/optical network terminal (ONU/ONT Optical Network Unit/Optical Network Terminal). The difference is that ONT directly lies in the client, and between the ONU and the user there are other networks, such as Ethernet, as well as Element Management System (EMS) usually using multipoint tree topology.

The outstanding advantage of PON network is the elimination of outdoor active equipment, all signal processing functions are performed at the switch and the user equipment. Meanwhile, the initial investment of this access method is small, and most of the money can be deferred to invest after the users truly get the access. Its transmission distance is shorter than that of the active optical access system, and the coverage is smaller. But the cost is low and they don't need a separate room, which is easy to maintain. Therefore, this structure can be economical for home users.

Brief Introduction of PON

Fiber is so "cheap and easy to use", so for the next-generation broadband solution, FTTx (Fiber To The X, optical access) is widely used to provide users with high-bandwidth and full-service access platform. And FTTH (Fiber To The Home, FTTH, optical fiber directly connected to the user's home). It is known as the best business transparent network, which is the ultimate way of access network development.

How does the FTTx achieve it? In a variety of solutions, for the multipoint (P2MP) fiber access PON (Passive Optical Network, Passive Optical Network) is the best choice. PON is used in the access network, the central network and a plurality of CPE (ONU / ONT). It's composed of the passive optical cable, optical branching device/optical combiner.

ODN (Optical Distribution Network)
OLT (Optical Line Terminal)
ONU (Optical Network Unit)
ONT (Optical Network Terminal) (as the picture below)

ONU and ONT both belong to the CPE, the difference between which lies directly at the client ONT. Between the user and ONT there are other networks, such as Ethernet.

The key "passive" is that ODN between OLT and ONU is the optical access network without any active electronic devices. Because of this "passive" features, this pure media PON network equipment can avoid external electromagnetic interference and lightning effects, reducing lines and external equipment failure rate, and improving system reliability, and reducing maintenance costs at the same time.

PON technology is developed from the beginning of the 1990s, ITU (International Telecommunication Union) from APON (155 M), and then BPON (622 M), as well as to GPON (2.5 G); And in the early century, due to the wide use of the ethernet technology,

IEEE also developed EPON technology based on Ethernet technology. Currently PON technology for broadband access mainly are EPON and GPON both of which use two different standards. The future development should pay attention to higher bandwidth. For example, EPON / GPON technology developed 10GEPON/10GGPON, which made the higher bandwidth.

Feature

The complexity of PON lies in the signal processing techniques. In the downstream direction, the signal sent by the switch is the broadcast that sent to all users. In the upstream direction, each ONU must use some kinds of multiple access protocols. For example, time division multiple access TDMA (Time Division Multiple Access) is the protocol to complete the channel access to information. Currently PON technology for broadband access are mainly: EPON and GPON.

Standard

ITU-T G.983

APON (ATM PON, ATM Passive Optical Network) is the first passive optical network standard, which is based on ATM, mainly used for commercial applications.

BPON (broadband PON, Broadband Passive Optical Network) is a standard based on APON. This standard adds support for WDM and dynamic bandwidth allocation, linking the high-speed, and supporting the durability. BPON also has created a management interface standard OMCI---mixed supplier network authorized by the OLT and ONU / ONT.

IEEE 802.3ah

EPON or GEPON (Ethernet PON Ethernet Passive Optical Network) is a use Ethernet packet data IEEE / EFM standard. 802.3ah standard is now a part of the IEEE 802.3 standard. Now there are about fifteen million EPON ports being used. In 2008, China vigorously developed EPON technology. It is estimated that, in the end of 2008, China had a total of 2 million EPON installing users.

ITU-T G.984

GPON (Gigabit PON, Gigabit Passive Optical Network) is developing from the BPON standard. GPON supports higher rates, enhanced security, and an optional second layer protocol (ATM, GEM, Ethernet). In mid-2008, Verizon Telecom has installed 800,000 lines. BT (British Telecom) and the American Telephone and Telegraph Company (AT & T) had advanced tests. Other companies such as Separate Optical Network Company (Independent fiber networks LTD) is working with the service supplier. They see the potential business chances to build higher-speed GPON access and fiber to the home (FTTH-fiber to the home).

IEEE P802.3av

10G-EPON (10 Gigabit Ethernet PON) is an IEEE specialized project. In order to achieve 10Gbit/s rate, it is backward compatible with 802.3ah standard EPON. 10GigEPON will use separating wavelengths for 10G and 1G downstream. 802.3av will continue to use TDMA isolation of individual wavelengths, which makes the use in the uplink between 1G and 10G possible. 10G-EPON will be compatible with WDM-PON (according to the definition of WDM-PON), which will make multi-wavelengths change between the two directions possible.

SCTE IPS910

RFoG (RFoverGlass) is sub-committee standard of interface practice which is applied to the wavelength plan compatible multipoint data (P2MP) operations, such as EPON, GEPON or 10GigEPON. RFoG provides a FTTH PON ( FTTH PON) and we just do not have to select the MSOs or deploy PON architectures.

Background

From the whole network, due to the large number of laying, Many new technologies such as DWDM made a breakthrough in fiber-optic backbone networks. At the same time due to advances in Ethernet technology, its dominant LAN bandwidth was also developing from 10M, 100M to 1G or 10G.

And now everyone's attention is the network backbone and LAN connection as well as home users, it is often said as "the last one kilometer" which is a bottleneck. Only breaking this bottleneck can we usher in a new world of cyberspace. It is as if the state highway systems, trunk and regional roads have been built with high grade, but the door leading to the family and business are still narrow pass, thus the road network can not act effectively.

After years' development, APON is still not really entering the market. The main reason is the complicated ATM protocol. With respect to the access network equipment market it is still relatively expensive. At the same time due to the rapid development of Ethernet technology, ATM technology is completely out of the local area network. So as to how to combine the simple and economical Ethernet technology and PON transmission structure has caused great attention by the technical communities and network operators since 2000. Meanwhile, the industry generally believe that there are many shortcomings of ATM PON, such as the lack of video transmission capabilities, limited bandwidth, system complexity and high costs, and so on. These shortcomings will not exist in EPON.

The first target of OAN evolution are FTTB (Fiber To The Building) and FTTC (Fiber To The Curb) system, then the development of FTTH (Fiber To The Home) which includes data by providing a simple platform for the user. There are comprehensive services, including video and voice. EPON can provide higher bandwidth and more comprehensive services than APON , and the cost is very low, while EPON architecture is also in line with most of the requirements G.983 standard.

Advantages

1)relatively low cost, easy to maintain, easy to expand, and easy to upgrade. PON structure can transit without power and electronic parts. Thus it is easy to lay, and basically no maintenance, which can save much long-term operating costs and management cost.

2) passive optical network is a pure media network,completely avoiding electromagnetic interference and lightning effects, very suitable for using in areas of poor natural conditions.

3) PON system takes up very little resources for infrastructure, the initial system investment is low, easy expansion, high return on investment.

4) EPON currently can apply for the down the line symmetrical 1.25Gb / s of bandwidth, and with the development of Ethernet technology it can be upgraded to 10Gb/s. GPON is up to 2.5Gb/s bandwidth.

5) As a multipoint network, PON save resources of CO and service large numbers of users in a fan-shaped structure. The fact that mode users can share infrastructure equipment and fiber is saving the users' investment.

6) The quality of service (QoS) is guaranteed. There is a complete system for G/EPON system to guarante the bandwidth, which can realize the user-level SLA.

PON Technological Development

Conventional PON system downstream data uses the broadcast technology, and the upstream uses TDMA technology to solve complex problems of multiple users in each direction of the signal. Conventional PON technology uses WDM technology, and realizes single fiber bidirectional transmission over fiber to solve the multiplex transmission of 2 direction signals. PON is usually composed of optical line terminal (OLT), splitter (ODU), and 3 parts subscriber terminal (ONU).

Currently widely used PON technologies in the existing network include two mainstream technologies: EPON and GPON. EPON uplink and downlink bandwidth are 1.25 Gbit/s. The GPON downstream bandwidth is 2.5Gbit/s and upstream bandwidth is 1.25 Gbit/s.

Currently in the applications of FTTx , most EPON / GPON are configured with only the Ethernet interface, optional POTS and 2M interface. However, from technical standards, both EPON / GPON can achieve IP and TDM services such as multi-service access, and achieve QoS classification.

EPON/GPON can transmit clock synchronization signal and can be extracted frequency synchronization signal from an external circuit through the OLT STM-1 interface or GE interface. Then OLT should support synchronous Ethernet; You can also enter from an external BITS on the OLT clock signal as a common clock source of the PON. ONU should keep pace with the clock source to maintain frequency synchronization.

Although PON and 10G EPON are not commercial in large scale, 10 Gbit/s rate PON technology over the last two years is the research focus of FSAN and ITU-T. And related technical standards of XG-PON1 are mature now, such as NG-PON2 standard XG-PON1 after ITU-T on GPON, XG-PON1 standards and NGPON2 ITU-T on GPON, XG-PON1 standards and NGPON2. The framework has been basically completed. The focus now is the extension to multi-wavelength technology. FSAN has made it clear that TWDM-PON will be the choice of future technology NG-PON2, but a variety of technical specifications in the ITU-T SG15 G.multi standard hasbeen basically completed, which means that a plurality of multi-wavelength extended technical schools battle are far from over.

WDM System

Optical terminology

Wavelength Division Multiplexing(WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. Each signal modulated through the data (text, voice, video, etc.) transmit in its unique zone. WDM enables telephone companies and other operators to increase the capacity of existing fiber optical infrastructure. Manufacturers have introduced a WDM system, also called DWDM (Dense Wavelength Division Multiplexing) system.

DWDM can support more than 150 light beams with different wavelengths transmit simultaneously and each light beam can reach up to 10Gb/s data transfer rate at the highest. This kind of system can provide more than 1Tb/s data transfer rate in fiber optic cable which is thinner than hair.

Optical communication is a transmission mode to carry and transmit the signal through light. People used to name with the wavelength instead of frequency in the field of optical communications. Therefore, the socalled wavelength division multiplexing (WDM, Wavelength Division Multiplexing) is essentially just frequency division multiplexing. WDM carries a plurality of wavelengths (channels) in one optical fiber, and convert it to a number of "virtual" fibers. Of course, each "virtual fiber" work independently at different wavelengths, which dramatically increases the transmission capacity of optical fiber. The economy and effectiveness of WDM systems technology, make them the primary means to expand the current optical fiber communication network. As a system concept, WDM technology usually has three kinds of multiplexing schemes, namely 1 310 nm and 1 550 nm wavelength division multiplexing, coarse wavelength division multiplexing (CWDM) and dense wave division multiplexing (DWDM).

Two wavelengths

This kind of multiplexing only use two wavelengths in the early 1970s: 1310 nm wavelength window, 1550 nm wavelength window, using the WDM technology to achieve single fiber dual windows transmission, which is the initial use of wavelength division multiplexing.

1.Coarse wavelength division multiplexing

Following the application of the backbone network and long-distance networks, WDM technology began to be used in the MAN, which mainly refers to the coarse wavelength division multiplexing technology. CWDM use 1200 ~ 1700nm wide windows, mainly used in the 1550 nm wavelength systems. Of course, the 1310nm wavelength WDM is also being developed. The adjacent channel spacing of Coarse Wavelength Division Multiplexing (large wavelength interval) is generally over 20nm, the number of which are usually 4 or 8 waves or up to 16 waves at most. When the number of channels is 16 or less, since the system uses CWDM DFB laser cooling is not required, in terms of cost, power requirements, and equipment dimensions, CWDM system has more advantages than DWDM systems, CWDM is increasingly widely accepted by the industry. CWDM need to select the expensive dense wavelength division multiplexer and "optical amplification" EDFA, and just need to use the cheap multi-channel laser transceiver as a relay, thus the cost is greatly reduced. Today, many manufacturers have been able to provide commercial CWDM systems with 2 to 8 wavelengths which are suitable for using in the cities that geographical scope is not particularly large, data services development is not very fast.

2.Dense wavelength division multiplexing

Dense wavelength division multiplexing technology (DWDM) can carry 8 to 160 wavelengths, and with the continuous development of DWDM technology, the upper limit of the sub-wave number continues to grow, and the interval is generally less than 1.6 nm, which is mainly used in long distance transmission systems. The dispersion compensation technology (multi-wavelength system to overcome nonlinear distortion - the four-wave mixing phenomenon) is required in all DWDM systems. 16 waves DWDM systems generally use conventional dispersion compensating fiber to compensate, but 40 waves of DWDM systems must use the dispersion slope compensating fiber to compensate. DWDM can be put in the same fiber to combine and transmit the different wavelengths simultaneously. To ensure efficient transmission, an optical fiber is converted to a plurality of virtual fibers. Using the DWDM technology, a single optical fiber can transmit data flow rates up to 400 Gbit/s. As manufacturers added more channels in per fiber, per second transmission speed just around the corner.

3.Technological level

On the perspective of the test level of existing transmission capacity of WDM systems, the Nortel and other companies' 1.6Tbit/s (160 (10Gbit/s) WDM system has been successful. In the subsequent exhibition, Nortel released 80Gbit / s of WDM system, the total capacity of which is 6.4Tbit/s. In addition, Lucent uses 80nm spectral width of the optical amplifier to create the world record of a number of wavelengths up to 1022. At the same time, we know that some of the indicators of the world famous company's existing WDM systems.

In China, the research and development of WDM technology are not only active, but also develop very fast. Wuhan Research Institute of Posts and Telecommunications (WRI), Peking University, Tsinghua University, the Ministry of Posts and Telecommunications have successively carried out the transmission experiments or construction of pilot project. For example, Wuhan Research Institute of Posts and Telecommunications successfully carried out 16 (2.5Gbit/s 600km unidirectional transmission system in October 1997. It showed 32 (2.5Gbit/s of WDM transmission system, and conducted transmission experiments of a capacity of 40 (10Gbit/s WDM system in October 1998 at the Beijing 98 International Telecommunications Exhibition. And the higher level WDM systems are under experiments. Huawei, Ericsson, ZTE, flames and other manufacturers all have WDM relevant layout, Huawei's WDM global market share has jumped to first place. 100G WDM products have been officially used in business, and 400G technology validation and experimental tests have been carried out in the laboratory.

4.The developing prospects

WDM is a multiplexing technique in the optical domain and it forms an optical layer network "alloptical network", which will be the highest stage of optical communications. The establishment of a WDM and OXC (optical cross-connect) -based optical network layer, the achievement of all-optical network users to connect end to end, the using of a pure "all-optical network" to eliminate bottlenecks photoelectric conversion will be the future trend. WDM technology is still based on the way of point to point , but as the first step of all-optical network communication, the point to point WDM technology is also the most important step, the application and practice of which are based on the development of all-optical network.

5.Application

DWDM can combine and transmit the different wavelengths in the same fiber simultaneously. In order to ensure effectiveness, an optical fiber is transmitted into multiple virtual fibers. So, if you intend to reuse eight fiber optic carrier (OC), ie an 8- way optical fiber transmission signals, the transmission capacity will reach from 2.5 Gb/s up to 20 Gb/s. Becasue of the DWDM technology, a single optical fiber can transmit the maximum 40Gb/s. As manufacturers added more channels in per fiber, the transmission speed terabit per second is just around the corner.

6.Technology

Wavelength Division Multiplexing (WDM) is a technology which uses a multiplexer (also known as multiplexer, Multiplexer) at the transmitter to join two or more different wavelengths of light carrier signal (carry a variety of information) at the confluence of the sender , and coupled to the light the same fiber lines for transmission of technology; At the receiving end, the demultiplexer (also known as a demultiplexer or demultiplexer said, Demultiplexer) separate various wavelengths of light carrier, and then the optical receiver for further processed to recover the original signal. This simultaneous transmission of two or a number of different wavelengths of light signals in the same fiber technology is called wavelength division multiplexing (as the picture below).

WDM is essentially a frequency-division multiplexed FDM technology in optical domain. Each wavelength channel is divided by a frequency domain implementation. Each wavelength channel occupies the bandwidth of the optical fiber section. The wavelength of WDM system is different, that is a specific standard wavelength. In order to distinguish SDH system ordinary wavelength, sometimes called color optical interface, and the optical interface of ordinary light system as "white light mouth" or "white mouth.

Different communication system design makes the interval between each wavelength also different. According to different channel spacing, WDM can be subdivided into CWDM (Coarse Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing). The channel spacing of CWDM is 20nm, and DWDM channel spacing from 0.2nm to 1.2nm. So compared with DWDM, CWDM is called coarse wavelength division multiplexing technique.

7.Feature

(1) Large-capacity transmission.

Since the multiplexed optical channel rate of WDM system can reach 2.5Gbit / s, and 10Gbit / s, etc., while the number of channels can be 4,8,16,32 path, and even more, the transmission capacity of the system can reach 300 -400Gbit / s, or even greater.

(2) Fiber resources conservation.

For a single wavelength system, an SDH system will need a pair of fibers; and for WDM system, no matter how many SDH sub-systems, entire multiplexing system requires only a pair of optical fibers. For example, for 16 2.5Gbit / s systems, single-wavelength systems require 32 optical fibers, while the WDM system requires only two fibers.

(3) Each channel transparent transmission, smooth upgrade, expansion.

Just adding multiplex channels number and devices can increase the transmission capacity of the system to achieve the expansion. Because each multiplex channel of WDM systems is independent from each other, so each channel can separately transparently transmit different service signals, such as voice, data, and images, etc., not interfering with each other, which brings the user great convenience.

(4) The use of EDFA to achieve ultra-long haul transmission.

EDFA has the advantages of a high gain, wide bandwidth, low noise, etc., and its optical zoom range can reach 1530 (1565nm, but its gain curve is relatively flat section 1540 (1560nm), which can cover almost the operating wavelength range of 1550nm WDM system. So with a very wide bandwidth of EDFA we can just multiplex optical path signal while amplifying WDM system, to achieve ultra-long haul transmission, and avoid the situation that each of the optical transmission system needs an optical amplifier. The long transmission distance of WDM can reach up to several hundred kilometers while saving a lot of repeaters, and reducing costs.

(5) Improving of the reliability of system.

Since most of the WDM system is photovoltaic device which is with high reliability, therefore, the reliability of the system can be guaranteed.

(6) Can be composed of all-optical networks.

All-optical network is the future direction of the optical fiber transmission network. In the all-optical network, from top to bottom, the various services are all in the optical path through scheduling the optical signal, thereby eliminating bottlenecks of E / O converter in electronic devices. WDM systems can be mixed with OADM, OXC, to form a high degree of flexibility, reliability, survivability of all-optical networks to meet the development of bandwidth transport networks.

8.Advantage

A key advantage of DWDM is the irrelevance of its protocol and transmission speed. Because DWDM-based network can use IP protocol, ATM, SONET / SDH, Ethernet protocols to transfer data and the processing data is between 100 Mb / s and 2.5 Gb / s, the DWDM-based network can transmit different types of data traffic in a laser channel transmission at different speeds. From QoS (Quality of Service) viewpoint, DWDM-based networks now quickly respond to changing bandwidth requirements and protocols changes of customers in a low cost way. Science and technology is increasingly updating. The using of 1600G, 800G and 400G are very common at the national trunk, provincial and municipal trunk. Take 1600G as an example, theoretically, an optical fiber can go 160 10G services in the fully equipped cable, greatly improving the utilization of the optical fiber. Of course, the demand of cable quality is also high. The theoretical values and actual values are also biased. In the practical application, to avoid failure rate we rarely use a hundred channels on the same fiber business.