Category Archives: WDM & Optical Access

Are You Familiar with Fiber Optic Coupler?

Optical coupler is the extremely important component in a number of phonics devices and systems that couple or split light through wave-guides or fibers. Fiber optic couplers can be either active or passive devices. The difference between active and passive couplers is that a passive coupler redistributes the optical signal without optical-to-electrical conversion. Active couplers are electronic devices that split or combine the signal electrically and use fiber optic detectors and sources for input and output.

fiber optic coupler

A basic fiber optic coupler has N input ports and M output ports (showed in the above picture) which typically range from 1 to 64. But generally, they are four-port devices and their operation relies on the distributed coupling between two individual waveguides in close proximity, which results in a gradual power transfer between modes supported by the two waveguides. The brief principles of four-ports fiber optic coupler is given in the following picture. If light enters into the port 1, it will be splitted into the output ports between ports 3 and 4. And port 2 functions in the same way. And sometimes, one of port 1 or port 2 is unused, so the fiber optic coupler will act as a Y or T coupler (Y or T stands for the form of transmission route).

brief principles of four-ports fiber optic coupler

As we have known before, fiber optic coupler can couple or split light, so it also can be called fiber optic splitter. In fact, splitter is named for the function of the device, coulper named for its working principle. These days, the most popular types are fused fiber optic couplers and planar lightwave circuit (PLC) splitter.

Fused fiber optic coupler is a kind of fiber optic couplers, which is formed based on fused biconical taper (FBT) technology. Therefore, it is also known as FBT coupler. It can work on three different operating bands such as 850nm, 1310 nm and 1550nm.

Planar Lightwave Circuit (PLC) Splitter is designed to manage the power of optical signals through splitting and routing. It can provide reliable light distribution and is based on planar lightwave circuit technology. Compared with FBT fused coupler of lower cost, PLC splitter has wider operating wavelength range which is from 1260 nm to 1620 nm, and wider temperature range from -40ºC to +85ºC, better uniformity, higher reliability and smaller size.

Currently, fiber optic coupler is widely used in that it can support FTTX (FTTP, FTTH, FTTN, FTTC), passive optical networks (PON), local area networks (LAN), CATV systems, amplifying, monitoring system and test equipment. As a result, fiber optic coupler with good quality is required. Fiberstore can offer you various kinds of fiber optic couplers with good quality, including fused fiber optic coupler and Planar Lightwave Circuit (PLC) Splitter. For more information, you can visit Fiberstore.

PON – a Better Network Solution

When choosing a best fiber architecture for the network, many planners may choose PON today. PON, short for passive optical networks, 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. “Passive” means optical transmission has no power requirements or active electronic parts when the signal is going through the network. It is the core underpinning of fiber optical service.

Introduction of PON

Passive optical network is widely applied in fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), or fiber-to-the-home (FTTH), which is decided by the places it terminates. Commonly, it is made up of an optical line terminal (OLT) in the central office and a number of optical network units (ONU) near end users. From the picture below, we can get a brief understanding of the working process of it.

First and foremost, the data or the signals in the central office will be transmitted over a single optical fiber without interfered by each other, because encryption can prevent eavesdropping. And then the passive splitter will separate the signals into several optical network units which can be up to 64 units.

PON

Classifications of PON

The first PON systems which is based on Asynchronous Transfer Mode (ATM, or “cell switching”) were called “APON”. It has been achieved significant commercial deployment and still be applied in someplace today. The “Broadband PON” comes after APON. Typically, these two systems both have downstream capacity of 155 Mbps or 622 Mbps and upstream capacity of 155 Mbps.

And as the technology advanced, there is a growing requirements of higher capacity. As a result, APON and BPON is gradually replaced by GPON. GPON, short for Gigabit-capable passive optical network, is the successor of APON and BPON, and also based on ATM transport. Typically, its capacity of upstream ranges from 622 Mbps to 1.25 Gbps, while the downstream capacity ranges from 622 Mbps to 2.5 Gbps. In today’s fiber-to-the-home (FTTH) networks, GPON is most widely deployed, which is generally considered suitable for consumer broadband services for the next 5 to 10 years.

EPON (Ethernet passive optical network) is the rival of GPON, using Ethernet packets instead of ATM cells. It is cheaper to deploy than GPON, but it has not garnered the level of acceptance of GPON.

And WDM PON (wavelength-division multiplexing passive optical network) is a network that combines WDM technology with PON system. It can use wavelength-division multiplexing to split each signal into different branches.

Advantages of PON

Compared with the traditional enterprise network, PON network is obvious superior to it. And there are several advantages of PON.

Energy savings – PON system does not need rack mount switches and other active devices in remote locations so that it can reduce a number of heat generating devices that must be cooled and powered, thereby generating energy savings. Also, there are reduced HVAC (Heating Ventilation Air Conditioning) requirements, since there is no radiant heat with fiber cabling.

Lower cost – Due to lower power consumption, reduction in floor space, and yearly reduced maintenance costs, the enterprise will realize significant operational expense savings over the life of the system of 45-70% over that of a traditional copper based system, as well.

Optimized bandwidth utilization – with dynamic allocation of bandwidth, the system can provide optimized network connectivity to those application and users requiring the greatest bandwidth, while facilitating future proofing.

Now, the Ethernet market becomes more and more popular, so PON is gradually getting into a bright future. With these significant advantages, PON can meet the changing demands of the enterprise network more quickly and easily. And at present, the most popular network systems are GPON and EPON. Fiberstore offers various PON products, including optical line terminals and optical network units, and if you want to deploy your network most efficiently, Fiberstore is your best choice.

Related article: https://www.chinacablesbuy.com/a-guide-for-pon.html

Guide to Optical Amplifier

In pursuit of high transmission capacity, people have been tried many ways. For example, they pave more cables or use the TDM (time domain multiplexer) to improve the transmission capacity. But in these traditional ways, signals could become weaker in power through the fiber link. And the further they are transmitted, the weaker the signals will be until they can not be detected. With the advanced of technology, optical amplifier which is a better solution to improve the transmission capacity came around. It can strengthen the attenuated signals and even can bring them back to the original level. And now it is mainly applied in DWDM technology so that DWDM technology can support long-haul transmission.

Working Principles of Optical Amplifier

Optical amplifier is a device that can amplifier optical signals directly, which does not need to convert optical signals to electric signals first. And we will take the common kind for example to explain its working principles, namely, EDFA (erbium doped fiber amplifier). Optical fiber is often doped with rare-earth elements, such as erbium or praseodymium which can be pumped into a excited state by pump laser. When input signals pass by the fiber, they will stimulate the excited atoms of erbium so that the atoms of erbium can release their energy in the form of emitted light photons. It is the emitted light photons who has the same phase and wavelength with input signals that amplify the optical signals.

Working Principles of EDFA

Working Principles of EDFA

Types of Optical Amplifier

Optical amplifier can be divided into three types now. They are the doped fiber amplifier, the semiconductor optical amplifier and the Raman amplifier. Next we will introduce each of amplifiers.

Doped fiber amplifier has several types according to the kinds of rare earth elements. Erbium-doped fiber amplifier is the most common one. Just like we said before, its amplifying medium is the fiber doped with erbium elements. The amplified light’s wavelength is around 1550 nm, which suffers minimum attenuation. And this amplifier has low noise and is applied in the long-haul telecommunication networks. The second is semiconductor optical amplifier whose gain medium is undoped InGaAsP. Compared with EDFA, it is less expensive and more suitable for local networks. Raman amplifier’s gain medium is undoped optical fiber. It is made with Raman scattering effect which is an important non-linear effect. By the early part of 2000s, it is used for long-haul (typically between 300 and 800 km) or ultra-long-haul (typically longer than 800 km) fiber-optics transmission system. And this amplifier has been commercialized these days, with sold at a high price.

The advent of optical amplifier is a great success in optical fiber communication technology. At present, it has been become a basic device in modern telecommunication networks and brings much effectiveness to economy and society, which presents a good trend for the market prospect.

What Is CWDM?

As we all known, WDM (wavelength division multiplexing) is a technology that can transmit multiple different wavelength lasers on a single optical fiber, and widely used in optical networks. CWDM (coarse wavelength division multiplexing), as one type of WDM technology, first came in the 1980s, mainly being used to transmit digital video signal in the multimode fiber. However, it did not interest telecommunication service providers much until now. In recent years, with the development of metropolitan area network which has short transmission distance and do not need optical amplifier, there is a growing technology investment for it because it is a cost-effective solution for telecommunication service providers. We could say this is the time that CWDM exists with great significance.

Introduction of CWDM

As we said above, CWDM is one type of WDM technology, oriented to metropolitan area network. According to ITU-T G.694.2 standard, it has three wavelength bands: O band, E band and S+C+L band. The wavelength of O band is about 1270 nm, 1290 nm, 1310 nm, 1330 nm and 1350 nm. The wavelength of E band is about 1370 nm, 1390 nm, 1410 nm, 1430 nm and 1450 nm. As to S+C+L band, the wavelength is about 1470 nm, 1490 nm , 1510 nm, 1530 nm, 1550 nm, 1570 nm, 1590 nm and 1610 nm. And the channel spacing in CWDM system is typically 20 nm as the picture shows below. So the number of its channels on the same link can be up to 18. And due to its wide channel spacing the temperature control could not be so rigid. Typically, its operating temperature is from 0 to 70°C. And the use of uncooled lasers brings a low cost.

Typical transmittance for coarse wavelength multiplexer

Advantages of CWDM

One of the biggest advantage of CWDM is low cost. As we have mentioned before, CWDM with the wider channel spacing do not need rigid temperature stability control, so the construction of laser device could be simplified. This feature of it is of great help to reduce the cost.

Another advantage of CWDM is that it has small volume and low power consumption. The laser in CWDM system do not need semiconductor cooler and temperature controlling, so it can reduce the power consumption obviously. Its power consumption is only 0.5 W. And the laser module which is simplified in CWDM system can make the volume of optical transceiver module reduced so that it can save a lot of room space.

Application of CWDM

With these advantages, CWDM technology is applied in various areas now, such as enterprise LAN and SAN connection, central office to customer premise interconnection and so on. And one of the most commonly devices is CWDM SFP. CWDM SFP is the transceiver which made by CWDM technology. It is of great simplicity, flexibility and interoperability. Mostly there are eight center wavelengths available from 1470nm to 1610nm, with each step 20 nm. Of course, there are some other CWDM devices,too. But today we are not going to list the products.

In a word, because of its good capacity and low cost, CWDM provides a better solution for metropolitan area network. I believe it will be a hot spot in metropolitan area network construction in the next few years.

WDM Overview

With the development of the computers, mobile phones and some other things, there is an increasing eagerness for more traffic volume of telecommunication. So WDM, with more bandwidth and faster data transmission rate, comes into being.

WDM is a technology to send multiple different wavelength lasers on a single optical fiber. As shown in the picture below, there are different signals coming from different channels. when through the multiplexer, they can be transmitted on a single fiber without obstructed by each other at a high speed. And then, when they are through the demultiplexer, they will be allocated into different channels. The multiplexer and the demultiplexer are the most important parts in WDM systems, just like transmitter and receiver. When signals are transmitted to the network medium on the fiber links, they will be amplified. And after through the network medium, the signals will still be amplified on the fiber links untill they are received by the receiver.

WDM-wavelength division multiplexing

Currently, there are two types of it in the market. CWDM, short for coarse wavelength division multiplexing, is a low-cost WDM transmission technology. Another type is DWDM, namely, dense wavelength division multiplexing. The primary difference between them is the channel spacing. The channel spacing of CWDM is wider than DWDM, so that the number of its channels on the same link could be reduced relatively. As a result, its optical interface components does not need to be precise as same as DWDM.

Now the technology of WDM is widely used in optical networks. Why can it be so widely used? The reasons is closely linked to its features. First, it has Super capacity transmission technology. The transmission capacity can be up to 300-400 Gbit/s or even larger. Second, it can save fiber resources. No matter how many SDH subsystems there are, the whole reuse system only needs a pair of optical fiber. Third, it can work with EDFA that strengthens and restores the attenuated signals in the long-distance transmission, so that it can reduce the cost. Forth, it can improve the reliability of the system. Because most WDM systems are the photoelectric devices which have high reliability. This is a guarantee for the system reliability.

As the optical communication technology progressed further, WDM will be developed in some aspects. In terms of DWDM, Something still needs to be improved such as cost, so that more customers can adopt it.

Optical Amplifier Is a Key Technology for Restoring Signals

Optical communications are more and more prevailing for the high demand for telecommunication, video and data transmission. The optical fiber is capable of transmitting many signals over long distance to meet people’s various requirements. But the signals are easily attenuated in the long-distance high speed networks. Amplifiers are a key enabling technology for strengthening optical signals. Electrical amplifiers are originally used but gradually replaced by optical amplifiers.

Optical amplifier is a device that can amplifier optical signals directly without the need to convert them into electrical ones. Electrical amplifier is originally used but gradually replaced by optical amplifier. It is a much cheaper solution in comparison with electrical amplifier which has costly conversions from optical to electrical signal. The longer the transmission distance is, the more electrical signals need to be converted, which makes the cost of electrical amplification higher and higher. So optical amplifier is used in an increasing number. More detailed information about it is as followed.

Optical amplifiers can be used as power boosters, in-line amplifiers and detector pre-amplifiers in fiber optical data links. Booster amplifiers are used to increase the optical output of optical transmitters when signals haven’t entered the optical fibers. Once transmitted, the optical signals are attenuated by 0.2dB/km. In-line amplifiers are then used to restore the optical signals to its original power level. At the end of the data link are pre-amplifiers which are used to increase the sensitivity of an optical receiver.

optical ampplifier functions

optical amplifier: functions

There are three most important types of optical amplifiers including erbium-doped fiber amplifier(EDFA), semiconductor optical amplifier (SOA) and Raman amplifier. Here will introduce them briefly.

Erbium-Doped fiber amplifier: it is an optical or IR repeater that amplifies a modulated laser beam directly without optical to electrical conversion. It uses a short length of optical fiber doped with the rare-earth element erbium. The signals-carrying laser beams are usually at IR wavelengths with application of external energy. It has low noise and capable of amplifying many wavelengths simultaneously, which is an excellent choice in optical communications.

Semiconductor optical amplifier: it is an optical amplifier which uses a semiconductor to provide the gain medium. The gain medium is undoped InGaAsP. This material can be tailored to provide optical amplification at wavelengths near 1.3 µm or near 1.5 µm which are important wavelengths for optical communications. It makes fewer noises than EDFA and generates less handle power. But it is more suitable to be used in networks where the best performance is not required for it is less expensive.

Raman amplifier: it is an optical amplifier based on Raman gain created by Raman scattering, which works entirely differently from EDFA or SOA. Raman optical amplifier have two key elements: the pump laser and the directional coupler. The pump laser has a wavelength of 90 nm to 1500 nm. The circulator provides a convenient means of injecting light backwards in to the transmission path with minimal optical loss. Raman amplification occurs throughout the length of transmission fiber, which makes Raman amplifier known as distributed amplifier.

For more information about optical amplifier, please visit www.fs.com.

A Guide for PON

Nowadays, there is a growing popularity of Video-on-Demand (VoD), VoIP and increased IPTV deployment. Providers aim to offering fiber-to-the-home (FTTH), (fiber-to-the-building) FTTB and fiber-to-the-curb (FTTC) solutions through advancing passive optical network (PON) technology. The term “PON” may confuse you for its complexity and extensiveness. Details are as followed.

PON is a single, shared optical fiber that uses inexpensive optical splitters to divide the single fiber into separate strands. It can build up a point-to-point topology supporting 1Gbps transmission to home and business typically within 20km. PON system is called “passive” because that there are no active electronics within the access network. It uses optical splitters to separate and collect signals rather than electrically powered switching equipment.

PON consists of an Optical Line Terminal (OLT) connected to multiple Optical Network Units (ONUs) via an Optical Distribution Network (ODN).

OLT: it is a device at the service provider’s central office, performing conversion between the electrical signals used by the service provider’s equipment and the fiber optic signals used by the passive optical network and coordinating the multiplexing between the conversion devices on the other end of that network.

ODN: it is used for distributing signals to users in a telecommunications network by optical fiber. ODN has been made up entirely of passive optical components particularly singlemode optical fibers and optical splitters.

ONUs: they are devices near end users, delivering traffic-load information provided by OLTs to each end user.

PON System

PON system has achieved significant deployment in today’s FTTx networks especially in FTTH networks as the development of Gigabit passive optical network (GPON) and Ethernet passive optical network (EPON). Nowadays, GPON and EPON are the mostly widely used types of PON for their low cost, high bandwidth, great flexibility and easy management, etc.

GPON: it is defined by ITU-T recommendation series G.984.1 through G.984.6. It can transport not only Ethernet, but also ATM and TDM (PSTN, ISDN, E1 and E3) traffic. It supports services like carrying video and delivering video on single fiber distribution, allowing low-consuming transmission, more efficient maintenance, cabling and overall performance.

EPON: it is defined by the Ethernet standard rather than by the ATM standard, making you utilize the economies-of-scale of Ethernet. It can provide simple and easy-to-manage connectivity to Ethernet-based, IP equipment both at the customer premises and at the central office. It is perfect for voice and video traffic solution as with other Gigabit Ethernet media.

GPON and EPON

 For more information about OLTs, Optical Splitters and ONUs, please visit www.fs.com.

Originally published at: www.fiber-optic-equipment.com/a-guide-for-pon.html

All-optical Switch Overview

Nowadays the growing demand for optical capacity has fueled the development of long-haul optical network systems. As one of perfect solutions for higher bandwidth, WDM technology is widely applied for its multiple transmission channels. However, WDM only delivers raw capacity and the bandwidth needed to be managed by carriers: optical switches. This article will depict one kind of optical switch: all-optical switch in the following content.

Introduction of All-optical Switch

All-optical switch is a device that enables phonotic signals in optical fibers or integrated optical circuits (IOCs) to be switched directly form one circuit to another. It manipulates signals in the form of light, either by redirecting all signals in a fiber or by selecting signals at certain wavelengths in wavelength-division multiplexed systems. It is a lower-cost solution for there is no need for expensive high-speed electronics in the switching process.

Technology of All-optical Switch

There are numerous technologies as how to implement light switching between optical fibers. One of commonly used technologies for developing an economically viable, scalable all-optical switch is micro-electromechanical system (MEMS). MEMS consists of mirrors no larger in diameter that are arranged on special pivots so that they can be moved in three dimensions (3D). Light from an input fiber is aimed at mirror, which is directed to move the light to another mirror on a facing array. Then the mirror reflects the light down towards the desired output fiber. As so many mirrors on a single chip, the cost per switching element is relatively low.

Advantages of All-optical Switch

All-optical switch is a lower-cost solution for there is no need for expensive high-speed electronics in the switching process by using MEMS technology. It can provide a 96% reduction in power consumption. It performs the same function as the OEO switches but features higher performance. All-optical switches can support 1000×1000 ports which are available in a space of two to four bays of equipment. A 3D all-optical switches is even expected to support 8000×8000 ports in the future. Thus all-optical switch makes the networks more flexible and even more dynamic.

Fiberstore SolutionsFiberstore offers a wide range of MEMS switches with different configurations include 1×4, 1×8 and 1×16 configurations for single-mode or multimode fibers. Details information are as follows. All these solutions are highly against environmental variations of temperature and vibration with unmatched low cost due to its novel and unique design. They are tested in-house prior to shipment with commitment that they will reach the destination in perfect physical and working condition. For more information, please visit www.fs.com.

Mobile Internet strategy – Increase broadband

As the use of mobile applications and services that require increasingly more bandwidth continues to grow, wireless service providers must find cost-effective and efficient methods for meeting the bandwidth demand. Legacy transport networks are no longer capable of adequately serving today’s cell sites. Newer technologies such as GPON, WDM-PON, and Ethernet over CWDM/DWDM are all well-suited to cost-effectively address the growing bandwidth needs of wireless service providers. Regardless of the technology used, Fiberstore product is an integral part of the solution.

GPON

While GPON has been adopted as a technology of choice in high-speed access networks for inexpensive residential service delivery, more recently, it has begun to spread into business access.  With the ability to deliver up to 10Gbps per GPON OLT port, it can also be a cost-effective technology for delivering higher bandwidth to cell towers.
GPON

Figure 1: GPON Network

Whether the GPON splitters are collocated with the OLT or distributed in the field, it is likely that a multiple of splitter modules would be needed to handle each serving area.  To aid with this, the SplitLight HD can provide up to 16 GPON splitters in a single, 1RU chassis, while traditional solutions can only provide a single GPON splitter in the same footprint. In addition, legacy LGX solutions would require at least 4RU to deliver the same density.

WDM-PON

Building on the advantages of GPON, shared infrastructure and a single OLT transponder, WDM-PON provides the added advantage of delivering a dedicated wavelength to each GPON ONT. WDM-PON does not use a splitter. Instead, an Arrayed Waveguide Grating (AWG) is used to multiplex and de-multiplex wavelengths between the feeder fibers and distribution fibers. The result is dedicated bandwidth and a more secure network for each subscriber, or in this case, cell tower. Another advantage of WDM-PON is the ability to add/drop wavelengths at intermediate cell towers that lie between mobile switching centers.
WDM-PON

Figure 2: WDM-PON Network
As with GPON splitters, it is likely that multiple AWGs would be required at both ends of the WDM-PON network. The SplitLight HD can also house up to 12 AWGs in a single, 1RU chassis. In addition, the SplitLight HD has the flexibility to also house passive OADMs for the intermediate add/drops.

There are four key points of 10G EPON technology

With the major carriers “Broadband speed”, “Light of Copper” project extensively, The future will be a multimedia broadband services, video on demand, interactive games as the main feature, high-bandwidth, integrated operators will be judged promoted by the merits of the standard broadband products.

Under the broadband Fiber Optic Network in the trend, PON technology has become the world’s attention to various telecom operators hot technology is one of the operators to implement “broadband speed”, “Light of Copper” engineering technology base. Wheter EPON, or GPON, which provides only for the uplink and downlink bandwidth of

1. Defines six 10G EPON optical power budget, in view of the asymmetric mode PRX10, PRX20 and PRX30 as well as for symmetric mode PR10, PR20 and PR30, these six kinds of optical power budget model is basically to meet the construction needs of the service provider network;

2. 10G EPON technology in achieving the 1G EPON conventional multi-point control protocol layer (MPCP) based on the forward compatibility, also extended the original message type, for reporting optical terminal equipment, EPON OLT/EPON ONU Fiber Transceiver switch time to meet the 10G EPON network requirements;

3. 10G EPON uses (255, 223) Forward Error Correction (FEC) encoding method, the encoded with FEC coding for the same strain of 1G EPON, but its strong support 10G EPON coding gain can lower the sensitivity of the optical receiver;

4. 10G EPON uplink and downlink wavelength for the re-planning, downlink using 1268-1280nm wavelength, then reuse the original uplink of 1G EPON 1575-1580 nm wavelength, the wavelength in order to avoid conflicts, 10G EPON uplink only use time division multiple access (TDMA) manner.

Has been released G.987.1 standard that defines 10G GPON system’s overall technical requirements and system architecture, clearly put forward the 10G GPON system to ensure good QoS, based on the traditional telecom services to fully support all emerging businesses and the same time, also provides dynamic Bandwidth Allocation (DBA) algorithm, energy saving, authentication and encryption related content to inherit the original 1G GPON suppliers; The G.987.2 is the focus of standardized 10G GPON physical layer parameters, including downlink rate, ODN power budget, splitting ratio, up and down the line wavelength range and line coding, etc., although down the line of 10G EPON same wavelength range and 10G EPON, GPON but due to the wavelength with 1G is not conflict, therefore, 10G GPON uplink and downlink are used wavelength division multiple access (WDMA) manner.

A complete industrial chain, including chip PON, optical modules and equipment three links. If to analysis PON industry chain, it need to start from the three links, analysis of every link current development status and future development trend.

Overall, 10G EPON and 10G GPON is currently not reach the requirements of large-scale commercial applications, although some equipment manufacturers have recently introduced a 10G EPON or 10G GPON products, and with operators, the creation of some experimental inning, but still in the laboratory testing phase, is still some distance away from the large-scale commercial.
10G PON technology to meet future access networks, “large-capacity, fewer offices,” the direction of development, while improving access speed, supports larger branching ratio, covering more users. Therefore, 10G PON technology will become the future telecom operators to achieve “broadband speed”, “Light of Copper” and other broadband network construction hot technology for sustainable development.