Category Archives: WDM System

How to Save Cost for 500Gbps Metro Network Over Long Distance?

Increasing bandwidth has always been the most important task of telecom engineers. Through decades of research and engineering effort, 40Gbps and 100Gbps solutions have been used for network applications. But 40G and 100G transceivers can’t support too much long distance (QSFP-40G-ER4 for 40 km, QSFP-100G-LR4 for 10 km). How to extend the 500Gbps link to thousands of kilometers in Metro network within limited budget?

Save Fiber Cost–500Gbps Over Single Fiber Cable

Fiber cable cost takes a certain percentage in the whole network budget. Point to point connection needs many cables, while WDM technology take well care of this issue. In a metro network, usually multiple 10Gbps signals are transmitted by the use of DWDM Mux/Demux over a single fiber cable, which can save lots of money on multiple fiber cables and cable management issues. Then how to save cost to transmit 500Gbps signals over single fiber cable?

It sounds unbelievable. But we have the cost-effective solution. As we know, it will cost too much to replace all the current network system for upgrading to higher data rate. To save cost for increasing bandwidth, some producers add an extra port on DWDM Mux/Demux and that is 1310nm or 1550nm port. This port supports 1310nm or 1550nm transceiver. With such port, you can add 1G/10G/40G/100G to the existing DWDM network. For instance, we use 40-channel C21-C60 dual fiber DWDM Mux/Demux with 1310nm port and 1310nm band port for 1G/10G/40G/100G “grey” light. Plug 10G DWDM SFP+ transceivers into 40 channels, the overload is 400Gbps. Once plugging a 1310 40G QSFP+ LR4/ER4, then the total link reach up to 440G (400G + 40G). If install a 100G QSFP28 LR4 transceiver into 1310 port, the whole transport will be 500Gbps (400G + 100G). See this solution realize the goal of saving cost to run such huge network load over a single fiber.

500g dwdm network

40ch dwdm mux-demux

Extend 500G Transmission Distance

Since 500G signals can be transmitted over a single fiber cable, we have another issue to be solved. 500G transmission distance is needed far more than few kilometers in real life, maybe thousand of kilometers. How to extend the transmission distance?

According to IEEE standard, LR4 and ER4 transceivers can support the reach of 10 km and 40 km in the in ideal conditions, not considering fiber loss or connector loss. To extend 500Gpbs transmission distance, we need SOA (Semiconductor Optical Amplifier) and EDFA (Erbium Doped Fiber Amplifier). Add an SOA to support 40G/100GBASE-LR4 transceiver (over 1310 nm). The SOA is used to amplify incoming (Rx) signal on the receiving side of the link. So that the distances can reach up to 60 km. In 10Gbps DWDM networks, the signal transmission distance can be extended to hundreds of kilometers by the use of and EDFA (Erbium Doped Fiber Amplifier).

500g dwdm network-1

Recommended DWDM Solutions for 500Gbps Metro Network
ID# FS Part Number Description
35887 40MDD-1RU-A1-FSDWDM 40 Ch 1RU Duplex DWDM MUX DEMUX C21 to C60 with 1310nm Port and Monitor Port
14491 DWDM-SFP10G-40 10GBASE 100GHz DWDM SFP+ 40km, LC Duplex Interface, C21 to C60
31533 DWDM-SFP10G-80 10GBASE 100GHz DWDM SFP+ 80km, LC Duplex Interface, C21 to C60
14599 DWDM-XFP10G-40 10GBASE 100GHz DWDM XFP 40km, LC Duplex Interface, C21 to C60
14650 DWDM-XFP10G-80 10GBASE 100GHz DWDM XFP 80km, LC Duplex Interface, C21 to C60
35208 QSFP-LR4-40G 40G QSFP+ LR4 1310nm 10km, LC Duplex Interface
35210 QSFP-ER4-40G 40G QSFP+ ER4 1310nm 40km, LC Duplex Interface
35014 CFP2-LR4-100G 100G CFP2 LR4 1310nm 10km, LC Duplex Interface
35192 FS-SOA-G10 10dB Gain 1310nm Semiconductor Optical Amplifier
31366 EDFA-BAO22 20dBm Output C-band 40 Channels 26dB Gain Booster EDFA


DWDM technology is very necessary to extend Metro Network reach. In this 500Gpbs Metro network, I have introduced very detailed cost-effective solutions. Remember all the indispensable DWDM equipment such as DWDM transceivers, DWDM Mux/Demux, EDFA, etc. For more information, please visit the site about FS.COM Long Haul DWDM Network Solution.

Related articles:

How to Extend 40G Connection up to 80 km?
Economically Increase Network Capacity With CWDM Mux/DeMux

Economically Increase Network Capacity With CWDM Mux/DeMux

As the demands for voice, video and data networks are increasing dramatically, more bandwidth and higher transmission speed over long distances are needed. To meet these demands, it means that service providers should depend on more fiber optics which definitely cause more costs for optical devices. But they apply Wavelength Division Multiplexing (WDM) technologies which is a cost-effective way to increase capacity on the existing fiber infrastructure.

CWDM Technology

WDM technology multiplexes multiple optical signals onto a single fiber by suing different wavelengths, or colors, of light. WDM can expand the network capacity using existing fiber infrastructure in an economical way. It includes CWDM (Coarse Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing).

CWDM is a technology multiplexing 16 channels onto one single fiber between the wavelengths from 1270 nm to 1610 nm. It’s designed for city and access network. Since the channel spacing is 20 nm, CWDM is a more cost-effective method to maximize existing fiber by decreasing the channel spacing between wavelengths. CWDM is a passive technology, therefore, CWDM equipment needs no electrical power.


Figure 1

CWDM technology has been applied into wide areas, such as CWDM optical transceivers, CWDM OADM and CWDM Mux/DeMux. CWDM Mux/DeMux modules are multiplexers and demultiplexers which provide long distance coverage with premium optical technology to enhance fiber optic systems. It multiplexes signals of different wavelengths on one single fiber and demultiplexes wavelengths to individual fibers. CWDM Mux/DeMux can offer low-cost bandwidth and upgrade the existing system without leading spare costs on more fibers. CWDM Mux/DeMux can hold up to 18 channels of different standards (for example, Fibre Channel, Gigabit Ethernet) and data rates over one fiber optic link without interruption. FS.COM offers a full series of CWDM Mux/DeMux, including 2, 4, 8, 9, 12, 16, 18 channels with or without monitor port and expansion port in 1RU 19” rack chassis or pigtailed ABS module. The following will show you how to use a 18-channel CWDM Mux/DeMux to increase the data rates up to 180 Gbps on a fiber pair.

In Figure2, all Cisco compatible 10G CWDM SFP+ 1270-1610 nm 40km DOM transceivers on the switch are connected with the CWDM Mux/DeMux by LC-LC fiber patch cords. This CWDM Mux/DeMux has 18 channels and is designed as 1 RU rack mount size, covering the wavelengths from 1270 nm to 1610 nm and supporting LC UPC port. During the long distance transmission, only one single-mode armored LC fiber patch cord is needed to achieve 180 Gbps by connecting the two 18-channel CWDM Mux/DeMux. Thus, it greatly saves the cost for increasing the bandwidth on the existing fiber infrastructure.


Figure 2

FMU CWDM Mux/Demux

To increase the capacity, it requires more space and cable management is also a big trouble. So Fiberstore independently researched and developed FMU CWDM Mux/DeMux to solve this problem. We provide FMU 16-ch 1U Rack CWDM MUX/DEMUX specially designed as 2-slot plug and play style, which allows you to add or remove fiber fiber optic cables and plug-in-modules freely according to your applications. There are two separate CWDM plug-in modules. One is high band (1470nm-1610nm) module with an expansion port and the other is low band (1270nm-1450nm, skip 1390nm, 1410nm) module without expansion port. Via this expansion port, channels can be expanded over one pair of fiber without interruption. You can also insert two CWDM Mux/DeMux FMU-plug-in modules without expansion port for two separated 8-channel connections. Besides, you can mix CWDM and DWDM system by adding CWDM Mux/DeMux FMU-plug-in modules and DWDM Mux/DeMux FMU-plug-in modules with matching wavelengths.


Figure 3

FS.COM FMU Plug-in Modules

The table below lists both single fiber and dual fiber FMU plu-in modules for 2-slot CWDM Mux/DeMux. You can choose suitable modules according to you specific requirements. Custom service is available, too.

ID# Description
30431 2, 4, 5, 8, 9 Channels, CWDM Mux Demux, Single Fiber, Type A, Plug-in Module
30447 2, 4, 5, 8, 9 channels, CWDM Mux Demux, Single fiber, type B, Plug-and-play module
43553 4 Channels 1490-1610nm Single Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
43554 4 Channels 1470-1590nm Single Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
48393 4 Channels 1470-1590nm Single Fiber CWDM Mux Demux with Expansion Port, FMU Plug-in Module, LC/UPC
48394 4 Channels 1490-1610nm Single Fiber CWDM Mux Demux with Expansion Port, FMU Plug-in Module, LC/UPC
43779 8 Channels 1310-1610nm Single Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
43780 8 Channels 1290-1590nm Single Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
43699 9 Channels 1290-1610nm Single Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
43711 9 Channels 1270-1590nm Single Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
30414 2, 4, 5, 8, 9 Channels, CWDM Mux Demux, Dual Fiber, Plug-in Module
42944 4 Channels 1510-1570nm Dual Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
42972 4 Channels 1270-1330nm Dual Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
42973 4 Channels 1510-1570nm Dual Fiber CWDM Mux Demux with Expansion Port, FMU Plug-in Module, LC/UPC
42945 8 Channels 1290-1430nm Dual Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
43097 8 Channels 1470-1610nm Dual Fiber CWDM Mux Demux, FMU Plug-in Module, LC/UPC
43099 8 Channels 1470-1610nm Dual Fiber CWDM Mux Demux with Expansion Port, FMU Plug-in Module, LC/UPC

If you would like to increase your network bandwidth while spend less money on changing existing infrastructure, CWDM Mux/DeMux is an economical solution. FS.COM brings you high quality CWDM Mux/DeMux module and newly self-developed FMU 2-slot CWDM Mux/DeMux modules & FMU plug-in modules. For detailed information, please visit our site or contact us through

Check out All CWDM Transceiver Modules

Coarse Wavelength Division Multiplexing (CWDM) is one of WDM technologies. It uses up to 20 different wavelengths for data transmission over a single fiber. CWDM applies coarse wavelength grid and it allows low-cost, uncooled lasers, which makes CWDM systems less expensive and consuming less power. There are many optical equipment applying CWDM technology. This article will introduce CWDM optical transceivers.


CWDM Transceivers

CWDM transceiver is a kind of optical modules employing CWDM technology. CWDM transceivers enable connectivity between existing network equipment and CWDM Multiplexers/DeMultiplexers (Mux/DeMux). When used with CWDM Mux/DeMux, CWDM transceivers can increase network capacity by transmitting multiple data channels with separate optical wavelengths (1270 nm to 1610 nm) over the same single fiber. CWDM transceivers are also useful for reducing network equipment inventories by eliminating the need to maintain surplus units/ devices of various fiber types for network repairs or upgrades. CWDM transceivers include four types, such as CWDM SFP, CWDM SFP+, CWDM XFP and CWDM X2. The following shows more details about these CWDM transceiver modules.

CWDM Transceiver Module Types

CWDM SFPs are hot-pluggable transceiver modules. CWDM SFP transceivers are SFP MSA (Multi Sourcing Agreement) and IEEE 802.3 & ROHS compliant. CWDM SFPs can provide data rates including 1G, 2G and 4G over the link distance of up to 200 km by connecting with duplex LC single-mode patch cords. CWDM SFPs transmit multiple data channels by combining separate optical wavelengths onto a single fiber to increase network capacity. CWDM SFPs can be used to support the CWDM passive optical system combing CWDM OADM (optical add/drop multiplexer). When CWDM SFPs used with transponders and media converters, these two optical components offer convenient method to convert existing legacy equipment with standard wavelengths or copper ports to CWDM wavelengths.

CWDM SFP+ offers service providers and enterprise companies an easy way to get a scalable 10 Gigabit Ethernet network. It is a cost-effective solution for 10 Gigabit Ethernet applications in campus, data center and metropolitan area access networks. CWDM SFP+ can transport up to eight channels of 10 Gigabit Ethernet over single-mode fiber strands at the wavelengths including 1610 nm, 1590 nm, 1570 nm, 1550 nm, 1530 nm, 1510 nm, 1490 nm, and 1470 nm. CWDM SFP+ solution is helpful to increase the bandwidth of an existing 10 Gigabit Ethernet optical infrastructure without adding new fiber strands. The solution can be used in parallel with other SFP+ devices on the same platform.

CWDM XFP is a hot-pluggable module designed in Z-direction and mainly used for typical routers and switch line card applications. CWDM XFP transceivers are designed for Storage, IP network and LAN. They comply with CWDM XFP MSA. CWDM XFPs cover the wavelengths from 1270 nm to 1610 nm. These modules can support the distance up to 100 km, which depends on the wavelengths, fiber types and the CWDM Mux/DeMux insertion loss.

CWDM X2 transceiver is designed for CWDM optical data communications such as 10G Ethernet and 10G Fibre Channel applications. CWDM X2 wavelengths are available from 1270 nm to 1610 nm. CWDM X2 is MSA Compliant. It supports the transmission distance up to 80 km connecting with duplex SC single-mode fiber cable.


CWDM technology provides a low-cost solution which allows scalable and easy-to-deploy Gigabit Ethernet and Fibre Channel services. CWDM transceivers enable a more flexible and highly available multi-service network with the combinations of CWDM OADMs and CWDM Mux/DeMux. FS.COM offers all kinds of CWDM transceivers like CWDM SFP, CWDM SFP+, CWDM XFP, CWDM X2. Our CWDM transceivers are compatible with most famous brands and all these optics have been fully tested to make sure high compatibility. For more details about Fiberstore CWDM transceivers and other CWDM equipment, please visit our site or contact us via

User Guide for CWDM MUX/DEMUX

Is there a way to enhance your network system but also save cost, time and effort? Do you want to give up traditional model of using many fiber cables? The cost-effective way is to use the CWDM MUX/DEMUX (coarse wavelength division multiplexing multiplexer/demultiplexer). If you are the first time to use it, you are lucky to read the following content.


CWDM Mux/Demux Introduction

First you need to know what CWDM is. CWDM is a technology which multiplexes multiple optical signals on a single fiber by using different wavelengths of the laser light to carry different signals. CWDM MUX/DEMUX applies this principle. A CWDM MUX/DEMUX can maximize capacity and increase bandwidth over a single or dual fiber cable. It mixes the signals in different wavelengths onto a single fiber and splits it again into the original signals at the end of a link. This kind of device is used to reduce the number of required fiber cables and get other independent data links. CWDM MUX/DEMUX modules are wide from 2 channels to 18 channels in the form of 1RU 19’’ rack chassis. The following will take 9 channels 1290-1610nm single fiber CWDM Mux/Demux as an example. It’s a half 19’’/1RU module for LC/UPC connection.

Features are as follows:
  • Support up to 9 data streams
  • Wavelength range: 1260~1620 nm
  • Low insertion loss, half 19’’/1RU module low profile modular design
  • Passive, no electric power required
  • Simplex LC/UPC for line port
  • Duplex LC/UPC for CWDM channel port, easily support duplex patch cables between the transceiver and passive unit
  • Operating temperature: 0~70℃
  • Storage temperature: -40~85℃
Preparation for Installation

To connect the CWDM Mux/Demux, you need two strands of 9/125μm single-mode fiber cables. Supportable transceivers cover the wavelengths of 1290 nm, 1370 nm, 1410 nm, 1450 nm, 1490 nm, 1530 nm, 1570 nm 1610 nm. And this device is used together with 9 CWDM-2759-LC-LGX-SFB.


To ensure a reliable and safe long-term operation, please note the points below:

  • Only use in dry and indoor environments.
  • Do not locate CWDM Mux/Demux in an enclosed space without airflow since the box will generate heat.
  • Do not place a power supplies directly on top of a unit.
  • Do not obstruct a unit’s ventilation existing holes.
System Installation Procedures

1.To install CWDM MUX/DEMUX system, switch off all devices.
2.Install CWDM transceivers. Remember each channel has a unique transceiver with a certain wavelength. So each transceiver must be plugged into the appropriate channel and must not be used more than once in the system. Devices pairs must carry transceivers with the same wavelength.
3.Connect CWDM MUX/DEMUX units with matching cables (single-mode fiber). Before connecting cable, you should first inspect if the connectors are lean. Never forget cleaning work is an important factor to achieve a better network performance. The guidelines:

  • Keep connectors covered when not in use to prevent damage.
  • Usually inspect fiber ends for signs of damage.
  • Always clean and inspect fiber connectors before make a connection.

4. Power up the system.


When you connect the system, but you find there is not data link. Then you need to do:

  • 1. Check the attached devices by directly connecting CWDM MUX/DEMUX units using a short fiber cable.
  • 2. Check the fiber cables and fiber connectors.
  • 3. Check that each wavelength doesn’t occur more than once at the CWDM MUX/DEMUX units.
  • 4. Check if the transceivers are inserted into the matching port at the CWDM MUX/DEMUX units.

CWDM MUX/DEMUX is a cost-effective solution for expanding bandwidth capacity for short link communication. Besides saving costs, CWDM lasers consume less power and take up less space. FS.COM offers both CWDM MUX/DEMUX and DWDM MUX/DEMUX with high quality. If you are the first time to use these devices, keep in mind the above notes.

EPON — An Ideal Optical Access Network Solution

In recent years, the telecommunications backbone has experienced huge growth. The tremendous growth of Internet traffic has far surpassed the network capacity. The “last mile” still remains the bottle neck between high-capacity local area networks and the backbone network. So a new technology for optical access network, which is simple, scalable but not expensive, is needed. And that is Ethernet passive optical network (EPON).

EPON Definition

EPON, unlike other PON technologies which are based on the ATM standard, is based on the Ethernet standard. 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. As with other Gigabit Ethernet media, it is well-suited to carry packetized traffic, which is dominant at the access layer, as well as time-sensitive voice and video traffic.

EPON Network

An EPON network includes two parts: an optical line terminal (OLT) and an optical network unit (ONU).

The OLT resides in the central office (CO). This could typically be an Ethernet switch or Media Converter platform. OLT is mainly designed for controlling the information float across the optical distribution network (ODN). OLT has two float directions: upstream (getting an distributing different type of data and voice traffic from users) and downstream (getting data, voice and video traffic from metro network or from a long-haul network and sending it to all ONU modules on the ODN.

The ONU resides at or near the customer premise, in a building, or on the curb outside. It uses optical fiber for connecting to the PON on the one side, while interfacing with customers on the other side.

EPON Upstream and Downstream Traffic

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

In the downstream direction (from network to user), Ethernet frames transmitted by OLT pass through a 1:N (N represents the number of subscribers each fiber can serve) passive splitter and reach each ONU. Splitting ratios are usually between 4 and 64. At the splitter, the traffic is divided into separate signals, each carrying all of the ONU–specific packets. When the data reaches the ONU, it accepts the packets that are intended for it and discards the packets that are intended for other ONUs.


In the upstream direction (from user to network ), due to the directional properties of a passive combiner (optical splitter), data frames from any ONU will only reach the OLT, not other ONUs. Frames in EPON from different ONUs transmitted simultaneously may collide. Thus, ONUs need to share the trunk fiber channel capacity and resources.


EPON Advantages

First, EPON uses a point-to-multipoint topology instead of point–to-point in the outside plant. Thus it saves much of the cost of running fiber from every customer to the CO, installing active electronics at both ends of each fiber and managing all of the fiber connections at the CO. And EPON also eliminates active electronic components, such as regenerators and amplifiers, and replaces them with passive optical couplers that are less-expensive, simpler, and longer lived than active ones. As to the cost of expensive electronic components and lasers in the OLT, it will be shared over many subscribers not paid by each subscriber.

Second, EPON offers high bandwidth to subscriber. The traffic rates of 1Gbps in downstream and return traffic of 800 Mbps have been achieved already. Compared with point–to-point technology, EPON is specially made to address the unique demands of the access work. So more bandwidth can be got by each subscriber.

At last, the main advantage of EPON is that it can eliminate complex and expensive asynchronous transfer mode (ATM) and SONET elements and simplify the networks dramatically. Traditional telecom networks use a complex and multilayered architecture. While this architecture requires a router network to carry IP traffic, ATM switches to create virtual circuits, add/drop multiplexers (ADM) and digital cross-connects to manage SONET rings, and point-to-point DWDM optical links.


EPON is suitable for Fiber-to-the-Home/Building/Business applications, including voice, data and video services. EPON is a shared network but with much higher bandwidth. It’s a highly attractive access solution for service providers to extend fiber into the last mile because of low cost and good performance, resulting from their nature as passive networks, point-to-multipoint architecture, and native Ethernet protocol.

Erbium Doped Fiber Amplifier (EDFA) Used in WDM System

The capacity of fiber optical communication systems has undergone enormous growth during the last few years in response to huge capacity demand for data transmission. With the available wavelength division multiplexing (WDM) equipment, commercial system can transport more than 100 channels over a single fiber. However, increasing the number of channels in such systems will eventually result in the usage of optical signal demultiplexing components with greater values of optical attenuation. Besides, when transmitted over long distances, the optical signal is highly attenuated. Therefore, to restore the optical power budget, it is necessary to implement optical signal amplification. This article may mainly tell you  why EDFA is used in WDM system and how does it work.

Why Use EDFA in WDM System?

EDFA stands for erbium-doped fiber amplifiers, which is an optical amplifier that uses a doped optical fiber as a gain medium to amplify an optical signal. EDFA has large gain bandwidth, which is typically tens of nanometers and thus actually it is enough to amplify data channels with the highest data rates. A single EDFA may be used for simultaneously amplifying many data channels at different wavelengths within the gain region. Before such fiber amplifiers were available, there was no practical method for amplifying all channels between long fiber spans of a fiber-optic link. There are practically two wavelength widows C-Band (1530nm-1560nm) and L-Band (1560nm-1600nm). EDFA can amplify a wide wavelength range (1500nm-1600nm) simultaneously, which just satisfies the DWDM application, hence it is very useful in WDM for amplification.

How Does EDFA Work ?

The basic configuration for incorporating the EDFA in an optical fiber link is shown in the picture below. The signals and pump are combined through a WDM coupler and launched into an erbium-doped fiber (EDF). The amplified output signals can be transmitted through 60-100km before further amplification is required.

Erbium-doped fiber is the core technology of EDFA, which is a conventional silica fiber doped with erbium ions as the gain medium. Erbium ions (Er3+) are having the optical fluorescent properties that are suitable for the optical amplification. When an optical signal such as 1550nm wavelength signal enters the EDFA from input, the signal is combined with a 980nm or 1480nm pump laser through a wavelength division multiplexer device. The input signal and pump laser signal pass through erbium-doped fiber. Here the 1550nm signal is amplified through interaction with doped erbium ions. This can be well understood by the energy level diagram of Er3+ ions given in the following figure.


Where to Buy EDFA for Your WDM System ?

To ensure the required level of amplification over the frequency band used for transmission, it is highly important to choose the optimal configuration of the EDFAs. Before you buy a EDFA, keep in mind that the flatness and the level of the obtained amplification, and the amount of EDFA produced noise are highly dependent on each of the many parameters of the amplifier. Fiberstore provide many kinds of EDFAs, especially the DWDM EDFAs (shown in the picture below), which have many output options (12dBm-35dBm). Besides, they are very professional in optical amplifiers. Whatever doubts you have, they can give a clear reply.


WDM Multiplexer Is an Ideal Component Optimized for WDM Aplications

Wavelength-division multiplexing (WDM) is a technology which allows multiple signals to be transmitted at different wavelengths over a single optical transmission medium. It can dramatically expand the total capacity of an optical network, for many signals are able to be transported simultaneously. This core technology makes optical network capacity to be gradually efficiently increased to meet the higher demand for bandwidth. To construct WDM networks, a wide range of optical components optimized for WDM applications are required to be researched and created. One of the important components is WDM multiplexer.

WDM multiplexer is a electronic device that uses WDM technology. It is able to combine light signals with different wavelengths coming from different fibers on to a single fiber. A multiplexer usually has two signal inputs, one control input and one output. The input end of a WDM multiplexer is coupler that combines all the inputs into one putout fiber. And each channel in a WDM multiplexer is designed to transmit a specific optical wavelength. For example, an 16-channel multiplexer would have the ability to combine sixteen different channels or wavelengths from separate optical fibers onto one optical fiber. And the separated signals will be recovered by another multiplexer called demultiplexer. The following picture shows how the signals are transported.

multiplexer and demultiplexer

WDM multiplexer is available with various configurations such as 2,4, 8, 16, 32, 64, etc. The types of multiplexers can be divided by channel spacing. They can be called CWDM multiplexers, wideband or crossband ones, and DWDM multiplexers, narrowband or dense ones. Compared to DWDM multiplexers, CWDM multiplexers combines signals at fewer channels for its larger channel spacing. CWDM multiplexers is usually with configurations such as 8, 16 and so on, while DWDM multiplexers is commonly with configurations including 32, 96, 128, etc. CWDM multiplexers are able to combine a broad range of wavelengths such as l310 nm and 1550 nm. DWDM multiplexers are able to combines wavelengths with 100 GHz channel spacing. It typically provides a broad range of wavelengths in 1.55-μm region within C-band.

WDM multiplexer, an advanced optical component, is widely used in optical links. It can increase connectivity and bandwidth of processing systems by interconnecting different channels. Most WDM multiplexers employ one of three technologies: arrayed waveguide grating (AWG), filter and dispersive element, primarily diffraction grating. Some multiplexers based on filters exhibit high insertion loss for devices with many channels, which makes them are not suitable in the application of multimode and bi-directional transmission. But the multiplexers with AWG technology offers many advantages over them including low cost for many channels, low loss, little crosstalk, and receiving much attention. With AWG technology, WDM multiplexer is ideal for the application of high throughput optical links in parallel processing and computing.

It is concluded that WDM multiplexer with WDM technology is a key component in optical links and even in the high throughput optical links.

Fiber Optic Sensor Overview

Due to the advantages of fiber optical transmission over electrical transmission, optical fibers have been researched extensively. Among those researches, one of the fields of optical fibers is designing a sensing system based on optical fibers and optical sensors. And as optical fibers are being deployed in an increasing number with lowering cost, fiber optic sensors (FOSs) replaced ordinary ones and keep growing. It is also expected that optical sensors will have a broad prospect. In this article, the fundamentals of fiber optic sensors will be reviewed, along with the basic introduction, types, applications and prospect.

Introduction of Fiber Optic Sensor

Fiber optic sensor is a sensor that uses optical fiber either as the sensing element or as a means of relaying signals from a remote sensor to the electronics that process the signals. It consists of optical source (LASER, laser diode, LED, etc), optical fiber as transmission channel, sensing element, optical detector and end processed devices (oscilloscope, optical spectrum analyzer, etc). Compared to conventional electronics sensors, it has numerous advantages such as compact size, light weight, immunity to electromagnetic interface, high performance and larger bandwidth, etc.

Types of Fiber Optic Sensor

Fiber optic sensors can be classified by different standards including the sensing location, the operating principal and applications. By the first standard, they can be classified into intrinsic or extrinsic sensors. By the second standard, they can be divided into intensity, phase, frequency or polarization sensors. And by the last standard, they can be classified into physical, chemical, bio-chemical sensors. Here is a brief introduction of intrinsic and extrinsic sensors.

Intrinsic fiber optic sensor: it has a sensing region within the fiber and light never goes out of fiber.

Extrinsic fiber optic sensor: the light in it has to leave the fiber and reach the sensing region outside and then comes back to the fiber.Extrinsic Fiber Optic Sensor and Intrinsic Fiber Optic Sensor

Applications of Fiber Optic Sensor
  • Mechanical measurements: force, pressure, strain/stress, displacement, temperature, acceleration, vibration, acoustics
  • Electrical and magnetic measurements
  • Chemical and biological sensing
Prospect of Fiber Optic Sensor

Fiber optic sensor market is potential in the future. It is 1.99billion in 2014 and expected to reach 3.15 billion by 2019, at a compound annual growth rate (CAGR) of 9.6%. According to the picture, the market is growing at an increasing rate, up from 5.2% to 10.4%. It will give rise to greater implementation of optical sensors in regular life for their transparent advantages over electronic sensors and various applications in physical, chemical and bio-chemical fields. China has dominated the fiber optic sensor market and plans to expand its market share at higher speed.Fiber-Optic-Sensor-Market

For more information, please visit

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 amplify 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.

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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 Fiberstore.