A Brief Introduction to Cisco Single-Mode SFP Modules


Small form-factor pluggable (SFP) module is a hot-pluggable interface transceiver which links switches and routers to network. These small, modular optical interface transceivers offer a convenient and cost effective solution for the adoption of Gigabit Ethernet and Fibre Channel in data center. Cisco’s industry-standard SFPs can be used and interchanged on a wide variety of Cisco products and can be intermixed in combinations of IEEE 802.3z compliant 1000BaseSX, 1000BaseLX/LH, or 1000BaseZX interfaces on a port-by-port basis. Cisco SFP modules are commonly available in several different types: 1000BASE-T, 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-EX, 1000BASE-ZX, and 1000BASE-BX-D/U. This post will give an introduction to Cisco single-mode SFP modules.

Cisco 1G single-mode SFP

Cisco 1G Single-Mode SFP Modules

Cisco 1G single-mode SFP modules consist of 1000BASE-LX/LH, 1000BASE-EX, 1000BASE-ZX, 1000BASE-BX-U, 1000BASE-BX-D, GLC-BX40-D-I, GLC-BX40-DA-I, GLC-BX40-U-I, GLC-BX80-D-I, and GLC-BX80-U-I. The 1000BASE-LX/LH SFP is compatible with the IEEE 802.3z 1000BASE-LX standard, functions on single-mode fiber-optic link and its transmission range can cover 550 m to 10 km on any multimode fibers. 1000BASE-EX SFP functions on standard single-mode fiber-optic link with spanning up to 40 km in length. 1000BASE-ZX SFP functions on standard single-mode fiber-optic link and its transmission range reaches approximately 70 km in length.

The 1000BASE-BX-D and 1000BASE-BX-U SFPs which are compatible with the IEEE 802.3ah 1000BASE-BX10-D and 1000BASE-BX10-U standards function on a single strand of standard SMF (Single-Mode Fiber) and its operating transmission range covers up to 10 km. The Cisco GLC-BX40-D-I, GLC-BX40-DA-I, and GLC-BX40-U-I SFPs also operate on a single strand of standard SMF and its transmission range can reach 40 km. A GLC-BX80-D-I and GLC-BX80-U-I device function on a single strand of standard SMF with an operating transmission range up to 80 km.

Another difference between these SFP modules is the transmission direction: 1000BASE-LX/LH, 1000BASE-EX and 1000BASE-ZX’ transmission is duplex while 1000BASE-BX-U, 1000BASE-BX-D, GLC-BX40-D-I, GLC-BX40-DA-I, GLC-BX40-U-I, GLC-BX80-D-I, and GLC-BX80-U-I’s transmission is simplex. One thing they have in common is that all these Cisco single-mode SFP modules adopt LC interfaces and Cisco SFP 1G transceivers can transmit optical signals through simplex or duplex LC patch cable.

Transmission of a Single Strand of SMF

Features and Benefits

Cisco single-mode SFP modules feature a variety of different types of modules supporting different transmission ranges and direction, and they are also compatible with products of other categories. The hot-swappable input/output device directly plugs into an Ethernet SFP port of a Cisco switch, which maximizes uptime and simplifies serviceability when installing or replacing. The robust design enhances capability and the small factor features great density per chassis. Its flexibility of media and interface choice on a port-by-port basis bring you convenience. “Pay as you Populate” model lowers initial costs. It can support digital optical monitoring (DOM) capability for strong diagnostic capabilities. Cisco quality identification (ID) feature enables a Cisco platform to identify whether the module is certified and tested by Cisco and it can be interoperable with other IEEE-compliant 1000BASE interfaces where applicable.


This post briefly introduces Cisco single-mode SFP modules, covering its definition, types of these SFPs and introduction of each type, and features and benefits of Cisco single-mode SFP modules. Now there are a number of modules for you to choose, but be sure to find the right one based just on your needs and at the same time take a few factors into consideration.

Switches Used in LAN Network

LAN refers to local area network, which is a network of computers that are in the same general physical location, usually within a building or a campus, share a common communications line or wireless link to a server. Typically, LAN can achieve file management, application software sharing, printer sharing, workgroup scheduling, e-mail and fax communication services and so on. A local area network may serve several hundred users in a larger office, which comprises cables, switches, routers and other components that let users connect to internal servers, websites and other LANs via wide area networks.

LAN network

Figure 1. LAN Frame

How Does LAN Work?

When two or more network devices have data to send at the same time, the data packets from one user may collide with another, because multiple devices cannot talk on the network simultaneously. For this reason, there should be some methods for the data to access the cable without disturbing another at a time.

Access methods define a set of rules governing how computers access the network – put data onto the network cable and take data from the cable at the same time.This is done in two main methods:

Carrier-Sense Multiple Access with Collision Detection (CSMA/CD)
  • All computers listen for traffic on the LAN.
  • If no traffic, computer that wishes to transmit may transmit data.
  • If a collision occurs, computers must wait a random amount of time.(The busier a network becomes, the more collisions occur)
  • The computer with the smallest random number send again first. (In most cases, a collision will not occur again between the two computers.)
Token Passing
  • All computers need the token which is passed around the network.
  • If a computer has data to send, it must wait until it has the token and then sends its data.
  • When the data transmission is completed, the token is released.
  • It helps to calculate the maximum time when a computer has the chance to send data.
Switches used in LAN Network

Switches that provide a separate connection for each computer in the internal network are called LAN switches. Essentially, a LAN switch creates a series of instant networks that contain only the two devices communicating with each other at that particular moment. LAN switches are designed to switch data frames at high speed. LAN switches are the “cornerstone” of building a network platform,which require less configuration, smaller space, fewer cabling, cheaper prices, and higher and more reliable performance.

Switching technologies are crucial to network design that is a form of packet switching used in LAN. LAN switching uses different kinds of network switches. A standard switch is known as a layer 2 switch and is commonly found in nearly any LAN. Layer 3 or layer 4 switches require advanced technology and are more expensive, and thus are usually only found in larger LANs or in special network environments. Here are two main LAN access switches:


S3800-24F4S mode contains one console port that connects to computer for Command Line Interface (CLI) management, four 1GE combo ports, in which RJ45 and SFP ports with same figure are a couple of shared ports, 20 100/1000BASE SFP ports and 4 10GE SFP+ ports.

lan switches


As for S3800-24T4S mode, it offers one console port, 24 100/1000BASE-T ports and 4 10GE SFP+ ports.

lan switches 1

S3800-24F4S and S3800-24T4S high performance Metro Ethernet switches are designed to meet the demand of cost-effective Gigabit access or aggregation for enterprise networks and operators customers, which adopt high performance and low power processor to provide full speed forwarding and line-dormant capacity. Besides, they support multiple configuration modes to make it easy for network management and maintenance and offer flexible port combination form to facilitate user operations so that you can directly connect to a high-performance storage server or deploy a long-distance uplink to another switch.

Outstanding Features of These Switches:
  • Enterprise-Class Features: support advanced Layer 2+ switching and max transfer rate of single port can reach 10GE compared to Layer
  • High-Capacity Uplinks: every port can be used as the uplink port. SFP+ ports support uplinks of up to 10GE. For high-capacity uplinks, the SFP+ ports can reach 40GE via WEB or order.
  • Switching Capacity: offer 128Gbps switching capacity to simultaneously process traffic on all ports at line rate without any packet loss.
  • Line-Dormant Support: the ports will switch to power saving mode when date traffic is relatively small.

The network switch plays an integral role in most modern Ethernet LAN, because the LAN switches greatly improve the rate of data transmission and the user experience. In addition, LAN access switches are the fundamental solutions to help you save time and focus on more strategic initiatives, which provide high-speed connectivity, application, and communication systems that efficiently and securely manage bandwidth-intensive data transmission.

Time-to-Link Test for 1000BASE-T and 10GBASE-T


This post is composed on the basis of the physical layer (PHY) behavior assessment of 1000BASE-T and 10GBASE-T. In order to understand the test results and the meaning of this discussion, some terminologies have to be introduced first.

The Meaning of Time-to-Link

Time-to-link (TTL) is a system performance standard that characterizes and measures the PHY behavior through autonegotiation (AN) and 1G/10GBASE-T startup sequences (correspond to training). It is one of the two primary performance measures (the other is bit error rate) used to characterize BASE-T PHY link rate interoperability.

For Ethernet over twisted pair, autonegotiation is defined in clause 28 of IEEE 802.3. It is a procedure by which two connected devices choose common transmission parameters. In this process, the link partner firstly share their capabilities, such as speed, duplex mode, and flow control, and then choose the highest performance transmission mode they both support.

Since servers networking drivers must meet the third party certifications, the TTL standard used to measure link interoperability becomes rather important. Otherwise, long TTLs (>6s) can lead to device certification failures.

How to Measure the Link Interoperability?

There are several representative link interoperability metrics associated with TTL. Their meanings are explained as follows:

TTL: time to achieve link after link initiate event.

Link attempts number: number of attempts made to resolve Master/Slave status for each link. Within a link, one link partner is designated as the master timing source for transmitted signals in both directions. One partner is Master and one partner is Slave.

Link drops number: number of link drops observed after link is established.

Clock recovery: Some digital data streams, especially high-speed serial data streams, such as Ethernet, are sent without an accompanying clock signal. The receiver generates a clock from an approximate frequency reference, and then phase-aligns the clock to the transitions in the data stream with a phase-locked loop (PLL). This is one method of performing a process commonly known as clock and data recovery (CDR). Here it is also called Master/Slave resolution.

TTL distribution: percentage of links by link time.

Speed downshift/downgrade: resolved speed if other than 10Gbps.

Presentation and Analysis of the Results

Totally 1550 link tests are performed, and the results are:

  • 1,050 out of 1,550 tests, or 67% of the total number of link tests, achieved a link state in 7s or less (green slice).
  • 499 out of 1,550 tests, or 32% of the total number of link tests, achieved a link state somewhere between 7s and 15s (blue slice).
  • 1 out of 1,550 tests, or < 1 % (actually 0.15%) of the total number of link tests, achieved a link state longer than 15s (exactly 16.4s; yellow splice, actually it should be smaller than presented in the pie chart).

TTL % of total trials pie chart

Source: http://www.ieee802.org

Characterizing TTL behavior

Cumulative percentage (%) TTL is the distribution of measured link times as a percentage of total measured link time. Total link time recorded for all 1,550 tests is 10,837,835ms or about 3h 0min 38sec. The measured link time and cumulative percentage of each result is recorded in following table and chart:

Cumulative percentage TTL

Source: http://www.ieee802.org

TTL behavior

Source: http://www.ieee802.org

TTL Distribution and Master/Salve Resolution by Channel Length

In this part, the example of 10GBASE-T TTL measured from 2m to 115m channels (9790 links) will be given. The average TTL across 2m to 100m is 7.5s; the average time in autonegotiation is 5s; the average time in training is 2.6s. The following two charts illustrate the TTL distribution and clock recovery results by channel lengths from 2m to 115m.

TTL distribution by channel length

Source: http://www.ieee802.org

clock recovery distribution by channel length

Source: http://www.ieee802.org

According to the charts, we can see that there is an apparent loop timing trend towards Master preference with increasing channel length. And very long TTLs (>15s) at >100m channels are associated with downshits to 1Gb link speed.

AN & Training Times for 1000BASE-T and 10GBASE-T

Measured autonegotiation and training times from 1550 1Gb links for 10GBASE-T device to 1000BASE-T link partner, and 10GBASE-T device to 10GBASE-T link partner are respectively:

AN & traning times and TLL


From the test results on 1000BASE-T and 10GBASE-T, user TTL experience of 1000BASE-T installed over Cat5e cable or better is between 3s and 4s, and 10GBASE-T installed over Cat6a or better is about 7s, or longer in some cases. And the measured autonegotiation times for 1000BASE-T and 10GBASE-T are comparable. And for future 2.5/5GBASE-T, it is highly desirable that their autonegotiation and startup times can be improved, and that total TTL be minimized, so as to be more aligned with end-users’ expectations and requirements.

Appendix: AN & Training Times for 1000BASE-T and 10GBASE-T

1G AN time ditribution

1G traning time ditribution

10G AN time ditribution

10G traning time ditribution

Source: http://www.ieee802.org

Comparison Between Single Mode Transceiver and Multimode Transceiver

Fiber optic transceiver is a commonly used device which can send or receive data in optical links. As the growing demand for higher speed and bandwidth, more high-speed optical transceivers like 40G QSFP+, 100G CFP and QSFP28 springs up in the market. And we cannot divide them according to data rate, but also the transmission mode—single mode transceiver and mulitmode transceiver. Then what’s the difference between them? Let’s uncover it.

Overview of Single Mode Transceiver and Multimode Transceiver

It’s known to us that fiber optic cables can be classified into single mode and multimode according to its transmission mode. It’s same to fiber optic transceiver. Single mode fiber is a type of transceiver that allows one mode to propagate. It uses single mode fiber cable to receive and transmit data, which make it suitable for longer transmission. While multimode fiber optic transceiver support multiple mode transmission, and works with multimode fiber cable which has a larger core than single mode fiber cable. It’s transmission distance is less than that of single mode fiber transceiver because of dispersion.

single mode fiber transceiver vs multimode fiber transceiver

Single Mode Transceiver Vs. Multimode Transceiver: What’s the Differences?

Since there are so many types of optical transceivers in the market, choosing which types and cabling systems to install isn’t an easy thing. Therefore, knowing the differences between them is important. Here are the differences between single mode transceiver and multimode transceiver.

Laser sources: multimode optical transceiver often uses VCSEL which offers lower manufacturing package cost when compared with edge-emitting lasers. While single mode fiber has a core diameter of 9µm, which has less tolerance to fiber core misalignment as compared to multimode fiber. Therefore, it has higher requirement and cost for lasers.

Power consumption: multimode transceivers consume less power than a single mode transceivers, which is an important consideration especially when assessing the cost of powering and cooling a data center.

Distance: the reach distance of the two types transceiver is different. The multimode optical transceivers generally have a reach of approximately 550 meters, while the single mode transceivers can get you through 10 km, 40 km, 80 km and even farther.

Speed: in telecom applications where the fiber cost is high due to long-distance data transmission, single mode transceivers can support higher speed rates with fast response time, advanced modulation formats and wavelength division multiplexing (WDM) technology.

Cost: in terms of cost, single mode transceiver are nearly two or three times higher in price when compared to multimode transceiver. Because single mode fiber cables cost more to make and are more “fragile” in nature, which makes them more expensive than multimode fiber cables.


This post gives a simple comparison between single mode transceiver and multimode transceiver. Both of them have their own advantages in data center applications. Whether you choose the single mode or multimode transceiver, it’s important to note that different optical transceivers aren’t interchangeable due to the differences in fiber core size and wavelengths. FS.COM, as a professional optical products supplier, offers various fiber optic transceiver to meet customers’ diverse needs. If you have any need, please visit www.fs.com for more detailed information.

Optical Amplifier Used in CATV Transmission Network

CATV technology has matured steadily over the past several years, and has expanded into diverse applications. However, as the quick expansion in technology and services, it’s important to improve CATV network component performance for higher visual and audio signals transmission. Optical amplifier for CATV application is the key element in such transmission. This post intends to give a clear introduction of optical CATV amplifier and its application in CATV transmission.

Introduction to CATV Amplifier

CATV amplifier is also a type of EDFA (Erbium Doped Fiber Amplifier) amplifier which is the most popular optical amplifier in optical network communications. It is mainly used to amplify damped TV signals (compensation for loss) for improved signal quality before sending them to each subscriber. Moreover, CATV amplifiers not only amplify the signal, but also amplify the noise on the line, and bring some return loss. That’s why a quality CATV amplifier price is a little high, because it can provide better performance for the whole network transmission.

Why CATV Amplifier Is Needed?

As we all know, CATV network is a multi-channel TV system to transmit high quality video and sound signal from a large number of digital or analog broadcast television and radio channel via fiber optic cable or coaxial cable. CATV amplifier often acts as booster optical amplifier in this system to get satisfying transmission effect. The following picture illustrates a basic long haul CATV transmission system using EDFA amplifier.

catv amplifier 1

In most cases, the satellite providers deliver high quality digital video and audio to users’ home depending on the users’ equipment. However, the signal incoming cable feed is connected to more than one equipment with use of optical splitters. And if the incoming signal gets fragmented and rerouted, the overall speed and quality will be worse. Under this condition, an optical amplifier can be used to boost the signal power and help users get better services.

CATV Amplifier in Long-Haul CATV Transmission System

As have mentioned above, a basic long-haul CATV communication link consists of head end, transmitter, receiver, optical amplifier, and sometimes fiber splitter is also needed in this type of transmission network. The head end receives TV signals off the air or from satellite feeds, and supplies them to the transmission system. The optical splitters are often utilized in a poin-to-multipoint configuration. Here are two CATV fiber network cases using CATV booster amplifier.

Case one

This is a point-to-multipoint medium size private CATV network. In the head end, the transmitter receives signals from the RF combiner on the 1310nm or 1550nm wavelength. Then the signals split into several parts and are received by the CATV receiver. Finally, all the signals are amplified by the CATV amplifier and sent to the subscriber.

catv amplifier 2

Case two

In the above application case, the optical amplifier lies behind the CATV receiver, but in this case, it’s a little different.

catv amplifier 3

As we can see from the graph, the CATV amplifier lies in the front of the receiver to boost the transmission distance longer. Except for that, this transmission network also deploys two DWDM Mux/Demux to multiply the eight different wavelengths into one fiber for better transmitting. Please note that this graph just illustrates part of the long-haul CATV system.


CATV amplifiers are used to boost the quality of optical signals and improve the speed and reliability of the services that users get. FS.COM offers various CATV amplifiers with different values and CATV optical transmitter. All of them are high quality. If you are interested, please contact us via sales@fs.com.

Understanding WDM MUX/DEMUX Ports and Its Application

Wavelength division multiplexing (WDM) is a commonly used technology in optical communications. It combines multiple wavelengths to transmit signals on a single fiber. To realize this process, CWDM and DWDM mux/demux are the essential part. As we all know, there are several different ports on the WDM mux and demux. This article will give a clear explanation to these ports and their applications in WDM network.

Overview of Different Ports on WDM MUX/DEMUX
Line Port

Line port, sometimes also called as common port, is the one of the must-have ports on CWDM and DWDM Mux/Demux. The outside fibers are connected to the Mux/Demux unit through this port, and they are often marked as Tx and Rx. All the WDM channels are multiplexed and demultiplexed over this port.

Channel Port

Like the line port, channel ports are another must-have ports. They transmit and receive signals on specific WDM wavelengths. CWDM Mux/Demux supports up to 18 channels from 1270nm to 1610nm with a channel space of 20nm. While DWDM Mux/Demux uses wavelengths from 1470nm to 1625nm usually with channel space of 0.8nm (100GHz) or 0.4nm (50GHz). Services or circuits can be added in any order to the Mux/Demux unit.

40ch dwdm mux demux

Monitor Port

Monitor port on CWDM and DWDM Mux/Demux offers a way to test the dB level of the signal without service interruption, which enable users the ability to monitor and troubleshoot networks. If the Mux/Demux is a sing-fiber unit, the monitor port also should be a simplex one, and vice verse.

Expansion Port

Expansion port on WDM Mux/Demux is used to add or expand more wavelengths or channels to the network. By using this port, network managers can increase the network capacity easily by connecting the expansion port with the line port of another Mux/Demux supporting different wavelengths. However, not every WDM Mux/Demux has an expansion port.

dwdm mux demux

1310nm and 1550nm Port

1310nm and 1550nm are one of WDM wavelengths. Many optical transceivers, especially the CWDM and DWDM SFP/SFP+ transceiver, support long runs transmission over these two wavelengths. By connecting with the same wavelength optical transceivers, these two ports can be used to add 1310nm or 1550nm wavelengths into existing WDM networks.

Application Cases of Different Ports on WDM MUX/DEMUX

Although there are several different ports on WDM Mux/Demux, not all of them are used at the same time. Here are some examples of these functioning ports in different connections.

Example One: Using 8 Channels CWDM Mux/Demux with Monitor Port

cwdm mux demux with monitor port

This example is a typical point-to-point network where two switches/routers are connected over CWDM wavelength 1511nm. The CWDM Mux/Demux used has a monitor port and 1310nm port, but the 1310nm does not put into use. In addition, an optical power meter is used to monitor the power on fibers connecting the site A and B.

Example Two: Achieve 500Gbps at Existing Fiber Network with 1310nm Port

dwdm mux with 1310nm port

In this example, two 40 channels DWDM Mux/Demux with monitor port and 1310nm port are used to achieve total 500Gbps services. How to achieve this? First, plug a 1310nm 40G or 100G fiber optical transceiver into the terminal equipment, then use the patch cable to connect it to the existing DWDM network via the 1310nm port on the DWDM Mux/Demux. Since the 1310nm port is combined into a 40 channels DWDM Mux, then this set-up allows the transport of up to 40x10Gbps plus 100Gbpx over one fiber pair, which is total 500Gbps. If use 1550nm port, then the transceiver should be available on the wavelength of 1550nm.

Example Three: Stack Two CWDM MUX/DEMUX Using Expansion Port

cwdm mux with expansion port

The connection in this example is similar to the last one. The difference is that this connection is achieved with expansion port not 1310nm port. On the left side in the cases, a 8 channels CWDM Mux/Demux and a 4 channels CWDM Mux/Demux are stacked via the expansion port on the latter Mux/Demux. And the two 4 channels CWDM Mux/Demux are combined with the line port. If there is a need, more Mux/Demux modules can be added to increase the wavelengths and expand network capacity.


Different ports on the CWDM and DWDM Mux/Demux have different functions. Knowing more their function is helpful in WDM network deployment. FS.COM supplies various types of CWDM and DWDM Mux/Demux for your preference. And customer services are also available. If you have any needs, welcome to visit our website www.fs.com.

Application Cases of 10G CWDM Network

CWDM network, as an easy-to-deploy and cost-effective solution, has been applied in many areas. Although CWDM network is not as perfect as DWDM networks in data capacity, it still can satisfy a wide range of applications in optical applications. And CWDM is a passive network, allowing any protocol to be transported over the link, as long as it is at the specific wavelength. This article is going to describe several application cases of 10G CWDM networks in different areas.

Benefits of 10G CWDM Network

Although 40G and 100G networks are developing rapidly, many of them still need to grow on the basis of 10G networks. And due to the high cost of 40G and 100G, 10G networks are still the most common networks to be deployed. Here are the main benefits of 10G CWDM networks.

  • CWDM Mux/Demux is a passive component and requires no extra power, offering a cost-effective choice for network designers.
  • Increased network connections and easy to evolve from 10G to 40G and 100G networks. For example, 10G CWDM network can combine DWDM wavelengths using the 1550nm channel on CWDM Mux/Demux. And if an operator want to upgrade its 10G network to 40G or 100G, there are various fiber components in market that can help him realize this conversion.
  • Lower cost. 10G hardware has become cheaper, which make 10G CWDM network more economical. For example, buying one pcs 8 channels CWDM Mux/Demux which is the most often used in CWDM networks needs less than 330 dollars in some stores. And 10G CWDM optical transceivers are also very cheap now.
10G CWDM Network Infrastructure

As has mentioned above, 10G CWDM network has been widely deployed in different areas. Here are the common CWDM network infrastructures.

Point-to-point 10G CWDM Network

A point-to-point CWDM network is the simplest network structure of CWDM networks, but it is the basis of other complex network infrastructures. By adding other components like CWDM OADM, the point-to-point CWDM network is easy to be changed into more complicated networks. The following figure shows a point-to-point CWDM network using 8 channels CWDM Mux/Demux.

point-to-point CWDM

10G CWDM Ring Network

CWDM ring links are suitable for interconnecting geographically dispersed LANs and storage area networks. Business can benefit from CWDM by using multiple Gigabit Ethernet. As shown in the below picture, the four buildings are connected by several 8 channels CWDM Mux/Demuxes.

CWDM ring network

Application Cases of 10G CWDM Network
Applications in Service Providers

CWDM uses different wavelengths to carry different signals over a single optical fiber, which offers many benefits to service providers that need to better utilize the existing fiber infrastructure. In this application, two Cisco switches are connected together through four 8 channels CWDM Mux/Demuxes. Signals are multiplexed and then transmitted through two strands fiber cables.

CWDM network

10G CWDM Application in Campus Network

As the scale expansion of many campus, the need for adding bandwidth of new applications is increasing too. And the new campus, school teaching and student life Internet require a lot of bandwidth resources, so building a new network is undoubtedly needs a large investment. Then how to make a full use of existing fibers is a problem needed to be resolved.

CWDM in campus

In this case, four 8 channels CWDM Mux/Demux with expansion port are used to double the capacity on the existing fiber without the need for installing or leasing additional fibers, which reduce cost and labor.


As the development of WDM technology and market, the deployment of CWDM network will be more lower. FS.COM provides affordable CWDM network components at a low price. Following is a list of our products.

Product ID Description
42945 8 channels 1290-1430nm dual fiber CWDM Mux Demux
43099 8 channels 1470-1610nm dual fiber CWDM Mux Demux with expansion port
19367 Cisco Compatible 10G CWDM SFP+ 1470nm 80km DOM Transceiver
31290 Cisco Compatible 10G CWDM SFP+ 1290nm 40km DOM Transceiver

How to Calculate Power Budget and Link Distance in CWDM Network

By multiplexing separated wavelengths from multiple ports onto a single fiber in the network, coarse wavelength division multiplexing (CWDM) network increases fiber capacity at a low cost. And all the CWDM components are passive and do not need power, which requires lower investment than DWDM networks and make it popular. This article intends to explore how to calculate the power budget and link distance in CWDM network, offering more conveniences for your CWDM network deployment.

Understand Optical Power Budget in CWDM System

One important factor of network design, including various optical networks like DWDM and PON, is the optical power budget. Optical power budget is the amount of light available to make a fiber optic connection. The difference between the output power of the transmitter and the input power requirements of the receiver is referred to as the power budget. The power budget with various losses in an optical fiber, as shown in the picture below, is obtained by first determining the optical power emitted by the source, usually expressed in dBm, and subtracting the power (expressed in same units, e.g., dBm) required by the detector to achieve the design quality of performance (Receiver Sensitivity). Here is a common equation that can be used to calculate the power budget in a decided length fiber link.

Link Power Budget = Min Transmit Power – Min Receiver Sensitivity

optical power budget CWDM

Calculate Power Budget in CWDM Network

When designing a CWDM network, power budget is often used to determine the maximum distance that a link can support. The transmission power budget is the difference between the optical transmitter output power and the receiver sensitivity. In order to explain the calculation process clearly, all the equations will be given an example for illustrating.

Power Budget = Tx Power – Rx Sensitivity.

Example one. A -2 dBm optical transmitter and a -25 dBm receiver provide a total transmission power budget of 23 dB.

Power Budget = Tx Power – Rx Sensitivity = -2 dBm – (-25 dBm) = 23 dB

As we all know, in a CWDM system, CWDM Mux/Demux, CWDM OADM and other components are common. And each one of them will introduce loss once added into the CWDM system. For example, when using a CWDM OADM in CWDM network, the point where a channel is dropped, added, or passed will cause a loss of signal strength. Therefore, when calculating power budget for a CWDM link, all losses must be added together. As shown in the following equation.

Power Budget = Tx Power – Rx Sensitivity – Losses

Example two. Here is a link A shown as below. There are four CWDM Mux/Demuxes and two CWDM SFP transceivers in this link. The Mux/Demux #1 and Mux/Demux #4 are 8-channel CWDM Mux/Demux. The left two is 4-channel CWDM Mux/Demux. Link A is the distance from CWDM SFP #1 and CWDM SFP#4. Each CWDM Mux/Demux has a low insertion loss. For instance, the insertion loss of the 8-channel CWDM Mux/Demux is less than 3.1dB (including connectors and adapters).

CWDM network

Here is the calculating process.

Power Budget = Tx Power – Rx Sensitivity – Losses

Tx Power = 2 dBm

Rx Sensitivity = -23 dBm

Losses = (8-channel Mux/Demux #1 loss) + (4-channel Mux/Demux #2 loss) + (4-channel Mux/Demux #3 loss) + (8-channel Mux/Demux #4 loss)

= 2.5 dB + 2.0 dB + 2.0 dB + 2.5 dB = 9.0 dB

Power Budget = Tx Power – Rx Sensitivity – Losses = 2 dBm – (-23 dBm) – 9.0 dB = 16 dB

Calculate Maximum Link Distance in CWDM Network

After determining the power budget for a fiber link, we can use the value to calculate the maximum distance that the link can support. The calculation equation is shown as below.

Power Budget = Buffer Distance/Fiber Attenuation

Usually, a buffer of 2 dB is subtracted from the power budget to account for other factors that may affect the loss of transmission power. These factors include fiber aging, temperature, poor splice, etc. Fiber attenuation is the loss of signal strength as it travels through the fiber. The attenuation varies with the wavelength. Typical values are 0.2 to 0.35 dB/km.

Then we will calculate the maximum supported distance of link A in example two. Here we take the worst value for the fiber attenuation. The distance is:

Distance = (16 dB-2 dB)/0.35dB/km = 40km

The maximum supported distance of link A is 40km.


Knowing how to calculate the power budget and transmission distance can help engineers estimate the CWDM network deployment cost, and also can avoid some unnecessary problems in network design. This post gives a clear illustration to calculate them. Hope it would help you. In addition, FS.COM is a professional manufacturer and supplier of optical components. If you have any need, welcome to visit our website www.fs.com.

How to Expand Bandwidth in PON Network with CWDM Technology?

PON (passive optical network) is one of a common optical fiber network architectures. It is characterized by the “splitting” of the optical fiber one or more times, resulting in the sharing of optical fiber among multiple users. However, as networks grow in terms of subscriber counts, the scope and number of services offered, expanding the network bandwidth is inevitable. Coarse Wave Division Multiplexing (CWDM), known for its low cost and scalability to increase fiber capacity as needed, is a preferred method for PON network expansion. This article will focus on using CWDM technology to overcome bandwidth limitations in PON access networks.

CWDM Mux/Demux and OADM (Optical Add-Drop Multiplexer) in Access PON

Fibers in a PON are typically shared with several users. Hence the bandwidth of the fiber originating at the CO (center office) is shared among a group of users. The splitting of the network is accomplished by optical splitters. These splitters can split the fiber 2-32 times, which may introduce high losses in the network. Besides, as different places in a same network need different wavelengths, CWDM Mux is often deployed to multiplex these signals on a single fiber.

In PON (Passive Optical Network) network, whether in ring structures or point-to-point arrangements, different optical nodes need specific wavelengths. Therefore, at each node, a CWDM OADM is used to drop or add certain channels from the fiber as required,. Then the signals will be transmitted to the user through optical fibers. The following picture shows a simple PON network.


How to Expand Bandwidth of PON Network Using CWDM Technology?
Upgrading Access PONs Using Passive CWDM Mux/Demux

In PON networks, 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 send it to all ONT modules on the ODN).

The following figure represents a situation where existing subscribers intend to upgrade to higher value added bandwidth services. In order to satisfy customers’ needs for IPTV, VoIP, video on demand etc., the 622 Mb/s downstream capacity between the CO and the OLT, providing roughly 20 Mb/s to each subscriber, must increase.

PON network

Considering there may be new subscribers and services added, the targeted bandwidth requires at least a downstream CO/OLT link bandwidth of 2.5Gb/s. Therefore, four CWDM wavelengths are introduced to multiply the channels passing between the CO and OLT. This introduction of passive CWDM Mux/Demux can relieve the fiber exhaust effectively. The below figure shows the upgrading process.

PON upgrade

Advantages of This Upgrade

Compared with laying a new fiber cable, the upgrade with passive CWDM is easily accomplished within hours after some modest investment in network planning. And the sum of material, labor, equipment and training expense is far less, which explain why many enterprises, private business users of LAN and data storage networks use passive CWDM too.

Expanding EPON Bandwidth Using CWDM Mux/Demux

EPON stands for Ethernet passive optical network. It is an enabling technology that benefits consumers. Here is an EPON network, which was conceived to serve up to 64 subscribers. All users share a single bidirectional optical feed line. With the need for IPTV, HDTV and other higher bandwidth services growing, the downstream capacity 16Mb/s should be improved.


The picture below shows the same EPON deployment upgraded to 4Gb/s bandwidth capacity.

EPON network

This upgrade uses 4 channels passive CWDM Mux/Demux to extend the whole network capacity, allowing the downstream capacity increase four times without affecting the upstream traffic.

Advantage of This Expansion

Using CWDM Mux/Demux effectively increases the network bandwidth capacity and reduces the cost. At the same time, it requires minimal modification of the existing infrastructure, which also saves labors.


CWDM technology offers significant benefits of low investment, minimal operating cost and very simple and straightforward upgrade planning and implementation. In addition, passive CWDM also provides scalability and network flexibility for network growth and bandwidth demands in the future. FS.COM supplies different channels of CWDM components. Welcome to contact us via sales@fs.com.

Related article:Examples of CWDM Network Deployment Solution

Examples of CWDM Network Deployment Solution

Based on the same concept of using multiple wavelengths of light on a single fiber, CWDM and DWDM are two important technologies in fiber optical communications. As we all know, although the transmission distance of CWDM network is shorter than that of DWDM, it costs less and has the scalability to grow fiber capacity as needed. This article intends to give a simple introduction of components in CWDM networks and to explore some examples of CWDM network deployment cases.

Common Components Used in CWDM Networks
CWDM Mux/Demux

CWDM Mux/Demux, which is based on the film filter technology, is the basic component in CWDM networks. It can combine up to 4, 8 or 16 different wavelength signals from different fiber extenders to a single optical fiber, or it can separate the same wavelengths coming from a single CWDM source. That’s why CWDM can extend existing fiber capacity.

CWDM OADM (Optical Add-Drop Multiplexer)

A CWDM OADM is a device that can add (multiplex) and drop (demultiplex) channels on both directions in a CWDM network. It can add new access points anywhere in CWDM systems without impacting the remaining channels traversing the network. With this ability of OADM, the access points can be added to liner, bus, and ring networks, where the dual direction ring design provides redundant protected architecture.

CWDM Optical Transceiver

Optical transceiver is a necessary element in optical networks. And CWDM optical transceiver is a type of module supporting CWDM network application with CWDM wavelengths. When connected with CWDM Mux/Demux, CWDM transceiver can increase network capacity by allowing different data channels to use separate optical wavelengths (1270nm to 1610nm) on the same fiber. And the common CWDM transceiver type is SFP, SFP+, XFP, XENPAK, X2, etc.

CWDM Network Deployment Solution
Example One

Description: there are five buildings (Sheriff, Courthouse, Admin, Police & Fire, & Public Works) connected via multimode fiber cables (MMF) or single mode fiber cables (SMF). These buildings are linked via multimode SFPs in an existing D-link switches to create one network for internal use of the city offices. Below is a simple graph to show the situation.

CWDM Network 1

Requirements: the goal is to install a single mode fiber network in town to connect numerous buildings. Some of these buildings have access to the city LAN. The Public Works building need to connect with Youth & Recreation Center, Library, Immanuel Lutheran School and the Senior Center. And all these buildings should have unfiltered Internet. Besides, the Waster Water Treatment Plant should be connected passing through the Senior Center. All these services are achieved using CWDM technology.

Solution: according to the requirements, this is a CWDM networks with several buildings to connect with. Here is the solution diagram.

CWDM Network

In the diagram above, we can see there is an 8CH CWDM Mux/Demux connected with the switches. According to the requirements, Youth & Recreation Center, Library, Immanuel Lutheran School and Senior Citizen Center should be connected with the Public Works and need unfiltered services. Therefore, a 4CH CWDM OADM is placed after the CWDM Mux/Demux. Then the four wavelengths will be drop and into the four buildings. In addition, another CWDM OADM is deployed in Senior center to connect the Waster Water Treatment Plant, to meet the requirement. And each site also needs to use CWDM optical transceivers.

Example Two

Description: on site A, there are three Ethernet switches and a T3 router. And their working wavelengths 1470nm, 1490nm, 1510nm, 1530nm and 1610nm. Other three sites B, C, and D also have three Ethernet switches. And a T3 router is in site E. As the following figure shows.


Requirements: Considering the cost, all the wavelengths should be transmitted on a single fiber using CWDM technology.

Solution: according to the requirements, here is a simple diagram showing the solution.

CWDM Mux Demux

In order to save cost, a 4CH CWDM Mux/Demux is used to multiplex four wavelengths (from three switches and one router) into one single fiber. At the first site B, a 1CH CWDM OADM is installed to remove one wavelength which is associated with network B. And other three sites are the same—dropping one wavelength associated with corresponding switch or router.


This article mainly introduces two CWDM network deployment examples. All the components like the CWDM Mux/Demux, CWDM OADM and CWDM transceiver are available in FS.COM. If you are interested in them, please contact us via sales@fs.com.

Related article:Differences between CWDM and DWDM