Introduction to the Components Used in CWDM System

CWDM system is a passive optical solution for increasing the flexibility and capacity of existing fiber lines in high-speed networks. It increases fiber capacity by placing widely spaced, separate wavelengths (between 1310 nm and 1610 nm) from multiple ports onto a single-mode fiber pair on the network. The CWDM system components are passive and require no power supplies. This article will introduce the components used in CWDM system.

CWDM System Components

 

Generally, there are three basic components in a CWDM system, which are the multiplexer/demultiplexer (Mux/Demux), the drop/pass module and drop/insert module. CWDM applications are described in terms of an east-west connection. Different colors represent individual channels. Westbound traffic is represented by dashed lines, while eastbound traffic is shown with solid lines.

 

Mux/Demux

 

The Mux/Demux based on film filter is the most mature component used in CWDM system. It combines different channels onto a single outbound (TX) fiber. Simultaneously, the Mux/Demux receives the same channels from a single inbound (RX) fiber, separates them into individual wavelengths, and delivers each to the appropriate local interface. This process expand the capacity of the existing network fiber cable. The following is an example of four channel Mux/Demux.

 

The four-channel Mux/Demux can be configured to support additional channels through the expansion port. By cascading the modules in series, you can increase the total number of available network channels. The channels connecting to the expansion port must differ from those on the Mux/Demux to which they are being cascaded.

Drop/Pass Module

 

The drop/pass module removes one wavelength-specific channel from the east-bound fiber and allows the remaining channels to pass straight through to other nodes along the network. When the drop/pass module drops the channel from the network, it sends the data to a local interface. The local interface sends the same channel back to the drop/pass module for transmission in the westbound direction, thus completing the point-to-point connection between the local interface and another device located in the west. That other device may be a Mux/Demux, drop/pass, or drop/insert module.

 

Drop/Insert Module

 

The drop/insert module provides two local interface ports. One port removes a wavelength-specific channel from the network fiber in one direction, and the other port adds that same channel back onto the fiber in the opposite direction. Because the drop/insert module supports two separate pathways going in opposite directions, network viability in a ring topology is ensured even if there is a break in the network.

On the west side, the drop/insert module removes a wavelength-specific channel from the eastbound fiber and sends it to Local Interface A. To complete the westbound connection, the drop/insert module receives the same channel from Local Interface A and inserts it onto the westbound fiber. The same happens on the east side, except in the opposite direction. The drop/insert module removes the channel from the westbound fiber and sends it to Local Interface B. To complete the eastbound connection, the drop/insert module receives the same channel from Local Interface B and inserts it onto the east-bound fiber. The drop and insert completes the point-to-point connections between the two local interfaces and two other devices located in the east and west. The other device may be a Mux/Demux, drop/pass, or drop/insert module.

 

Summary

 

CWDM is a simple and affordable method to maximize existing fiber by decreasing the channel spacing between wavelengths. Since CWDM is a passive technology, it allows for any protocol to be transported over the link, as long as it is at a specific wavelength. Because the multiplexers simply refract light at any network speed, regardless of the protocol being deployed, CWDM can help to future proof the networking infrastructure. In all, CWDM is a low-cost and effortless technology to implement. FS.COM provides a whole series of WDM system components including CWDM and DWDM. If you need, you can visit www.fs.com for the details.

Originally published: www.fiberopticshare.com/introduction-components-used-cwdm-system.html

Related article: CWDM & DWDM Mux/Demux Overview

 

Related article: Traditional CWDM Mux/DeMux vs. FMU Series CWDM Mux/DeMux

CWDM & DWDM Mux/Demux Overview

As we all know, WDM (wavelength-division multiplexing) is a method of multiplexing a number of optical carrier signals onto a single optical fiber by using different wavelengths (colors) of laser light. It enables bidirectional communications over one strand of fiber, as well as multiplication of capacity. In a WDM system, a multiplexer (Mux) is used at the transmitter to join the several signals together, and a demultiplexer (Demux) is used at the receiver to split the signals apart. This article will focus on the CWDM & DWDM Mux/Demux.

CWDM Mux/Demux

 

CWDM (coarse wavelength division multiplexing) is an excellent choice for increasing bandwidth capacity while keeping costs down in short-range communication networks. CWDM Mux/Demux modules are bidirectional passive optical multiplexers and demultiplexers, allowing multiple optical signals at different wavelengths to pass through a single optical fiber strand. It can combine up to 18 different wavelength signals from different optical fibers into a single optical fiber, or separates up to 18 different wavelength signals coming from a single optical fiber to 18 separate optical fibers. The following picture shows the front panel of 18 channels 1270-1610nm dual fiber CWDM Mux Demux with monitor port.

DWDM Mux/Demux

 

DWDM (dense wavelength division multiplexing) solution is the preferred option for long-haul transmission. The DWDM Mux/Demux modules deliver the benefits of DWDM technology in a fully passive solution. Usually, they are used for long-distance transmission where wavelengths are packed tightly together over the C-band range of wavelengths, up to 48 wavelengths in 100GHz grid (0.8nm) and 96 wavelengths in 50GHz grid (0.4nm). Currently, the most common configuration of DWDM Mux/Demux is from 8 channels to 96 channels. The following picture shows the front panel of 40 channels C21-C60 dual fiber DWDM Mux Demux with monitor port and 1310nm port, which is ideally suited for high-density add/drop requirements in DWDM networks.

 

Comparison Between CWDM and DWDM System

 

Price difference—CWDM system carries less data, but the cabling used to run is less expensive and less complex. A DWDM system has much denser cabling and can carry a significantly larger amount of data, but it can be cost prohibitive, especially where there is a need for a large amount of cabling in an application.

Transmission distance—DWDM system is designed for longer distance transmission as stated above. They can transmit more data over a significantly larger run of cable with less interference than a comparable CWDM system. If there is a need for transmitting the data over a long range, DWDM system will likely be the best in terms of functionality of the data transmittal and the lessened interference over the longer distances that the wavelengths must travel.

CWDM system cannot transmit over long distances because the wavelengths are not amplified, and therefore CWDM is limited in its functionality over longer distances. Typically, CWDM can travel anywhere up to about 100 miles (160 km), while an amplified DWDM system can go much further as the signal strength is boosted periodically throughout the run. As a result of the additional cost required to provide signal amplification, the CWDM solution is best for short runs that do not have mission critical data.

FS.COM CWDM & DWDM Mux/Demux Solution

 

Multiplexing enables a high density, scalable fiber solution. It allows an increase in the fiber utilization by carrying multiple signals down an individual fiber connection, rather than investing in more fibers. As a professional manufacturer and supplier in telecommunication industry, FS.COM offers a full range of CWDM & DWDM Mux/Demux. Our Mux/Demux modules are designed for the best possible performance levels, which helps to expand the bandwidth of optical communication networks with lower loss and greater distance capacities. They are protocol transparent and perfectly suit various applications, such as PDH, SDH/SONET, Fibre Channel, etc. With different housing options, the end users can easily add CWDM or DWDM capabilities to their existing or new networks. For more details, please visit www.fs.com.

Originally published: www.fiberopticshare.com/cwdm-dwdm-muxdemux-overview.html

 

Which to Choose for 40GBASE-LR4 QSFP+ Transceiver: PSM or CWDM?

It is well known that 40GBASE-SR4 QSFP+ transceiver uses a parallel multimode fiber (MMF) link to achieve 40G. It offers four independent transmit and receive channels and each channel is capable of 10G operation for an aggregate data rate of 40G with distances up to 100 meters on OM3 MMF or 150 meters on OM4 MMF. However, for 40GBASE-LR4 QSFP+ transceivers, two kinds of links are available. One is parallel single-mode fiber (PSM), and the other is coarse wavelength division multiplexing (CWDM). What is the difference between the two? Keep reading this article and you will find the answer.

40GBASE-LR4 PSM QSFP+ Transceiver

PSM QSFP+ transceiver is a parallel single-mode optical transceiver with an MTP/MPO fiber ribbon connector. Moreover, it offers four independent transmit and receive channels and each channel is capable of 10G operation for an aggregate data rate of 40G on 10 km of single-mode fiber. The guide pins inside the receptacle could ensure proper alignment. Usually, the cable cannot be twisted for proper channel to channel alignment. For a PSM QSFP+ transceiver, the transmitter module accepts electrical input signals compatible with common mode logic (CML) levels. All input data signals are differential and internally terminated. The receiver module converts parallel optical input signals via a photo detector array into parallel electrical output signals. The receiver module outputs electrical signals are also voltage compatible with CML levels. All data signals are differential and support a data rates up to 10.3G per channel.

40GBASE-LR4 CWDM QSFP+ Transceiver

The 40GBASE-LR4 CWDM QSFP+ transceiver like QSFP-40GE-LR4 is compliant to 40GBASE-LR4 of the IEEE P802.3ba standard. It has a duplex LC connector for the optical interface and its maximum transmission distance is 10 kilometers. Single-mode fiber (SMF) has to be used to minimize the optical dispersion in the long-haul system. This transceiver converts 4 inputs channels of 10G electrical data to 4 CWDM optical signals by a driven 4-wavelength distributed feedback (DFB) laser array, and then multiplexes them into a single channel for 40G optical transmission, propagating out of the transmitter module from the SMF. Reversely, the receiver module accepts the 40G CWDM optical signals input, and demultiplexes it into four individual 10G channels with different wavelengths. The central wavelengths of the four CWDM channels are 1271, 1291, 1311 and 1331 nm as members of the CWDM wavelength grid defined in ITU-T G694.2. Moreover, each wavelength channel is collected by a discrete photo diode and output as electric data after being amplified by a transimpedance amplifier (TIA).

Differences Between the Two

From the perspective of an optical transceiver module structure, PSM seems more cost effective as it uses a single uncooled CW laser splitting its output power into four integrated silicon modulators. Moreover, its array-fiber coupling to an MTP connector is relatively simple. However, from the perspective of an infrastructure, PSM would be more expensive when the link distance is long, because it uses 8 optical single-mode fibers while CWDM only uses 2 optical single-mode fibers. The following table illustrates the main differences between CWDM and PSM.

In addition, the caveat is that the entire optical fiber infrastructure within a data center, including patch panels, has to be changed to accommodate MTP connectors and ribbon cables, which are more expensive than conventional LC connectors and regular SMF cables. Moreover, it is not a straightforward tack to clean MTP connectors. So CWDM is a more profitable and popular 40G QSFP link.

Summary

For 40GBASE-LR4 QSFP+ transceivers, either CWDM link or PSM link, the maximum transmission distance is both 10 km. 40GBASE-LR4 PSM QSFP+ transceiver uses an MTP/MPO fiber ribbon connector via 8 optical single-mode fibers to reach 40G, while 40GBASE-LR4 CWDM QSFP+ transceiver uses a duplex LC connector via 2 optical single-mode fibers to achieve 40G. Thus, CWDM QSFP+ enables data center operators to upgrade to 40G connectivity without making any changes to the previous 10G fiber cable plant, which is more cost-effective and widely used by people.

 Article source: www.fiberopticshare.com/which-to-choose-for-40gbase-lr4-qsfp-transceiver-psm-or-cwdm.html

Differences between CWDM and DWDM

In fiber-optic communications, WDM (wavelength-division multiplexing) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This technique enables bidirectional communications over one strand of fiber as well as multiplication of capacity. Generally, WDM technology is applied to an optical carrier which is typically described by its wavelength.

WDM system uses a multiplexer at the transmitter to join the signals together, and a demultiplexer at the receiver to split the signals apart (see Figure 1). WDM system is very popular in the telecommunication industry because it allows the capacity of the network to be expanded without laying more fiber. By utilizing WDM and optical amplifiers, users can accommodate several generations of technology development in their optical infrastructure without having to overhaul the backbone network. Moreover, the capacity of a given link can be expanded simply by upgrading the multiplexers and demultiplexers at each end.

Figure 1

WDM could be divided into CWDM (coarse wavelength division multiplexing) and DWDM (dense wavelength division multiplexing). DWDM and CWDM are based on the same concept of using multiple wavelengths of light on a single fiber but differ in the spacing of the wavelengths, number of channels, and the ability to amplify the multiplexed signals in the optical space. Below part will introduce some differences between CWDM and DWDM system.

Wavelength Spacing

CWDM provides 8 channels with 8 wavelengths (from 1470nm through 1610nm) with a channel spacing of 20nm. While DWDM can accommodate 40, 80 or even 160 wavelengths with narrower wavelength spans which are as small as 0.8nm, 0.4nm or even 0.2nm (see Figure 2).

Figure 2

Transmission Distance

DWDM multiplexing system is capable of having a longer haul transmittal by keeping the wavelengths tightly packed. It can transmit more data over a larger run of cable with less interference than CWDM system. CWDM system cannot transmit data over long distance as the wavelengths are not amplified. Usually, CWDM can transmit data up to 100 miles (160km).

Power Requirements

The power requirements for DWDM are significantly higher. For instance, DWDM lasers are temperature-stabilized with Peltier coolers integrated into their module package. The cooler along with associated monitor and control circuitry consumes around 4W per wavelength. Meanwhile, an uncooled CWDM laser transmitter uses about 0.5W of power.

Price

The DWDM price is typically four or five times higher than that of the CWDM counterparts. The higher cost of DWDM is attributed to the factors related to the lasers. The manufacturing wavelength tolerance of a DWDM laser die compared to a CWDM die is a key factor. Typical wavelength tolerances for DWDM lasers are on the order of ±0.1 nm, while tolerances for CWDM laser die are ±2-3 nm. Lower die yields also drive up the costs of DWDM lasers relative to CWDM lasers. Moreover, packaging DWDM laser die for temperature stabilization with a Peltier cooler and thermister in a butterfly package is more expensive than the uncooled CWDM coaxial laser packing.

To sum up, CWDM and DWDM have different features. Choosing CWDM or DWDM is a difficult decision. We should first understand the differences between them. Fiberstore has various kinds of WDM products, such as 10GBASE DWDM, 40 channel DWDM Mux, CWDM Mux/Demux module and so on. It is an excellent option for choosing CWDM and DWDM equipment.

Article source: www.fiber-optic-components.com/differences-between-cwdm-and-dwdm-2.html