Hybrid CWDM-DWDM System Boosts Your Network Capacity

Should I choose a medium capacity but more cost-effective CWDM solution, or to adopt the cost-prohibitive DWDM approach with comparably enhanced capacity? This is a problem that consistently faced by WDM technology users. The wrong decision, however, may inevitably lead to bandwidth shortage or even potential bankruptcy derived from unnecessary capacity investment. This article introduces the hybrid CWDM-DWDM solution that combines both CWDM and DWDM technologies within a single system, helping decrease costs and simplify installation while maintain the flexibility to upgrade.

Hybrid CWDM-DWDM System Explanation

Hybrid CWDM-DWDM system utilizes the technology to merge DWDM and CWDM traffic seamlessly at the optical layer. Which allows carriers to add many channels to networks originally designed for the more limited CWDM capacity and reach. In other words, hybrid CWDM-DWDM system is used to empower CWDM system by integrating CWDM and DWDM equipment. Hybrid CWDM-DWDM system deliver true pay-as-you-grow capacity growth and investment protection. It offers a simple, plug-and-play option for creating hybrid system of DWDM channels interleaved with existing CWDM channel plans.

Benefits of Hybrid CWDM-DWDM System

Hybrid CWDM-DWDM system typically provides three benefits for carriers and users:

• Reduced Cost: CWDM is more cost-effective than DWDM due to the lower cost of lasers and the filters used in CWDM modules. This cost saving becomes quite significant for large deployments.
• Pay-As-You-Grow: Adding one new channels at a time allows for on-demand service introduction with minimal initial investment—a critical feature in terms of reduced OPEX and CAPEX spending.
• Investment Protection: Carriers and end-users need always to bear the future growth in mind. With hybrid CWDM-DWDM system, carriers no longer have to choose between CWDM and DWDM—both options can be deployed simultaneously or as part of future growth. This module can be used in either CWDM or DWDM system. Current capital investment can always be used in the upgraded network.

How to Deploy Hybrid CWDM-DWDM System

The CWDM wavelength grid typically has 16 channels spacing at 20 nm intervals, with 8 channels (1470 nm-1610 nm) of them are most commonly used. Within the pass band of these channels, it is capable of adding 25 100 GHz spaced DWDM channels under the 1530nm envelope and 25 more under the 1550nm envelope. However, it is not so practical to add 25 DWDM channels in the pass-band of both the 1530nm and 1550nm CWDM channels. DWDM filter technology does allow 38 additional channels to clear the CWDM archway, which is shown as following.

To add more DWDM channels to the MUX side of the conventional CWDM system, one need to plug in a DWDM MUX with the appropriate channels under the pass band of the existing CWDM filters. The picture below illustrates the configuration of a CWDM system upgraded with 38 additional 100 GHz spaced DWDM channels. This hybrid CWDM-DWDM system consists of 38 DWDM channels and the existing 6 CWDM channels. The equipment required to go from the first architecture to the second are 2 DWDM MUX/DEMUXs, as well as the additional transmitter and receiver pairs. The additional loss incurred by the upgrade is equal to the additional loss of the DWDM elements and the additional connection points.

Flexible Hybrid CWDM-DWDM System Solution by FS.COM

The most vital elements concerning hybrid CWDM-DWDM system are the CWDM MUX/DEMUX and DWDM MUX/DEMUX. FS.COM developed and introduces FMU series products to facilitate installation and operation of WDM MUX/DEMUX. The prominent feature of this series products is that they combine the MUX/DEMUX into half-U plug-in modules, which can be installed in a 1U rack. As for hybrid CWDM-DWDM system, a FMU CWDM MUX/DEMUX and a DWDM half-U plug-in module can be installed together in a FMU 1U rack chassis, facilitating connections of these two modules while allowing for better cable management and network operation in hybrid CWDM-DWDM system.

Conclusion

Hybrid CWDM-DWDM system generally offers a cost-effective and future-proofing approach for service providers and end-users, by overcoming the obstacles faced by users of WDM technology today, providing a starting platform that scales smoothly and protecting the investment. A user can commence with the more cost-effective CWDM technology and then later add DWDM in the when the capacity is required. FS.COM FMU series WDM solution makes the process even easier and more flexible. For more information, please visit www.fs.com or contact sales@fs.com.

Source: http://www.fiber-optic-solutions.com/hybrid-cwdm-dwdm-boost-network-capacity.html

Optical Transponder (O-E-O) Used in WDM Network

WDM technology is commonly used in today’s optical network. It basically assigns each service (10G LAN, SONET/SDH, Fiber Channel, etc) an independent dedicated wavelength—which then is multiplexed into one single fiber. Eliminating the use of multiple fibers while increasing fiber capacity, WDM system is beneficial to both service providers and end users. Optical transponder, also referred to as O-E-O (optical-electrical-optical), serves as an integrated part of WDM system and it is critical for signal transmission in the whole system. This article will guide you through how optical transponder operates in a WDM network.

Basics of Optical Transponder (O-E-O)

The optical transponder (O-E-O) works as a re-generator which converts an optical input signal into electrical form, then generates a logical copy of an input signal and uses this signal to drive a transmitter to generate an optical signal at the new wavelength (optical-electrical-optical). Its most prominent feature is that it automatically receives, amplifies, and then re-transmits a signal on a different wavelength without altering the data/signal content. Clients can be electrical or optical (1310 or 1550 nm), co-located or some distance away. Line side interfaces can be fiber, CWDM or DWDM with a variety of reaches supported.

Common Applications of Optical Transponder (O-E-O)

Optical transponder is widely accepted in WDM networking and many other applications. let’s go through some commonly used ones.

1. Multimode to single-mode conversion

Some optical transponders can convert from multimode to single-mode fiber, short reach to long reach lasers, and/or 850/1310 nm to 1550 nm wavelengths. Each optical transponder module is protocol transparent and operates fully independent of the adjacent channels.

2. Redundant fiber path

Each optical transponder module can also include a redundant fiber path option for extra protection. The redundant fiber option transmits the source signal over two different optical paths to two redundant receivers at the other end. If the primary path is lost, the backup receiver is switched on. Since this is done electronically, it is much faster and more reliable.

3. Repeater

As an optical repeater, some optical transponders effectively extend an optical signal to cover the desired distance. With the clock recovery option, a degraded signal can be dejittered and retransmitted to optimize signal quality.

4. Mode Conversion

Mode conversion is one of the quickest and simplest ways of extending multimode optical signals over greater distances on signal-mode fiber optics. And most receivers are capable of receiving both multimode and single-mode optical signals.

5. Wavelength Conversion

Wavelength conversion in commercial networks today is only carried out by optical transponder. We know that optical network equipment with conventional fiber interfaces like LC, SC, ST, etc operates over legacy wavelength of 850 nm, 1310 nm, and 1550 nm. Which means they must be converted to CWDM or DWDM wavelength to fit in the system, and this is what WDM transponders used for—converse wavelength by automatically receiving, amplifying, and re-transmitting a signal on a different wavelength without altering the data/signal content. The following picture depicts the conversion process: a 10G switch (with signal output of 1310 nm) is to be linked to a CWDM Mux/Demux channel port (1610 nm). An optical transponder with a standard SMF SFP+ and a 1610nm CWDM SFP+ is adopted between the switch and CWDM Mux/Demux, thus the wavelength conversion is realized by the optical transponder.

Network Structure with Optical Transponder

Then how exactly optical transponder benefits your network system? Here we provide two possible configurations of network over WDM ring which deploys optical transponder.

For line network over a WDM ring

The line network consists basically of two point-to-point links between A-B and B-C, each requiring transponders at the endpoints. If node B fails, communication between A and C should still be possible, because B can be bypassed by the two adjacent optical transponders. For this the protection in/outputs of the transponders are connected by a bypass link. If node B fails, S1 in both transponders switch to the protection connection.

For star network over a WDM ring

As for a star network over a WDM ring, where the nodes A, C and D are connected to the star node B. Node B has a backup node B’ for redundancy. Here the protection in/outputs of the transponders are used to connect the nodes A, C and D to node B’ if node B failed.

Conclusion

Optical transponder holds a critical position in WDM networking system and cannot simply be underestimate. We have illustrated the functionality and applications of optical transponder, as well as presenting possible configurations of network over WDM rings. Hope that may help you to have a better understanding of the optical transponder.

Source: http://www.fiber-optic-solutions.com/optical-transponder-o-e-o-wdm-network.html

How to Overcome the Challenges of Adopting WDM-PON in FTTx?

The bandwidth demand in the access network has been increasing rapidly over the past several years. Passive optical networks (PONs), as the most economical FTTx architecture that needs no power supply, have evolved to provide much higher bandwidth in the access network. A PON is a point-to-multipoint optical network, where an optical line terminal (OLT) at the central office (CO) is connected to many optical network units (ONUs) at remote nodes through one or multiple 1:N optical splitters. WDM-PON combines the virtues of point-to-point dedicated connections with the fiber efficiency and economics of PON, which is considered as a candidate solution for FTTx network. This article offers solutions for deploying WDM-PON in regard to its cost and technical challenges.

WDM-PON Technology Explanation

WDM-PON is the passive optical network (PON) based on wavelength division multiplexing (WDM) technology, which delivers higher network security. This system allows ONUs to have light sources at different tuned wavelengths coexisting in the same fiber, increasing the total network bandwidth and the number of users served in the optical access network. The CO contains multiple transceivers at different wavelengths with each output wavelength creating a dedicated path or channel for a particular user by passing through a wavelength selective/dependent element at the remote node (RN). Wavelength selection can also be achieved by filtering at the user. The upstream connection similarly utilizes a dedicated wavelength channel.

Why Apply WDM-PON in FTTx Networks?

We have known that WDM-PON supplies each subscriber with a wavelength instead of sharing wavelength among 32 or even more subscribers in TDM PON, thus providing higher bandwidth provisioning. WDM-PON is regarded as a candidate solution for next-generation PON systems in competition with TDM PON for possessing the following advantages:

• WDM-PON allows each user being dedicated with one or more wavelengths, thus allowing each subscriber to access the full bandwidth accommodated by the wavelengths.
• WDM-PON networks typically provide better security and scalability because each home only receives its own wavelength.
• The MAC layer control in WDM-PON is more simplified as compared to TDM PON because WDM-PON provides P2P connections between the OLT and the ONU, and does not require the point-to-multipoint (P2MP) media access controllers found in other PON networks.
• Wavelength in a WDM-PON network is effectively a P2P link, thus allowing each link to run at a different speed and with a different protocol for maximum flexibility and pay-as-you-grow upgrades.

WDM-PON Challenges: How to Deal with Them?

Despite these attractive features, there are also some demerits that hinder the implementation of WDM-PON networks.

1. When implementing WDM-PON, one should apply wavelength routers or power splitters in the ONUs, and both of the methods need a colorless ONU.
2. As for long reach WDM-PON system, the protection is necessary to ensure the network reliability and performance.

Concerning the challenges that remain in WDM-PON deployment, here we provide some solutions for your reference.

For Colorless ONU

The ONUs in WDM-PON need to be colorless, which means no ONU is wavelength specific in order to reduce the costs of operation, administration, maintenance and production. Local emission is proposed to solve this problem. There basically exist two local emission approaches: wavelength tuning and spectrum slicing. The ONU of the wavelength tuning approach consists of a tunable laser diode (TLD) as a transmitter (Tx), an optical receiver (Rx) with wavelength selector (WS), and a WDM coupler that divides or combines the upstream and downstream signals. The configuration of the ONU in the spectrum slicing approach is similar to that of wavelength tuning approach, except that a broadband light source (BLS) with WS is used instead of the TLD.

For Long-Reach Protection

As for long-reach network, protecting the feeder fiber that transmits data from potential damage is vital. Then how to achieve the protection? It is suggested to adopt 3-dB optical couplers, which can be used to split or combine the path of WDM signals to or from both the working and protection fibers in the OLT or in the wavelength router. Note that the OLT and the wavelength router are typically located in the central office (CO) and in the access node (AN) respectively. However, this protection method has a low loss budget because of the adoption of the 3-dB optical couplers. To this end, a wavelength-shifted protection scheme has been proposed, which is deploying the cyclic property of the 2×N athermal arrayed-waveguide grating (AWG) and two wavelength allocations for working and protection. In this case, 3-dB optical couplers are not needed.

Conclusion

WDM-PON is proving to be the most promising long-term, scalable solution for delivering high bandwidth to the end user. Meanwhile, advances in key device technologies had laid the foundation for realization of a high performance, low cost WDM based PON system. Thus, in competition with other high-speed access network technologies, WDM-PON is considered the most favorable for the required bandwidth in the near future.

Source: http://www.fiber-optic-solutions.com/overcome-challenges-wdm-pon-fttx.html