Implementing Passive CWDM to Upgrade Access PONs

Coarse Wavelength Division Multiplexing (CWDM) has proven itself to be a preferred approach to elevate the bandwidth of optical access networks, offering quicker and simpler installation and lower overall cost. Passive CWDM, which requires no electrical power at all, is considered reliable and robust to deploy in the most demanding environment. It generally offers lower cost and more flexible installation and network expansion. This article demonstrates how to use passive CWDM technology to upgrade access PONs.

Why Passive CWDM for Access PONs?

Passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components. CWDM multiplexing components are compact enough to easily retrofit into existing fiber splice cassettes for installation into street cabinets or other forms of outside enclosure. Besides, it also processes the following merits:

• Predictably low equipment and operating cost
• Quick and efficient network upgrade
• Simplicity of specification and simplicity of deployment
• Sufficiently flexible solutions that facilitate expansion
• Open standards, nothing proprietary

CWDM and Add/Drop With Access PONs

For PON networks, be it in the ring or point-to-point structures, not all capacity is needed at a single optical node. Therefore, data transported over certain channels may be added/dropped from the fiber as required. And it may be implemented at any CWDM node at any location in the field. The picture below illustrates how to achieve this. This is generally cost effective and simple to perform. A passive CWDM upgrade simply eliminates the need for deployment of additional network equipment.

The advantages of the PON architecture above lies in the low CAPEX, low OPEX and no electrical power required. And that it can be quickly and inexpensively upgraded when additional bandwidth demands arise.

How to Upgrade Access PONs With Passive CWDM?

With the prevalence of FTTH networks, access networks between the central office (CO) and the subscribes must be upgraded to keep pace with the hunger bandwidth. The figure below shows a typical PON architecture, with an optical line terminal (OLT) located in the CO to transmit traffic to approximately 16 to 32 residential drop points, and PON splitters located at fiber distribution hubs between the OLTs and subscribers’ optical network terminals (ONTs), enabling one OLT port and laser transceiver to be shared across many drop points.

Passive CWDM enables better fiber capacity utilization and supports far greater data traffic as the bandwidth demands from the ONTs increase. It permits network operators to implement many more optical nodes over multiple locations with minimal capital investment and virtually no additional operating cost. The following case presents how to use passive CWDM for access PONs upgrade.

Case: In this case, existing subscribers intend to upgrade to higher value-added bandwidth services. The 622 Mb/s downstream capacity between the CO and the OLT, appropriately 20 Mb/s to each subscriber is proven insufficient, which must to increase.

Solution: The adequate bandwidth requires a downstream CO/OLT link bandwidth of 2.5 Gb/s. Multiplying the number of bidirectional channels traveling between the CO and OLT by four demands four CWDM wavelengths. The upgraded passive CWDM based network (shown below) relives the fiber exhaust and boosts the bandwidth of the CO/OLT link. This installation requires four channel-specific (color coded) transceivers plugging into the router/switch, the associated patch cables, the rack-mounted CWDM module and the snap in passive CWDM cassette located in the OLT.

Benefits: The passive CWDM upgrade can be accomplished within hours, while the cost concerning material, labor, equipment and training is far less than that of laying a new fiber cable. Which is both energy-saving and cost-efficient.

Using CWDM to Expand EPON Bandwidth

Passive CWDM is also beneficial to Ethernet PON (EPON). Let’s see how it works in EPON through the case below.

Case: The figure below shows a common EPON architecture, which serves up to 64 subscribers, all sharing a single 1.25Gbps bidirectional optical Ethernet feed line. The theoretical maximum sustainable data-rate for each is roughly 16 Mb/s. The 16Mb/S downstream capacity should be increased since higher bandwidth services become available.

Solution: A four channel passive CWDM extension effectively multiplies the downstream capacity without affecting the upstream traffic. A rack-mounted CWDM unit in the CO and a miniature hardened CWDM module deployed in the fiber distribution hub increases the revenue earning potential while minimizes OPEX and CAPEX.

Benefits: In this case, the four channel CWDM upgrade promotes the throughput of the downlink by a factor of four while demanding minimal modification of the existing infrastructure.

Conclusion

A passive CWDM method provides the unique advantages of low CAPEX, minimal OPEX and rather simple yet reliable upgrade planning and implementation. More importantly, passive CWDM also preserves scalability and network flexibility for future network expansion and bandwidth demand changes. Hope this article is informative enough for getting a better understanding towards passive CWDM.

Source: http://www.fiber-optic-solutions.com/passive-cwdm-upgrade-access-pons.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

Comparison of FBT and PLC Fiber Optic Splitters

The past few years have witnessed a great leap in advancements of fiber optic communication technologies, these progresses are made to cater to the ever accelerating demand for better and more efficient optical performances. Fiber optic splitter, which plays a significant role in optical networks by allowing signals on an optical fiber to be shared among two or more fibers. Basically, there are two types of fiber optic splitters: fused biconical taper splitter (FBT) and planar lightwave circuit splitter (PLC). And each of them obtains some merits and demerits respectively. This article intends to make a comparison of these two thus to provide some useful information about optical splitters.

Introduction to Fiber Optic Splitter

Fiber optic splitter, known as beam splitter as well, is suitable for a fiber optic signal to be decomposed into multi-channel optical signal output. It divides out a main light source into 1-N optical path and synthesizes 1-N optical path into a main light source and recovers this source. The picture below shows how light in a single input fiber can split between four individual fibers.

Basically, there are two types of optical splitters classified by their working principle: one is fused biconical taper splitter (FBT Splitter) made by the traditional optical passive device manufacturers using the traditional biconical taper coupler technology. The other one is planar optical waveguide splitter (PLC Splitter) based on optical integration technology. Since both of them have their own advantages, users can rationally choose different types of optical splitters depending on the occasion and demand. Besides, it is better to follow a brief introduction of these two devices just for reference.

FBT Splitter

FBT is the traditional technology in which two fibers are placed closely together, typically twisted around each other and fused together by applying heat. The fused fibers are protected by a glass substrate and then protected by a stainless steel tube. The quality of FBT splitters has improved over time and they can be deployed in a cost-effective manner. FBT splitters are widely accepted and used in passive optical networks, especially for where the split configuration is no more than 1×4.

However, when larger split configurations such as 1×16, 1×32 and 1×64 are needed. FBT technology is limited to the number of splits that can be achieved with one coupling. Under such circumstance, multiple FBT splitters can be spliced together in concatenation to multiply the amount of splits available. This is also known as a tree splitter or coupler. When using this design, the package size and the insertion loss increases with the additional splitters and splices used.

PLC Splitter

PLC splitters are used to separate or combine optical signals. A PLC is a micro-optical component based on planar lightwave circuit technology and provides a low cost light distribution solution with small form factor and high reliability. PLC splitters have high quality performance, such as low insertion loss, low PDL, high return loss and excellent uniformity over a wide wavelength range from 1260 nm to 1620 nm and have an operating temperature -40℃ to 85℃. When high split counts are needed and small package size and low insertion loss is critical, a PLC splitter is more ideal.

Differences Between FBT Splitter and PLC Splitter

In this part, we will take a look at the main differences between FBT splitter and PLC splitter from eight perspectives, which are listed in the following diagram.

Parameters	FBT Splitter	PLC Splitter
Fabrication Method	Two or more pieces of optical fibers are bound together and put on a fused-taper fiber device. The fibers are then drawn out according to the output branch and ratio with one fiber being singled out as the input.	Consists of one optical chip and several optical arrays depending on the output ratio. The optical arrays are coupled on both ends of the chip.
Operating Wavelength	1310 nm and ISSO nm (standard), 850 nm (custom)	1260 nm-1650 nm (full wavelength)
Application	HFC (network of fiber and coaxial for CATV), All FTIH applications.	Same
Performance	Up to 1:8—reliable. For larger splits reliability can become an issue.	Good for all splits. High level of reliability and stability.
Input/Output	One or two inputs with an output maximum of 32 fibers.	One or two inputs with an output maximun of 64 fibers.
Package	Steel Tube (used mainly in equipment), ABS Black Module (Conventional)	Same
Input/Output Cable	Bare optical fiber, 0.9 mm, 2.0 mm, and 3.0 mm	Same
Part Number Example	FOSPLT-T-FBT-1/2-E-SM-SC/APC	FOSPLT-T-PLC-1/2-E-SM-SC/APC

Conclusion

Although the outer appearance and size of FBT and PLC splitters seem rather similar, their internal technologies and specifications differ in various ways. I hope the comparison made by this article would help you have a better understanding of these two types of optical splitters, so you could choose a more appropriate solution for your network infrastructure.

First published: http://www.fiber-optic-solutions.com/comparison-fbt-plc-fiber-optic-splitters.html

Introduction to Passive Optical Network

It is universally known that fiber optics transmit data by light signals. And as this data moves across a fiber, there needs a way to separate it so that it gets to the proper destination. Generally, there exist two essential types of systems that make fiber-to-the-home broadband connections possible, which are active optical networks (AON) and passive optical networks (PON). Both of them provide ways to separate data and route it to the proper place. Nowadays, service providers invest billions of dollars in their access networks to meet the ever increasing demand for high-bandwidth broadband. In addition to technology longevity, service providers also like to see technology evolution to ensure future consumer demands can be met by staying within the same technology family. Consequently, the development of passive optical networking is on the rise.

The Definition of PON

A passive optical network (PON) is a system that brings optical fiber cabling and signals all or most of the way to the end user. It is a telecommunication technology that implements a point-to-multipoint architecture, in which unpowered fiber optic splitters are used to enable a single optical fiber to serve multiple end-points such as customers, without having to provision individual fibers between the hub and customer. The system can be described as fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), or fiber-to-the-home (FTTH).

A PON consists of an optical line termination (OLT) at the service provider’s central office and a number of optical network units (ONUs) near end users. Typically, up to 32 ONUs can be connected to an OLT. The passive optical network simply describes the fact that optical transmission has no power requirements or active electronic parts once the signal is going through the network.

A PON system makes it possible to share expensive components for FTTH. A passive splitter that takes one input and splits it to broadcast to many users, which help cut the cost of the links substantially by sharing, for example, one expensive laser with up to 32 homes. PON splitters are bi-directional, that is signals can be sent downstream from the central office, broadcast to all users, and signals from the users can be sent upstream and combined into one fiber to communicate with the central office.

Difference Between AON and PON

As it was mentioned above, AON and PON serve as the two main methods of building CWDM and DWDM backbone network. Each of them has their own merits and demerits.

An active optical system uses electrically powered switching equipment, such as a router or a switch aggregator, to manage signal distribution and direction signals to specific customers. This switch directs the incoming and outgoing signals to the proper place by opening and closing in various ways. In such a system, a customer may have a dedicated fiber running to his or her house. The reliance of AON on Ethernet technology makes interoperability among vendors easy. Subscribers can select hardware that delivers an appropriate data transmission rate and scale up as their needs increase without having to restructure the network. However, AON require at least one switch aggregator for every 48 subscribes. Since it requires power, an active optical network inherently is less reliable than a passive optical network.

A passive optical network, on the other hand, does not include electrically powered switching equipment, instead, it uses optical splitters to separate and collect optical signals as they move through the network. A PON shares fiber optic strands for portions of the network. Powered equipment is required only at the source and receiving ends of the signal. PONs are efficient since each fiber optic strand can serve up to 32 users. Besides, PONs have a low building cost compared with active optical networks along with lower maintenance cost. However, PONs also have some demerits. They have less range than an AON, which means subscribes must be geographically closer to the central source of the data. When a failure occurs, it is rather difficult to isolate it in a PONs. Moreover, because the bandwidth in a PON is not dedicated to individual subscribers, data transmission speed may slow down during peak usage times in an effect known as latency. And latency would quickly degrade services such as audio and video, which need a smooth rate to maintain quality.

The Benefits of PON

As early as the year 2009, PONs began appearing in corporate networks. Users were adopting these networks because they were cheaper, faster, lower in power consumption, easier to provision for voice, data and video, and easier to manage, since they were originally designed to connect millions of homes for telephone, Internet and TV services.

Passive Optical Networks (PON) provide high-speed, high-bandwidth and secure voice, video and data service delivery over a combined fiber network. The main benefits of PON are listed below:

• Lower network operational costs
• Elimination of Ethernet switches in the network
• Elimination of recurring costs associated with a fabric of Ethernet switches in the network
• Lower installation (CapEx) costs for a new or upgraded network (min 200 users)
• Lower network energy (OpEx) costs
• Less network infrastructure
• You can reclaim wiring closet (IDF) real estate
• Large bundles of copper cable are replaced with small single mode optical fiber cable
• PON provides increased distance between data center and desktop (>20 kilometers)
• Network maintenance is easier and less expensive
• Fiber is more secured than copper. It is harder to tap. There is no available sniffer port on a passive optical splitter. Data is encrypted between the OLT and the ONT.

Conclusion

From what we have discussed above, you may at least have a brief understanding of the passive optical network. In fact, PON has been around for many years in the service provider space. Now PON is finally making its way into the enterprise space by providing opportunities for customers deploying new infrastructure or new construction. The technology is catching on. Now, PON mainly captures the commercial market, which performs well in healthcare, college campuses, hotels and office buildings. A PON network eliminates the need for switches and a wiring closet, which means fewer points of failure.

First published: http://www.fiber-optic-solutions.com/introduction-to-passive-optical-network.html