As a provider of Optical Modulation Index (OMI) Instruments used for optimizing laser transmitter performance, our organization has the opportunity to work closely with many of the talented technicians and engineers at the leading CATV operators around the world. As a result of the many discussions related to both the importance and use of OMI for maximizing system performance, there have been a number of consistent topics we have seen regarding the deployment of transmitters in the network.
One question that always comes up from engineers when discussing why they need to use an OMI instrument is: "When I purchase a new transmitter from our vendor, shouldn't it already be optimized for maximum performance? " In theory this is correct, but in reality, this is not often the case when it is deployed, due to a number of variables. This is not to say that the transmitter you purchased is not a great device, as there are many models available from the most reputable vendors that deliver high quality equipment. However, there is almost always room for improvement, from an optimization perspective, to get the most out of that particular transmitter.
Variables That Can Lead to Non-Optimization
Before a laser or transmitter is shipped, it goes through a number of processes and specification-setting procedures. All of these procedures are prone to inaccuracies that, in the end, can and often add up to a major shift in performance.
Laser OMI is determined and specified by the laser manufacturer
Variable - manufacturers typically use un-modulated carriers
Variable - manufacturers set the specification using a specific number of channels, which is almost never the exact channel setting of the end-user, given that every live network is unique in terms of total channel counts, analog-to-digital ratios, etc.
Lasers are purchased and installed by the transmitter manufacturer
Variable - laser driver circuits introduced between the input and laser
Variable - transmitter manufacturers typically use un-modulated carriers
Variable - transmitter manufacturers typically do not openly divulge the OMI for the device. Usually the RF per channel level necessary to drive the transmitter is given. Since manufacturers want to ensure the transmitter will work for a variety of scenarios in each unique CATV network, this provides a buffer for any variations normally encountered in manufacturing optical equipment.
Transmitters sometimes have front panel “set up” indicators
Variable – the circuit tolerances can cause the OMI setting window to shift, becoming smaller or larger, and thereby allowing the OMI setting to have a fairly wide range
The final result is that the user sets the RF input level for the number of channels used. This may be a change from the original OMI/channel setting. With modulated carriers and all of the above other variables, the setting is almost certain to not be optimal.
In fact, in most deployments where the FOS 1000A OMI instrument has been used for the first time, the majority of laser transmitters are under-driven, with a total OMI value in the 13 to 17 range. A good DFB laser that is optimized typically results in a total OMI value in the 19 to 25 range. In these cases, while the under-driven total OMI value may be a "safe" number, there is a lot of room for improvement in terms of achieving the best performance from your lasers.
Since you have made the investment in a high quality laser transmitter, it only makes sense to take the extra step to maximize their value. A healthy system leads to happy subscribers, which is a key goal of any CATV operator.
Learn More About OMI & Optimizing Laser Transmitters:
As the use of mobile applications and services that require increasingly more bandwidth continues to grow, wireless service providers must find cost-effective and efficient methods for meeting the bandwidth demand. Legacy transport networks are no longer capable of adequately serving today’s cell sites. Newer technologies such as GPON, WDM-PON, and Ethernet over CWDM/DWDM are all well-suited to cost-effectively address the growing bandwidth needs of wireless service providers. Regardless of the technology used, M2 Optics’ SplitLight product is an integral part of the solution.
While GPON has been adopted as a technology of choice in high-speed access networks for inexpensive residential service delivery, more recently, it has begun to spread into business access. With the ability to deliver up to 10Gbps per GPON port, it can also be a cost-effective technology for delivering higher bandwidth to cell towers.
Figure 1: GPON Network
Whether the GPON splitters are collocated with the OLT or distributed in the field, it is likely that a multiple of splitter modules would be needed to handle each serving area. To aid with this, the SplitLight HD can provide up to 16 GPON splitters in a single, 1RU chassis, while traditional solutions can only provide a single GPON splitter in the same footprint. In addition, legacy LGX solutions would require at least 4RU to deliver the same density.
Building on the advantages of GPON, shared infrastructure and a single OLT transponder, WDM-PON provides the added advantage of delivering a dedicated wavelength to each ONT. Unlike GPON, WDM-PON does not use a splitter. Instead, an Arrayed Waveguide Grating (AWG) is used to multiplex and de-multiplex wavelengths between the feeder fibers and distribution fibers. The result is dedicated bandwidth and a more secure network for each subscriber, or in this case, cell tower. Another advantage of WDM-PON is the ability to add/drop wavelengths at intermediate cell towers that lie between mobile switching centers.
Figure 2: WDM-PON Network
As with GPON splitters, it is likely that multiple AWGs would be required at both ends of the WDM-PON network. The SplitLight HD can also house up to 12 AWGs in a single, 1RU chassis. In addition, the SplitLight HD has the flexibility to also house passive OADMs for the intermediate add/drops.
Ethernet over CWDM/DWDM
Of course, one of the best ways to increase bandwidth to fiber-served cell towers is to simply increase the bandwidth capacity by delivering multiple wavelengths to sites that are approaching network saturation. The simplest way to do this is to use passive CWDM and DWDM multiplexers/de-multiplexers.
Figure 3: Ethernet over CWDM/DWDM
As with WDM-PON, passive OADMs (Optical Add-Drop Multiplexers) can be used to add/drop one or more wavelengths at cell towers between mobile switching centers.
Figure 4: OADM Function
Similar to the other technologies previously mentioned, M2 Optics’ SplitLight HD is capable of providing both the CWDM/DWDM muxes as well as the passive OADMs. Up to 16 mux/OADM modules can be housed within a single SplitLight HD chassis.
As mobile data traffic continues to increase, carriers must find the most cost-effective and efficient solutions for delivering bandwidth to each tower. Technologies that allow for a shared infrastructure enable carriers to realize a more immediate ROI. However, proven solutions for FTTH, such as GPON, might not be enough for mobile backhaul due to their shared bandwidth, which will likely experience more contention for bandwidth even on 10G GPONs. In such cases, WDM-PON or Ethernet over CWDM/DWDM solutions could be the answer. Regardless of the underlying technology, SplitLight can accommodate any passive optical networking need in the most cost-effective and efficient manner.
Currently, one of the challenges in deploying new, higher speed services to both enterprise customers as well as MDU/MTU customers is how to deliver these services using the least amount of space possible, while maintaining network flexibility and service quality. M2 Optics’ recent release of the SplitLighttm High-Density Platform (HDP) enables unprecedented space savings and enhanced flexibility without sacrificing performance.
As previously introduced in a recent article, the SplitLighttm HDP form-factor offers the most density available in a single RU for optical combiners/splitters (up to 192 each 1x2, 128 each 1x4, or 16 each 1x32) through its patent-pending, 3D architecture. In addition to combiners/splitters, the SplitLighttm HDP can also house passive optical wavelength multiplexers (mux) and demultiplexers (demux). In fact, it can house up to 16 of these mux/demuxes. Furthermore, the SplitLighttm HDP can be configured to support both applications simultaneously within a single chassis. As a result, in just 1RU of space, GPON, 10G GPON, WDM-PON, and network monitoring applications can all be supported from a single chassis. Typically, this scenario would have required the following:
A patch panel with integrated tap for monitoring at the service demarcation point
GPON splitter shelf (3 or 4RUs) or wall mount cabinet combiners/splitters to split the signal from the feeder fiber onto the distribution fibers
WDM mux/demux, which may fit in the splitter shelf or may be a separate shelf (another 3 or 4 RUs)
By using the SplitLighttm HDP, all of these functions can be accomplished in a single chassis, reducing the required rack space from as many as 4-6 RUs or more down to just 1RU. M2 accomplishes this by using MTP connectors to reduce the front panel space needed for connectors and the patent-pending 3D architecture of the system.
Figure 1: GPON or WDM-PON Using SplitLighttm
Doing More with Less – Future Proofing The Network
In today’s business environment, companies are being forced to do more with less. As previously mentioned, the SplitLighttm HDP allows companies to simultaneously tap signals for network monitoring, split signals to provide access via the GPON, and/or demux the wavelengths to provide access via the WDM-PON. Combining the functionality of multiple passive network elements into a single network element decreases the size without limiting flexibility. In addition, the SplitLighttm HDP can provide front panel, rear panel, or both, connectivity with customized labeling. The connectivity flexibility coupled with the 3D architecture of the SplitLighttm HDP, enables companies and service providers to have even more flexibility in future-proofing their networks.
Figure 2: Both GPON & WDM-PON Using SplitLighttm
M2 Optics’ SplitLighttm HDP uses low-loss components, including official US Conec MTP Elitetm connectors. Using bend-insensitve fiber and MTP Elite connectors coupled with M2 Optic’s comprehensive testing ensures the lowest possible loss across all connections while providing the size and functionality benefits previously mentioned. As a result, the SplitLighttm HDP surpasses the capabilities of all other solutions in the market.
The Ultimate Solution
Using a single chassis with the integrated taps for network monitoring, GPON combiners/splitters, and WDM-PON mux/demux provides unmatched flexibility and density in a single 1RU platform. Couple these attributes with high performance components and the SplitLighttm HDP delivers the ultimate solution for today’s high-bandwidth, enterprise and MDU/MTU PON networks.
If your company is like most that are involved with building or utilizing fiber optic systems, chances are you have a few spools of bare optical fiber laying around the lab. Since it is critical to ensure fiber-based equipment works as intended prior to deployment in the field, it is a recommended and common practice for engineers to simulate networks using spools of bare optical fiber. Because there have been a variety of different fibers available over the years, engineers can end up with fair amount of spools at their disposal.
As a leading provider of packaged optical fibers for over a decade, our team at M2 has come across a lot of different setups for working with optical fibers in the testing environment. While we often assist customers with new fiber requirements, we also receive a lot of inquiries that say something to the extent of “I already own a lot of fiber, but I am not seeing consistent performance, how can I improve this?” or “We have fiber spools, but I’m not 100% certain what type they are and/or if any may be damaged – can you help?” As a result, we wanted to share a few straightforward tips and practices that one can follow in order to ensure you get the most out of your fiber spools.
Invest in a Quality Fiber Spool Enclosure
While your first reaction to the above statement may be to cringe at the idea of having to spend money, the word “invest” is used because taking this action is both a necessary step and one that will provide long-term benefits.
Most engineers will prefer to use a high quality testing platform, but we’ve seen quite a few eye-opening, makeshift setups from exposed fiber hanging from a shelf in the ceiling to spools sitting on the floor in cardboard boxes – all of which the engineers admitted were not the most ideal setups. In many cases taking this step also requires convincing others, so here are some reasons why the most reputable test labs always follow this best practice:
A quality enclosure will protect against damage to both the fiber itself and the connectors, which occurs pretty regularly when using and handling unsecured fiber spools. By protecting the fiber from breaks or bends (which are not often easily visible), you can ensure that your fiber will offer consistent performance over the long-term.
Optical fibers are more easily identified and organized when packaged into a suitable enclosure. In this manner, you know what you are working with and do not have to waste time finding and trying to determine that what you are using is indeed the correct optical fiber.
A quality enclosure offers a more professional look, which is something not always considered when using optical fibers. Many test labs often receive visitors, from business partners to customers, so it is important to have a nice setup. When your most important customer comes to see a new product that you claim will meet their requirements, which will give them more confidence – a bunch of spools laying on a bench with exposed fibers all over, or an organized rack or shelf setup? The answer is clear and this does in fact make a difference to people.
Ultimately, it comes down to the question “do I invest a little bit extra now, or do I run the risk of having to invest a lot more later if/when we have an issue?” By making the extra investment now, you will be a lot happier knowing that you are getting results that you can rely on, while improving testing practices in the lab. In addition, a quality vendor will be able to work closely with you to determine and customize the most ideal setup for your requirements, while offering a number of enclosure types for you to choose from.
Always Clean the Connectors
Since there is so much information out there as to why connectors should always be clean, I won’t go into too much detail on this topic. This should be a common practice of anyone working with fiber optic equipment and it is no different when testing with your optical fibers. Even when your optical fiber is protected in an enclosure and you have followed all other best practices, a dirty connector will still lead to undesired results. There are a number of very useful cleaning devices that make it quick and easy to clean the connectors of your fiber spools and connection cables, so always incorporate this into your testing procedures.
By following these practices, it will go a long way to ensuring that you are getting maximum benefit out of your optical fiber spools, whether they are brand new or ones that you already own.
Traditionally, products have gone down the path of modularity for two reasons: cost and/or ease of replacement without effecting existing services. When the LGX form factor was first created for optical splitters, it made sense to have a modular approach for the first reason and to a lesser extent, the latter reason. When optical splitter modules were first put into the LGX form factor, the cost per splitter was considerably higher than it is today. Therefore, inserting modules into a chassis became a cost effective way to “grow” as needed. At the same time, the quality of those modules was not as high nor as repeatable as it is today, so despite any changes being service effecting (passive elements are not capable of protection switching around an outage) having the ability to replace the modules was also a key advantage.
Current Requirements & Challenges
Today, the cost of optical splitters has significantly dropped while the quality has improved, negating the previous advantages of the LGX form factor. In fact, as networks grow exponentially in bandwidth, they are decreasing exponentially in physical footprint due to virtualization and cloud technologies. The driving factors behind this market shift have been related to the space available for service providers and data centers to offer the services their customers need. For this reason, the LGX form factor no longer works. Taking up 4RUs in a rack (at a minimum) is unacceptable for passive elements in today’s networks, yet this is what is required for a modest number of LGX splitter modules. Even with the maximum number of optical splitter modules installed in the highest density 4RU LGX rack, the total number of splitters is limited to only 128.
Recognizing this market shift, M2 Optics has recently launched its SplitLightTM High-Density Platform (HDP) family of products. Each platform, or chassis, is only 1RU. Unlike, traditional approaches that have bulkhead modules, the SplitLightTM HDP uses a patent-pending 3D approach to provide the industry’s most dense solution in a single rack unit. As a result, up to 192 splitters can be installed in a single, SplitLightTM HDP. While the SplitLightTM HDP provides significantly more density per RU than an LGX solution, it also maintains the flexibility of those solutions in terms of chassis depth, flexible mounting options, and both front and rear connector customization.
In recent years, companies have shown the benefits of “copying” and sending traffic from network backbones to purpose-built monitoring devices…no interference with the existing, “live” traffic and the traffic can be analyzed in real-time or stored for later playback. However, the best approaches to “copying” and sending the traffic to be monitored has been a source of contention. As 40/100G becomes more prevalent, how the traffic is accessed will become increasingly important.
Initially, the Switched Port Analyzer (SPAN) ports were used to deliver copies of traffic to analyzers, but this has posed several problems at the 1G and 10G data rates, which likely will increase exponentially with 40/100G:
- SPAN ports are part of the switch/router and operate in much the same way as typical ports, so the data is not always an exact copy
- Traffic congestion both on the router and on the SPAN port itself can result in increased latency or the traffic to be dropped completely
- Relying on a device that could be creating the problem to help identify it can be a self-defeating exercise
Figure 1: Network Monitoring with SPAN Ports
The practice most recently deployed, uses passive taps to send an exact copy of the traffic to the analyzer(s). While this accomplishes the task of not interfering with the “live” network, it presents issues in terms of cost and data accessibility. For example, if a network has 10x10Gbps backbones that require monitoring, the network must also have 10 analyzer ports available for the monitoring. That may not seem that daunting at first, but suppose you are a service provider or data center and you have 144/288 fibers that require monitoring. Now, you need that many analyzer ports as well, which are expensive even at 10Gbps, so what happens when the customer migrates to 40/100G?
Figure 2: Network Monitoring with Passive Taps
Of course, a practical approach to this issue would be to connect the “monitor” ports from the tap, storage device ports, and a few analyzer ports to a patch panel. If a 1x3 tap is used (creates two monitoring ports for each backbone), all of the traffic can be stored for replay using one of the monitoring ports, and the analyzer(s) can be patched into the other monitoring port as needed. This enables all traffic on the network backbones to be captured while simultaneously monitoring the most critical paths (the paths of most interest) in real-time.
Figure 3: Network Monitoring with Passive Taps and a Patch Panel
While the approach above does solve the problem of capturing everything and reducing the cost of the analyzing equipment, it does present one key problem: manually patching in the storage device or backbone that you want to monitor can be time consuming, error prone, and increase the risk of creating a network issue. Using a Layer 1 switch or an automated patch panel can eliminate or reduce these issues. For example, connecting the “monitor” ports from the tap to a Layer 1 switch or an automated patch panel reduces the time needed to make connections because now they can be made remotely and at the click of a mouse. Furthermore, using a switch or automated patch panel reduces errors as generally some intelligence keeps the user from making an inappropriate connection (software may be intelligent enough to prevent a 10G port connection to a 100G port). In addition, making the connections inside the switch or automated patch panel reduces exposure to the elements preventing network errors that can occur, such as dirt on the end of a fiber optic connector.
Figure 4: Network Monitoring using Passive Taps and Symmetrical Switch
Ideally, the Layer 1 switch or automated patch panel would be used to “patch” either a monitor port directly from the network or a storage device port to the analyzer as needed. As a result, one of the “monitor” ports can be statically connected through a patch panel to the storage device’s Rx port. In this case, all of the storage device’s Tx ports and the other “monitor” ports from the tap should be connected to the input ports on the Layer 1 switch or automated patch panel. With that in mind, the output ports of the Layer 1 switch or automated patch panel should be connected to the Rx port(s) on the analyzer. This approach further reduces the cost of capturing the traffic on the network because it requires a patch panel, a passive optical tap, a highly asymmetrical Layer 1 switch or automated patch panel, and only a handful of analyzer ports. The cost savings of this approach versus the previous one above is primarily due to the asymmetrical Layer 1 switch or automated patch panel cost versus a symmetrical switch.
Figure 5: Network Monitoring using Passive Taps and Asymmetrical Switch
In summary, as we move toward 40/100G networks, the same problems seen in monitoring networks at 10G still exist but are compounded with the additional cost and complexity associated with 40/100G. The best and most cost-effective approach to ensuring that all data is quickly, reliably, and easily captured is to deploy passive optical taps coupled with either optical switches or automated patch panels, which connect the network backbones to storage devices and network analyzers.
Learning to operate an OTDR properly is a very important skill for technicians at companies managing and servicing fiber optic networks. The OTDR is used frequently to determine length and loss characteristics, as well as for testing optical fibers for faults and related issues that can negatively affect network performance.
There are a number of different types of OTDR devices in the market, from small portable units designed for field use, to sophisticated laboratory-grade devices that can provide a wide range of features intended for the most advanced users. Regardless of the type of OTDR itself, the one complimentary item that is always required for training is a length of test fiber. (Note: An OTDR launch fiber may also be required for overcoming the “dead zone” of a fiber-under-test, which is covered here).
While most training classes will use lengths of fiber on unsecured spools or in makeshift types of enclosures, this is generally not “best practice” as the delicate fiber is frequently at risk of damage, and often not very easy to handle. Considering that the test fiber will be used by many students over time, it is a benefit to most classes to use a more professional solution for OTDR training.
By utilizing one of the many Fiber Lab solutions for OTDR training from M2 Optics, instructors and students both receive a number of benefits not available when using a traditional, unsecured fiber spool. For convenience, we have outlined a number of key benefits below.
Key Benefits of Using a Fiber Lab for OTDR Training:
Easy-to-handle, stable enclosures protect fiber from accidental damage while providing consistent results
Any type of fiber is available, as well as any custom length, for simulating a number of different network scenarios
Fiber can include user-specified attenuations that represent field splices, good or poor connectors, or other “events” that a student must learn to identify with an OTDR
Ultimately, a Fiber Lab provides every student with a real optical network in an efficient package, customized to include common events that they will experience in live networks. For the instructors, it is a great value to have a handy tool that can be used for teaching demonstrations, as well as testing students to ensure they have learned the OTDR skills necessary to be successful. Lastly, instructors do not have to spend time attempting to build their own solution when an ideal platform is already available.
As virtualization and cloud applications become more and more prevalent in Data Centers, POPs, Head-ends, and Central Offices, the available rack space needed to house the equipment for these applications is shrinking. While the space needed to store, process, route, or switch the data becomes more compact, one thing that remains difficult to reduce is the physical layer infrastructure. As traffic enters or exits a facility, most providers want the capability to monitor what is being delivered or sent to/from their site. At the larger sites, this data traffic is riding on fiber, and in many cases, there are a number of fibers coming into or out of a given site. To be able to accurately monitor this traffic, a passive optical tap is used to duplicate the traffic and send it to a monitoring device that can analyze the header information native to the traffic type. In the past, these optical taps were relatively expensive and bulky. Even today, most vendors cannot provide more than 24 taps in a single 1RU footprint.
For most companies, the ideal scenario would be to not only have a lower cost, higher density optical tap solution, but also one that offers adequate customization for flexibility. For example, in some cases a company may want a 50:50 optical power tap ratio, while another may want a 90:10 ratio. Or, a company may have multiple monitoring devices each serving a different purpose, so more than a 1x2 splitter/coupler is required. Furthermore, some applications require single mode optical fiber, while others require multimode fiber, thus it is crucial to have a solution that can meet a wide array of requirements.
While the common approach has always been to add more chassis in order to meet varying levels of customization and/or higher density requirements, this is not a viable option when rack space is at a premium. Fortunately, some vendors have re-thought this situation and developed a new generation of optical tap solutions. As an example, the SplitLight HD from M2 Optics can accommodate up to 128, 1x2 splitters of varying power ratios and fiber types in single 1RU chassis. Compared to a traditional alternative with 10-20 total optical taps, this new solution can easily reduce the rack space required by 75% or more. How is this possible? Unlike most traditional optical taps which are very limited as a result of using standard connectors (LC or SC type), the SplitLight HD was designed in a unique way to incorporate multi-fiber MTP® connectors, which results in a much higher density in the same physical space.
With the increasing need for more sophisticated communications equipment to meet market demands, it is crucial that companies deploying and managing optical networks utilize solutions that help to maximize system performance, while also addressing equally important, related issues like rack space usage. By doing this and aligning themselves with partners that understand the challenges they face, these companies can continue to deliver high quality services for years to come.
With most of the world now relying on fiber optic systems for communication, a key component to ensuring a high level of performance from operators is network monitoring. When we think of network monitoring, much of the focus is usually on the equipment itself, as well as the management of all the data flowing through the system. As a result, an area often overlooked when deploying and monitoring a network is the actual fiber optic cable, through which all the data is sent from one location to another.
While network operators aim to protect fiber optic cables as best they can, it is a relatively common occurrence to hear via the local news or industry reports that a fiber optic cable was accidentally cut and some type of outage immediately followed. A recent article on AllAfrica.com by Eric Bright serves as a great example in highlighting some recent events in Europe and Africa along these lines. This is especially true in the developing countries, where there may not yet be the same level of protection or advanced routing options readily available.
To deal with these types of issues in the past, most operators would need to physically check the line using an OTDR to determine the location and then travel to that specific point to service the issue. With every second of downtime counting negatively towards the operator in several ways, this process often took up valuable time before a resolution could be completed.
Fortunately, Remote Fiber Test Systems (RFTS) are available to assist operators in servicing these fiber-related issues in the most efficient manner. By installing a remote fiber test system, an operator is able to monitor fibers around-the-clock from anywhere and receive immediate alerts of breaks, degraded connections, and even malicious intrusion attempts. In addition to the quick notification, most fiber test systems will provide a near-exact location of the issue, so the service team will not have to waste as much time determining where to go. The positive end result is increased network availability via another layer of network monitoring.
When looking into deploying a remote fiber test system, there are several different alternatives available in the market that might be suitable for an operator’s requirements. While some have utilized solutions based on traditional OTDR technology, due to the extremely high price tag and ongoing budgetary pressure, many are finding new systems based on alternative technology to be sufficient for meeting their fiber monitoring goals. Since all networks are unique, it is important to obtain information on a number of different systems to find the solution that best fits all the objectives of the operator.
This new, free whitepaper from M2 Optics Inc. discusses the importance of simulating a physical fiber optic network in the laboratory and best practices for achieving maximum results.
Prior to deploying new equipment into a live fiber optic network, communications equipment manufacturers, service providers, and carriers must ensure that their systems will work exact as intended. As a result, these organizations strive to exactly simulate the live network in a laboratory environment. While the consensus in the industry agrees that using real optical fiber will yield the most accurate measurements, traditional methods of using unsecured bare optical fiber spools can often lead to experiencing inefficiencies and marginal results.
As the demand for more bandwidth grows and the march towards 100G systems continues, laboratories must address this crucial aspect of their testing process, or risk falling behind. This is most certainly the case with that large laboratories that are performing 24/7 testing on multiple networks at a time, or seeking to consolidate operations and require frequent changes to the test setups.
Fortunately, there are several best practices that test engineers can follow to help maximize both efficiency and results when seeking to simulate a fiber optic network. After reading this brief whitepaper, readers will have a better understanding of how taking just a few simple steps can significantly and positively impact their efforts in this area.