Fiber Optic Blog | M2 Optics

Fiber Optic Attenuators with Doped Fiber

What are Fiber Optic Attenuators?

Fiber optic attenuators are used in applications where the optical signal is too strong and needs to be reduced. There are many reasons why this need may arise.  You may need to equalize channel strength in a multi-wavelength system or reduce the optical level to meet the input specifications of an optical receiver. In both of these cases, a point reduction in optical signal strength is required.

Types of Fiber Optic Attenuators

Optical attenuators can take a number of different forms and are typically classified as fixed or variable. Fixed attenuators can be broken down into either build out style or incorporated into a patch cord. The build out variety is a small (~ 1.25 inch long) attenuator with a male connector interface on one end and a female interface connector on the opposite end. The build out style is typically fabricated with either air gap attenuation or doped fiber attenuation.

Air Gap Attenuators

In air gap attenuators, the specified loss of optical power is accomplished by two fibers that are separated by air to yield the correct loss. Air gap attenuators are susceptible to dust contamination and can be sensitive to moisture and temperature variations. And if air gap attenuators are applied in multi-channel analog systems such as those used by CATV companies, it can be a huge mistake as the attenuator itself can create second order distortions that hamper the performance of the system.

Doped Fiber Attenuators & Benefits

Doped fiber attenuators are exactly as the name implies. A short piece of fiber with metal ion doping that provides the specified attenuation and the interface between the male and female connections on the attenuator. The doped fiber attenuator is the preferred component for a number of reasons. Doped fiber is not susceptible to dirt build up, moisture, or temperature variations. And they are made to perform with stability over wide wavelength variations and band passes.  Attenuation incorporated into a patch cord can be fabricated with either a fusion splice or the leg of a fused coupler.  These types can sometimes be wavelength sensitive because of how they are fabricated. 

Doped fiber attenuators are the preferred attenuators for all of the reasons provided above in the appropriate point reduction of an optical signal. However, they can also be mistakenly applied when testing the performance of optical equipment and using attenuators (in place of real fiber lengths) to simulate a fiber length/distance or network.  Only real fiber lengths simulate the various chromatic and polarization dispersions with which real systems must operate. Therefore, real fiber should always be used whenever possible to test equipment that will utilize optical fiber in the field.

Commonly used Multimode Optical Fibers

Multimode optical fiber is a type of optical fiber widely used for shorter distance applications (data center, campus, premise, etc), due to its larger core sizes (62.5um and 50um), high capacity, and high reliability.

As the requirements for greater bandwidth have grown in recent years, many users look to purchase multimode fibers based on the ISO 11801 standards (OM1, OM2, OM3, & OM4) to meet the needs of their applications.

With several manufacturers providing multimode optical fibers, below are the most popular brand & types from each manufacturer:

OM1
      Corning InfiniCor
      Draka Standard Multimode
      OFS Standard Multimode

OM2
      Corning ClearCurve
      Draka MaxCap / BendBright
      OFS LaserWave G+ / Flex G+

OM3
      Corning Clearcurve
      Draka MaxCap / BendBright
      OFS LaserWave 300 / Flex 300

OM4
      Corning ClearCurve
      Draka MaxCap / BendBright
      OFS LaserWave 550 / Flex 550

Questions or requirements for any of the fibers listed above?
Click here for more information

Importance of Using Reliable Fiber Network Simulation Platforms

In many cases, the primary focus of a fiber network simulation platform is on the electro-optical equipment at both ends of the fiber optic link.  Since the purpose of network simulators is to evaluate the DUT (Device Under Test) equipment, it only makes sense that this is where the attention will be. However, it is a crucial mistake to forget about both the stability and consistency of the test fiber because the DUT test results (performance, pass/ fail, etc) totally depend on knowing that the optical fiber characteristics are consistent and very reliable.

As a provider of test fiber, we often hear statements such as “if we can get light through, it’s good enough” or “new fiber is too expensive, so we’ll just buy a used spool on EBay” or “the shipping package our fiber spool arrived in provides enough protection”.  Unfortunately, the reasoning behind these comments has everything to do with saving a very small amount of money and nothing to do with the expectation of being able to provide reliable test results that can confidently be presented to a customer or included on a data sheet. 

As many times as we hear the statements above, we also often hear “the fiber I am using is not providing consistent results”, “the second-hand fiber I purchased arrived damaged”, and “our fiber was broken accidentally while exposed on the bench.”  Fiber network simulation platforms are designed to resolve all of the potential issues arising from mishandling of fiber spools, including damaged connectors, pinched or bent fibers, and fiber movement on the spool due to improper storage.  By using these platforms, the risk of damage and breaks to fiber and connectors is greatly minimized, while protecting it from dust and debris.  In addition, connector interfaces (adapters) are secured, cleanable, and replaceable.  Lastly, only new fiber is used in these platforms to assure the quality of performance, so users do not have to worry about any issues with the fiber that might lead to poor performance and test results. 

If you do not take the appropriate measures to build a reliable test platform, you run the risk of inconsistent or marginal results which can lead to more serious issues down the line.  A small investment into a quality network simulation platform is an important, yet simple way to ensure the accuracy and performance of your equipment.

Fiber Optic Network Monitoring for Reducing Service Downtimes

With fiber optic equipment now widely used in most communications systems, it is crucial that administrators and service personnel have an efficient solution in place for dealing with issues directly related to the physical network.  While there are many Network Management Systems (NMS) being utilized, most will send an alert if a specific piece of equipment fails, but are not a help in locating the problem if it should occur to the line itself.  Therefore, while a failure will often be recognized quickly, much time can be lost in sending a technician out to locate and fix the specific issue.

Common issues that occur on a frequent basis include fiber faults or breaks due to accidental damage (ex: construction work), degraded connections, and even fiber tapping attempts to steal proprietary data for illegal use/activities.  In all cases, it is crucial that the problems be resolved rapidly, or else your business can be put in serious risk due to poor service and/or loss of valuable data.

Fortunately, cost-effective solutions are now available that provide real-time monitoring of optical network lines while pinpointing the issue(s) to within meters.  Since the monitoring interfaces are web-based, businesses can proactively ensure their network is running smoothly 365/24/7, while significantly reducing service downtimes when something should occur.  Fault localization allows technicians to spend far less time finding the problems and more time resolving them.  These solutions (like the FiSEC Fiber Monitor below) require minimal setup time, run on either active or dark fibers, and do not interfere with any of the data being transmitted. 

FiSEC Fiber Monitor

 

 

While risks vary by business or industry, a fiber optic network monitoring system can offer great benefits if it is not something that has already been implemented.  In addition, it will set your business apart from others in terms of your service offering, as you can quickly resolve issues before they have the chance to escalate.

Industries Actively Monitoring Optical Networks  (partial list) 

• Banking and Financial (monitor data to/from data centers, compliance laws)
• Telecom and Cable providers (PON & FTTx networks)
• Government and Military agencies (protect against terrorism/espionage)
• Utilities and Power Plants (ensure communication; protect against terrorism)
• Transportation (ensure communication for airports, railways, etc)
• IT & Network Installers (additional service offering for customers)

Why Test Fiber Optic Equipment Using Real Optical Fiber?

When testing fiber optic equipment intended for longer distances during the development/certification stages, it is vital that engineers ensure their products will operate as intended once installed in the field.  In order to do this, there are a few alternative methods that have been used to accomplish this task.  As a leading provider of network simulation platforms containing real optical fiber spools, questions we commonly receive include:

• "Why purchase specific or longer lengths of optical fiber when I can simply use attenuators?"
• "Why should I test using real optical fiber, as there are a variety of network simulation software packages available?"

To answer these questions simply, since real fiber is used in the field, only testing using real fiber will exactly simulate the performance of the equipment.  In greater detail, there are several factors that either using attenuators or a software programs typically do not account for:

• Chromatic Dispersion
• Polarization Mode Dispersion
  (Click for more detailed information)

These two factors play major roles in the performance of optical fibers and vary depending on the type of fiber being used.  If equipment is not tested using real fiber and the above factors are not accounted for, the results can vary significantly and put the manufacturer at risk.  In addition, fibers from various manufacturers are designed slightly different according to application requirements and features, so it only makes sense to test in a manner that will simulate the optical network as closely as possible.

For these reasons, many engineers now follow the best practice of testing using real fiber to exactly simulate field applications - and most often use the exact fiber type & manufacturer that is deployed in the network/system they are designing equipment for.

"Achieve Real Results Using Real Fiber"

Commonly Used Single Mode Optical Fibers

Single Mode Optical Fibers are commonly used throughout the world for fiber optic communications,  as they offer narrower modal dispersion characteristics, making them more suitable (than multimode fibers) for medium and longer distance transmissions.  With several manufacturers, as well as industry standards, it is important to understand what fibers are available when designing, installing, and testing fiber optic products and systems.

Single Mode Optical Fiber & Cable (ITU-T G.652)

Widely used around the world, this fiber is ideal for campus, metro, access, and FTTH networks

• Corning SMF-28e+
• Draka ESMF
• OFS AllWave

Non-Zero Dispersion Shifted (NZDSF) Single Mode Optical Fiber (ITU-T G.655)

Ideal for highest capacity, longest reach systems (long-haul, regional, metro)

• Corning LEAF
• Draka TeraLight Ultra
• OFS TrueWave Reach / RS

Extra flexibility and bend radius makes these fibers suitable for network installations and challenging environments where cable routing is a challenge or difficult.

• Corning ClearCurve
• Draka BendBright
• OFS Allwave Flex

Manufacturers typically supply fiber on spools of 50km or larger, however many vendors and distributors will re-spool fiber to shorter lengths if required.

For detailed specifications and additional types of single mode optical fibers, please visit the manufacturers websites above or contact us.

Network Simulation Platforms for Fiber Optic Equipment Testing

As the use of fiber optic equipment in communications systems continues to grow worldwide, network simulation testing has become vitally important for vendors seeking to integrate their equipment in the field.

In the past, many engineers and technicians were satisifed by using spools of optical fiber that were exposed and sitting out on the test bench.  This practice, although usually working for a short period of time, generally leads to a number of issues that cost users both time and money.

Potential Issues of Using Exposed Fiber Spools

• Bare optical fiber is easily damaged when exposed in the work environment
  
• Extra care must be used when moving spools or risk damage to the fiber
  
• Spools take up valuable workspace, especially in large facilities at vendors performing network simulation testing frequently
  

With the production/use of specialty optical fibers (carrying a higher cost) on the rise and more budget restrictions, engineers must be wary of these issues.  Fortunately, by purchasing an affordable network simulation platform, users can eliminate all the above issues, while making their fiber optic test routines much easier.

Types of Fiber Optic Network Simulation Platforms

Today, there are a variety of affordable network simulation platforms available in the marketplace.  Both portable enclosures for single spools, and rack-mount enclosures for multiple-spools (and longer distances) are available.  In addition, most are custom built exactly to customer specification, offering a vareity of optical fiber types, lengths, and connectors. Lastly, these plaforms offer testing stability and better organize the entire workspace.

  Multi-spool w/ 100km Optical Fiber

  Single Spool w/ 25km Optical Fiber

With optical fiber being extremely valuable for network simulation tesing, it only makes sense to protect the fiber and fortunately that is easily accomplished.