Fiber optics

New 1.5Gb/s and 3Gb/s video bandwidth requirements are driving broadcasters to embrace fiber.
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Most of us know that fiber optics have been around for nearly four decades. But as broadcasters, we tend to think fiber is for transporting video in and out of the plant — not within the facility. After all, fiber optics is really only for longer distances, isn't it?

Traditional fiber-optics usage

Other than telcos, broadcasters' traditional usage of fiber was strictly limited to specialized needs. I clearly can recall our first fiber customer in the early 1990s — a European broadcaster that needed to run seamless operations between two collocated buildings. As the buildings were close together and only 32 video feeds were required, this project wasn't really anything out of the ordinary. We would only need to pre- and post-equalize the signal, use the lowest loss cable available and suffer a little bit of added noise. Having 32 feeds precluded using microwave STL units due to costs.

The one catch in this installation was that the video requirement was serial digital (270Mb/s), not analog — hence, the move toward fiber. We quickly designed fiber I/O into our routing switchers and satisfied their requirements with 100-percent reliability. Nonetheless, when we discussed this solution with other customers, we soon found out most broadcasters would not embrace fiber. The general consensus was, “For feeds from outside the plant, we leave it up to the local telco/PTT to provide this service.”

For satellite distribution of feeds, receivers are often “remoted” from the receiving dish to provide basedband audio/video within the plant. To keep the RF loss to a minimum, remoting the RF connection is typically done by putting the L-Band RF signals onto fiber. Again, this is considered to be more of an external application to the plant.

New requirements for fiber

New requirements in today's industry are driving broadcasters to embrace fiber. As new facilities are built and older ones upgraded, broadcasters are implementing HD at both 1.5Gb/s and 3Gb/s data rates. At high data rates, coax installs need to be augmented with fiber to accommodate all necessary path lengths. Practically speaking, coax is really only good for 200ft maximum by the time one includes connectors, patches and some overhead for nonstandard/emergency patching. Even within a central equipment room, these seemingly short distances get chewed up very quickly in the facilities' cable trays. Meeting SMPTE 424 specs becomes more difficult as inexperienced installers often squeeze the coax with incorrect tray loading or tie wrapping.

Given these factors, more and more broadcast products now offer fiber interfaces. This makes a mixed-mode plant quite simple to consider now that typical products such as A/V processors, up/down/crossconverters, frame syncs, mux/de-muxers and distribution amplifiers offer optical. Mid- and large-size routers now offer user-customization of the I/O for coax or fiber by simply changing out I/O modules to provide the required quantity of optical ins and outs.

Looking at typical central equipment rooms, many sources come into either a central or distributed routing system. Some of these are from local in-house (studio) sources; others are from various remote feeds. Newer plant designs want to future-proof their basic infrastructure to cover 3Gb/s, and installing fiber makes this pretty simple. Take, for example, having a bank of serial digital frame synchronizers. Due to coaxial distance constraints, it actually was necessary to have a “bank” of frame syncs physically located beside the router. With fiber, there is no need. We can have several smaller groups, or even single units, at far greater distances than we had ever imagined.

Fiber has another unique characteristic over coax — multiple cables in a single jacket. With fiber counts of 6, 12, 24, 48, 72 and 96, install costs go down. Look at the sudden flexibility you've created. Consider a studio that had four outputs, two returns and house black yielding seven feeds. The plant designer dropped in a 12-count fiber. Six months later, this room was needed for a sudden pop-up 1080p event. They wheeled in a second switcher and suddenly were up and running without laying cables. The install time was cut in half.

By using passive splitters, the in-house studio feeds can be distributed to the central router and also additional rooms and routers within the facility at no extra power costs (keeping the install somewhat green). When using splitters, monitoring points basically come for free; this is a real bonus. (See Figure 1 on page 64.)

Using fiber is really scary

The only thing scary about fiber is that looking directly into an active fiber is dangerous. Don't do that. Besides, there is no point; you can't see the light anyway.

Years ago, broadcasters had similar apprehensions about accepting new connector technology such as simple RJ-11s. I recall having to design them out of the newer equipment due to complaints of the difficulty having such a customized connector and specialized training and equipment required to produce the mating ends. Look around any facility now, and you see literally thousands of the RJ-11's big brother, the RJ-45. We all had to take the time to learn how to use these connectors, and the same goes for fiber.

With any new technology, there are lots of confusing options. At a glance, fiber is no different: single-mode, multimode, macro and micro-bends, slack storage, angled and ultra connections and, for that matter, a half a dozen of different types of connectors all begging us to keep with BNC and coax technology. But seriously, the switch to digital has forced substantial changes in BNCs and coaxes over the past decade. And fortunately, a few broadcasters and manufacturers have been using fiber for close to 15 years now, so they have already worked out most of these kinks for you.

Finally, think about this: How many of you have connected up the audio optical out from your DVD player or set-top box into your home theater audio system. Was that difficult?

Smaller bits

With any new technology, we begin with a requirement, and then we need to learn about it — breaking the subject into smaller “need to know” pieces. When it comes to fiber, leave the heavy-lifting technology to the equipment suppliers, just as we do with most technology we use today. Learn about the I/O, appropriate test equipment and the constraints, and move on. Also remember that fiber systems are designed to go tens — even hundreds — of miles, but within the plant, we only need to focus on short distances. Hence, most of the complexity is removed.

Following are the basics on installing and operating fiber:

  • What type of fiber should I use? There are two types of fiber: single- and multimode. Although two options exist, the choice is actually quite simple: Just use single-mode. Multimode limits the distance even within a large building. Using single-mode, you can go for miles without calculating a link budget. Keep it simple: Only use single-mode fiber.
  • How do I choose connectors? People always complain about having too many connector options. Well, look in your plant that is filled with DB-9, DB-25, dozens of BNCs for different coax sizes, RJ-11, RJ-45, HDMI, VGA, DVIs, XLR3s in different flavors and min-DINs — not to mention all the specialized ones for cameras and remote operations.When it comes to connectors, the first thing you need to know is that there are two different ways to join fiber: Angled Physical Contact (APC) or Ultra Physical Contact (UPC). These methods are always indicated as part of the connector part number. The rule of thumb is to check specs on the product you are buying. Typically in broadcast products, only UPC is used. APC provides a more expensive, lower-loss connection when super long distances are required outside the plant. There is no need for APC inside the plant.Like choosing the fiber itself, making the choice of connector type is also pretty simple: Most broadcasters use SC or LC connectors. They both are snap-in and locking. Try to standardize on one type as much as possible; use patch cords with different ends to convert when required to use a different connector type.
  • What about test equipment? Don't even consider initiating a fiber install without having some test equipment on-hand. You don't need much to get started. The minimum is an optical power meter and a visible light source. (Choose one that is bright enough to be seen in daylight. This is very helpful for basic physical layer troubleshooting). Having an optical time domain reflectometer can help you quickly locate the physical position of any cable faults that may have occurred during installation or handling. (Remember that some installers ignore the “minimum sweep” rule.)For broadcasters, it can be beneficial to choose fiber products from a manufacturer that also offers optical test equipment tailored specifically for broadcast use. Many suppliers focus more on the higher volume telco users, whose products are used for installations of literally miles of fiber cable. When ordering test equipment, make sure that its connectors are removable and that you identify and order high-quality adaptors to match your system requirements.
  • Is cleaning important? With fiber, there's no reason to worry if the connectors are gold-plated or not; they don't corrode. Cables do come with protective end caps to keep them polished and clean. In most broadcast applications, simply removing the caps and making the connection is all you need to do.Again, in-plant operations have lots of link budget, so there's no need to fuss too much about connector cleaning. Should some cleaning ever be required, don't blow on them or wipe it clean with your finger or shirt. There are several inexpensive cleaning kits available.
  • How can I simplify installation? For years now, telcos have been installing lots of extra fiber once the ground has been opened up. Now with “fiber to the curb,” these efforts are paying off. The same goes for the previous studio example. Much of the cost is in the install, not the cable — so install more than you need.

Additionally, installation crews do need to know how to install fiber to ensure that it doesn't crack. You should know the cable specs for the bending radius and the crush tolerance due to too many cables on top of the fiber and, just like coax, incorrect tie-wrapping. Bending cable too sharply is the worst enemy in the optical world. When you check the cable specs, you will find the bending diameter is typically 1.5in; however, there are newer cable types that allow for bending as low as 0.6in.

Hidden benefits

Besides future-proofing your facility, increasing operational flexibility and eliminating traditional distance limitations, fiber offers a number of hidden benefits:

  • Green operationsPassive splitters provide monitoring points and distribution points without using power
  • Simplified digital systems timingFiber operates at light speeds. Electrical and optical conversions take less than 10ns, so there's no longer a need to calculate cable runs.
  • Improved house syncWith fiber, the distribution of color black within your plant — or even to external buildings — is simple. Again, there are no delay issues: Simply use analog video-to-fiber converters to distribute black and tone on fiber.
  • No more cable tracing nightmaresBecause fiber passes visible light, you simply put on a handheld visible light source and find your lost cable in seconds. Passing visible light into a fiber can also help you find faults.
  • Less noiseFiber is immune to interference. There is no need to fight ground loops and various electromagnetic or RF noise.
  • Simplified control and monitoringMany interfaces are now available to extend Ethernet, intercoms, RS-422, etc., networks over fiber with simple I/O modules. Taking advantage of these greatly unifies your operations.

Summary

After reading through this article and seeing how simple fiber is to use, you will likely ask yourself why you have not embraced fiber before. Don't wait around until you are suddenly forced into implementing a stronger 1.5Gb/s or 3Gb/s plant. After all, your upgraded IT infrastructures demand fiber, so why not use it for video too? Consider fiber today.

Stan Moote is vice president of corporate development at Harris Broadcast Communications.