Blog: Writings from Chromis Fiber Optics: Next Generation Plastic Optical Fibers

Long HDMI Cables—Why Optical Active Cables are So much Smaller, Lighter and More Flexible than Copper Cables
Posted by Whitney White, 5/4/12

If you’ve ever installed a long copper HDMI cable to go more than 30 feet or so, you probably noticed that it was heavy and stiff. For example, if you look at a typical 20-meter passive copper HDMI cable, it weighs about 5 or 6 pounds! The biggest reason for this is that the high-speed signal is carried over copper wires, and as those very short electrical pulses travel down copper wires, two things happen to them – they get weaker (this is called attenuation), and they get smeared out, so that they start to overlap with each other (this is called dispersion).

Moreover, the attenuation and dispersion impact the signal in a way that their impact increases very rapidly as a function of length. For example, attenuation diminishes the power of the signal exponentially with length, and the exponential decay rate increases very rapidly above 100 MHz. So in a typical 24-gauge copper twisted pair (the type found in most long copper HDMI cables), at the end of a 20-meter cable, the high-frequency components of the video signal can easily be a factor of 10 weaker by the time they exit the cable. If you would like to know more, Blue Jeans Cable has a wonderful discussion of the factors that determine long HDMI copper cable performance

One way to minimize the amount of attenuation and dispersion is to simply make the wires bigger, and to more accurately control the insulation and the twisting of the wires. Another way to help compensate for the reduced amplitude and clarity of the signal is to add layers of foils or braiding (called shielding layers). These shielding layers help reduce the amount of foreign electromagnetic interference picked up by the copper wires. As you can imagine, using bigger wire sizes and adding shielding layers increase not only the weight, but also the size and stiffness of the cable. That is how we get 20-meter copper HDMI cables that weigh 6 pounds, and where even favorable online reviews include comments like “It’s not easy to bend it at first, but it will come around after a while…” (This is an actual sentence from a positive review of an Accell UltraAV 20-meter cable on Amazon.com.) And, even with all that shielding and weight, many copper cables can’t deliver true HDMI 1.3 or 1.4. For example, the above Accell cable delivers a signal that has been degraded to the HDMI 1.2 standard, even if you give it an HDMI 1.3 input.

By comparison, for an optical long HDMI cable, the story is much simpler – the optical signal exits a 20-meter cable length looking almost exactly the same way it did going in. This is true whether the fiber used in the optical HDMI cable is made out of glass or plastic. In our plastic fiber HDMI cables, the optical signal strength typically decreases by only about 10 or 20% from beginning to end. And dispersion is negligible as well – the 10.2 Gigabit per second HDMI 1.3 video signal uses only a few percent of the bandwidth of our plastic fibers. Also, unlike copper wires, optical fibers don’t pick up stray electromagnetic interference.

Because the fiber performance is so much better and is inherently immune to electromagnetic noise, there is no need for shielding, or using heavier wires, or any of the other things that make long HDMI cables so large and heavy with copper wires. As a result, our 20 meter plastic fiber HDMI cables weigh only about 0.75 pounds – about a factor of 6 to 8 less than copper HDMI cables of the same length!

About Chromis Fiberoptics

Chromis Fiberoptics, located in Warren, NJ, is the world technology leader in the design and manufacturing of Plastic Optical Fibers (POF) and POF cables. Chromis' products enable optical networking over plastic fiber at speeds up to 10 Gb/s. Chromis supplies a variety of plastic fibers and cables for consumer electronics, active optical cables, and building networking applications. Chromis is funded by corporate strategic investors as well as angel investor groups, including Golden Seeds and New York Angels. For more information, please visit the company website at http://www.chromisfiber.com , or email your inquiries to info@chromisfiber.com.

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Long HDMI Cables—Why Plastic Optical Fibers are the Solution
Posted by Whitney White, 4/13/12

For consumers and businesses that need to make long HDMI cable runs, there have been few choices until now. In this article, I will try to explain what choices exist for long HDMI cable runs, as well as how a new optical technology, based on plastic fiberoptics, can save the day.

Although it is possible to find long HDMI cables made out of conventional copper cable construction, this is really pushing copper’s limit on distance. For one thing, the relatively high attenuation of the copper wires means that the strength of the signal decreases rapidly enough. Worse, the twisted pairs of wire found in copper cables have a relatively low bandwidth. And HDMI 1.3 asks for LOT of bandwidth – at least 10.2 Gigabits per second for just the video channels.

So although the electrical pulses that carry the video signal start out sharp and strong, by the time they pass through 15 or 20 meters of copper wiring, they have become much weaker, and have started to overlap. In practical terms, that means more errors and lower picture quality, or even intermittent blackouts.

Testing by Monster Cable has shown that many longer copper HDMI cables have a lot of transmission errors even at 10 meters. For really long HDMI cable runs, like 15 or 20 meters, very few vendors are able to make a copper HDMI cable that functions at all – and those who do want a premium for the product. Prices of $120 are pretty much the bottom of the market, and the higher-end offerings go well above $500. Because the only real solution for doing long distances with copper is to use larger wires, these copper long-distance HDMI cables are not only thick and stiff, but heavy – typically 4 or 5 pounds.

One solution to the problem of long HDMI cable runs has been to use extenders. These are boxes that convert the HDMI signal into one that can be carried over one (or more often two) Cat 5E or Cat6 unshielded twisted pair cables, the same cable that is commonly used for computer local area networks (LAN’s).

Extenders based on unshielded twisted pair cables have a tough job, especially in the case of HDMI 1.3. They have to reduce the 10.2 Gigabit/second HDMI 1.3 data stream into something that can be carried on a Cat 5E cable intended for 1 Gigabit/second. Not surprisingly, picture quality can suffer in longer lengths. Cat 6 works somewhat better, but even then, it is very sensitive to termination quality.

Although extender solutions serve some residential needs, they are more problematic in commercial or industrial installations, where numerous sources of electromagnetic interference can be a serious problem for unshielded copper cables. Some vendors deliver more robust extender boxes, but prices quickly reach for $300-400 or more for commercial-quality extenders – and the copper cables themselves aren’t included!

For the last few years, the premium, bullet-proof solution to long HDMI cables runs has been fiberoptics. In some cases, these optical fiber HDMI solutions were done with extender boxes that use optical fiber instead of copper cables to carry the signal. While optical HDMI extenders are generally quire reliable, and can serve very long distances (up to 300 meters, or even 1 km!), they are also extremely expensive. Many units are $1500 or more, and the “bargain-basement” glass fiber extenders are around $500.

Worse, just like copper cable extenders, the glass extenders are bulky and create a rat’s-nest of cables next to your beautiful next-generation display. This is why installations that need the power of fiber, but also need something compact and elegant, usually chose active optical cables. Active optical cables are basically an optical cable with tiny electronic-to-optical converters buried in the connectors at the ends of the cable. So the connectors at the end of the cable are the standard electrical connectors used with copper cables – but the cable has the longer reach, and potentially, the smaller size enabled by the use of fiber.

While active optical cables (AOC’s) made with glass fiber are an elegant, very reliable solution to long HDMI cable runs, they are also still very much a premium-priced solutions. Most offerings on the market start at about $400 for 10 or 20-meter cables, and go up to around $1500 or more for 100-meter cables.

But thanks to the recent introduction of plastic optical fiber for HDMI active optical cables – HDMI AOC’s have finally started to become an affordable solution that can be much more widely used. Compared with glass fibers, plastic fibers are much easier to terminate, much easier to connect to optical transmitters, and very durable. All of this it much easier, and cheaper, to assemble an HDMI active optical cable. As a result, HDMI AOC’s are now appearing on the market for less than $200. And they are much smaller and more flexible than their glass fiber cousins.

Want to try an active optical cable solution for you long HDMI cable needs? Check out the Chromis Fiberoptics HDMI AOC here : or email us at info@chromisfiber.com.