The fiber vs. copper debate has been ongoing for as long as the technologies have existed. As fiber’s cost continues to decrease over the years, its benefits over copper become even more attractive. It is no surprise that concepts like silicon photonics (SiPh) co-packaged optics (CPO) start to gain steam in the enterprise space. Most current research and developments have focused on the speed advantage of optical over a copper links. However, fiber optics cables can offer even more in the consumer domain. In this post, we will demystify what’s inside an HDMI active optical cable and the exciting opportunities they bring to the end users.

Fiber’s physical advantage

Have you ever wondered why most HDMI cables have gotten shorter AND heavier? To support the latest resolution and refresh rates (thus, much higher data rates), the copper conductors in a passive HDMI cable need to be shorter and thicker to reduce signal loss. This trend is not consumer friendly at all because it limits how the video/audio sources and displays can be connected. Bulky cables are also ugly cables – that’s why we do everything possible to cable management and hide them away.

That’s at least until fiber optical cables come onto the scene. Below is a cross-section cartoon to show the relative size and weight comparison between a fiber strand and a 26-AWG copper wire. Not only is the copper conductor core already larger than the fiber strand (including the outside coating), the insulation itself contributes significant size and weight. One can fit almost 20 fiber strands in the same cross-sectional area as a 26-AWG copper wire. Fiber is mostly made with glass, which is much lighter than copper. A copper wire weighs much more than a fiber strand of the same length.

It becomes obvious that the cables we use everyday can become much longer, thinner and lighter if all copper wires are replace with fibers. This is the equally important physical advantage of fiber that’s often overshadowed by its speed advantage.

Evolution from copper to pure optical

Let’s witness the HDMI cable’s evolution together by replacing copper with fibers. Without going in too many details, illustrated below is a simplified HDMI connector pinout, color coding each pin depending on its speed.

There are a total of 12 signal wires that need to be connected (8x high speed + 4x low speed), and typically one supply and ground wire is also needed, making it 14 wires in total. As discussed before, the high-speed wires need to be thicker for lower loss (typically thicker than 26 AWG), and precautions are taken to maintain signal integrity (e.g. shielding). Therefore, the cross-section of a typical passive copper cable might look like below, using the same color codes.

It is easy to see the 4 pairs of high-speed wires dominates the entire cable diameter, and fibers are the perfect solutions to replace these first. Here we meet the hybrid AOC. Note that only 4 fibers (normally come in a compact ribbon configuration) are necessary to replace the 8 wires, doubling the size advantage even further. Hybrid AOCs still directly connect the low-speed signals with copper. This allows direct bi-directional communication between sources and displays on the protocol level. The in-connector IC and optical component’s main job is then to convert between differential electrical signals and optical signals. The wires carrying low-speed signals can still be relatively thin at reasonable length, simplifying the IC design.

However, speed and length is relative – even kHz signals is considered fast in the context of hundreds of meters. If we want to push the AOC length even further, the remaining copper wires are bound to increase in thickness and weight again, while the fibers can still support high-speed signals. This becomes extremely limiting in commercial and infrastructural applications where cables are run between walls and floors.

By leveraging fiber’s speed capabilities, we could create a pure fiber AOC solution where the low-speed signals are combined onto two more fibers. Compare to where we started with the passive copper cables, the pure fiber AOC is a much longer, thinner and lighter cable, all thanks to the specialized ICs that process and deliver both the high-speed and low-speed signals. Pure Fi has existing hybrid and pure fiber optical solutions, and continues to work on next-generation products that push the pure fiber AOC frontiers.

A whole new look and experience

With pure fiber AOC’s length, form factor and weight, new cables and applications begin to emerge.

Take the gaming industry as an example. Now that the actual signaling core takes negligible space compare to the jacket, we can focus more on the cable’s appearance and ease of usage itself. What if the cable is not to be tucked away anymore, and it could become part of your awesome RGB gaming setup?

On the other front, mobile gaming handhelds like Steam Deck and Asus ROG Ally are providing PC gamers another form factor to bring their favorite games on the go. The consoles themselves contain powerful CPU/GPUs that can output 4k/144Hz content, but the screens are only up to 1080p resolution. These handhelds can be docked and essentially turned into mini gaming PCs for a better screen, but extra gaming accessories (keyboard, mouse, controller, etc.) are needed. As of now, it’s picking your poison between having a mobile experience on a small screen or a descent but sit-still PC gaming experience. What if there is a third option?

Imagine being able to sit on the couch, still use the handheld’s built-in controller, and enjoy the game’s visual/sound on a big screen. We need a cable that directly connects the handheld to the display. It needs to be at least 15ft long to comfortably reach the big screen from the couch (or even bed!). It needs to extremely lightweight to not interfere with the handheld controls. It needs to be very thin and nimble to be carried around when travelling. Pure fiber AOCs can provide the perfect solution to enable such an experience.

We at Pure Fi are using pure fiber AOC technology to create exciting new products that turn these new experiences into reality. We are going to showcase our new cables at the upcoming LTX Expo in Vancouver. The vibe is going to be lit! Find out more at pure-fi.com/ltx-expo-2023/