Semiconductor Fibers: What Will Replace Fiber Optic Cable Transmission Lines?

The Internet is a strange and wonderful place. I grew up at the end of the age of dial-up Internet when chat rooms were all the rage. Now, I occasionally enjoy using the Internet to play some online games, which was impossible back then. My telephone router and its copper network could barely support enough bandwidth to load an image. Now our networks have been upgraded with blazing fast fiber optics. While these communication systems are certainly better than the old copper ones, they still have a few disadvantages. This has led researchers to pursue a new kind of fiber optic, based on semiconductors instead of silica. This new kind of cable could become instrumental in signal transmission, both on the wider network and on PCBs.

Optical Fiber

While many of us think of the Internet as some kind of “thing” we link into, possibly hosted in the cloud, it’s just computers. Millions of computers are all connected. Fiber optic cables comprise many of the information highways that connect these computers. Optical fibers are made using glass and have blessed our networks with their high speeds and great signal quality. However, they come with some disadvantages. The main one we’re concerned about is the expense and complexity of the equipment needed to connect optical circuits with electrical ones.

Most fiber optic cables use silica, a.k.a. glass, to conduct light. Light is a great carrier of information and has a much greater bandwidth capacity than electronic wires. Companies are now discussing 40 Gbps Ethernet, but fiber has already reached speeds of up to 43 Tbps. Light also has a lower bit error rate and is resistant to electromagnetic interference. These characteristics have made it the transmission method of choice for long runs and networks where speed is the name of the game.

You might be thinking about getting a fiber connection to your house now, but you’d better look at the price tag before you do. One of the main complaints about fiber is the cost of the circuits used to convert the optical signals into electrical ones. This turns connection points into pain points when it comes to profits. That expensive equipment is also complex and difficult to hook up to electronics. That’s why some researchers have been developing optical fibers made from semiconductors.

Fiber optics have helped us plug into the World Wide Web more quickly than ever before.

Semiconductor Fiber Optics

Semiconductors are ubiquitous in the world of electronics. My gaming computer wouldn’t work without them. Several years ago several researchers saw how the benefits of semiconductors could be applied to fiber optic cabling. Since then they have been working on integrating the two technologies, with one recent breakthrough.

Fiber optic networks already have great bandwidth and good transmission characteristics, so what advantages could semiconductors bring? They could solve the one big sticking point for fiber optics--their conversion cost and complexity. Semiconductors can transmit both optical and electrical signals (optoelectronic properties) at the same time and can convert between the signals in transit. The electronic converter would essentially be assimilated into the cable itself. This speeds up the efficiency, performance, and bandwidth of the fiber.

Up until recently, there has been a major problem in putting this theory into practice. Researchers were using crystals to conduct both light and electrons in wires, but the crystals had too many boundary layers. Instead of one long crystal, the medium was made up of lots of short crystals. When light passed through the end of a crystal into another it would scatter. Research at Penn State University solved this problem by using lasers to form long contiguous crystals inside a cable. This method brings us one step closer to usable semiconductor fiber optics.

Maybe someday soon we’ll see this kind of cable being installed in our neighborhoods. Editorial credit: Hadrian / Shutterstock.com

Applications

What is the use of technology if you can’t find a use for it and write about it on the Internet? In my mind, semiconductor fiber optics have two interesting applications, one obvious and one not so obvious.

Most people talking about this technology seem interested in its macro applications. It could revolutionize networks, replacing traditional fiber optics and copper alike. While this is certainly true, I’m also quite interested in its possible applications for circuit-level transmission lines. EMI is a plague upon all kinds of PCBs, especially when you’re dealing with mixed signal circuits or high-speed signals. The thing about optical transmission is that it doesn’t radiate significant EMI and it is resistant to EMI. So, if you have a particularly noisy transmission line on your board, route it with a semiconductor fiber. It won’t radiate EMI on its way and it can be converted in the wire itself without using any extra chips. This technology hasn’t even been applied to its primary purpose so this is mostly conjecture. However, keep your eyes out for board-level applications once it’s commercially available.

When I first discovered the Internet, it was a wondrous thing. Now, it’s an old hat. Luckily, researchers are making exciting discoveries in the field of optics to renew excitement. Fiber optics brought us speed and signal integrity, but its cost and complexity have been sticking points. Optical fiber-optic cables made from semiconductors could combine the benefits of electrical conductors with optical ones and bring about a new era of communication.

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