It was once the most high-tech and futuristic feature you could find: Transmit sound -- with light! Lasers! A cable not of copper, but glass!

Except, it was almost never glass, and was usually expensive. And while the optical cable was the digital audio transfer method of choice for decades, it has started to disappear. More and more products are dropping the optical connection.

This once cool cable is dying a very slow death. Here's how it happened.

Tech of the past

The official term for optical audio cable is "Toslink," short for Toshiba Link. Developed in the early '80s to connect their CD players to their receivers, it was a red laser optical version of the Sony/Phillips "Digital Interconnect Format" aka S/PDIF standard. You've seen standard S/PDIF connections a bunch too; they're often called "coax digital." Optical had certain benefits over copper cables, but they were also more fragile, and for a long time, more expensive. Though glass cables were available, for even more money, most optical cables were made from cheap plastic. This limited their range to in-room use, primarily.

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Through the '90s and 2000's, the optical cable was near-ubiquitous: The easiest way to get Dolby Digital and DTS from your cable/satellite box, TiVo, or DVD player to your receiver. Even in the early days of HDMI, right next to it would be the lowly optical cable, ready in case someone's receiver didn't accept HDMI. But now more and more gear are dropping optical. It's gone completely on the latest Roku and Apple TV 4K, for example. It's also disappeared from many smaller TVs, though it lingers on in larger ones, a potentially redundant backup to HDMI with ARC. The reason for this? Soundbars. Most soundbars still persist with an optical connection, and they are one of the only thing that keeps the format holding on. Of course, on the audio side devices like the Chromecast Audio also use an optical connection and this is as much due to space constraints as anything else. The Chromecast Audio uses the mini-Toslink variant which fits inside a 3.5mm analog jack.

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So where'd it go? Doesn't optical have the potential for significantly more bandwidth than HDMI? Well… no. "Potential" is the key word there. In theory, optical cables can transmit tremendous amounts of data. But the optical audio connection is far more limited. So limited, it can't even transmit the high-resolution audio formats that came out with Blu-ray more than a decade ago, such as Dolby TrueHD and DTS Master Audio. Unlike HDMI, which has expanded its capabilities significantly over the short time it's been available, Toslink has remained largely the same. Because there is no specification for the optical connection to handle high-res audio, it can't do it. With no specification, one piece of gear can't talk to another piece of gear.

So yes, in theory optical can do a lot of things, but because everyone jumped onto HDMI, optical was left to languish.

Perhaps ironically, many custom installers use optical to transmit HDMI data. HDMI-over-fiber is usually more expensive than wireless, but significantly less prone to interference and issues. It's also capable of far longer runs than traditional HDMI cables. These cousins of the Toslink connection may share lasers and copperless cables, but they're Ferraris to Toslink's bicycle.

The once and future cable

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Cry not for the humble optical cable. While it may someday disappear from inside of your home, it lives on, even thrives, outside. Google Fiber, Verizon FIOS, AT&T Fiber, and others are fiber-optic broadband lines that supply hundreds of megabits, and in some places even a gigabit, per second to your home. Fiber-optic cables are also becoming the backbone of the Internet itself. Facebook and Microsoft, for example, just finished laying MAREA, a trans-Atlantic cable with a bundle of eight fiber-optic threads that together can transmit up to 160 terabits per second.

So while for most people the optical cable has been replaced by HDMI and forgotten, the optical cable technology is here to stay.

After all, lasers!

How about you? How many optical cables do you still use in your A/V system?

Got a question for Geoff? First, check out all the other articles he's written on topics like why all HDMI cables are the same, TV resolutions explained, LED LCD vs. OLED and more. Still have a question? Tweet at him @TechWriterGeoff then check out his travel photography on Instagram. He also thinks you should check out his best-selling sci-fi novel and its sequel.