Optical Audio Cable: 5 Powerful Facts & Simple Setup Guide

An optical audio cable (also called TOSLINK) transmits digital sound as pulses of light through a fiber optic strand. It is the same technology that powers the internet — fibre optics — applied to audio. The cable carries compressed 5.1 surround sound or uncompressed stereo from your TV, game console, or CD player to a soundbar, AV receiver, or speaker system.

Here is what we cover: what an optical audio cable is, how it works (the physics of light through fibre), how it compares to HDMI and coaxial digital audio, and a simple setup guide.

What Is an Optical Audio Cable?

An optical audio cable is a digital connection that uses fibre optic technology to send audio signals as light pulses. The connector is called TOSLINK — short for Toshiba Link — because Toshiba created the standard in 1983 to connect their CD players to their receivers.

The end of the cable has a distinctive square-ish plug with a small rectangular opening. When plugged in, you can often see a faint red glow inside — that is the infrared light carrying your audio signal.

Optical audio cables carry two types of signal:

• Uncompressed stereo PCM — two-channel audio, the same format as a CD
• Compressed 5.1 surround sound — Dolby Digital and DTS, used by DVDs, Blu-rays, and streaming services

They do not carry video, high-resolution formats like Dolby TrueHD, or object-based surround like Dolby Atmos (the lossless versions).

How an Optical Audio Cable Works

Inside an optical audio cable, there is a thin strand of plastic or glass optical fibre. The source device — say, your TV — converts the electrical audio signal into a stream of light pulses using an LED or laser diode. These pulses travel through the fibre by total internal reflection, the same physics that keeps light trapped in a glass fibre for kilometres.

Here is the picture. Imagine a ball bouncing down a long, narrow hallway. Every time it hits the wall, it bounces back toward the centre. Inside the fibre, light does the same thing. It enters the core of the fibre, hits the core–cladding boundary at a shallow angle, and reflects perfectly back inside — over and over, for the entire length of the cable, until it reaches the far end.

At the receiving end, a photodiode detects the light pulses and converts them back into an electrical signal that your soundbar or receiver can amplify and play through speakers.

The light is infrared, with a wavelength of about 650 nm — visible as a faint red glow. The data rate is modest by modern standards: the S/PDIF protocol that TOSLINK uses runs at about 3.1 Mbit/s for standard PCM audio, and common receivers handle up to about 15 Mbit/s. This is far less than the gigabits that data fibre carries, but more than enough for CD-quality surround sound.

Optical Audio vs HDMI: Which Should You Use?

This is the most common question about optical audio cables. The answer depends on what you need.

Use HDMI when:

• You want to send both audio and video in one cable
• You need high-resolution audio formats (Dolby TrueHD, DTS-HD Master Audio, Dolby Atmos)
• Your devices support HDMI ARC or eARC (simplifies connections)
• You want the simplest setup with a single cable per device

Use optical audio when:

• Your AV receiver or soundbar lacks HDMI inputs
• You want to separate audio from video (e.g., send TV audio to an older receiver)
• You need to eliminate ground loop hum — optical cables provide galvanic isolation, meaning no electrical connection exists between the two devices
• Your devices are far apart (optical cables can run up to 10 m without issues)

For stereo music or compressed 5.1 surround sound, the audio quality is identical between optical and HDMI. The difference only matters with high-resolution audio formats.

Optical Audio vs Coaxial Digital Audio

Optical and coaxial digital audio are both forms of S/PDIF (Sony/Philips Digital Interface). They carry the same data and offer the same audio quality. The only difference is the physical medium:

• Optical uses light through a fibre optic cable
• Coaxial uses electricity through an RCA cable

Advantages of optical: complete electrical isolation (no ground loops, no hum), immunity to radio frequency interference (RFI), and no risk of electrical damage between devices.

Advantages of coaxial: slightly cheaper cables, more rugged connectors, and potentially longer runs with high-quality coax.

For nearly all home setups, the choice is a matter of convenience — use whichever connection your devices support. If you hear hum or buzzing through coaxial, switch to optical.

How to Set Up an Optical Audio Connection

Setting up an optical audio connection takes about two minutes:

1. Locate the optical ports on your source (TV, game console) and your audio device (soundbar, receiver). They are usually labelled OPTICAL, OPT, or TOSLINK, and covered by a small plastic flap or cap.

2. Remove the protective caps from both ends of the cable and from the ports.

3. Plug the cable in. The square TOSLINK connector only fits one way. Push gently until it clicks into place. You should see a faint red glow at the connector if the source is on and sending audio.

4. Change the audio output setting on your source device. On a TV, go to Settings → Sound → Audio Output and select Optical or PCM/Dolby Digital. On a game console, select Optical in the audio output menu.

5. Select the correct input on your soundbar or receiver. Use the remote to choose the optical input (usually labelled OPT 1, OPT 2, or similar).

6. Test with known content. Play a movie or song with clear audio. If you hear crackling or no sound, check that the cable is fully seated and that the source output format matches what your receiver supports (PCM for stereo, Dolby Digital for surround).

For most setups, this is all you need. The cable carries both the audio data and the clock timing in the S/PDIF bitstream, so there is no separate configuration needed for synchronisation.

A Common Misconception: Fibre Is Fragile and Easy to Break

A common worry about optical audio cables is that the fibre inside is fragile and will break if you bend the cable. This is mostly outdated. Modern TOSLINK cables use plastic optical fibre (POF) that is surprisingly flexible and durable for normal home use. You can bend it around corners with a radius of about 25 mm without damage.

The real limitation is length, not fragility. Plastic optical fibre has high attenuation — about 1 dB per metre at 650 nm — which means the light gets weaker the longer the cable runs. Beyond about 5 metres, the signal may become too weak for the receiver to read reliably. Glass optical fibre cables exist for longer runs but are less common and more expensive.

Another concern: the window on the connector can get scratched, reducing light transmission. Keep the protective caps on when the cable is not in use, and wipe the connector with a dry cloth if needed. The plastic fibre inside will last for years under normal conditions.

External resources

• TOSLINK — Wikipedia — technical reference covering history, connector types, specifications, and compatibility
• What Is a TOSLINK Cable? — AEANET — clear guide explaining TOSLINK functionality, advantages, and common questions

For the physics that makes optical audio possible, start with what is optical fiber. For the complete list of applications, read what are fiber optic cables used for. The principle of total internal reflection that traps light in the cable is explained in our total internal reflection guide.

Recommended Products

• TOSLINK Optical Audio Cable on Amazon — standard plastic optical fibre cable for connecting TVs, soundbars, and receivers
• Mini-TOSLINK to TOSLINK Cable on Amazon — adapter cable for connecting laptops and computers with 3.5mm optical outputs
• Optical Audio Switch on Amazon — 3-in-1 or 4-in-1 switch for connecting multiple optical sources to a single input