An optical audio cable, commonly known as a TOSLINK cable due to its origins as the TOSHIBA-cable, is a fiber-optic connection that is quickly becoming the standard for audio cables. Optical cables rely on fiber optics that convert the audio and relay them via light, typically red LED light. Before you go to buy one, there are a few things you need to know.
Any length that is over 10 meters is a poor choice as it causes the reliability of the transmission to go down. Most optical audio cables will not be longer than 5 meters without a signal booster. If you need lengths exceeding a hundred feet, an optical cable made with melted quartz is the better choice as it will yield better quality. If all you need is a short cable, you can use a cable with plastic optical fibers as no difference in quality will be detected unless you are farther away than a hundred feet and transmitting at high bandwidth levels.
There are no differences in the performance between the 5 mm and the 8 mm as it is only the outer diameter of the cable itself and therefore does not affect the connectors at all. What you may want to consider, though, is that the thicker cables are more durable and that they usually come with a protective nylon mesh covering on the outside.
Optical audio cables do not differ greatly from brand to brand. Unless you have a very good ear and possess a remarkably high-rate system, it is not likely that you will hear any differences when using a cheaper brand than when you use a more expensive brand.
When compared to digital coaxial cables, the optical audio cables can be a little more expensive. But, in exchange, they give a better performance when it comes to reproducing digital signals as there is no interference from surrounding electronic devices. What will greatly affect your price is the type of optical cable you invest in. Standard 5 meter, plastic fiber cables are drastically cheaper than the quartz ones mentioned earlier. Some cables might come with 24k gold plated connectors to enhance signal transfer and help avoid corrosion, and this can also bump up the price a great deal.
It is a good idea to make certain that there are no sharp kinks in the optical audio cable as this will cause it to not work properly or at all. Curves are okay and unavoidable, but bending prevents the LED light from transferring properly down the length of the cable.
For the best performance, your cable should have a bandwidth of 9MHz to 11MHz. The higher this bandwidth is, the better it will work. Keep in mind that smaller consumer products, such as CD players, aren't going to see a drop in quality due to low bandwidth in the way that a home theater system would.