There are two main types of optical cable adaptors, each of which serves a different purpose. One type of optical cable adaptor is used to convert a digital optical signal to a digital or analog radio frequency (RF) signal. This is necessary in order to connect certain equipment when one device has an optical output and another has only coaxial inputs. The other type of optical cable adaptor can be used to plug a traditional Toshiba link (TOSLINK™) optical cable into a mini-TOSLINK™ jack. Since both of these formats are digital, this type of adaptor does not involve any type of analog conversion hardware.
Optical cables, which typically conform to the TOSLINK™ standardized format, are used to transfer information digitally. The optical jack on an output device, such as a compact disc (CD) or digital versatile disc (DVD) player, generates light that acts as a carrier wave. Digital audio or video information is transmitted by this light-based carrier wave, and the optical jack on an input device is capable of reading it. The actual cables are composed of optical fiber that is capable of transmitting light-based carrier waves for about 20 feet (6 meters) before the signal attenuation becomes too great.
In order to connect a device that uses an optical output to a device that uses coaxial inputs, some type of adaptor unit is required. There are two different types of optical cable adaptors that can be used for this purpose, since various devices can use either digital or analog coaxial inputs. A digital to digital optical cable adaptor has a TOSLINK™ input on one side and a Radio Corporation of America (RCA) connector on the other. These devices typically require an external power source as well to facilitate the conversion process.
Other optical cable adaptors can also convert between digital and analog. This type of optical cable adaptor typically also has a standard TOSLINK™ input, but contains multiple RCA outputs. Each RCA output carries a single analog signal, such as a right or left audio channel. Despite the fact that both of these adaptors use RCA outputs, they are typically not compatible due to the difference between digital and analog RF signals.
The other type of optical cable adaptor is simply used to convert between differently sized optical plugs and jacks. There is one main size for TOSLINK™ plugs and jacks, though some devices use the smaller mini-TOSLINK™ instead. These jacks use the same encoding format to transfer digital information on a light-based carrier wave, so a TOSLINK to mini-TOSLINK adaptor simply converts between the different sizes.